The attractiveness of e-textile and wearable devices are their ease in collecting biological information in day-to-day lives and exercises. However, even with conductive fibers or threads, the conventional weaving method was not good enough to pattern fine electrodes and wires. This is why more simplified process, such as printing, to directly pattern durable and conductive materials on a fabric was widely awaited. We have developed novel ink that functions electronically, and succeeded in printing through one printing process a tough elastic conductor. This printable conductor keeps its high conductivity even when it is expanded more than 3 times in size. We printed elastic wires and electrodes with this ink on a fabric and achieved a textile electromyograph sensor. This easy to print textile bio-info sensor can be used in sports, healthcare and medicine.

In organic/metal hybrid materials, the thermal boundary conductance across the metal/organic interface plays a significant role in overall thermal conductivity of the film. The conductivity of the organic or hybrid thin film not only plays a critical role in the thermal stability of the organic devices, but also governs the heat transfer mechanisms. Here by embedding metal nanoparticles into organic semiconductor, we have successively developed a thermistor for direct temperature sensing. By integrating the thermistor with the active matrix organic transistor array, we fabricated a large area 16 × 16 temperature sensor which can be directly used for temperature mapping of objects with various shape. Simultaneously, we apply 3-omega; method to measure the effective conductivity of the thin film and the results are compared with the finite element modeling. By carefully controlling the concentration of the silver nanoparticles, we can modify the sensitivity of different temperature sensors. For a thin layer of Ag and intermixed with DNTT (10% volume ratio), the thermal conductivity decrease from 0.363W/m-K (pure DNTT) to 0.305W/m-K which shows the importance of the thermal boundary conductance. In the integrated temperature sensor array, the hyrbid thermistors are connected in series to the drain contacts and the whole array is developed on flexible substrate. By optimizing the anodization growth of the alumium oxide (AlO_x) dielectric, the tempearture array can be powered under 5V with dynamic range higher than 10 bits, which clealy shows their capability in portable temperature sensing applications. The low voltage flexible thermal sensor array is suitable for portable electronic devices and potentially scale up for electronic skin applications. Other application directions such as health monitoring or use as surgery tools can be achieved.

Photodiodes with high specific detectivity, which entails high external quantum efficiency (EQE) and low dark current, and large pixel sizes enable optical systems capable of imaging lower light intensities. Additionally, the ability of a photodiode to operate under high electric fields at reverse bias increases the amount of photogenerated charge that may be capacitively stored during a single integration period, which is known as the well capacity. Using only the highly scalable printing techniques of blade coating and screen printing to deposit the layers on plastic, flexible organic photodiode arrays are reported with average specific detectivities of 3.45×10¹³ cmmiddot;Hz^0.5middot;W^-1 at a bias of -5 V. Polyethylenimine is blade coated over PEDOT:PSS to form the bottom cathode on these inverted devices, which exhibits excellent uniformity in work function modification on the microscale (20 meV standard deviation) as well as over centimetric areas. Furthermore, it is found that the polyethylenimine interlayer is not only essentially for lowering the work function of the electrode to increase EQE but also serves as a hole blocking layer to decrease the dark current density to an average of 150 pA/cm². Photodiodes fabricated with a screen printed PEDOT:PSS top anode exhibit dark current shunt resistances an order of magnitude higher than devices fabricated using thermally evaporated top electrodes as a result of the creation of defects in the active layer which serve as leakage paths. This results in a lower dark current at high reverse biases for devices with a screen printed top anode than the devices with thermally evaporated metal electrodes. Additionally, these devices show excellent bias stress stability under high applied fields (88 kV/cm) and low variability, with a coefficient of variation of 15% in specific detectivity for 24 pixels across an array with perfect yield. Integration of these photodiodes with organic thin film transistor arrays and charge integrators will also be demonstrated.

Colloidal quantum dots are highly versatile optoelectronic components that combine size- and shape-tunable properties with the attractiveness of cost-effective solution-phase processing. As such, they are ideal building blocks for the formation of artificial solids in which the colloidal assembly profits from the carefully engineered properties of the individual quantum dots. A variety of quantum-dot-based optoelectronic devices have been reported recently, including light-emitting diodes¹ and lasers with tunable emission across the entire visible range,² as well as demonstrations of efficient solar cells³ and photodetectors.⁴ It is interesting to consider complementing the nanoscale-structure of the quantum dot assembly with wavelength-scale patterning. This would allow for the creation of hierarchical photonic structures.
Here, we present a template stripping technique that allows for high-resolution wafer-scale patterning of colloidal quantum-dot films.⁵ We combine simple drop-casting of colloidal dispersions with template stripping using hard silicon templates with lithographically defined patterns. Using this technique, large-area patterns of arbitrary shapes can be transferred with high fidelity onto the quantum-dot film itself. We will show that carefully designed photonic patterns can significantly modify the optical properties of these films, yielding enhanced outcoupling of fluorescence and improved absorption of irradiation. Our technique is compatible with commonly used ligand-exchange strategies for improved electronic properties and can potentially be applied to other solution processable materials such as metallic nanoparticles or organic polymers.
We will discuss the significant improvements that patterned quantum-dot films can offer in the performance of light emitting and light harvesting optoelectronic devices.
References
(1) Mashford, B. S. et al. Nat. Photonics2013, 7, 407-412.
(2) Dang, C. et al. Nat. Nanotechnol.2012, 7, 335-339.
(3) Chuang, C.-H. M. et al. Nat. Mater.2014, 13, 796-801.
(4) Konstantatos, G. et al. Nature2006, 442, 180-183.
(5) Prins, F. et al. in preparation2015.

Ag nanowires (AgNWs) have low sheet resistance and high optical transmittance and are therefore good candidates for use as an alternative to conventional transparent indium-tin-oxide (ITO) electrodes. However, use of conventional short AgNWs has allowed fabrication of only randomly-dispersed sheet-type transparent electrodes, so the approach it cannot take full advantage of nano-sized electrodes (nanoelectrode). Moreover, the conventional solution-dispersed AgNWs have the limitations such as low dispersion uniformity, poor surface roughness, high optical haze and low controllability, which should be resolved. Here, we report use of Electrohydrodynamic Nanowire Printing (ENP) as a simple, fast and inexpensive method to print Ag nanofibers (Ag NFs) for use as transparent electrode. ENP produces highly-aligned and individually position-controllable Ag NFs with average diameter of 695 nm and low resistivity ρ = 5.7 µOmega;#8729;cm, which is comparable with that of bulk Ag (ρ = 1.6 µOmega;#8729;cm). We fabricated various FETs including all-NF FETs (carrier mobility ~ 2.08 cm²middot;V^-1middot;s^-1) that use two strings of Ag NFs, one as a nano-sized source nanoelectrode and one as a drain nanoelectrode. We also demonstrated organic light emitting diodes (OLEDs), transparent heaters and touch screen panels, thereby proving the feasibility using of printed Ag NF transparent electrodes. ENP will be useful for fabrication of various kinds of future nanoelectronics.

Through the use of digital printing methods, custom electronic systems can be additively fabricated in an on-demand fashion. Many device types (logic circuits, sensors, memory, power sources, etc) can be printed entirely from solution-based inks of conductors, semiconductors, dielectrics and stimuli-responsive materials. However, all-printed systems incorporating these devices are often constrained in the appliations they can address by the performance of the printed circuits, which are typically limited by print resolution and materials properties. In order to best take advantage of the assortment of printed components available a hybrid approach that incorporates low-profile Si-CMOS components into the printed system can be used to provide a balance between electrical and mechanial performance, customizability and cost. Following this approach, examples of digitally fabricated hybrid electronic systems for wireless multimodal sensing will be described as will approaches for providing power to these distributed systems. Additionally, a print-like method of programmable micro-assembly to directly transport and orient large numbers of pre-fabricated silicon chips using electrostatic fields will also be discussed.

Envisaged as key enablers of molecular electronics, plasmonic and spintronic devices, nanogaop electrodes have become a growing area of research in recent years. Many routes towards such structures have been investigated, including mechanical break junctions, electromigration, oblique-angle shadow evaporation and electron beam lithography. However, such nanofabrication processes suffer from low throughput, poor scalability and multiple complex processing steps. Furthermore few of these methods can be readily applied to produce nanogaps between dissimilar electrodes, hence closing the door to the fabrication of devices that rely on ambipolar carrier injection (e.g. light-emitting diodes) or extraction (solar cells, photodetectors etc.).
Here, we present a unique technique, namely adhesion lithography (a-Lith), capable of fabricating such asymmetric nanogap structures, and doing so at an unprecedentedly large scale¹. The process relies on the selective tuning of electrode surface energies using self-assembled monolayers (SAMs) and the application of adhesive forces. The bulk of the process is done via solution and features on the order of 10 nm with aspect ratios of over 10⁶ have been demonstrated.
One such application of this structure is the co-planar nano-Schottky diode. The latter type of diodes may be fabricated by a single step deposition of the semiconductor material directly onto the nanogap electrode structures. The mismatch between electrode work functions allows current flow in one direction only, the small active area reduces device resistance, while the planar structure minimises device geometric capacitance. Thus we demonstrate devices with extremely high rectification ratio (>10⁶) and minimal RC constants due to the co-planar device architecture. The result is the demonstration of nano-Schottky diode operating at radio frequencies (>20 MHz) while they can be made using various semiconductors, including low temperature (<200°C) solution processed ZnO as well as solution deposited C₆₀. Such large-area, low-cost devices could be the ideal candidate for integration into printable RFID tags, and enablers of future technologies such as widespread RFID supply chain management and the Internet of Things.
1. Beesley, D. J.; Semple, J.; Jagadamma, L. K.; Amassian, A.; McLachlan, M. A.; Anthopoulos, T. D. Nature communications 2014, 5.

Direct printing of conductive inks made from metallic nanoparticles is an attractive approach for scalable low-cost manufacturing of flexible electronics, such as thin film transistors and transparent electrodes for organic displays and solar cells. Accordingly, the traditional methods including screen, gravure, offset, flexography, and inkjet printing have significant commercial uses. Although each method has its own characteristics and advantages, the common limitation in device fabrication is the printing resolution, limited to smallest feature size of approximately 20 mu;m. In case of flexography, the solid elastomeric stamps load a thin layer of ink on the top surfaces of the stamp features, which is prone to film instability and liquid spreading as feature size becomes smaller. For emerging applications of printed electronics such as high-resolution flexible displays or metal grid transparent electrodes, it is necessary to print conductive patterns in 1-10 mu;m size range.
We have developed a nanoporous stamp material enabling direct printing of electronic materials with micron-scale resolution. The stamps comprise vertically aligned carbon nanotubes (CNT “forests”) coated with poly(perfluorodecyl acrylate), (pPFDA), via initiated chemical vapor deposition. The stamp structures have high porosity (>90%), possess structural robustness against capillary forces upon liquid infiltration/evaporation, and are sufficiently compliant (elastic modulus of ~30 MPa) for conformal contact against the target substrate. For printing, the nanoporous stamps are used in the same way as the solid elastomeric stamps in flexography, as the ink is transferred from compliant and raised stamp structures to the target substrate via local contact. However, the high porosity of the new stamp allows the ink to be confined inside the microstructures. As a result, upon contact with the target substrate, ink is transferred locally via the porous surface, realizing excellent replication of stamp pattern with uniform thickness. Using the engineered CNT stamps, we demonstrate scalable patterning of silver nanoparticles approaching micrometer dimensions with high fidelity (e.g. sharp corner radius ~3 mu;m, fine edge roughness <1 mu;m, and uniform thickness <100 nm). After sintering, the silver patterns show maximum conductivity of ~4.0×10⁷ S/m (~60% of bulk silver). Printed silver honeycomb patterns, with minimum linewidth of 3 mu;m, are also directly fabricated on glass plate and PET films. After annealing, this pattern exhibits ~89% transmission at 200-800 nm wavelength with 6.4-13.1 Omega;/#9633; sheet resistance, which is significantly lower than ITO (20-100 Omega;/#9633; over 80% transparency). We further discuss the contact and fluid mechanics of ink transfer, and analyze the potential for continuous operation of nanoporous stamps for micron-scale patterning at high speed (~m/s) which would overcome the mutual limitations of existing patterning methods for manufacturing of printed electronics.

Logic circuits are necessary to fulfill the vision of low cost, large area organic electronics, made with organic semiconductors (OSC) as the charge transfer layer. However, these circuits have stringent requirements. Primarily, all the thin film transistors (TFTs) participating in the circuit need to have a low variation in charge transfer characteristics (charge carrier mobility, threshold voltage, current, etc.). Additionally, organic circuits should be operated with low power consumption. To this end, research is being performed to pattern OSCs on the organic circuit to reduce parasitic current leakage. These twin requirements of low variability and OSC patterning set up conflicting goals, as the variability increases if each TFT is patterned individually. Moreover, patterning TFTs such that every TFT works, for the numerous TFTs required for logic circuits, is difficult with conventional methods such as ink jet printing due to patterning errors over large areas.
Here, we show a self-patterning method that does not require an extra patterning step to deposit the OSC layer onto the organic circuit. We have developed a surface functionalization procedure for a variety of oxide and metal surfaces, which, when paired with controlled solvent flow, can pattern OSCs in the TFT channel region only. Using this method, we show 100% viability of the patterned TFTs with low variability of charge carrier mobility and current. This method has been used to form logic gates and other organic circuits.

Potential applications of organic thin-film transistors (TFTs) are flexible displays, and the addition of active electronic anti-counterfeiting and tracking features to the existing passive security features on banknotes. For these applications, certain requirements such as low-voltage operation, a good shelf-life stability and high switching speeds have to be fulfilled not only on smooth Si wafers substrates used for material screenings but also on realistic plastic and paper substrates.
In this work, the low-voltage operation of the TFTs was enabled by employing a very thin hybrid gate dielectric consisting of a thin AlO_x layer and a self-assembled monolayer of either an alkylphosphonic acid or a fluoroalkyphosphonic.^[1] The small thickness of the gate dielectrics leads to a large gate-dielectric capacitance and therefore allows operating voltages below 3V.
The utilized small-molecule semiconductors DNTT and its derivatives C₁₀-DNTT and DPh-DNTT provide large carrier mobilities and an excellent air stability.^[2]
However, a good dynamic performance can be accomplished only by minimizing the parasitic capacitances, i.e., by employing TFTs with small lateral dimensions. In this work TFTs with channel lengths (L) ranging from 100µm down to 0.5µm were fabricated using high-resolution silicon stencil masks^[3,4] that allow the accurate patterning of organic TFTs with small dimensions and an excellent parameter uniformity.
For DPh-DNTT TFTs on plastic substrates, carrier mobilities of 2.4cm²/Vs (L=100µm) and 0.6cm²/Vs (L=1µm) were measured. To test the suitability of the TFTs for real applications, we fabricated 11-stage unipolar and complementary ring oscillators on plastic substrates and on a 5-Euro banknote. For DPh#8209;DNTT TFTs with L=1µm on the plastic substrates, a signal delay per stage of 240ns was measured in ambient air at a supply voltage of 4V, which is the smallest signal delay reported to date for organic TFTs on flexible plastic substrates at operating voltages below 10V. For complementary circuits with p-channel DPh-DNTT TFTs and n#8209;channel PTCDI-(CN)₂-(CH₂C₃F₇)₂ TFTs, the stage delay at 5V was as short as 3.1mu;s.
Despite the rough fibrous surface of the banknotes, the TFTs have mobilities up to 1.2cm²/Vs (p-channel TFTs) and 0.17cm²/Vs (n#8209;channel TFTs). The latter value is among the largest reported for organic n-channel TFTs on paper substrates. The thin gate dielectric allows the bending of the devices and in our tests no significant influence on the carrier mobility and the gate current was observed.. At 4 V, the measured stage delays are 2.5µs (unipolar) and 10µs (complementary). In comparison to earlier reports on organic circuits on paper substrates, these ring oscillators operate faster and at lower voltages.
[1] U. Kraft et al., Adv. Mater., 2015, 27, 207
[2] U. Kraft et al., DRC, Santa Barbara, USA, 2014,
[3] F. Ante et al., Small, 2012, 8, 73
[4] F. Letzkus et al., Microelectron. Eng., 2000, 53, 609

Flexible electronics has been demonstrated using both organic and inorganic semiconductors on a variety of substrates and using a wide range of fabrication approaches. Roll-to-roll processing has gained interest for high-throughput manufacturing, but presents challenges for in vacuum deposition, photolithography, and alignment between layers, complicated by substrate flatness and dimensional stability issues. Flexible substrates laminated onto rigid carriers (usually glass or Si) allow device fabrication using more standard equipment and processes, but often only partially solves substrate flatness and dimensional stability problems. We have used few micron thick polyimide layers solution-cast and cured on rigid glass or Si carriers to fabricate thin film transistors on flexible substrates. The thin polyimide layers reproduce the carrier flatness and typically have few nm surface roughness. Dimensional stability for small (few cm) substrates is excellent with only few ppm level distortion after processing steps including heating to 200 °C, photolithography (including exposure to organic solvents), and vacuum deposition. At the completion of device processing the thin flexible substrate can be released from the substrate by etching a sacrificial layer or by simple mechanical stripping. Thin solution-cast flexible substrates also provide advantages for applications that require small bending radius. Ignoring effects from device and other added layers, strain is proportional to substrate thickness. Thin substrates allow smaller bending radius than thicker substrates before the strain level that results in device and interconnect degradation is reached. Oxide semiconductor n-channel TFTs integrated with organic p-channel TFTs provide a simple complementary circuit technology. ZnO thin film transistors fabricated on thin solution-cast polyimide substrates have characteristics very similar to devices fabricated on glass. Substrates released by mechanical stripping were flexed 50,000 times with only small changes in device characteristics. Solution cast polymeric substrates provide a simple path to flexible active electronics.
1. Y. V. Li, D. A. Mourey, M. A. Loth, D. A. Zhao, J. E. Anthony, and T. N. Jackson, “Hybrid Inorganic/Organic Complementary Circuits using PEALD ZnO and Ink-Jet Printed DiF-TESADT TFTs,” Organic Electronics, 14, pp. 2411-7 (October 2013).
2. H. Li and T. N. Jackson, “Oxide Semiconductor Thin Film Transistors on Thin Solution-Cast Flexible Substrates,” IEEE Electron Device Letters, 33, pp. 35-37 (January 2015).

After nearly three decades of thorough development, small molecule organic light emitting diodes (OLEDs) have reached a point where their operational lifetimes are now compatible with the requirements in a range of commercial applications (in particular by the flat panel display industry). However, from a fabrication point of view, one of the main drawbacks of the technology remains its incompatibility with many solution based processes. Any exposure of devices to water or organic solvents tends to degrade device performance and frequently has catastrophic impact on device lifetime. This prevents the use of photolithography - widely used in the CMOS and PCB industry - for the fabrication of full-color OLED displays and renders packaging and lamination of OLEDs challenging.
Hydrofluoroethers (HFE) have been proposed as an orthogonal material system which can be brought in contact with OLEDs and other organic devices without damaging the material. Here, we show that HFE based solvents enable patterning of state-of-the-art phosphorescent OLEDs by a photolithographic lift-off process without any impact on device efficiency or device lifetime. For devices exposed to our HFE process, the extrapolated t_0.75 lifetime at an initial luminance of 500 cd m^#8209;2 remains at over 100,000 h.
Using a similar concept we have also found that HFE polymers allow solution based deposition of additional layers on top of fully functioning OLEDs. This may prove useful in a range of scenarios e.g. as initial barrier layers in thin-film encapsulation, for mechanical balancing in flexible devices, hellip; . Here, we study ways of enhancing the efficiency of light extraction by depositing HFE polymers loaded with high-refractive index nanoparticles onto top-emitting OLEDs. We find that the outcoupling efficiency of white top-emitting OLEDs is enhanced by 1.5 to 2.3 fold using this approach and that their angular emission characteristics, i.e. the change in color with viewing angle, is also greatly improved.
[1] S. Krotkus, F. Ventsch , D. Kasemann, A. A. Zakhidov, S. Hofmann , K. Leo, M. C. Gather, “Photo-patterning of Highly Efficient State-of-the-Art Phosphorescent OLEDs Using Orthogonal Hydrofluoroethers”, Adv. Optical Mater.2, 1043 (2014)
[2] T. Schaefer, T. Schwab, S. Lenk, M. C. Gather, “White top-emitting OLEDs with solution-processed nano-particle scattering layers”, submitted

Nowadays there are many applications for optoelectronic films as solar cells, photodetectors or LEDs. Currently, the most common materials for commercial devices are either organic or inorganic. However since few years optoelectronic organic/inorganic hybrid films are also studied. The latter ones can provide durability and intermediate costs between organic or inorganic films. Recently, photoconducting hybrid films were electrodeposited by an auto-assemblage of an inorganic ZnO semi-conducting network and an organic network of light absorbing and conducting 3-methylquinquethiophene dicarboxylic acid molecules¹. In this context, we explored systems to generate new hybrid films for light emission by similar electrodeposition techniques. We will present here results on new photoluminescent ZnO / naphthoate hybrid films.
Prior to electrodeposition synthesis, the ZnO / naphthoate system was investigated by solution and hydrothermal synthesis. A new ZnO / naphthoate hybrid phase denoted H1 was isolated, the crystal structure was determined by single crystal X-Ray diffraction and thermal stability by thermogravimetric analysis.
Electrosynthesis and deposition of H1 on transparent electrodes were secondly optimized by varying concentration bath, temperature and deposition potential. Purity, quality and crystal structure of films were checked using single crystal structure of H1, the film microstructure was studied by scanning electron microscopy. Transmittance and photoluminescence properties were analyzed by photoluminescence and photoluminescence excitation spectroscopy. The H1 film exhibits a blue emission through UV excitation.
In order to study further electroluminescence properties, devices based on H1 were developed. Since H1 films deposited on transparent electrodes are sparse, embedding by resins to prevent shortings and deposition of metallic back electrodes were optimized. X-Ray diffraction and photoluminescence analysis have been performed on devices to ensure the preservation of H1 hybrid material during successive fabrication steps.
The synthesis of the H1 hybrid phase and its crystal structure, the film electrodeposition and its microstructure, the photoluminescence properties and the device fabrication based on luminescent H1 hybrid films, will be presented.
(1) Sofos, M.; Goldberger, J.; Stone, D. A.; Allen, J. E.; Ma, Q.; Herman, D. J.; Tsai, W.-W.; Lauhon, L. J.; Stupp, S. I. Nat. Mater. 2009, 8 (1), 68-75.

A major drawback of Ag-based transparent OLED is a limited lifetime, mostly due to diffusion from the Ag cathode into the organic layers. In this study, a new approach using Ag-free transparent contacts is investigated. A 1 nm Ti precoat and a thin Au anode (8 nm) are deposited on glass substrates suppressing lateral guided modes [Slawinski, M., et al., MRS Proceedings 1627, 2014]. Hole injection is improved by a 2 nm MoO_x layer. The organic stack deposited by OVPD (organic vapor phase deposition) is comprised of NPB as HTL, Ir(MDQ)₂(acac) doped in a cross-faded NPB/TMM matrix [Lindla, F., et al., Applied Physics Letters 95, 213305, 2009] and Alq₃ as ETL. Subsequently, an inorganic electron injection layer (EIL) of 1 nm LiF and 2 nm Al is formed and coated with a thin Au film (16 nm) to constitute the transparent OLED cathode. The active area measures 2 cm². The OLED are encapsulated with a glass cover without getter package to maintain transparency.
For lifetime comparison, transparent reference OLED with thin Ag films (20 nm) as cathode material on top of the EIL have been fabricated. We will show a 6 fold increase in lifetime (LT₅₀, 4 mA/cm²) from 27 h to 172 h when replacing Ag by Au as cathode material with similar electro-optical characteristics. In wavelength-dependent transmittance measurements, the OLED with Au contacts show an average in transparency of about 30% in the range of VIS-light including absorption and reflection of the glass substrate and cover. In terms of turn-on voltage, all transparent OLED (Ag & Au cathode) feature almost identical values to a standard non-transparent OLED (anode: oxygen plasma activated ITO; cathode: LiF/Al) comprising the same organic stack. This confirms similar charge injection in those devices.
J-V characteristics show a considerable series resistance which we attribute to the different anode design and higher sheet resistance of the thin Au film compared to the thick Al cathode in the standard OLED (20 Omega;/sq to <1 Omega;/sq). J-V-L-measurements reveal a strong influence of substrate temperature during the OVPD process on the current efficacy of the OLED. Optimization of substrate temperature is crucial for good wettability of the substrate by NPB and smooth morphology of the organic layers.
Top-side (cathode) light emission is about 70% of bottom-side (anode) emission measured on an encapsulated OLED. This is owed to the fact that the top Au film is thicker than the bottom Au film due to a somewhat larger roughness to achieve similar sheet resistance. Additional losses are caused by the air gap between the cathode contact and the glass cover.
To further increase lifetime, we are currently working on an inverted transparent OLED structure to bury the reactive LiF/Al EIL turning it less accessible for oxygen and moisture. First results show difficulties in electron injection when depositing Al/LiF below the organic stack which may be attributed to insufficient thermal activation of the EIL.

The ability to assemble nanomaterials, such as quantum dots, could enable the creation of functional devices that present unique optical and electronic properties. For instance, light-emitting diodes with exceptional color purity could be printed via the evaporative-driven assembly of quantum dots. Nevertheless, current studies of the colloidal deposition of quantum dots have been limited to the surfaces of a planar substrate. Here, we investigate the evaporation-driven assembly of quantum dots inside a confined cylindrical geometry. Specifically, we observe distinct deposition, coating patterns and cracks formation of quantum dots at different positions along the length of a capillary tube. Such changes of coating behavior could be influenced by the evaporation speed as well as the concentration of quantum dots. Understanding the factors governing the coating process could provide a means to control the assembly of nanomaterials inside a capillary tube, ultimately enabling the creation of novel electronics devices.

Large-area organic light emitting diodes (OLEDs) suffer from inhomogeneous luminance caused by the large lateral voltage drop inside the transparent electrode. To improve the device performance, the conductivity of the transparent electrode is typically increased by integration of metal grids with the transparent electrode.[1] However, these grid lines make the anode and cathode of the device prone to shorting. Shorting of the electrodes can be avoided by applying a passivation layer on the grid lines. The grid as well as the passivation layer decreases the device active area, thus making the accurate alignment of the passivation layer crucial. We have developed a novel Joule heating based self-alignment process for solution-processable polymer insulators to increase the localization of the insulator on the grid lines. [2, 3]
Here, we report passivation of an OLED anode and its implementation in an OLED device. The grid lines were deposited onto an indium tin oxide (ITO) electrode. A cross-linkable polymer dielectric was then patterned using a Joule heating process. The Joule heating enables very precise alignment of the passivation layer with the grid line, and thus optimizes the OLED active area, and it has the potential for cost effective industrial scale production. None of the Joule heating steps require vacuum processes or time consuming and expensive microscale registration.
[1] K. Neyts, M. Marescaux, A. U. Nieto, A. Elschner, W. Lovenich, K. Fehse, Q. Huang, K. Walzer, and K. Leo. Inhomogeneous luminance in organic light emitting diodes related to electrode resistivity, J. Appl. Phys.,100, 114513 (2006).
[2] M. Janka, S. Tuukkanen, T. Joutsenoja, and D. Lupo. Self-alignment method for solution-processable dielectric structures via joule heating. Thin Solid Films, 519, 6587 (2011).
[3] Janka, M., Saukko, E., Raumonen, P., and Lupo, D. Optimization of large-area OLED current distribution grids with self-aligned passivation. Organic Electronics,15, 3431 (2014).

The active layer of organic photovoltaic cells is typically a mixture of p- and n-type semiconducting materials, and the vertical distribution of these materials has significant impact on the device performance. Along this line, the present contribution shows that the vertical composition profile in photovoltaic active layers can be effectively controlled through a unique solution process which we call “photoprecursor approach”.
The precursor approach enables solution deposition of organic semiconductors by a stepwise process, in which a precursor compound is solution deposited then converted to a target semiconducting material by in-situ chemical conversion. When the solubility of the post-conversion film is low enough, one can construct multi-layer structures by repeating the deposition/conversion cycle. This allows sequential deposition of different materials through solution-based processes, and thus high degree of control over the vertical composition profile in the resulting films.
Among various types of precursor compounds, a-diketone-type photoprecursors of acenes are characterized by the mild reaction conditions for their conversion, where only visible-light irradiation is required. In a previous work, we employed this photochemistry to prepare p-i-n-type photovoltaic active layers based on 2,6-dithienylanthracene (DTA) as p-type material and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as n-type material. The resulting device showed a power-conversion efficiency (PCE) of 1.50%, which was 67% higher than that of the corresponding bulk-heterojunction (BHJ) single-layer structure (0.90%) [1]. We also reported that the PCE could be improved to 2.89% by employing three-component p-i-n films containing another donor 2,6-bis(5'-(2-ethylhexyl)-(2,2'-bithiophen)-5-yl)anthracene (EH-DBTA).
The present report deals with our recent efforts, in which we have improved the PCE to be as high as 4.20%. This was achieved by employing a newly synthesized diketopyrrolopyrrole-anthrathiophene conjugate (AtD2T) as p-type material. The i-layer composed of AtD2T and PC₇₁BM can absorb the whole range of visible light, and AtD2T has an ideal energy level of the highest occupied molecular orbital. These features lead to a relatively high short-circuit current density and open-circuit voltage (9.92 mA cm^-2 and 0.89 V, respectively). Importantly, the PCE of the corresponding BHJ device stays as low as ca. 2%, highlighting again the advantage of the p-i-n structure and thus the importance of controlling the vertical composition profile. The presentation will also include the examination of the vertical profile through cross-section scanning-electron microscopy.
[1] Y. Yamaguchi et al. Sci. Rep.4 (2014), 7151.

Conductive polymers have been widely used in organic electronic devices such as organic solar cells, thin film transistors, and light emitting diodes because of their unique optical and electrical properties together with excellent flexibility and processability. The fabrication of micropatterned conducting polymer is also an important research area for their practical applications. In order to construct various flexible electronic devices such as neural electrodes and MEMS resonators, patterning the conductive polymers with an accuracy of hundreds of micrometers without decreasing their conductivity are required. To date, several patterning strategies have been reported such as soft-lithography, dip-pen lithography, template-assisted synthesis, photolithography, and electrochemical deposition. These methods are useful but still limited to achieve cost effectiveness, facile pattern design and process, and large-scale fabrication.
In this talk, we will report a facile approach to fabricate a micropatterned conductive polymer (PEDOT:PSS) on a negative photoresist (SU-8). Because the thick conducting polymer was strongly adhered to the patterned SU-8 substrate by covalent bonding, we were able to further deposit thick copper electrodes uniformly on top of it by using electrodeposition. Furthermore, we will show that the free standing conductive polymer on SU-8 can be fabricated by controlling adhesion between SU-8 and glass substrate. This patterned free standing films with the thickness of around 20 micrometers show excellent flexibility and maintain their conductivity after severe bending test.
To make a patterned PEDOT:PSS on a SU-8 thin film, we applied an SU-8 on a glass substrate and exposed it with UV light via a photomask. UV exposed portions of SU-8 were cross-linked during the pose expose baking on a hotplate. We then spin-coated a PEDOT:PSS on top of it. SU-8/PEDOT:PSS films were annealed at 170 °C for 30 minutes and then the films were developed using 1-Methoxy-2-propyl acetate, creating patterned SU-8 structures coated with the PEDOT:PSS. PEDOT:PSS on top of unexposed SU-8 was easily removed during the developing process. We found that the deposited PEDOT:PSS can be linked with remaining epoxide groups on top of cross-linked SU-8 by forming sulfonyl ester. Through this condensation reaction between epoxides in SU-8 and styrene sulfonic acid groups in PEDOT:PSS, the chemically crosslinked micropatterned SU-8 structures coated with PEDOT:PSS are obtained. We further applied this patterned conducting films as a seed layer for electroplating of copper electrodes. The electroplating of copper with a thickness of up to 15 µm was successfully demonstrated. We believe that the patterned microelectrodes on SU-8 substrates can be a promising platform for realization of several practical organic electronics and bioelectronics devices.

We report the development of advanced polymer hole-injection and electron-injection layers in collaboration with our industry partner that are now able to provide ohmic hole injection into organic semiconductors with ionization potentials up to 6.0 eV and ohmic electron injection into organic semiconductors with electron affinities down to 3.7 eV. The layers are based on new concepts in p-doped and n-doped polymers that can overcome the challenges of stability and dopant profile migration at these extreme values. We demonstrate novel device architectures including fully-solution-processed inverted organic solar cells without the use of low-workfunction metals, and the first organic CMOS circuit elements based on differentiated electrodes with the p- and n-doped charge-injection layers. This opens new device architectures leading to new possibilities for higher efficiency and performance not accessible previously.

Organic semiconductors offer very promising and unique properties towards light sensing applications e.g. tunable absorption spectra, solution processability, mechanical flexibility and high internal quantum efficiencies. For that reason, optical sensors using these materials fabricated by industrial relevant printing techniques will become more and more relevant for many applications in e.g. health sensing in wearables and medical diagnostics, environmental monitoring, or automotive industry, and even integrated and customer designed printed electronics. In this work we present highly efficient multi-layer organic photodiodes based on the polymer-fullerene blend PTB7:PC70BM, an AZO electron transport layer, and HC PEDOT:PSS electrodes, which have been entirely aerosol jet printed (AJP) on flexible PET substrates. AJP is a digital printing technique which allows for very precise deposition of a large variety of inks with a feature size down to a few micrometers. We present a comprehensive electrical and optical characterization of the printed layers and devices in dependency of the active layer thicknesses, surface topography and transparency. Devices with specific detectivities of >1E12 Jones over a broad wavelength range (400-750 nm) and maximum responsivities of 0.25 A/W have been prepared.
[1] R. Eckstein et al. Advanced Electronic Materials. doi: 10.1002/aelm.201500101 (2015)

We developed a new combinatorial approach to analyze in situ growth of organometallic crystallites within polymer matrices using one-pot solution-processing methods, and to control the distribution of organometallic particles. We controlled the distribution and orientation of particles by exploiting geometric confinement in addition to guiding the direction of solvent evaporation with physical gradients. We visually characterized the morphology using microscopy and measured the Seebeck coefficients and conductivities to compare performances. We show that the optimal additive concentration and distribution can be estimated quickly with the added advantage of comparing properties of parts of a sample that are prepared from the same source under the same conditions.
First we used templated 2D wells of various shapes during drop-casting because the growth direction of secondary phase particles was determined by the evaporation of the solvent or the solidification wave front of the bulk film that both occur from the outside in towards the center (directly observed under microscope by taking pictures over time). For example, using square wells the crystals grow radially inward. Knowing this we can control how crystals grow locally with respect to pre-deposited electrodes, and obtain crystals that orient all perpendicular or all parallel to the electrodes.
Secondly, we used physical gradients to obtain a distribution in morphologies and additive concentration along the entire sample by guiding the direction of solvent evaporation. This was achieved using elongated wells (rectangles) and by imposing a gradient along the length, suitable for high-throughput screening to quickly find optimal composite compositions or to test ranges in the special distribution of second phases. Without the gradient we obtain homogenous morphology and concentration along the sample, but having radial orientation of crystals due to evaporation ending at the film center.
Temperature gradients resulted in a greater range in distribution of particle concentrations across the sample, but their orientation was mostly random. Samples that were sloped slightly (i.e. gravitational gradient) showed greater uniform macroscopic order and differed less over the length of the sample, with crystals that grow predominately in the direction of solvent evaporation. The bulk films solidify first at either the hot side or the top of the slope, resulting in the lowest concentration of second phase component in that region due to zone refinement and smaller particle dimensions due to film thinning. A combination of the two gradients provides the ultimate range of both composition and morphology in single samples.
The inorganic material work and electrical measurements were supported by the National Science Foundation, Division of Materials Research, Grant Number 1005398. Polymer synthesis was supported by the Department of Energy, Office of Basic Energy Sciences, Grant Number DE-FG02-07ER46465.

Atomic layer deposition (ALD) has been demonstrated to afford excellent gas permeation barriers, e.g. for the encapsulation of organic electronic devices [1]. Conventional ALD is vacuum based and requires long processing times. Towards high-throughput and roll-to-roll manufacturing, spatial ALD has been introduced [2]. Most of the work on spatial ALD relies on thermal processes (e.g. diethyl zinc and water). At low processing temperatures, thermal ALD in general is less favourable and plasma enhanced ALD (P-ALD) is a promising alternative [3]. Work on spatial plasma enhanced ALD at atmospheric pressure (spatial APP-ALD) is very limited, as of yet. Until now, no gas permeation barriers prepared by spatial APP-ALD have been demonstrated.
In this work, we report on Al₂O₃ thin films deposited by spatial APP-ALD from TMA and Ar/O₂ plasma with a growth per cycle of 0.18 nm. This in line with reports for reactor based low pressure P-ALD of Al₂O₃ [4]. Processing speed and precursor saturation were investigated and compared to those found for spatial ALD based on water and ozone. Barrier properties were measured using an optical calcium test. We demonstrate that APP-ALD affords Al₂O₃ layers with water vapour transmission rates (WVTR) on the order of 10^-4 gm^-2d^-1_, comparable to that of films made by conventional thermal ALD.
[1] J. Meyer, P. Görrn, F. Bertram, S. Hamwi, T. Winkler, H.-H. Johannes, T. Weimann, P. Hinze, T. Riedl, and W. Kowalsky, Adv. Mater. 21, 1845-1849 (2009)
[2] P. Poodt, R. Knaapen, A. Illiberi, F. Roozeboom and A. van Asten, Journal of Vacuum Science & Technology A 30, 01A142 (2012)
[3] H. B. Profijt, S. E. Potts, M. C. M. van de Sanden, and W. M. M. Kessels, J. Vac. Sci. Technol. A 29(5) (Sep/Oct 2011)
[4] T.O. Kääriäinen, D.C. Cameron, Plasma Process. Polym, 6, S237-S241 (2009)

Organic light-emitting diodes (OLEDs) are regarded as cutting-edge, next-generation displays due to the advantage of being easily adopted in transparent and flexible displays. However, the low out-coupling efficiency, approximately 20% in the case of typical OLEDs, should be enhanced for efficient display devices [1]. Among the several ways of enhancing the out-coupling efficiency, inserting nanostructures to OLEDs is an effective method to extract trapped modes [2,3]. We fabricate a quasi-periodic nanoparticle layer by a one-step spin-coating approach without lithography or an imprint or lift-off process. The nanoparticle layer was adopted to emboss the OLED structure, resulting in improved performance of OLEDs. Inorganic SiO2 nanoparticles were quasi-periodically spread on the surface of indium tin oxide used as an anode in the OLED by spin-coating a SiO2 nanoparticle solution under appropriate parameters. A poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, CLEVIOSTM P VP.Al 4083) layer was further coated as a hole injection layer (HIL). Due to the underlying nanoparticles, the PEDOT:PSS layer was naturally embossed. The height of the embossment was controlled by varying the size of the nanoparticles. Over the embossed PEDOT:PSS HIL, organic layers and a cathode were thermally deposited: 50 nm NPB (hole transporting layer) / 50 nm Alq3 (emitting layer) / 1 nm LiF (electron injection layer) / 100 nm Al (cathode). Compared with a flat OLED without the nanoparticles, the uneven OLED with the nanoparticles showed 0.2 V lower turn-on voltage at 1 cd/m2, 30% higher external quantum efficiency, and 60% higher power efficiency at 1000 cd/m2. The spin-coated PEDOT:PSS layer surrounding the nanoparticles injected holes to the NPB layer by detouring the inorganic nanoparticles. The embossment effectively shortens the distance between the PEDOT:PSS and Al layer, resulting in a higher electric field with lower driving voltage [4,5]. The nanostructured cathode layer helps to extract light from the waveguide and surface plasmon modes by Bragg diffraction.
Acknowledgement: This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP)(CAFDC 5-1(0), NRF-2007-0056090) and was also supported by the Global Leading Technology Program funded by the Ministry of Trade, Industry and Energy, Republic of Korea (10042477).
References:
[1] K. Saxena, V. K. Jain, D. S. Mehta, Opt. Mater. (Amst). 2009, 32, 221.
[2] J. Y. Kim, C. S. Choi, W. H. Kim, D. Y. Kim, D. H. Kim, K. C. Choi, Opt. Express 2013, 21, 5424.
[3] C. S. Choi, S.-M. Lee, M. S. Lim, K. C. Choi, D. Kim, D. Y. Jeon, Y. Yang, O. O. Park, Opt. Express 2012, 20 Suppl 2, A309.
[4] J. Y. Kim, W. H. Kim, D. H. Kim, K. C. Choi, Org. Electron. 2014, 15, 260.
[5] M. Fujita, T. Ueno, K. Ishihara, T. Asano, S. Noda, H. Ohata, T. Tsuji, H. Nakada, N. Shimoji, Appl. Phys. Lett. 2004, 85, 5769.

#8203;A new D-A structured conjugated polymer (PBDO-T-TDP) based on electron-rich benzo[1,2-b:4,5-bprime;] difuron (BDO) containing conjugated alkylthiophene side chains with electron-deficient diketo- pyrrolopyrrole (DPP) derivative is designed and synthesized. The polymer shows a narrow band gap with broad UV-Visible absorption spectra, which complements with that of P3HT:PCBM binary blend. Further, its energy levels can meet the energetic requirement of the cascaded energy levels of P3HT and PCBM. Therefore, PBDO-T-TDP is used as a sensitizer in P3HT:PCBM based BHJ solar cells and its effect on the photovoltaic properties has been investigated by blending them together at various weight ratios. It is observed that the resulting ternary blend system exhibited a significant improvement in the device performance (~3.10 %) as compared with their binary ones (~2.15 %). Ternary blend devices showed improved current density of 12.6mA/cm2. But showed inferior in fill factor compared P3HT:PCBM. To understand its decrease in fill factor, CELIV was carried out. Which showed increase in bimolecular recombination for the ternary blend. Which indicate increase in disorder in the morphology of these films. TRMC was carried to understand photoconducantance properties of these films. Which indicate binary mixture (PBDOT-T-TDP with P3HT and PCBM) showed similar #8710;G to that of P3HT:PCBM binary mixture. Inorder to understand free charges generated PL measurments were carried out, which showed efficient quenching from these binary and ternary blends.

Demands for transparent stretchable electrodes have increased with the development of stretchable electronic devices such as a wearable strain sensor, triboelectric generator, and electronic skins. Among various stretchable substrate materials, poly(dimethylsiloxane) (PDMS) is most extensively used due to its superior mechanical stretchability, bio-compatibility, and optical transparency to other candidate materials. As the stretchable electrode, silver nanowire networks (AgNWs) are known to be the most promising candidate. With a high degree of stretchability, AgNWs generally have R_s as low as 25 Omega;/sq. at the transparency of 90 %. However, AgNWs have a high degree of surface roughness and non-uniform areal density with disconnected ends, which limits interface formation with the organic layers deposited atop the electrodes and results in electrical short in devices, respectively. Engineers have addressed these issues by embedding AgNWs into the PDMS. However, due to the low surface energy of PDMS, embedding of AgNWs into PDMS is challenging. In this study, we improved the transfer efficiency of AgNWs from the release substrate to the PDMS by inserting an interfacial layer of porous nano-particles between the AgNWs and PDMS. As the nano-particles have highly enhanced van der Waals interaction forces, the interfacial layer functions like a glue to transfer AgNWs from the release substrate to PDMS. AgNWs were spin-coated on a glass substrate, and the nano-particles were coated atop the networks. Then, the liquid PDMS was coated and thermally cured. After curing, PDMS and the release substrate were separated in the deionized water. This fabrication process is all-solution process; hence, can be applied to produce large area PDMS with the embedded electrodes. The surface roughness and area uniformity of the embedded electrodes were analyzed using atomic force microscopy and by Joule heating test, respectively. The strechability of the electrode was investigated by cyclic tension tests. According to our analysis results, there was little change in Rs of AgNWs before and after the transfer. The areal uniformity of AgNW distribution by the interfacial layer was also confirmed. Furthermore, the surface roughness of the embedded AgNWs is less than the AgNW-coating by more than an order. As the interfacial layer tightly hold the AgNWs, the AgNWs were highly deformed, but firmly welded with the PDMS under the stretching. As a result, the change in R_s after 1000 cycles of 25 % tensional strain was less than 10 Omega;/sq., which is a significant improvement compared to the previously reported results. On these embedded electrodes, stretchable organic light emitting diodes and triboelectric generators were successfully fabricated, which confirmed the great potential of the PDMS with embedded AgNWs as the substrates for various stretchable devices.

Conductive films of high optical transparency are required in a myriad of optoelectronic applications, including lighting displays, touch sensors, and photovoltaics. Indium tin oxide (ITO) is the most widely used transparent conductive material due to the combination of low sheet resistance and high transparency when grown on a variety of substrates. However, alternative materials that do not require indium nor vacuum processing are desired. One possible ITO alternative is poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which consists of insoluble PEDOT that is charge stabilized by PSS, affording good solubility in aqueous formulations. While there are many methods that can be used to deposit this and other polymer solutions, spin casting is the most popular laboratory scale technique due to its simplicity and ability to deposit high quality films with a variety of materials. However, spin casting is a batch process that is difficult to implement on a continuous mass production scale. Conversely, solution shearing enables scalable and controllable thin film fabrication. The tunable deposition conditions afforded by this technique enable kinetic control of morphology, composition, and ordering.
Herein, we utilize solution shearing to fabricate highly conductive thin films of PEDOT:PSS. Specific control over deposition conditions allows for tunable phase separation and preferential PEDOT backbone alignment, leading to superior performance to spin-casted films. Optical and x-ray measurements indicate PEDOT ordering with respect to the shearing direction. Optimized conditions enable electrical conductivities of 4600 ± 100 S/cm and reach sheet resistances of 17 ± 1 Omega;/#9633; at 97.2 ± 0.4 % transmission. Additionally, these high performance TC PEDOT:PSS films were utilized as patterned electrodes in capacitive touch sensors and organic photovoltaics to demonstrate their practical viability in optoelectronic applications.

Ultra-fast laser processes are attractive as alternative patterning techniques to photolithographic methods, and they have the advantage for implementation to roll-to-roll (r2r) manufacturing processes for the low-cost and large area production of flexible Organic Electronic devices, such as Organic Photovoltaics (OPVs) and Organic Thin Film Transistors (OTFTs). Laser processes offer much higher resolution than printing methods, whereas scribing by laser methods allows closer spacing of the P1, P2 P3 laser scribes, increasing the active area of the printed OPV device, which contribute to the increase of the OPV efficiency.
In this work, we present the innovative approach for the implementation of in-line laser scribing technique on a r2r printing pilot line for the ultra-fast laser scribing of inorganic and organic nanomaterials for flexible OPVs. These include state-of-the-art inorganic nanomaterials (e.g. Indium Tin Oxide-ITO, Zinc Oxide-ZnO), as well as transparent polymers (e.g. PEDOT:PSS) and photoactive blends consisting of mixtures of polymers as electron donors (e.g. polythiophenes) with fullerene-based electron acceptors (e.g. PCBM) in single and multilayer structures. The above innovative methodology opens the way for the wide implementation of ultra-fast laser processes for the r2r manufacturing of Organic and Printed Electronics devices.

This work presents a study on the effects of plasma treatment on the wettability of silicon and fused silica for the deposition of Poly (3,4 ethyldioxythiophene) Polystyrene Sulfonate (PEDOT:PSS) via drop-casting or spin-coating. Silicon and fused silica substrates were sonicated in acetone, isopropyl alcohol, and methanol for 5 minutes each, then plasma treated for various amounts of time (i.e., 30, 60, 300, and 600 seconds) in either 100 parts oxygen plasma or 3 parts nitrogen and 100 parts oxygen plasma. To determine which conditions yielded the optimal surface energy, and thus wettability, the contact angles of PEDOT:PSS were measured via two methods, namely, 1) goniometry by using a Rame-Hart 290 instrument and 2) profilometry by using a KLA Tencor P-7 stylus profiler. Preliminary results show that both methods yield similar results for the lowest contact angle. The presented results are of interest for academic and industrial processing of hybrid photovoltaic devices.

We have recently reported that the photoprecursor approach can serve as an effective means to prepare multi-layer thin films through solution processes.¹ There, we employed 2,6-dithienylanthracene diketone (DTADK) as a photo-reactive precursor of p-type material 2,6-dithienylanthracene (DTA). Since DTA is essentially insoluble to most organic solvents, one can solution-deposit a different material on top of a DTA film, or even a composite film of DTA and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). We constructed p-i-n active layers by taking advantage of this characteristics, which showed much higher power conversion efficiency than that of the corresponding bulk heterojunction (BHJ) device (1.50% for the p-i-n, and 0.88% for the BHJ device, respectively). ¹ While this preliminary work showed the advantage of p-i-n structure, it also indicated that there was much room for improvement in the BHJ system prepared by the photoprecursor approach. This study presents the effect of solvent additive on the morphology and electric properties of DTA:PC₇₁BM BHJ films.
In this work, we compare BHJ films deposited by using chloroform as a solo solvent and those deposited using o-dichlorobenzene (ODCB) as an additive in chloroform. The structure of these device can generally be described as [ITO/PEDOT:PSS/DTA:PC₇₁BM/Ca/Al]. Without the ODCB additive, the resulting device showed a PCE of 0.44% associated with a low short-circuit current density (Jsc) of 1.75 mA cm^-2 and fill factor (FF) of 24.4%, and a significantly high series resistance (Rs) of 471 W cm². When chloroform containing 15% ODCB was used as deposition solvent, the PCE was greatly improved to 2.11% associated with a FF of 50.4% and Rs of 44 W cm², and Jsc of 4.45 mA cm^-2. Two-dimensional grazing-incidence X-ray diffraction (2D-GIXD) analyses showed that the latter BHJ film has randomly oriented microcrystalline domains of DTA, while the former is essentially amorphous. It was assumed that the higher boiling-point solvent remained during the photoreaction from DTADK to DTA, allowing DTA molecules to reorganize to form microcrystals, which might be advantageous in forming effective charge-carrier paths in the film. It would be worth noting that adding too much ODCB (>20%) resulting in the enhancement of the end-on mode packing of DTA, which is unfavorable for vertical carrier transport, thereby leading to lower PCEs.
These results clearly demonstrate the positive impact of solvent additive in improving the performance of the BHJ system prepared by the photoprecursor approach. Further investigation into processing conditions is underway employing different photoconvertible materials. This presentation will also include the updates along these lines.
(1) Yamaguchi, Y et al., Sci. Rep., 2014, 4, 7151.

Ultra-thin polymeric films combined with conductive materials and/or embedding electronic devices are envisioned as ideal candidate materials for the development of unperceivable personal monitoring systems to be used in healthcare and sport, in particular as regards skin-contact applications.[1] Indeed, their ultra-low thickness (few micrometers or less) allows for the intimate contact between such films and target surfaces onto which they conformally adhere, including skin. The challenge, in this view, is to reduce the overall thickness and at the same time to provide for reliable and robust strategies for production, handling, release and positioning of these extremely thin films, while maintaining the structural integrity and function of electrodes (used, as example, for physiological signals recording) and other on-board electronic components.[2] On the other hand, the adoption of industry-ready, high throughput, large area fabrication processes is demanded for achieving cost-effectiveness and speed of execution, towards mass-scale manufacturing.
Based on our previous studies dedicated to fabrication and patterning of free-standing conducting polymer nanosheets prepared by spin coating on small scale substrates,[3-4] here we report a roll-to-roll (R2R) process which permits the upscaling of this technology to large area and continuous manufacturing. R2R conductive nanosheets are obtained as bilayer structures with overall thickness 60 < t < 350 nm, comprising a functional layer of poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT:PSS) and a support layer of poly(D,L lactic acid) (PDLLA). Their release as free-standing films from a temporary substrate (plastic film roll) permits their transfer in conformal contact to any target surface with arbitrary shape, curvature and surface topography (including biological tissues and skin) to whom nanosheets strongly adhere without the use of any adhesive, as evaluated in adhesiveness tests. Specific high-conductivity formulations of PEDOT:PSS have been optimized making use of dimethylsulfoxide or butylene glycol (BG) as dopants. The latter, a dermatologically approved ingredient, is specifically intended for skin-contact applications. As a first demonstration of application in bioelectrical sensing, the R2R nanosheets are tested as unperceivable surface electromyography electrodes able to record muscle electric activity. Nanosheets have comparable performance with respect to standard pregelled electrodes used in clinical practice, in terms of signal to noise ratio. Moreover, nanosheets worn on the skin shows very good mechanical and electrical stability against body movement and sweating, also after prolonged use (several hours).
References
1. M. Kaltenbrunner et al., Nature499, 458 (2013).
2. D. H. Kim et al., Science333, 838 (2011).
3. F. Greco et al., Soft Matter 7, 10642 (2011).
4. F. Greco et al., ACS Appl. Mater. Interf. 5, 9461 (2013).

We report on thin tungsten trioxide (WO₃) films in electrolyte-gated transistor configuration using, as the electrolyte, ion-gels, such asPS-PMMA-PS/[EMIM] [TFSI] and PS-PEO-PS/[EMIM] [TFSI]. These ion gels are known to self-assemble into different microstructures depending on the copolymer/ionic liquid ratio [1]. We therefore studied these microstructures for applications in electrolyte-gated WO₃ electrochromic transistors [2]. Thin films of sol-gel tungsten trioxide were drop cast on pre-patterned chemically-etched ITO on glass and thermally treated at ca 450 °C; ion-gels were spin-coated on the WO₃ films [3].
We performed spectroelectrochemistry measurements on our transistors, coupling a hyperspectral imaging system (Pariss) to a semiconductor parameter analyser. We extracted the transmission spectra of the WO₃ films from different locations within the transistor channel, both in the ON (electrical bias applied, V_gs ca 2 V and V_ds ca 1 V) and in the OFF state. We established an extended correlation between the nature of the electrolyte selected (in particular of its viscosity and ionic conductivity) and the microstructure of the ion-gel (characterized by AFM) to quantitatively describe the advancement of the doping front in the electrochromic transistors.
Efforts are underway to render the sol gel synthesis of the films compatible with the deposition on flexible substrates. This would permit to demonstrate flexible electrochromic transistors to reach new applications in the automotive industry, smart labelling and inventory tracking.
[1] P. M. Simone and T. P. Lodge, “Phase behavior and ionic conductivity of concentrated solutions of polystyrene-poly(ethylene oxide) diblock copolymers in an ionic liquid.,” ACS Appl. Mater. Interfaces, vol. 1, no. 12, pp. 2812-20, Dec. 2009.
[2] C. G. Granqvist, Handbook of Inorganic Electrochromic Materials. Elsevier, 1995, pp. 499-518.
[3] K. H. Lee, S. Zhang, T. P. Lodge, and C. D. Frisbie, “Electrical impedance of spin-coatable ion gel films.,” J. Phys. Chem. B, vol. 115, no. 13, pp. 3315-21, Apr. 2011.

Ternary bulk heterojunction (BHJ) organic solar cells are a novel concept to overcome the limited absorption spectrum of organic semiconductors. In this concept the spectral sensitivity is enhanced by adding infrared sensitizers to the host system consisting of a wide bandgap polymer blended with fullerene derivatives to enhance light harvesting properties as well as the power performance of the single BHJ organic solar cell.¹ Such sensitizers have a strong impact on the morphology of the active layer, which in turn decisively influences the performance of the ternary organic solar cell. In this work the nanocomposite structure of a ternary organic solar cell is investigated by combining advanced techniques of analytical transmission electron microscopy (TEM). To the best of our knowledge this is the first time that the material distribution of an active layer in a ternary solar cell is visualized for all three organic materials using analytical TEM.
The ternary organic solar cell under investigation comprises the high band gap polymer indacenodithieno[3,2-b]thiophene,2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ), the near infrared (NIR) active sensitizer poly[(4,4&’-bis(2-ethylhexyl)dithieno[3,2-b:2&’,3&’-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5&’-diyl] (Si-PCPDTBT) and the fullerene [6,6]-phenyl C70 butyric acid methyl ester (PC₇₀BM). The cell features a pronounced sensitization effect resulting in a power conversion efficiency of more than 6% at 0.01 suns (1 mW cm^-2).
Electron energy-loss spectroscopy (EELS) and energy filtered TEM (EFTEM) were combined with energy-dispersive X-ray spectroscopy (EDXS) to successfully identify and distinguish the three materials in the blend. In the case of the mixing ratio PIDTTQ:Si-PCPDTBT:PC₇₀BM 0.5:0.5:2 the fullerene forms domains with diameters in the range of about 200 nm and the host polymer PIDTTQ surrounds these domains. In comparison to the binary blend, where the fullerene domains are in the range of 50 nm, the PC₇₀BM domain size is increased tremendously in the ternary blend. The sensitizer Si-PCPDTBT forms needle or plate like structures that are equally distributed in the whole blend. These Si-PCPDTBT structures are found in the polymer as well as in the fullerene domains as well as at the interfaces. Further mixing ratios will be investigated to elucidate the phase formation of this ternary blend system.
Acknowledgements
Financial support by the Marie Curie Initial Training Network (ITN) within the European Union&’s Seventh Framework Programme (Grant agreement no. 607585, OSNIRO), the German Science Foundation (DFG) via the Cluster of Excellence EXC 315 “Engineering of Advanced Materials”, the SFB953 “Synthetic C-Allotropes” and “Solar Technologies go Hybrid” (SolTech) is gratefully acknowledged.
References
1) T. Ameri, P. Khoram, J. Min, C.J. Brabec, Adv. Mater. 25 (2013) 4245-4266

White organic light emitting diodes (WOLEDs) attract huge research and commercial interest due to their high efficiency, inherent flexibility, lightweight and large-area emission, showing great potential to contribute strongly to general illumination in the future [1]. Besides, the possibility to reliably tune the emission color of WOLEDs - both for lighting and display applications - is also desired. While most of the research is focused on devices containing multiple emission layers, such WOLEDs suffer from the undesired voltage-dependent spectrum resulting from a variety of complex physical mechanisms which make controlled color change while keeping the brightness level constant hardly possible.
On the other hand, lateral alignment of monochrome OLED devices and addressing them via separate current drivers enables combination of efficient and stable illumination together with the possibility of controlled tuning of the emission color. However, such approach requires complicated and expensive processing when fine metal masks are used for structuring of the OLEDs, which ultimately leads to limitations in resolution and substrate size and is hence seldom used to fabricate WOLED devices.
Whereas photo-lithographic patterning is a well-established, up-scalable, high yield/resolution technique persistently used in inorganic semiconductor industry, its use in structuring organic electronic devices to date is rather limited, due to the processing of organic and/or water-based solvents, etchants and photoresists. The latter are known to be detrimental to most of the organic semiconductors. Recently, our group presented highly efficient vacuum deposited single color OLED photo-patterned down to the tens of micrometers using orthogonal processing approach [2]. Our method is based on a bilayer concept, enabling lift-off in hydrofluorother solvents, which are shown to be compatible with state-of-the-art OLED technology.
In this work, we present laterally aligned micro-OLED array consisting of efficient fluorescent blue and phosphorescent yellow devices comprising organic layer sequence optimized for orthogonal processing. Photo-structuring of the OLEDs down to 20µm was achieved by lift-off in HFEs. The resulting sub-units sit side-by-side without gap in between and can be addressed separately leading to reliable control of the emission color from blue to cold white to warm white to yellow under constant luminance. Furthermore, photo-lithographic size control of each of the subunits and its effect on device lifetime is discussed. Finally, ways to extend the photo-lithographic approach to structure three or more monochrome devices are presented.
[1] S. Reineke, “Complementary LED Technologies”, Nature Mater. 14, 459 (2015)
[2] S. Krotkus, F. Ventsch , D. Kasemann, A. A. Zakhidov, S. Hofmann , K. Leo, M. C. Gather, “Photo-patterning of Highly Efficient State-of-the-Art Phosphorescent OLEDs Using Orthogonal Hydrofluoroethers”, Adv. Optical Mater. 2, 1043 (2014)

Transparent semiconducting metal-oxides like zinc oxide (ZnO), indium zinc oxide (IZO) and indium gallium oxide (IGZO) have been widely used as active layer of thin-film transistors (TFTs) envisaging applications in large-area active matrix displays and in totally transparent circuitry due to their considerably high charge-carrier mobility, optical transparency in the visible range of the electromagnetic spectrum and stability. Recently, TFTs comprising solution-processed metal oxides obtained via hydrolysis/pyrolysis of an organic precursor have achieved electrical performance which challenges metal-oxide TFTs produced by traditional deposition methods (e.g. RF sputtering), presenting attractive characteristics as low manufacturing cost and possibility to cover large-areas. However, solution-processed metal oxide thin films still suffer from undesirable characteristics such as film non-uniformity, high porosity and unstable electrical response. In order to circumvent these problems, we have used an alternative method, based on a polymeric precursor route (Pecchini) to obtain more compact and uniform metal oxide films via solution processing. The elimination of the organic phase and the formation of inorganic thin-films was carried out by thermal treatment at different temperatures (ranging from 200^oC to 500 ^oC) and at different times (from 5 min to 2 hours) and was monitored by optical absorption in the UV-vis and the IR ranges (FTIR). It was observed that, for temperatures above 350^oC and times superior to 30 min, the organic phase was completely eliminated and the metal oxide phase was achieved. The optical bandgap of the resulting ZnO films, determined from UV-vis absorption, is about 3.4 eV. Film crystallinity and stoichiometric composition of the thin-films were determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX), respectively. Film morphology and thickness were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The electrical properties were performed by d.c. current-voltage measurements (output and transfer curves) in a bottom-gate, bottom-contact thin-film field effect transistor structure using p-type Si substrates with a thermal grown SiO₂ dielectric layer (90 nm to 300 nm), by capacitance-voltage measurements and by impedance spectroscopy. The electrical properties (charge-carrier mobility, threshold voltage, semiconductor capacitance dependence on voltage and excitation frequency and current stability) of the fabricated electronic devices show a significant improvement of the films obtained via the polymeric precursor route in comparison to devices built using semiconductor active layer obtained from the thermal conversion of the pure organic precursor. This improvement is due to the better film uniformity and lower concentration of defects from grain interfaces. (Authors acknowledge FAPESP grant # 2013/24461-7).

A novel transparent touch sensor was fabricated with a drop-on-demand inkjet printing technique on borosilicate glass and flexible polyethylene terephthalate (PET) substrates. Conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and dielectric poly(methylsiloxane) were deposited on a desired area to form a capacitive touch sensor structure. The properties of the printed sensors (optical transparency, electrical resistance and touch sensing performance) were investigated with varying PEDOT: PSS printing passes. A novel transparent touch sensor fabricated with an all-inkjet-printing method is demonstrated for the first time. This process holds industrially viable potential to fabricate transparent touch sensors with an inkjet printing technique on both rigid and flexible substrates for a wide range of applications.

Printed, flexible electronics have gained interest in recent years as low-cost, recyclable alternatives to conventional semiconductor devices. Cellulosic materials can be used as substrates for large-area, roll-to-roll manufacturing of flexible electronics and are being explored for applications such as smart packaging, biosensors and roll-up displays. The main challenge in producing these flexible devices is the delivery of the semiconducting polymer to the paper substrate.
This work presents an improved and environmentally friendly approach to deliver a semiconducting polymer, poly(3-hexylthiophene) or P3HT, to paper substrates. Cerato ulmin (CU), a natural protein Janus hydrophobin, is used to encapsulate solutions of P3HT, and cellulose nanocrystals, CNCs in an aqueous medium. CNCs form cholesteric liquid crystals that drive P3HT alignment, facilitating easy electron hoping. Furthermore, the self-assembled CU membranes stabilize and constrict the P3HT-CNC mixture into elongated cylindrical structures, which also enforces P3HT alignment.
By encapsulating P3HT in CU, the volume of chlorinated solvent required can be reduced by 90% because it is replaced by water. This “green” processing will render a highly conductive, P3HT-CNC-based ink suitable for inkjet printing onto paper to create recyclable electronic devices that can bend and fold. Enhanced charge transport in the dried P3HT thin films is expected due to the liquid crystal ordering within the CU-stabilized structures.

Recently, transparent organic light-emitting diodes (TOLEDs) have attracted much interest, because they can open new applications for bi-directional displays, transparent displays, wearable displays, smart glass, and window lighting. Typically, the device structure of TOLEDs needs to consist of an ITO bottom anode, emitting layer, and a thin metal cathode. To protect underlying organic layer from sputtering damage, a thin metal-based semi-transparent cathode was necessarily used by thermal evaporation. In this system, there were many problems in application of ITO electrodes to high efficient TOLEDs.
First, these TOLEDs usually have a preferential one-sided emission due to differences in reflection between ITO and Ag electrodes. In particular, the ITO-side emission ratio has a strong intensity which is more than 70% of the total emission ratio because of the relatively low reflection of ITO compared with Ag film. Second, the majority of the light generated in the organic layers is confined in the ITO anode and glass substrates due to the large difference in the refractive index between their layers. This results in out-coupling efficiencies of around only 20% due to the total internal reflection at the ITO / glass and glass / air interfaces. These problems can be solved by employing a thin metal (Ag) electrode as an ITO alternative. However, it is very difficult to form smooth and very thin Ag layers for transparent anode. Ag layers exhibit three-dimensional island growth as a result of the poor wettability of Ag on the substrate. A discrete Ag film consisting of an island structure exhibits strong absorption and scattering of incident light, because of localized surface plasmon resonance. Thus, thin Ag film was not considered as a transparent electrode for TOLED.
Here, we demonstrate an innovative method to make transparent and high performance OLEDs on substrates using only ultra-thin Ag electrodes as both the top and bottom transparent electrodes. We show that merely a minute-plasma treatment on the glass before the deposition of Ag layer leads to significantly improved growth homogeneity of the Ag layer. The ultra-thin Ag film is formed after oxygen plasma treatment, leading to improved visible range transmittance and sheet resistance. By designing the weak micro-cavity structure with the ultra-thin Ag electrodes, waveguide modes could be suppressed and optical transmittance of TOLEDs could be improved. According to FDTD simulation, waveguide modes in ITO and glass substrate can be remarkably extracted because of weak micro-cavity effect. Consequently, the luminance of TOLED could be improved by 47 %. In addition, the transmittance of TOLED with the ultra-thin Ag electrode showed a high transmittance (73.84 %), which was similar than that of ITO (73.19%). The optimized weak micro-cavity structured shows the high optical transmittance, identical emission rate and reduced wave-guided mode were achieved, enhancing the luminance of devices.

In this research, organic photovoltaic device (OPV) with low cost, facile and well light harvesting is investigated. We used zinc oxide (ZnO) nanoparticle as a hole-extracting buffer layer at anode to increase the efficiency and stability of the device are deposited on a cleaned ITO by hydrothermal method and annealed at 200 °C. The optimum condition of the ZnO layer is investigated by varying different dipping time. UV ozone treated and without UV ozone treated ZnO are investigated to observe the influence of UV ozone on the efficiency of the devices. UV treated ZnO device has the least current leakage. Boron subphthalocyanine chloride (SubPC) and fullerene (C₆₀) are the donor and acceptor in the cell respectively. The power efficiency can reach 3.12%, which is around 25% higher than a standard SubPC opv device when the dipping time is 7 min. It is due to the large values of the short circuit current density (Jsc) and open circuit voltage (Voc). The short circuit current (J_sc), open circuit voltage (V_oc) and Fill factor (FF) are 5.91Acm^-2, 1.06V and 0.52 respectively. This optimum fabricating condition of ZnO is affected by the morphology of ZnO layer. When the dipping time increased, the surface roughness also increased until the time reached 7 min. This is beneficial in J_sc, Voc and efficiency. The stability of the ZnO device&’s efficiency is improved when compare with standard device.

Side chain engineering has a significant impact on supramolecular assemblies in conjugated polymer systems. A decrease of regioregularity could lead to an improvement of material mechanical flexibility, which is favorable for the fabrication of flexible organic field effect transistors (OFETs), however, the concomitant decrease in thin-film crystallinity severely deteriorates charge transport performance. Herein, flexible OFETs using regioregular (RR) and regiorandom (RRa) poly(3-hexylthiophene) (P3HT) blend thin-films as the active layer for devices fabricated via solution processing on polyethylene terephthalate (PET) substrates was demonstrated. In contrast to devices using single component RR-P3HT, the blend thin-films can preserve the prominent average charge carrier mobility at 0.12 cm² V^-1 s^-1 with negligible hysteresis even when the active component comprises a small proportion of the blend. Also, transistor performance does not degrade upon application of an external strain of 3.2% owing to the dispersion of the conductive material into the flexible insulating RRa-P3HT matrix. The phase separation of the blend films and their charge transport performance are found to be strongly dependent on the choice of solvent. High solvent boiling point is one of the prerequisites to ensure the formation of an effective charge transport pathway during a rapid spin coating process when the insulator becomes the major component of the blend films. The highly ordered RR-P3HT nanofibrillar structures induced by ultrasonication and their impact on semiconductor-polymer dielectric interfaces was also systematically investigated via X-ray diffraction, atomic force microscopy and optical absorption measurements respectively, as a function of blend composition. The blend thin films facilitate identification of an orthogonal solvent for subsequent dielectric deposition, thus enabling a top gate-bottom contact configuration, which is favorable for ambient stability: the top gate architecture allows the dielectric to serve as an encapsulation layer to protect the underlying semiconductor from atmospheric oxygen and moisture. The fabrication of flexible OFETs required no surface treatment or annealing steps, and processing was conducted under ambient conditions, suggesting a promising method that can meet the manufacturing requirements for roll-to-roll large scale production.

With polymer-based organic photovoltaic (OPV) cell power conversion efficiencies exceeding 10%, interest in their commercial fabrication is escalating. Along with the need to move to linear deposition techniques, such as spray, inkjet, and slot die coating, photovoltaic devices using thick layers (>200 nm) ensure reproducibility and high yield. However, in thick OPV active layers featuring semiconductors with relatively low charge carrier mobilities, space charge (SC) limited photocurrent is known to limit charge extraction.[1] Specifically, a SC region builds up at the electrode that extracts the slowest carrier. The resulting band banding at this electrode considerably reduces the electric field in the rest of the photoactive layer, effectively limiting the charge collection to only the carriers generated in the space charge region, setting a thickness limit for an efficient OPV cell.
In this work, we use the large area technique of concurrently pumped ultrasonic spray coating [2] to precisely and thoroughly probe the device optimization for both inverted and conventional architectures of diketopyrrolopyrrole-based (pDPP5T-2) photovoltaic devices. Donor:acceptor ratios and thicknesses were simultaneously swept, achieving peak device efficiencies of 6.5%. Implemented for single carrier devices, the electron mobility for thin layers was found to increase (from 10^-6 to 10^-2 cm²V^-1s^-1) with acceptor concentration, but to be constant and low (10^-5 cm²V^-1s^-1) at large thickness (1400 nm). In contrast, the bulk heterojunction hole mobility is high and constant (10^-2 cm²V^-1s^-1), regardless of acceptor concentration and thickness. Since these calculations assume that a SC is the limiting factor for current, it is plausible that another factor begins to dominate carrier extraction in thick devices.
Unexpectedly, the measured external quantum efficiency (EQE) spectra for thick inverted OPV devices could only be opto-electronically modelled with three zones of current collection. All devices show a high quantum efficiency region near the cathode, consistent with SC limited current. However, contrary to the two-region model commonly used for SC limited devices,[3] a wide zone at the reflective anodic contact contributes to the EQE signal for inverted devices. We propose that this unexpected current contribution results from carrier diffusion in a low carrier density zone. We further validate this model with semi-transparent devices. Using this three-region model, we accurately reproduce measured EQE spectra from devices illuminated through the ITO and through the thin metal contact side. With the phenomenon of three regions current extraction in thick organic photovoltaics elucidated, the performance limitations of these devices can be pushed further toward manufacturability.
[1] V.D. Mihailetchi, et al, Physical Review Letters, 2005, 126602
[2] J.G. Tait, et al, IEEE Journal of Photovoltaics, 2014, 1538
[3] G. Dibb, et al, Scientific Reports, 2013, 333

For flexible thin-film transistors (TFTs), hybrid gate dielectric materials are great current interest because of their high mechanical properties, low temperature processability, low-cost, and operating at low voltages. In this study we report here a vacuum-free solution processed novel organic/inorganic hybrid dielectric layer composed of HfO_x-PMMA precursor solutions. The effect of hybrid solutions are studied with and without cross linking agent 3-Glycidoxy propyl trimethoxy silane (GPTMS). Dielectric films are readily prepared by Spin/Dip coating process with controlled thickness (~100nm) and then followed by cured at low temperatures (le;200⁰C) for compatibility of plastic substrates. The optical properties of the hybrid films are determined by UV-vis spectroscopy and the films are optically transparent in the visible range (400-700nm). The morphologies and microstructure of the films depended on the amount of GPTMS in the precursor solution and were characterized by FE-SEM. The films are homogeneous, amorphous moreover high smooth enough and very low roughness (le;1nm) observed by AFM. The chemical composition of the films and functional groups studied by XPS and followed by Fourier transform infrared spectroscopy (FTIR). Additionally these hybrid amorphous films are desired for electrical and dielectric properties such as reduced leakage current and Capacitance -voltage properties of TFTs.

Development of solution based small-molecule organic multilayer thin film deposition technique is an attractive step for further prevalent of organic devices. We have been investigated deposition characteristics of organic and inorganic thin films with a three-electrode-type electrospray deposition (ESD) system named nano-mist deposition (NMD) with an extraction electrode near the nozzle tip to improve the controllability of conventional ESD with two electrodes.
In this study we present two important progress of solution based small-molecule organic thin film deposition with NMD. One is smooth (RMS<5nm) pinhole-free uniform deposition of films using a multi-jet (MJ) mode NMD, and the other is fabrication of Alq₃/α-NPD bilayer without dissolving of under layer by use of appropriate additive solvent.
The NMD system consisted of a glass syringe equipped with a metal nozzle (1st electrode), a syringe pump, an extraction ring electrode (2nd electrode), a ground plate (3rd electrode), and two high-voltage power supplies. The temperature of the ground plate was kept at 25 ^oC. The nozzle and extractor voltages were set to 4.8~5.3 kV and 3.0 kV, respectively. Deposition distance was varied from 4.0 to 10.0 cm to control the dry and wet condition of mists.
Three typical spraying modes of the Taylor-cone (TC), the convergent-jet (CJ) and the MJ were used to examine deposition characteristics of a small-molecule material by the NMD. A chlorobenzene solution of CBP:PBD:TPD:Ir(mppy)₃ (ratio of 60:15:10:5 in wt%) with 10 vol% dimethylsulfoxide (DMSO) were deposited on AZO/ITO coated glass substrates. A spin-coating of this material was difficult to form uniform thin films due to agglomeration and there were many pinholes. A slightly dry condition could form pinhole-free films for all spraying modes but the surface morphology was rough for TC and CJ modes due to inclusion of large size mists (>10mu;m in diameter). Using MJ mode, we could obtain pinhole-free smooth film (80 nm in thickness) with RMS roughness of 5 nm. It was revealed that the MJ mode can deposit smallest mists with narrowest size distribution (average diameter d_ave=1.6 mu;m) compare to those of TC mode (d_ave=10.4 mu;m) and CJ mode (d_ave=7.4 mu;m).
A typical light emitting small molecule of Alq₃ was deposited on a hole transparent small molecule of α-NPD layer by NMD using common solvent of dichloromethane (DCM) with DMSO as an additive solvent. It was found that α-NPD layer was dissolved by DCM mists and many pits were formed on the surface at the DMSO concentration of 10 % or less, however the surface erosion was remarkably suppressed at the DMSO concentration over 20 %. A photoluminescence analysis of Alq₃(60 nm)/α-NPD(25 nm) bilayer revealed that intermixing of both organic layers at the interface was effectively suppressed.

Organic electronics has recently attracted a great deal of interest because of its solution-processed potential applications in flexible, wearble, and even stretchable devices. This, however, serves as a trade-off when one tries to implement these processes in assembling practical electronic devices, since the as-deposited films would be fragile to subsequent solution processes. Consequently, conventional photolithography is hardly applicable to solution-processed organic semiconductor layers for getting high-resolution pattern.
In this talk, we demonstrate the whole new type of organic materials based on sol-gel chemistry, which is capable of remarkably showing chemical and mechanical stability during photolithography process. The critical step in a sol-gel reaction is the formation of a highly cross-linked network out of molecular precursors through hydrolysis and condensation reactions. By carefully manipulating this step, we could prepare self-assembled structures of either quasi-3D random or ladder characteristics. The resulting structures yielded films that are highly tolerant against harsh external stimuli. Moreover, the peculiar topology of organometallic gel network containing with molecular pores could be successfully utilized as a template to form a heterogeneous interpenetrated network (HIPN) with functional electronic organic units.
As a result, we could achieve micron scaled patterns of organic semiconductor through the standard photolithography. Based on electrical properties of thin-film transistors with patterned organic semiconductor layers, we successfully designed and demonstrated a CMOS inverter circuit with micro-patterned n- and p-type channels based orthogonal organic semiconductor gels through sequential solution processes.

Solution-based fabrication technique of organic thin films are desired an alternative to the vacuum evaporation process for organic electronic devices. Poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonic acid) (PEDOT:PSS) is commonly used in organic light emitting diodes (OLEDs) and organic solar cells as hole injection/transport layer. Control of the surface properties in nano-scale, such as molecular stacking, orientation, crystallinity and so on, are directly influence on electronic and optical properties. We discuss precise control of surface characteristics of PEDOT thin films in the different fabrication methods, applied a novel solution-based ultrasonic spray assisted mist vapor deposition technique and electrochemical polymerization.
In the mist-vapor deposition process, we prepared commercialized PEDOT:PSS solution and controlled the deposition time, concentration, substrate temperature, carrier gas concentration as forming parameters. On the other hand, in the electrochemical polymerization process, 2,3-Dihydrothieno[3,4-b][1,4]dioxine (EDOT) monomer solution is made preparations in advance and controlled polymerization time.
In order to characterize the film properties, UV-vis spectrometer, Fourier-transform infrared spectroscopy (FT-IR) are used and electric properties are discussed. It is possible to control the film thickness in molecular scale in the both forming technique. However, molecular orientation of the PEDOT on the electrode is highly controlled by the electrochemical polymerization than that of the mist-vapor deposition. This is because stacking of the EDOT monomer on the electrode is gradually increased at the primary stage of the polymerization reaction. This precise controlling in the film forming technique enables that the efficiency of the hole injection properties of the OLEDs and carrier separation of the solar cell will be improved.

Nanocomposite hybrid materials based on inorganic dielectric nanoparticles or nanorods are rapidly attracting increasing attention due to their potential as solution processable high-k dielectrics for organic electronics. Although there are several reports claiming the successful implementation of such dielectrics in organic-field-effect-transistors (OFETs), very little has been done on the in-depth characterization of the dielectric (impedance spectroscopy) and electric (leakage current) response of such hybrid systems. Here we present one of the first works addressing this matter by investigating and discussing the dielectric and electric behavior of films of titanium dioxide nanorods functionalized with oleic acid. The titanium dioxide nanorods considered in this work have the anatase phase and have an average diameter of 5 nm and length of 20 nm. Ligands other than oleic acid (e.g. phosphonic-acid and photocrosslinkable phosphonate terminated coumarin) and nanorods with rutile phase will be also discussed. The use of photocrosslinkable ligands is particularly attractive because it enables the fabrication of 1) devices (OFETs) without using orthogonal solvents as well as 2) devices based on stacks of hybrid thin films allowing thus to further tune the properties of the final dielectric stack. The functionalized nanorods can be solution processed in several common solvents and spin coated producing uniform thin films with RMS surface roughness of the order of 1-2 nm. It should be stressed that the material preparation, device fabrication and measurements are all carried out in air showing the huge potential of this approach in the organic electronic field. Metal-insulator-metal (MIM) and metal-oxide-semiconductor (MOS) devices were fabricated to assess the dielectric and electric properties of the hybrid materials. In those samples incorporating the crosslinkable material, ultraviolet light irradiation was used to make insoluble films prior to depositing the top electrode. The highest value of the relative dielectric constant is of the order of 30 at 1 MHz and the dielectric loss is of the order of 0.01. Furnace and laser sintering experiments (using a high purity furnace and a XeCl 6ns excimer laser at 308nm) will be also discussed in order to show the potential of these materials to show dielectric constants of 130 at 1MHz. We also investigated the alignment of these nanorods using several deposition techniques (e.g. doctor blade, drop casting, dip coating). Birefringence as well as anisotropic conductivity of the film will be presented and discussed.

Printable paper and nanofiber electronics have been drawing intensive attentions because of their low cost and environmental footprint. In addition to conventional polymer materials, one important class of nanocomposite materials for this application involves ultra-fine polysaccharide nanofibers (i.e., cellulose) with 5-10 nm diameters that have been demonstrated as nanofibrous composite membranes for water purification. This report describes recent results of an investigation of nanomaterials that can be printed and processed on flexible polyimides and nanofiber membranes. The demonstration of the controllable printing and sintering of the nanoparticle inks on the flexible materials by controllable thermal and laser sintering techniques provide promising leads to establishing printable nanomaterials for flexible sensors and electronics. The morphological, structural, and electrical properties of the printed paper-based electronics are characterized using different techniques, aiming at establishing their correlation with the detailed sintering parameters. Results on the device strain-performance characteristics and chemical/bio sensing properties will also be discussed.

Soft electronics is a key technology for next generation electronic products such as flexible displays and wearable devices. And polymer insulating layers have been intensively studied for the soft electronics due to their favorable characteristics such as low process temperature and high mechanical flexibility. While various solution processed polymers and self-assembled monolayers were proposed and applied to soft electronic devices, significant improvement should further be made to fulfill all the requirements desired by soft electronic devices, such as high capacitance, yield, uniformity, and large-area processability. Here we demonstrate polymer insulating layers deposited by initiated chemical vapor deposition (iCVD) as ultrathin yet reliable insulators key to low-power soft electronics [Nat. Mater.14, 628 (2015)].
The iCVD is a vacuum process to fabricate polymer films directly on a target surface from vaporized monomers on which a polymerization is started by additional initiators. The process produced conformal and pure polymer films at near room temperature. The insulating property of iCVD processed poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) layers showed the leakage current density of about 1 nF/cm² even with the thickness down to 6 nm. The temperature dependent measurement reveals these MIM devices exhibit tunneling-limited insulating characteristics, rather than defect-dominant conduction found in typical polymeric layers. This down-scaling capability results in high capacitance density (C_i) compensating relatively low dielectric constant of polymer insulating layers ( 2.2 for pV3D3 ), and thus enables low-voltage operation when the pV3D3 layer is applied to field-effect transistors (FETs) as a gate insulating layer (GI). Various low-voltage FETs with organic, oxide, and graphene channel layers are successfully fabricated using the ultra-thin pV3D3 GIs. Furthermore, by combining plasma-grown AlO_X on Al gate electrodes, AlO_X/pV3D3 bilayer GIs enabled much higher C_i and thus OTFTs switchable at 1 V.
In addition, the pV3D3 insulating layers were shown to maintain their insulating property for the tensile and compressive strain of 4% and 3% respectively. Together with the low process temperature, this high flexibility provides a high degree of freedom in designing soft electronic devices. Organic FETs with pV3D3 GIs, therefore, could be fabricated on plastic substrates of low thermal budget. For example, devices were fabricated even on cellophane tapes to demonstrate their potential as “peel-and-stick”-type electronics. Large area processability of the iCVD process was also tested by fabricating the metal/pV3D3/metal and organic FET arrays on the substrates with the range of 10 cm, and showed high yield and uniformity in their electrical characteristics. From these results, we believe that the iCVD processed polymer insulating layers should be considered as a potential key component to realize soft electronic devices.

Organic photovoltaic (OPV) devices, in particular polymer solar cells, made by solution processed organic materials have shown great promise as a disruptive technology for affordable electricity. Even though recent advances look impressive on paper, until now the commercialization of OPV has been hampered by the difficulty of converting lab produced “champion” cell figures into reliable industrial-scale product performances.
Despite a lot of paper are published from a lot of different universities and research gruos, relatively few of them are related to scale-up of the technology and process development to take OPV technology out of the labs toward industrial production.
In this paper we present the main results of an R&D activity focused on the development of roll to roll process to print organic solar modules on flexible substrate with scalable processes.
We will put into light many of the aspects that limit the efficiency of large area Roll to Roll printed OPV modules to a few percents, compared to over 10% efficiency reported for small scale devices. There are several reasons for this performance gap: (i) fundamental issues related to the dimension of the elementary cell; (ii) final synthetic accessibility and cost of the materials; and (iii) the current lack of ink formulations that are applicable for R2R processing techniques, which limits the range of materials transferable from the laboratory to the pilot and further to industrial scale. All these aspects make the most of the scientific results from the OPV research not immediately transferable if not transferable at all, to an industrial R2R printing process.
Indeed, the device behavior is greatly affected by the active layer morphology, which in turn depends on both the selected deposition technique, and the post-treatment and deposition conditions, and from the right stacked sequence of materials, but not all the materials and not all the processes that are suitable for small scale devices prepared in laboratories, can be easily transferred to a continuous roll to roll printing process. Furthermore, ink formulations for all layers must be re-optimized to achieve the proper rheological properties as well as the ideal nano- and micromorphologies with consideration of the chemical compatibility and wetting issues of the overlapping layers.
The main results of the research activity and the main lessons learned during this three year program will be presented and suggestions about how to drive academic research activity toward real technology development finalized to commercial success of OPV will be given.
'mso-ansi-language:EN-GB'>

Measurements on organic single crystals reveal remarkable optical and electrical characteristics compared to disordered films. However, practical device applications require uniform, pinhole-free films. Thus, there is a need to develop methods by which highly uniform, pinhole-free crystalline thin films can be fabricated. It was recently demonstrated that abruptly heating a thin film of amorphous rubrene can create a highly crystalline film.[1] The films, with grains on the order of tens of microns when grown on indium tin oxide, were found to be pinhole-free and therefore suitable for use in vertical devices, such as solar cells, where they yielded exciton diffusion lengths on the order of hundreds of nanometers.[2]
We have found that the addition of a thin (5 nm) layer of tris[4-(5-phenylthiophen-2-yl)phenyl]amine (TPTPA) underneath a ~25 nm rubrene film dramatically improves the crystallization process. Annealing for 7 minutes at 140 °C yields a complete crystalline rubrene film with grains on the order of hundreds of microns. Polarized optical microscope (POM) images reveal uniformly colored grains as a result of crystalline birefringence. Moreover, the now-crystalline rubrene film acts as a template for further rubrene deposition. POM images of templated films (~100 nm) show increased contrast between crystal grains. Imaging via atomic force microscopy of rubrene adlayers as a function of thickness (from 1 - 80 nm) reveals the presence of molecular terraces, indicating an island growth mode, as well as crystalline defects (line and hole defects). Grazing incidence x-ray diffraction reveals the rubrene crystals adopt the orthorhombic crystal structure with the (h00) planes parallel to the substrate. Subsequent deposition of C₆₀ atop crystalline and preferentially oriented rubrene results in templated crystallization in which C₆₀ adopts a highly oriented, face-centered cubic phase with the (111) plane parallel to the substrate. Finally, with the inclusion of the TPTPA under-layer we are further able to tune the rubrene crystals from uniformly colored grains to gradient colored grain spherulites by varying the heating temperature from ~140-180 °C, implying that competition between the rates of crystallization and molecular rotation determine the type of crystal formed.
Solar cells made from these highly crystalline films of rubrene and C₆₀ have enabled us to measure photocurrent from two charge transfer states (centered at 1.59 and ~1.30 eV), underscoring the implications of highly ordered systems on photocurrent generation.
[1] Lee, H. M. et al.Organic Electronics12, 1446-1453 (2011).
[2] Verreet, B. et al.Adv. Mater.25, 5504-5507 (2013).

Identifying novel strategies to modulate charge carrier density improves our current understanding of the fundamental electronic properties of semiconductors. Electrolyte gating offers the opportunity to achieve high charge density (>10¹⁴ cm^-2) by creating electric double-layers at the semiconductor/electrolyte interfaces.¹
Functional oxides are very promising materials for next-generation electronics as they could undergo transitions from insulator to semiconductor and further to metal as the charge carrier density increases. Nanocrystalline titanium dioxide (TiO₂) is one of the most investigated oxide materials that already found applications in sensing, electrochromics, photovoltaic, and photocatalytic devices.
We fabricated, using an unconventional patterning process, sol-gel based TiO₂ electrical double layer transistors (EDLTs). TiO₂ EDLTs make use high surface area activated carbon (AC), as a gate electrode, and the ionic liquid (IL) 1-Butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI] and [EMIM][TFSI] ion gels, as the gating media.
To explore the effect of the double layer capacitance on device performance we investigated bottom-contact top-gated transistor where we varied the area of the active layer and its overlap with the source/drain electrodes. To shed light on the doping mechanisms of such transistors we performed cyclic voltammetry, electrochemical impedance spectroscopy and spectroelectrochemistry measurements .
The operating voltage of the devices was lower than 2 V and the ON/OFF ratio as high as 10⁴. Preliminary results suggest that a nearly metallic state in TiO₂ is observable at the interface between the TiO₂ film and the electrolyte.
[1] Han, Luo, Li, Shen, Qu, Xiong, Dou, He and Nie, Physical Review B 90, 2014, 205107.

Printing organic semiconductors is a promising approach to achieve low-cost fabrication of large area flexible electronics. The ability to rapidly pattern and deposit multiple materials and control the thin-film morphology are significant challenges facing industrial scale production. Herein, we report a novel and simple pneumatic nozzle printing approach to control the crystallization of organic thin-films and deposit multiple materials on the same substrate. Pneumatic printing uses capillary action between the nozzle and substrate combined with control of air pressure to dispense the solution from a dispense tip with a reservoir. We can control the orientation and size of the crystals by tuning the printing direction, speed, and the temperature of the substrate. We demonstrate the dependence of the mobility of printed thin film 6,13-bis(triisopropylsilylethynyl) pentacene on printing conditions; formation of well-ordered crystals occurs at an optimal head translation speed. A maximum mobility of 0.4 cm^2/(Vs) is achieved with 0.4 mm/s printing speed at 50 C. We also deposit and pattern multiple materials including metal lines and n-type organic semiconductors on the same substrate using this technique. In addition, we fabricated inverters and integrated organic transistor with an OLED to demonstrate the feasibility of our printed transistors. In summary, pneumatic printing technique can be an attractive route to industrial scale large area flexible electronics fabrication.

Using multi-functional oxide films, we report on the development of an integration strategy for
scalable manufacturing of graphene-based transparent conducting electrodes (TCEs) for organic
electronics. A number of fundamental and process challenges exists for efficient graphene-based
TCEs, in particular, environmentally and thermally stable doping, interfacial band engineering for
efficient charge injection/extraction, effective wetting, and process compatibility including
masking and patterning.
Using complementary X-ray photoelectron spectroscopy (XPS) and Ultra-violet
photoelectron spectroscopy (UPS), we show that all of these challenges can be effectively addressed at
once by coating graphene with a thin (>10 nm) metal oxide layer. We demonstrate
graphene electrode patterning without the need for conventional lithography and thereby achieve
organic light emitting diodes with efficiencies exceeding those of standard indium tin oxide
reference devices on rigid and flexible substrates.
Sanders et al. Nanoscale (just accepted)
Kidambi et al. Applied Physics Letters (2015)
Kuruvila et al. Journal of Materials Chemistry C (2014)
Meyer et al. Scientific Reports (2014)

Silicon based Micro-electromechanical Systems (MEMS) gyroscopes are gaining a lot of attention in wide spectrum of sensors applications, such as in aerospace, biomedical, automotive, and electronic appliances, because of their high sensitivity and high performance [1]. However, there are issues with fabrication techniques of the silicon based MEMS devices that they require extensive care and expertise with detailed processing steps for layer by layer structure. In this study, we present a feasible approach of fabrication of a polymeric vibrating ring gyroscope (PVRG) by using three-dimensional printing technology (3DPT). The 3DPT is now being widely used in research and development area because of its rapid fabrication process, inexpensiveness and availability of materials with unique properties [2]. The PVRG with sixteen electrodes fabricated with VeroWhitetrade; and VeroBlacktrade; 3D printed polymeric material. The diameter of the ring of the PVRG is 1.5 cm and thickness of the spring and the ring is 1 mm. The structures of the PVRG and the electrodes are coated with Cu to provide electrical conductivity by using electroless plating method. The PVRG resonates electrostatically by driving electrodes at 90#730; angle and capacitive sensing is done by sensing electrodes placed at 45#730; angle from the driving electrodes. The resonance frequencies of the PVRG are calculated with excellent mode-matched values of 15393 Hz and 15401 Hz on driving and sensing axes respectively, the split between driving and sensing mode is only 8 Hz.

The use of silver nanoparticles in conductive inks and their printing technologies have been known in the past few years. However, the very high cost of silver material has limited the broad industrial applications. In this regard, copper ink is considered a good candidate as a replacement for silver ink because of its low price and high conductivity. The antioxidant conductive copper nanoparticles are synthesized by using a hydrazine-free copper reduction method. In this study, we have developed the antioxidant conductive copper ink which can be applied to spray-coating processes for both glass and flexible polyimide (PI) substrates, using antioxidant copper nanoparticles. Conductive copper ink was then prepared by mixing the powder and complex with a binder in isopropyl alcohol. Then conductive copper films were formed on PI substrate using spray-coating, and the films were sintered by thermal treatment in nitrogen atmosphere at 300°C for 10 minutes. The conducting films had sheet resistances as low as 0.15 Omega;/#9633; over areas up to 100 cm² with a thickness of 5 mu;m. The lowest resistivity of 7.8x10^-5 Omega;-cm was obtained with 2 % addition of polymer as a binder. The formed flexible copper film was analyzed by an optical microscope (OM), a field emission scanning electron microscope (FE-SEM), an X-ray diffractometer (XRD), a surface profiler (α-step), and a four-point probe to confirm the shape, microstructure, crystal structure of conductive lines, and electrical conductivity. As a result, spray coating of conductive ink using copper nanoparticles will has a great potential for many applications, such as transparent electrodes, flexible electronics, and biosensor.

Vertical organic field effect transistor is a growing research topic due to the industry demand for high-performance low-cost thin-film transistors. In vertical transistors the channel length is determined by the semiconductor film thickness. Therefore, it is possible to fabricate a short channel high-performance device in spite of the organic semiconductors&’ relative low mobilities. In our design of vertical transistors the gate electrode is located beneath the source electrode and controls the amount of carriers injected from the source electrode to the organic semiconductor. From the semiconductor the carriers swiftly cross the very short channel length towards the drain electrode. We developed a new fabrication processes of n-type and p-type vertical transistors reaching on/off over 10⁵ and current densities above 10mA per cm². Complementary inverters was successfully assembled using those transistors.
Owing to the patterned source electrode technic, the gate is able to induce an efficient potential barrier lowering between the source electrode and the semiconductor. The fabrication process is compatible with large-area and low-cost fabrication. Using simple one step photo-lithography and lift-off process patterned electrode with holes in sizes of 2-20 µm is fabricated. In this process a blocking layer is added on the top of the source electrode in order to reduce off currents for better performances. To achieve high on/off ratio there must be an injection energy barrier between the source and the organic semiconductor. When using gold as source electrode it is possible to fabricate P-type and N-type transistor at the same process just by changing the organic semiconductor casting.
In this presentation we will also discuss the holes diameter size in source electrode affect the device performances. The operation mechanism will also be explained using COMSOL simulation results.

The carbon nanotube enabled vertical field effect transistor (CN-VFET) is a new class of organic transistor constructed by sequentially stacking a gate electrode, dielectric layer, dilute carbon nanotube film, organic channel layer and drain electrode as a vertical stack. The gate field shifts the Fermi level of carbon nanotubes and modulates the Schottky barrier height and width that develops between nanotubes and semiconducting channel material to control the current through the device. The vertical architecture allows for naturally short channel lengths determined by the thickness of the thin organic channel layer overcoming the relatively low mobility of organic semiconductor with anticipated commensurate improvements in the operating speed. By analogy with complementary metal-oxide-semiconductor (CMOS) technology, combining p-type and n-type CN-VFETs to fabricate logic circuits would have important advantages in power consumption and noise immunity. However, the characteristics of p-type and n-type transistors including the threshold voltage, and the off and on currents must be well matched so that the complementary logic gates present large gain and noise margins to facilitate practical application. For traditional Si-MOSFET, these characteristics are usually controlled through ion implantation, for the CN-VFETs we resort to selecting suitable n- and p-type organic semiconductors and control over the carbon nanotube charge transfer doping to tune the nanotube work function. We have fabricated prototypical organic complementary inverters which demonstrate decent dynamic functionality. The mechanism and fabrication of CN-VFET logic gates, organic channel material selection, device performance and progress toward a CN-VFET ring oscillator will be presented.

Organic thin-film transistors (TFTs) create the possibility of implementing a wide range of electronic systems, such as sensors, information displays and integrated circuits, on a wide variety of substrates, including glass, textiles, plastics and paper. Paper is particularly intriguing, because unlike plastics, paper is a naturally renewable and easily recyclable material [1]. And while the performance of early organic TFTs fabricated on paper [2] used to be substantially inferior to that of organic TFTs fabricated on glass or plastics, there have recently been several encouraging reports on the successful realization of organic TFTs with impressive carrier mobilities and large on/off current ratios on a variety of types of paper [3,4]. Here we demonstrate bottom-gate, top-contact organic TFTs fabricated directly on the surface of commercially available paper, without applying a protective or planarization coating, using the vacuum-deposited small-molecule semiconductors dinaphtho[2,3-b:2&’,3&’-f]thieno[3,2-b]thiophene (DNTT [5]) and N,N&’-bis(2,2,3,3,4,4,4-heptafluorobutyl)-1,7-dicyano-perylene-(3,4:9,10)-tetracarboxylic diimide (Polyera ActivInk^TM N1100 [6]) for the p-channel and n-channel TFTs, respectively. A thin hybrid gate dielectric based on oxygen-plasma-grown aluminum oxide and a mixed alkyl/fluoroalkylphosphonic acid self-assembled monolayer (SAM) with a capacitance of 500 to 600 nF/cm² was employed, so that the TFTs can be operated with voltages of about 2 to 3 V. By adjusting the composition of the mixed alkyl/fluoroalkylphosphonic acid SAM [7], the threshold voltages of the TFTs can be tuned to obtain enhancement-mode characteristics for both the p-channel and n-channel TFTs. The DNTT p-channel TFTs have a charge-carrier mobility of 1.6 cm²/Vs, an on/off current ratio of 10⁶, and a subthreshold slope of 90 mV/decade, which is to our knowledge the steepest subthreshold slope reported for organic TFTs on paper. The N1100 n-channel TFTs have a carrier mobility of 0.3 cm²/Vs, an on/off current ratio of 10⁵, and a subthreshold slope of 140 mV/decade. The TFTs also display a very large differential output resistance, which is an important requirement for applications in analog circuits and active-matrix displays. [1] D. Tobjörk et al., Adv. Mater. 23, 1935, 2011. [2] F. Eder et al., Appl. Phys. Lett. 84, 2673, 2004. [3] T. Minari et al., Adv. Funct. Mater. 24, 4886, 2014. [4] B. Peng et al., Sci. Rep. 4, 6430, 2014. [5] T. Yamamoto et al., J. Am. Chem. Soc. 129, 2224, 2007. [6] B. A. Jones et al., Angew. Chem. Int. Ed. 43, 6363, 2004. [7] U. Zschieschang et al., Adv. Mater. 22, 4489, 2010.

While much of the flexible and organic electronics activity has been display-centric there is no doubt that as this technology matures the number of applications will continue to increase. Organic semiconductors are also very appealing for light detection applications. They combine effective light absorption from ultraviolet to near-infrared with good photogeneration yield, sensitivity and response time. By using solution-processed organic bulk heterojunction photodiodes rather than the usual amorphous silicon, process temperatures is reduced to be compatible with plastic film substrates, and a number of costly lithography steps are eliminated, opening the door to lower production costs. These materials can be processed from solution over large area, making them specifically attractive for large area imagers such as X-ray detectors for medical applications. Using our most recent flexible X-ray detectors^1-3 we will discuss the prospect and challenges of solution processed bulk heterojunction photodiodes. Improvements in materials and processing have resulted in the demonstration of uniform coatings on 30x30 cm substrate size by slot-die coating. With dark currents as low as 1 pA/mm2 and sensitivity of 0.2-0.5 A/W these organic photodetector meets first product requirements: a proof-of-concept detector delivers high-resolution, dynamic images at 10 frames per second (fps) and 200 pixels per inch (ppi) using X-ray doses as low as 3 microGy per frame³. The characteristics of the organic photodetectors will be discussed in detail. The insights thus obtained are used to design photodetectors that exploits their potential to the fullest. Finally, next-generation applications will be discussed, including hemispherical imagers and artificial retina. ¹ X-ray imager using solution processed organic transistor arrays and bulk heterojunction photodiodes on thin, flexible plastic substrate, G.H. Gelinck et al., Organic Electronics, 14 (2013) 2602-2609.
² Organic Imager on Readout Backplane Based on TFTs With Cross-Linkable Dielectrics, P.E. Malinowski et al., IEEE Photonics Technology Letters, 99 (2014) 1. ³ X-ray detector-on-plastic with high sensitivity using low cost, solution-processed organic photodiodes, G.H. Gelinck et al., in print for IEEE Transactions Electron Devices (special ‘imager&’ issue).

Organic thin-film transistors (TFTs) are of interest for flexible electronics applications, such as rollable or foldable displays and conformable sensor arrays. In advanced applications, such as integrated display drivers, the TFTs will have to be able to control electrical signals of a few volts at frequencies of several megahertz. The first requirement for achieving high switching frequencies is efficient charge transport in the semiconductor. This requirement can be met by choosing an organic semiconductor that provides good molecular ordering and large carrier mobilities even when processed at low temperatures. An example is the alkylated thienoacene C₁₀#8209;DNTT, for which mobilities up to 10 cm²/Vs have been measured [1]. The second requirement is a small channel length [2]. To meet this requirement we have developed a process in which the TFTs are patterned using high-resolution silicon stencil masks [3]. With this process, bottom-gate, top-contact organic TFTs with a channel length of 1 µm, an effective hole mobility of 1.2 cm²/Vs, an on/off current ratio of 10⁷, a subthreshold swing of 150 mV/decade, and a width-normalized transconductance of 1.2 S/m can be fabricated on flexible plastic substrates [4]. Owing to small thickness of the gate dielectric (5.3 nm), the TFTs can be operated with voltages of about 3 V. The third requirement for achieving high switching frequencies is a small gate capacitance. One component of the gate capacitance is the parasitic capacitance that is formed by the geometric overlaps between the gate electrode and the source/drain contacts, so reducing the gate overlap in addition to the channel length can be helpful in view of high-frequency TFT operation [2,3]. For 11-stage ring oscillator comprised of unipolar inverters with saturated load based on C₁₀#8209;DNTT TFTs with a channel length of 1 µm and a gate overlap of 5 µm, we have measured signal propagation delays of 1.9 µs at a supply voltage of 1 V, 420 ns at 3 V, and 300 ns at 4 V. [1] R. Hofmockel et al., Org. Electronics 14, 3213, 2013. [2] M. Kitamura et al., Appl. Phys. Express 4, 051601, 2011. [3] F. Ante et al., Small 8, 73, 2012. [4] U. Zschieschang et al., Org. Electronics 14, 1516, 2013.

Metal oxide and organic-based thin-film transistors (TFTs) are rapidly becoming the new building blocks in the emerging field of large-area, printable microelectronics. This is primarily due to the fact that the two families combine unique physical properties such as high charge carrier mobility and optical transparency with superior mechanical flexibility. Unlike organics, metal oxides have only recently shown to be compatible with inexpensive and temperature-sensitive substrates such as plastic paving the way to a host of exciting new applications that could well complement those based on their organic counterparts. Unfortunately, to date, the development of microelectronics based solely on organics or metal oxides is not practical enough primarily due to predominantly unipolar nature of best performing materials available, which in turn restricts their use in unipolar logic circuits that are known to be associated with numerous disadvantages. To this end, complementary logic technology (also known as CMOS) can provide a solution towards large-scale circuit integration. This however often comes at a cost in terms of manufacturing complexity since complementary technology relies on the combination of electron transporting (n-type) and hole transporting (p-type) semiconductors.
Here we report the development of hybrid organic-inorganic TFTs and simple logic circuits based on the combination of p-type organics and n-type metal oxide semiconductors. Different metal oxide layers were investigated and deposited from solution at temperatures below 200 °C in air. Similarly, different solution-processable organic semiconductors were investigated as the p-type materials. Optimized systems exhibited high hole and electron mobility values typically in the range of 5-10 cm²/Vs. Hybrid devices were then prepared by stacking the metal oxide and organic films to form a spatially separated ambipolar hetero-junction layer which was then incorporated into suitably designed device architectures. In these device structures, the gate geometry defines the operating character of the device (n-type or p-type), allowing for facile integration of p-type and n-type devices into functional logic circuits with minimum manufacturing complexity.

Various concepts for wearable devices have been recently introduced with the aid of remarkable advances in technologies for flexible and stretchable devices, including but not limited to wearable interactive human-machine interfaces and non-invasive health monitoring devices. However, the current generation of wearable electronics still suffer from practical problems. One such problem is related to the use of inorganic layers for the active channels, subject to mechanical cracks and/or breakdown in repetitive deformations and consequent accumulation of fatigues. The mechanical mismatch between the human tissues and inorganic semiconductors aggravate the problem of user discomfort and fragility, since human body consists of many non-flat surfaces and fine topology. Hence, electronics for wearable applications require soft, flexible, and stretchable materials and designs to overcome such mismatches. Through this work, we present materials and device design strategies for the core elements of wearable electronics, including transistors, charge-trap floating-gate memory units, and various logic gates, with stretchable form factors. Semiconducting carbon nanotubes were used as the channel material, in conjunction with embedded charge trap layers of Au thin film and ultra-thin dielectric layers of Al₂O₃. Statistical analysis on the material and electrical properties proved extremely high reliability and performance of the fabricated devices, where devices as many as 150 exhibited uniform electrical characteristics. Experimental and theoretical results demonstrated that the fabricated devices showed no sign of degradation after repetitive stretching test up to 20% strain, by virtue of serpentine-shaped interconnections and neutral mechanical plane layouts that effectively protected the active components of the devices.

Printed electronics has long been envisaged as the most viable route for fabricating large-area electronics and tremendous progress has been made in this regard over the last decade. The key driving force for printed electronics has so far been organic electronics based on carbon-based materials (conjugated polymers, small organic molecules, carbon nanotubes and more recently graphene) and traditional printing methods, namely screen, flexo, gravure, offset, inkjet printing, etc. Recently, significant development has also taken place regarding low-temperature metal-oxide based electronics for printed electronics applications. With the onset of internet of things (IoT) and wearable electronics, there is a renewed demand for “on-demand” and large-area electronics that creates a commercial opportunity for printed electronics.
We propose a low-temperature, relatively-fast scalable processing technique which can pave the way for creating n-type metal-oxide semiconductor-based roll-to-roll (R2R) integrated circuit fabrication. We use temperatures as low as 180°C and sintering time as low as 5 minutes to create transistors with mobility > 1cm²/(V.s) [1]. Latest results on this topic will be presented in the conference.
We also report the latest development in fully R2R printed p-type organic transistors suitable for commercial application. VTT's R2R pilot printing facility has been utilized to fabricate the devices. The key enabling technology for this process is the simple R2R etching step, which allows the production of thin and highly conducting bottom electrodes. In addition, we will discuss about results which show that the semiconducting polymer can be spontaneously oriented during the printing process and the orientation - and thus performance - can be controlled with the gravure cup shape. Transistors with mobility of ~ 0.03 cm²/(V.s) and ON/OFF-ratio of ~10³ were reached in the fully printed transistors [2].
Combination of the fully printed inorganic n-type and organic p-type transistors opens the possibility of doing CMOS electronics. This can be the essential building block for commercial application of printed electronics.
Apart from the processes used for enabling hybrid electronics, as described above, there is also a recent drive to use new R2R manufacturing methods, namely atomic layer deposition, magnetron sputtering, inert atmospheric processing, etching, high-resolution reverse-offset printing etc, than can also enable manufacturing of high-performance, large-area electronics [3]. Such methods will be briefly discussed.
[1] J.Leppäniemi, K. Ojanperä, T. Kololuoma, O.-H.Huttunen, J. Dahl, M. Tuominen, P. Laukkanen, H.Majumdar and A. Alastalo, Applied Physics Letters105, 113514 (2014).
[2] M. Vilkman, T. Hassinen, M. Keränen, R. Pretot, P. van der Schaaf, T. Ruostalainen, H.G.O. Sandberg, Organic Electronics20, 8 (2015).
[3] www.roll-out-2020.eu

I will present the recent progresses and future prospects of large-area, flexible sheet-type sensors. This work focuses on integration technologies of printed sensing-functional materials with TFT-based active device platform, manufactured on a thin-film flexible polymeric plastic substrate. Here I would like to demonstrate the new applications of imperceptible sensors for sophisticated real-time health monitoring of civil infrastructures. These large-area sensors serve as an important part of seamless cyberspace/real-world interfaces that are commonly referred to as cyber-physical systems (CPSs). For example, by taking advantage of an analog-front-end circuit (active device platform) that can amplify and transmit signals, we developed multi-channel active matrix environment monitoring systems. Furthermore, the technical issues and future prospects of health monitoring of civil infrastructures will be discussed.

Organic semiconductors are expected to simplify and economize the fabrication of new consumer electronics, allowing large-scale device fabrication by ultra-low-cost processes. In order to realize this goal, a we must develop a thorough understanding of the impact of molecular shape and functionality on the formation of high-quality organic semiconductor films. Here, we will discuss how issues of semiconductor functionality and isomer purity impact the microstructure and device performance of solution-deposited small-molecule organic semiconductors. In general, it appears that isomer purity is actually detrimental in cases where rapid solvent evaporation is required to yield large crystalline semiconductor grains, whereas under more thermodynamic conditions (such as solvent-vapor annealing), isomeric purity is preferred for the development of large-grained organic semiconductor films. Some new semiconductors that avoid issues of isomeric purity will also be discussed.

By stacking and connecting two or more single cells with complementary absorption spectra in series or parallel, the main loss-mechanisms of organic photovoltaic (OPV) devices, such as narrow absorption windows and thermalization losses, can be simultaneously addressed. Thus, the performance of OPV devices has the technical potential to exceed 20% by using the tandem concept, exhibiting an improvement by ~40% compared to the optimized single cells.¹ Power conversion efficiencies (PCEs) of 10-12% have been reported for organic tandem solar cells by using novel high-performance donor materials as well as meticulous device optimization. However, less attention has been paid to the development of fully-printed organic tandem solar cells and modules despite of their importance for realizing large-scale production and eventually commercial applications.
In this contribution, we will demonstrate processing perspectives on fully-printed organic tandem solar cells and modules, including design of fully-functional recombination layers,^1-3 development of solution-processed electrodes by engineering^4,5 and ultra-fast laser based module processing.^6-7 A series of high-performance donor materials are studied in single as well as tandem architectures to tap their performance potential when processed in air by using a roll-to-roll compatible deposition method. Air-processed organic tandem solar cells based on solution-processed recombination layers and commercially available active materials reach the promising PCEs of over 10%. Solution-processed silver nanowires and opaque silver are employed to realize the fully-printed organic tandem solar cells with promising performance. Organic tandem solar modules on glass and flexible substrates with high geometric fill factors will also be demonstrated and discussed in detail.
[1] N. Li et al., Advanced Energy Materials, 4, 1400084 (2014).
[2] N. Li et al., Advanced Energy Materials, 3, 1597-1605 (2013).
[3] N. Li et al., Advanced Energy Materials, 3, 301-307 (2013).
[4] F. Guo & N. Li et al., Energy Environ. Sci., 8, 1690-1697 (2015).
[5] F. Guo & N. Li et al., Nature Communications, in press.
[6] N. Li et al., Sol. Energy Mater. and Sol. Cells, 120, 701-708 (2014).
[7] G. D. Spyropoulos et al., Energy Environ. Sci., 7, 3284-3290 (2014).

The light weight, simple processability, and mechanical flexibility of π-conjugated organic small molecules and polymers has recently led to remarkable results, opening the way towards the realization of new opto-electronic devices. Moreover, organic materials can be deposited and grown by means of easy, low temperature and low cost technologies such as inkjet printing. In the field of ionizing radiation detection, organic semiconductors have been proposed so far mainly in the indirect conversion approach, i.e. as scintillators, which convert ionizing radiation into visible photons, or as photodiodes, which detect visible photons coming from a scintillator and convert them into an electrical signal.
Organic semiconductors are very promising candidates also for the direct detection of higher energy photons (X- and gamma rays) [1] and we recently reported how organic semiconducting single crystals provide a stable and linear electrical photo-response to increasing X-rays dose rates, at room temperature [2,3]. As organic materials are based on Carbon, their low effective atomic number is similar to the average human tissue-equivalent Z and makes them ideal candidates for radiotherapy and medical applications
We will report and discuss the different X-ray photo-response and sensitivity of different solution-grown organic semiconducting single crystals, based on molecules that impart the grown crystal quite different chemical and physical properties, from crystal shape to charge carrier mobility. The aim is twofold: i) to achieve a better understanding of the photo-conversion and charge transport processes within the organic semiconducting crystal, providing an adequate model to describe them; ii) to optimize and select the better performing molecules towards the implementation of a flexible, large-area 2D matrix of OSSCs pixel detectors fabricated with printing technologies
References
[1] B.Fraboni, A.Ciavatti, F.Merlo, L.Pasquini, A.Cavallini, A.Quaranta, A.Bonfiglio , A.Fraleoni-Morgera Adv.Mater. 24, 2289 (2012)
[2] B. Fraboni, A.Ciavatti, L. Basirico`and A. Fraleoni-Morgera Faraday Discussions 174, 219 (2014)
[3] L.Basiricograve;, A.Ciavatti, M.Sibilia, A.Fraleoni-Morgera, S.Trabattoni, A.Sassella and B.Fraboni IEEE Trans Nucl.Science 2015 in press

We demonstrate the use of solution-processable work function reducers for inverted organic electronic devices. A notable feature of these molecules is orthogonal solubility relative to solvents typically employed in the processing of organic semiconductors. A strong permanent dipole moment on the compounds was calculated by density functional theory. The interlayers reduced the work function of a broad range of electrodes [indium tin oxide (ITO), Au, Ag, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), Cu, Al, and even graphene] by over 1 eV. By employing an ultrathin interlaye, one can reduce the electron injection barrier between ITO and C₇₀ by 0.67 eV. As a result, the device performance of OPVs with interlayers are significantly improved, and enhanced electron injection is demonstrated in electron-only devices with ITO, PEDOT:PSS and graphene electrodes. This work makes available a new class of dipole-rich, counterion-free, pH insensitive interlayers for use as strong work function reducers for any electrode.

Printable, flexible electronics has emerged as a promising means to fabricate wearable sensors, bioelectronics devices, and displays. There are significant challenges to develop electronic devices that can be deposited directly on flexible substrates at low temperatures. Electrostatic double layer gating using ionic liquids (ILs) has been demonstrated as a means to achieve low voltage switching in printable semiconductor transistors. Such devices can have relatively stable operation within a window of electrochemical stability, but electrochemical changes can still occur in the semiconducting layer. We will describe our recent work to understand and control electrochemical effects in oxide thin film transistors gated by ILs. Through the addition of polyphenol additives to the IL gate, we have achieved significant enhancements in operational stability. This stability is gained through chemical control of reversible redox-reactions between the IL gate and the semiconducting oxide. The prospects for new types of hybrid devices enable by controlled electrochemical behavior will be discussed.

Solution processable organic solar cells (OSCs) consisting of conjugated polymers and fullerene derivatives support novel applications for photovoltaics, due to their tunable appearance in combination with their flexible, lightweight nature and cost-effective production from earth-abundant, non-toxic materials. All high efficient OSCs have one thing in common - the bulk heterojunction (BHJ) concept, a self-organized nano-assembly arising from an initial mixture of the used components. With the performance of the solar cells strongly correlated to the morphology within the OPV film, understanding and controlling the BHJ morphology is essential.
We have studied the effect of low volatile processing additives on the morphology evolution during film solidification of blade-coated organic bulk-heterojunctions via real-time photoluminescence (PL). The strong quenching of donor PL upon charge transfer to acceptor makes PL sensitive to both phase purity and domain size. In-situ PL in combination with real-time UV-Vis measurements allowed us to quantitatively determinate the average film morphology and molecular conformation in two OPV systems, of which one contains the high performance small molecule system 7,7&’-(4,4bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b&’]dithiophene-2,6-diyl)bis(6-fluoro-5-(5&’-hexyl-[2,2&’-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazaole), p-DTS(FBTTh₂)₂, a promising organic electron donor achieving over 7% power conversion efficiency (PCE) in BHJ. We find that the observed phase purification during solidification and the final phase separation between the blend components in the dry films is in good agreement with earlier in-situ synchrotron X-ray studies. Initial changes in molecular arrangement and order lead to significant changes in the overall PL-intensity as well as in the spectral emission characteristics consistent with a rapid to moderate evolution of aggregation after the removal of the main solvent and during the evaporation of the additive.

Polymer semiconductors based on donor-acceptor monomers have recently resulted in significant gains in field effect mobility in organic thin film transistors. In general, these polymers include fused aromatic rings and strong intermolecular coupling resulting in stiff and brittle films. The often complex synthesis of these materials can also result in increased production costs. Thus, developing a technique to improve mechanical behavior while lowering material consumption during fabrication will significantly improve opportunities for adoption in flexible electronics.
To achieve these goals, we consider blending a rigid high-performance donor-acceptor polymer poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b&’]dithiopen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] (PCDTPT) with ductile regioregular poly(3-hexylthiophene) (P3HT). We find that the ductility of the blend film is significantly improved compared to neat PCDTPT films. This provides an opportunity to strain align the polymer chains in the film to improve charge transport characteristics. The resulting film morphology is evaluated using a suite of tools including: AFM, optical spectroscopy, SIMS, and GIXD. The charge transport is characterized in a thin film transistor configuration. The amount of applied strain is shown to vary the level of in-plane backbone alignment resulting in charge mobility anisotropy where the mobility increases in the applied strain direction and decreases in the perpendicular direction. We find that the blend film significantly increases ductility, while strain-aligning the film results in saturated field effect mobility comparable to neat PCDTPT (~1.25 cm²/Vs). These results highlight material opportunities for high performance polymer blend film transistors that are electronically and mechanically optimized.

In this work, we use capillary force lithography (CFL) to pattern linear nanogratings of the semiconducting polymers PBTTT and P(NDI2OD-T2) with a pitch and height of 50 to 400 nm. CFL has primarily been used to pattern polymers with a low glass transition temperature such as polystyrene, but here we use it to pattern semicrystalline polymer films with applications for organic electronics by applying a hard PDMS stamp onto the films with light pressure and heating to above the melt temperature. By confining the polymer chains to the nanogrooves in the stamp, we preferentially orient the backbones along the lines and also achieve a varying degree of edge-on or face-on orientations.
We mapped the average cross-sectional shape and orientation of these polymer lines using variable-angle polarized resonant soft X-ray scattering (p-RSoXS) experiments and simulations. Combining variable-angle measurements with RSoXS is a recently developed technique that allows the characterization of the three-dimensional shape of periodic polymer patterns such as lines or block copolymer lamellae.^[1] By probing at the carbon 1s-π* transition energies and varying the incident polarization and angle, we were able to obtain information about not only the shape of the polymer lines but also the average orientation distribution of the conjugated planes within the polymer lines. This information is extracted by fitting simulated scattering patterns to the experimental ones using an inverse iterative algorithm. This processing method and characterization technique could be used to better control and understand the morphology and orientation of organic electronic devices.
[1] D. F. Sunday, M. R. Hammond, C. Wang, W. Wu, D. M. Delongchamp, M. Tjio, J. Y. Cheng, J. W. Pitera, R. J. Kline, ACS Nano2014, 8, 8426

In past few years the progress of low cost perovskite solar cells has been phenomenal with the present certified power conversion efficiency now above 20%. With a potential to be manufactured as low-cost large area cells (or large modules) this technology could result in a paradigm shift in solar cell development. However, often perovskite thin films suffer from pinholes that allow direct connection between the hole transporting layer and the electron transporting oxide layers, which in turn provides lower resistance (shunt) pathways. Lower shunt resistance is manifested in lower open circuit voltage (V_OC) and fill factor (FF) of a cell, resulting in an overall lower efficiency. These pinholes can occur from atmospheric dust, material defects, solution defects, or non-optimal processing parameters. When depositing material over a larger area, it is more likely for a pinhole to be present; as such the prevalence of pinholes is a major bottleneck to produce efficient large area cells or modules. Moreover, the issue is more severe in case of neutral colour semi-transparent cells where large absorber free area is needed to provide the desired transparency. Herein we present a simple, inexpensive and easily scalable wet chemical method to block these shunting paths via deposition of transparent, insulating molecular layers ( based on alkyl silanes) that preferentially bind to the uncovered oxide surface without hindering charge transport across the active layers. We show that this method improves the reproducibility as well as the performance in semitransparent cells, where the improvement in V_OC is up to 30% without impacting the photocurrent. Using this method, we achieved a remarkable PCE of 6% for a neutral coloursemi-transparent perovskite cell with 38% average visible transmittance (AVT). This simple shunt blocking technique has applications in improving the yield as well as efficiency of large area perovskite solar cells and light emitting devices

Intuitive interaction via touch and multi-touch gestures started a triumphal march over the last decade and made smart phones and touch surfaces a global phenomenon penetrating all fields where human-machine interaction is involved. However, with the advent of flexible displays novel modes of interaction are not only required but also enabled that allow translating simple 2D into 3D interaction by accounting for pressure, bending, folding and twisting user input.
Triggered by the appealing form factor of large-area flexible displays there is a strong need for large-area 3D-mode supporting input sensors that can be fabricated in a cost-effective way. We recently presented PyzoFlex, a sensor technology based on a piezoelectric sensor matrix that is printed on large format plastic sheets. PyzoFlex accounts for low-cost manufacturing in R2R, enables large-area sensing and supports novel types of interaction with flexible e-ink displays such as detecting touch pressure levels, bending modes as well as combined gesture modes such as grip and bend.
For a further improvement of the PyzoFlex input sensor it would be highly desirable to pass over from a passive to an active matrix concept. At this level, the integration of a thin film backplane based on printed (or R2R-fabricated) organic transistors (OTFT) is the natural solution since it is compatible with the printed sensor foils both in manufacturing as well as in form factor. Accordingly, we started to introduce our self-aligned OTFT technology as an active matrix for large-area piezoelectric sensors. This transistor technology is outstanding since it has small (even submicron) channel lengths, source and drain electrodes that are self-aligned to the gate electrodes and an intrinsically photopatternable organic gate dielectric. The latter facilitates the realization of versatile digital and analog OTFT circuits. The challenges in R2R-fabrication of the active matrix backplane as well as in hybrid integration of the OTFT matrix with the PyzoFlex foil will be discussed. Since there is also a strong need for a conversion of the sensor signals directly on the senor foil we also started to develop organic electronic ADC-stages.

A common production method for organic photovoltaic (OPV) modules consists in roll-to-roll printing on PET foils [1]. A promising future application is the integration of OPV modules into window panes [2]. Due to the high design freedom of inkjet printing, OPV modules can be directly printed onto the panes [3]. For large area printing, homogenous OPV films are crucial [1]. The solvents used in the ink formulation need to be non-destructive for the inkjet print heads [4]. Moreover, sufficiently slow drying solvents are needed for OPV inkjet printing [1] to avoid the so-called coffee ring effect, leading to a non-uniform printed layer. Naphthalene based solvents are suitable for the preparation of poly(3-hexylthiophene): phenyl-C-61-butyric acid methyl ester (P3HT:PCBM) inks in terms of inkjet printing behavior and ink stability. Inverted structure solar cells (glass/ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag) with inkjet printed P3HT:PCBM photo-active layer show efficiencies up to 3.3% (active area 27 mm²). We will show that the inks can be used for inkjet printing of P3HT:PCBM in OPV modules with an active area up to 134 cm². Inverted geometries, where electrons are collected by the transparent bottom electrode, are advantageous for large scale production, since vacuum processing can be avoided [5]. Poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT:PSS) is commonly used as hole transport layer (HTL), but has drawbacks in terms of long-term stability, due to its hygroscopic and acidic nature [5,6]. Here we replace the PEDOT:PSS layer by an inkjet printed graphene layer, taking advantage of the high electrical conductivity and stability of graphene [7]. Additives are used to improve the wetting of water based graphene inks on the underlying P3HT:PCBM active layer. The wetting is further improved by plasma activation. Post printing processes, such as washing to remove the non-conductive surfactants, are used to increase conductivity. The graphene HTL is inkjet printed on glass/ITO/P3HT:PCBM and solar cells are finalized with Ag electrodes. The cells have efficiencies up to 1.8 %.
[1] C. J. Brabec et al., MRSBulletin, 2008,33, 670
[2] K. Chen et al., Energy Environ.Sci., 2012, 5, 9551
[3] T. M. Eggenhuisen et al., J. Mater. Chem. A, 2015, 3, 7225
[4] G. Lim et al., Org. Electron, 2014, 15, 449
[5] K. Norrman et al., J. Am. Chem. Soc., 2010, 132, 16883
[6] Y. Sun et al., Adv. Mater. , 2011, 23, 1679
[7] A.C. Ferrari et al. Nanoscale, 2015,7, 4598

Organometallic halide perovskite solar cells combine low material costs with the possibility of high throughput large area fabrication. With record efficiencies of over 20% on lab scale sample sizes perovskite solar cells are on the route to become a serious competitor in the thin film photovoltaic market. To enable a market entry the upscaling from lab size processes to production scales is essential.
We present planar perovskite solar cell modules fabricated by upscalable deposition techniques. In combination with a low cost patterning technique we achieve geometrical fill factors of 95% resulting in device efficiencies exceeding 10% on the aperture area.
The device structure is based on an n-i-p concept applying electron-beam evaporated TiO₂ as electron transport layer on ITO coated glass substrates. Without an additional treatment the photoactive layer is coated from a solution of methylammonium iodide and lead chloride. Hole transport layers of doped poly(triaryl amine)(PTAA) or 2,2prime;7,7prime;-tetrakis-(N,N-di-p-methoxyphenyl amine)-9,9prime;-spirobifluorene (spiro-MeOTAD) are deposited subsequently. In the presented study, the solution processable films are fabricated for comparison either by spin coating or blade coating. After a device optimization on lab scale devices with 0.1cm² active area the fabrication parameters are transferred to a module process. The presented devices combine 8 subcells to an aperture area of 16cm². A standard interconnection geometry with three patterning steps (P1-P2-P3) contacts the subcells ensuring a low loss of the aperture area. We use a mechanical scribing technique to patterning the coated layers in the steps P2 and P3. The total area loss by the interconnection of the subcells is lower than 5%. The high electrical quality of the patterning process is represented by the module fill factors of over 70%. Based on this fabrication method we are able to demonstrate perovskite modules with high aperture area efficiencies similar to equivalent lab size counterparts.
We conclude our presentation with an outlook on perovskite module packaging and stress resistant electric feedthroughs for outdoor applications.

The morphology of the organometal trihalide perovskite (OTP) plays a critical role in the performance of solar cell device. Nevertheless it has been frequently reported the morphology of OTP films tend to be different from different laboratories even with the same film preparation procedure, which makes it very difficult to compare and understand the material and device physics. Here, we unravel a critical role of the stabilizer H₃PO₂ in the hydroiodic acid (HI), which has been largely ignored by the community, in the morphology control for the perovskite films by spin-coating and doctor blade coating methods. The direct reaction of methylammonium (MA) and HI forms impure MAI due to the H₃PO₂ stabilizer impurity, which need to be re-crystalized to get pure crystalline MAI. Surprisingly, we will show that the impure MAI is beneficial to the two-step deposition approach. The perovskite films fabricated using impure MAI are very uniform and continuous, while those using pure crystalline MAI are not uniform with millimeter size of spots. High efficiency of 19.3% can be reached by optimizing the hole transporting layers using the impure MAI. On the contrary, the stabilizer impurity is detrimental to the perovskite film formation in the one-step doctor blade coating approach. The stabilizer will react with the PbI₂ and forms insoluble impurity Pb(H₂PO₂)₂darr; which impedes the merging of adjacent domains. This finding gives a guide line on how to fabricate high quality perovskite films for both one-step and two-step deposition approaches from the raw precursor materials point of view.

Widely used conventional OPV device choose glass/transparent substrate. However for full utilization of this technology requires fabrication of these devices on more common substrates (opaque) such as foils, plastic substrates, paper etc. However these ubiquitous substrates are usually rough in nature. Also fabrication on opaque substrates mandate top illumination of the device. In this work, we have fabricated devices on Fiber Reinforced Plastic (FRP) substrate. These substrates are first planarized to workable roughness (due to its inherent roughness), using a unique chemical-spincoating based planarization. These planarized substrates are further characterized (AFM/DEKTAK) and bottom electrodes (Al and Ag) on FRP were deposited. Chromium was used as adhesion promoter to the electrodes. Adhesion properties were characterized using scratch test. On planarized substrate, device was fabricated using simple solution processed technique for top illumination. For top illumination electrode Ag Nanowire and PEDOT:PSS was used. Transmittance and conductivity of these electrodes was characterized. Further device performance was engineered by using buffer layers and blocking layers for enhanced performance of the device.

Low voltage Organic Field-Effect Transistors (OFETs) are fundamental building blocks for novel, portable electronic systems fabricated over plastic substrates at relatively low costs. Low voltage operation is generally obtained with the employment of ultra-thin dielectrics, which requires small area techniques, such as spin coating and physical vapor deposition, to be reliably fabricated.
Therefore a reproducible fabrication process for low voltage OFETs with high throughput large area techniques is still substantially missing. The activity here described is thus devoted to the definition of reliable approaches to low voltage OFET fabrication with large area techniques, with particular focus on the optimization of the fabrication of gate dielectrics . In particular, two different approaches will be reported
The first investigated strategy consists on the integration of two large area techniques easily up-scalable to the industrial size, namely inkjet printing and chemical vapor deposition (CVD). Parylene C, which can be deposited in nanometer-sized films over large areas by CVD, was considered as gate dielectrics in OFETs. Such thin dielectric layers (tens of nanometers) were employed in combination with carefully optimized inkjet-printed electrodes, patterned using different conductive inks, to define the transistor structure. Also the organic semiconductor active layer was deposited by inkjet printing: in particular, TIPS pentacene was employed. A proper optimization of the ink and of the printing parameters, allowed obtaining OFETs with ideal features, i.e. low threshold voltage (< 2 V), significantly high hole mobility (of about 0.1 cm²/Vs) and low leakage current (in the range of picoAmpere).
Starting from these results, the employment of a solution processable dielectric was investigated towards the fabrication of all-inkjet-printed OFETs. In particular, an home-made ink based on polyvinyl phenol (PVP) was considered. Several cross-linking agents have been tested to optimize the ink formulation; printing setup, as well as drying and cross-linking processes and final layer thickness, were investigated. To verify the dielectric features, electrical and morphological characterization has been carried out. Finally, the dielectric has been tested as the gate insulator in transistor structures with aluminum as the gate electrode, inkjet printed PEDOT:PSS as source and drain electrodes and TIPS pentacene as active layer. The fabricated devices can be operated at voltages as low as 2V, showing hole mobility up to 2.2x10^-2 cm²/Vs, Ion/Ioff up to 10³ and remarkably low leakage currents (10 pA). Such result represents a promising proof for the feasibility of the proposed ink for gate dielectric fabrication. Ongoing activities are related to the optimization of the printing process for all the transistor elements, with a particular attention devoted to the dielectric surface properties for its proper interfacing with organic semiconductors.

The bulk-heterojunction solar cells based on a blend of poly (N-9&’-heptadecanyl-2,7-carbazole-alt-5,5-(4&’,7&’-di-2-thienyl-2&’,1&’,3&’-benzothiadiazole) (PCDTBT): [6,6]-phenyl C70-butyric acid methyl ester (PC₇₀BM) have been widely investigated over the last few years and power conversion efficiencies higher than 6% have been reported. However, the process in all published work so far has been done by spin coating, which is not the ideal technique for exploring the full potential for the production of organic solar cells.
In this work, we investigated the effect of the blade-coating and flexo-printing processes on PCDTBT: PC₇₀BM film morphology and devices performance. We developed a printable and air stable Zinc oxide nanoparticles and sol-gel derived Vanadium oxide inks, used as electron and hole extraction layers for inverted structure. By using these interlayers, indium-tin-oxide and evaporated silver, as cathode and anode respectively, the non-encapsulated PCDTBT:PC₇₀BM-based solar cells demonstrated an excellent air stability after being stored in air for more than 6 months, without noticeable change in their power conversion efficiency.

Organic and nanocrystalline solar cells comprising novel materials require a considerable amount of effort in optimization for various parameters. These devices are notoriously sensitive to the morphology (e.g., size and orientation of crystallites), composition of the active materials (e.g., ratio of electron donor to electron acceptor), and to external effects such as mechanical or photochemical degradation. Current experimental methods for optimization, in which several devices must be fabricated in serial to test the effect of a single variable potentially introduce inconsistencies. This variability paints an incomplete picture of the parameters that determine photovoltaic performance. Such conventional methods also consume copious amounts of precious, non-commercial π-conjugated polymers and other materials. Due to how resource intensive these methods are, only a small number of variables for a new system of materials can be optimized. This paper describes the use of gradients in properties to measure spatially resolved photovoltaic and charge-transport properties through films of organic semiconductors. Gradients in one or more parameters—e.g., film thickness and temperature of the post-processed thermal annealing—can be used as a universal optimization process for any solution-processed organic solar cell system. A non-wetting, liquid metal probe (eutectic gallium-indium, EGaIn) was used to scan the surface of the semiconducting film, point-by-point. Our results demonstrate that our technique is capable of (1) providing a convenient method to understand structure-property relationship in ultrathin organic films, (2) improving the quality and reproducibility of data by ensuring that photovoltaic and morphological data are collected on a single substrate, (3) reducing the waste in scarce materials and time associated with conventional, serial approaches in optimization, and (4) allowing for the systematic optimization of photovoltaic devices by mapping multiple gradients on a single substrate. The main strengths of the technique will be the efficient use of precious materials and the experimenter&’s time and the generation of a single substrate comprising many devices that share the same processing history.

Ferromagnetic (FM) electrodes chemically bonded with thiol functionalized paramagnetic molecules can produce novel molecular spintronics devices (MSDs) for futuristic applications in computer logic and memory. However, major challenges lie in developing FM electrodes based commercially viable device fabrication scheme that consider FM electrodes&’ susceptibility to oxidation, chemical etching, and stress induced deformations during fabrication and usage. This paper studies NiFe, an alloy used in the present day memory devices and high-temperature engineering applications, as a candidate FM electrode for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe start oxidizing aggressively beyond ~90 #8304;C. The NiFe surfaces, aged for several months or heated for several minutes below ~90 #8304;C, exhibited remarkable electrochemical activity and were suitable for chemical bonding with the thiol functionalized molecular device elements. NiFe also demonstrated excellent etching resistance in widely used dichloromethane solvent, which has a tendency to form HCl acid with time. NiFe also reduced the mechanical stress induced deformities in other FM metal like cobalt. This paper also discusses the successful utilization of NiFe electrodes in the tunnel junction based molecular device fabrication approach. This research is expected to fill the knowledge gap impeding the experimental development of FM based MSDs for realizing novel logic and memory devices and observing the numerous theoretically predicted phenomenon.

Simple and low-cost process for micro-scale patterning is attractive for a development of soft electronic devices or large-area organic light emitting devices (OLEDs). In this presentation, we described the materials and patterning process for light emitting layer of OLED by direct printing, using the small-molecular host materials dispersed in homogeneous mixture of solvents. The mixture of solvents with different boiling point and surface tension is advantageous for a good film uniformity, mainly due to the reduction of coffee ring effect upon solvent drying. For the processes of inkjet printing and electrohydrodynamic (EHD) jetting, which accompanies the formation of ultrafine meniscus at flow nozzle by the application of electric field, were investigated in detail, focusing the improved pattern uniformity of thin-metal auxiliary electrodes and high-resolution light-emitting pixels of OLED. In the EHD process, solution viscosity and distance between nozzle tip and substrate was an important factor for the establishment of condition for multi-wave spray (random network) or fine-line linear metal-grid pattern, both cases were utilized as fine-line auxiliary electrodes of OLED. Therefore, specific condition for the network of metal grid formation on the polymer substrate was found, providing embedded wire network in polymeric substrates. Small-molecular light emitters, representatively 2,6-bis(3-)9H-carbazol-9-yl)phenyl)pyridine; 26DCZppy doped with Tris[2-(p-tolyl)pyridine]iridium(III); Ir(mppy)³ dopant, were inkjet-printed on top of various hole-transport layer with appropriate surface tension. With the variation of dot-per-inch jetting condition, emitter pixels with a range of stripe pattern width 32um to 100um were fabricated (sub-pixel pitch 42 to 120um; 200 to 70ppi resolution). Film morphology and uniformity was found to be improved at chlorobenzene/1,2-dichlorobenzene 1:1 mixture. Device structure for inkjet-printed OLED were glass/ITO(or polymer/inorganic hybrid film with embedded metal grid network)/PEDOT:PSS/HTL/green phosphorescent light emitter/Bphen/LiF/Al. At least in case of glass-based OLED, jet-printed devices showed comparable light emitting behavior and cd/A efficiency that of spin-coated ones, providing 20-23 cd/A at a brightness of 1000 cd/m² condition.

Vapor phase synthesis of conductive films includes chemical/physical vapor and/or particle deposition involving sputtering, plasma, laser and flame technologies for a broad spectrum of applications in organic hybrid (nanocomposite) electronics. Typically such films are made in one step and subsequently their conductivity is measured ex situ. Here a new method is presented where film synthesis and conductivity measurement are carried out simultaneously. That way, films with optimal thickness and conductive structure can be made.
This is demonstrated with synthesis of nanocomposite films consisting of silver nanoparticles deposited on glass, polymethylmethacrylate (PMMA) or polystyrene(PS). Ag nanoparticles are made by flame aerosol technology at ambient pressure and directly deposited onto such substrates. A polymer layer can be added to overcoat such Ag nanoparticle films by spin coating¹ resulting in thin (<500 nm) and flexible nanocomposite films having metal-equivalent conductivity, even during repetitive bending, making them applicable as flexible electrodes². For such electrodes, the conductive performance strongly depends on the formation of percolating nanoparticle structures that lead to high electrical conductivity. In order to optimize the deposition process, it is necessary to better understand the nanoparticle percolation behavior. This is achieved by a newly adapted technique which tracks in situ the resistance of the silver nanoparticle film during its deposition. So instantaneous feedback is obtained and related to process conditions. These include the deposition time, height and temperature as well as substrate material, precursor silver molarity, feed-rate and the spray gas dispersion flow. In comparison to conventional ex situ resistance measurements (e.g. 2-/4-point electrical resistance), the present technique offers the additional benefits of retaining the particle film structure during measurement as well as the ability to circumvent the potential influence of an oxide layer on the metallic silver.
1. Sotiriou GA, Blattmann CO, Pratsinis SE. Flexible, multifunctional, magnetically actuated nanocomposite films. Adv. Funct. Mater.23, 34-41. (2013)
2. Blattmann CO, Sotiriou GA, Pratsinis SE. Rapid synthesis of flexible conductive polymer nanocomposite films. Nanotechnology. 26, 125601. (2015)

Recently, cross-linked polymer-based dielectrics have received considerable attention due to their physical and chemical robustness. However, this polymeric dielectric has been deposited solely by the spin-coating method which has limitation to large-area film fabrication with precise thickness control. Herein, we report large-area printed cross-linked poly(vinylphenol) (cPVP) films for gate dielectric layers in solution-processed thin-film transistors. PVP was chosen for the gate dielectric layer because it exhibits decent insulating properties and crosslinking capability due to hydroxyl functionality which is reactive to dianhydride or trichlorosilane. The resultant cPVP films directly coated on large-area substrates exhibit not only precise thickness controllability and large-area uniformity but also very low leakage current density (~10^-8 cm²/Vs at 1MV/cm) and high areal capacitance (>50 nF/cm² at 10kHz) even below 100 nm thickness. Furthermore, their chemical stability against various organic solvents allows for fine metal electrode patterning via conventional photolithography for organic thin-film transistors with the top-contact bottom-gate configuration. We expect that our large-area processed cross-linked polymer dielectrics will serve as an essential component for various types of high-end large-area printable organic/hybrid thin film electronics.

Nanowires (NWs) are the most important and promising building blocks for high-performance nano-electronic and optoelectronic devices due to their narrow dimension for high-integration, excellent transparency and mechanical flexibility. In particular, conducting NWs are essential functional units for electrodes and interconnections in nano-devices and circuits. However, in contrast to extensive studies about semiconducting NWs and their device applications, large-scale devices using conducting NW array have not been intensively made despite its significance. Previously reported conducting NW preparation methods have several problems: i) short NW length of range from a few to tens of micrometers, ii) obtaining randomly entangled or dispersed networks which are hard to use in conducting path, and iii) requiring high temperature (> 200-300 °C) annealing process; these hinder demonstration of the large-scale all-wire electronics as well as fabrication of the large-scale conducing NW patterns on flexible substrate so far.
Here we report i) a novel method to fabricate long-stranded metal NW array on large-area for all-wire electronics: it does not require any high temperature heating or vacuum processes, and ii) a demonstration of all-nanowire based field-effect transistor (FET) array comprised of metal NWs electrodes and organic semiconducting NWs channels. First, we used organic NWs array as metallization templates prepared using our homebuilt electrohydrodynamic NW printing system which can print the ONWs rapidly in desired position and orientation. Then, as electroless-plating of a metal layer on the surface of ONWs, core-sheath conducting NW array that has extraordinarily high transmittance and flexibility was attained; it showed excellent electrical conductivity (average resistivity of 7.5 mu;Omega;middot;cm) without any heating process. Furthermore, we tried to demonstrate extremely transparent and flexible all-wire electronics. Using individually controllable metal NWs and semiconducting NWs, all-nanowire based FET array on large-area with very high average mu;_FET of 3.5 cm²middot;V^-1middot;s^-1 was achieved, which is the first demonstration of all-wire electronics composed of metal NWs and ONWs. Our simple and reliable method to fabricate conducting nanowire arrays can provide a feasible solution to realize transparent, textile, and flexible nano-electronics.

Lifetime and production yield remains a challange of organic photovoltaics (OPV). The investigation and understanding of processing defects by advanced imaging characterization strongly promotes novel thin film photovoltaics. Furthermore, various degradation scenarios exist, for example shunting due to impurities or electromigration, corrosion of the metal electrodes or deposition mismatch can strongly affect device performance. The reduction of the active area is experimentally investigated concerning the influence of different environmental conditions. Imaging experiments provide information on location and size of insulated areas induced by pinholes in the metal back contact. Time resolved measurements during degradation of the devices reveal the dynamics and rate of growth of these individual defects.
Finite element models (FEM) enables studying current pathways and resistive losses in laterally extended organic solar cells.
The FEM calculations yield spatial distributions of current densities and according resistive power losses. The peaking current distribution within the shunting defect is locally resolved, however, considerable currents are still spread over the entire device area.
From the resulting resistive loss patterns, the heat distribution and emission was derived and directly compared with lock-in thermography imaging.
Overall, imaging in combination with simulation offers advanced defect analysis, promoting OPV market introduction.

Flexible Plastic substrate such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC) and polyimide (PI) have received attention to substrate in flexible displays. Among them, transparent PI is the promising candidate for next-generation display windows due to its excellent mechanical, physical, chemical properties and thermal stability. Nevertheless, it&’s relatively low transmittance which is smaller than glass is the key factor to successfully replace conventional display windows. Recently, surface patterning on transparent substrate such as nano- or micro-scale pillars, cones, and parabolas have received significant attraction as a method to improve the transmittance of transparent flexible substrates because the patterns exhibit unique optical property in suppressing the unwanted surface reflection losses and increasing the transmittance. However, patterned surface induces scattering of light, resulting in blurred display images. The amount of scatted light is measured by haze and generally increases as the transmittance increases. Understanding behavior of the light in the patterned structure is necessary to eliminate the trade-off between total transmittance and haze for high-definition display.
We report a design rule for the transparent patterned surface to improve total transmittance without haze using the simulator of rigorous coupled wave analysis (RCWA). Well-designed nanostructure with optimum period (Λ), top-diameter to bottom-diameter ratio (R), and height (h) can achieve 99.4% average total transmittance in the visible light wavelength range (400 le; lambda; le; 800 nm) without haze. Furthermore, the nanostructured PI films maintained average T_total over 90% while varying the incident angle by 60°, thereby demonstrating an omni-directional property. The designed structure was fabricated into colorless PI films. The double-side patterned polyimide film shows 96.6% and 0.3% in average of total transmittance and haze, respectively. Furthermore, the total transmittance and haze remained after 50,000 bending cycles with r = 5 mm.

Electrolyte-gated (EG) thin film transistors (TFTs) are the focus of intense research due to their low-operation voltages (< 2 V) and high charge carrier density, enabled by the high capacitance of the electrolyte/transistor channel interface (ca 1-10 mu;F/cm²). The operating mechanism of EG-TFTs can be of different nature, e.g. electrostatic or Faradaic (electrochemical) nature. In the former case, ions
migrate to the electrolyte/channel interface and induce an opposite charge in the semiconductor. In the latter case, charge transfer takes place in the bulk of the channel, accompanied by ion penetration in the channel. A study of the electrolyte/channel interface is essential to reveal the fundamental physicochemical processes governing the doping mechanism of EG-TFTs, thus enabling the exploitation of their full technological potential.Here, we report an extended cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and transistor investigation of EG transistors based on sol-gel synthesized WO₃ thin films and ionic liquids as the gating
media. CV plots indicate that n-type doping of WO₃ takes place within 0.4 V and -1.3 V i.e. our WO₃ EG transistors can operate at
relatively low voltages. In addition, by comparing charge accumulated, as calculated from CV plots, i.e. ca 0.7 mC, and the total theoretical charge that is possible to accumulate in the material to reduce W from W6⁺ to W5.5⁺ [1], i.e. ca 12 mC, we deduce that that only ca 6% (i.e., 0.7mC/12 mC) of the total film is electrochemical doped in our experiments. These results suggest that the electrochemical doping
is actually confined at the WO₃ surface in contact with the electrolyte. This is in agreement with the large size of the cations (e.g. [EMIM]⁺ has a diameter estimated at ca 7 Å)[2] that should not able to enter into the relative smaller cages (ca 5.4 Å) existing in cubic WO₃ [3].
EIS measurements were also conducted to determine the interfacial capacitance between the electrolyte (ionic liquid) and the WO3 thin film. Interestingly, we were able to correlate the CV results (i.e. the redox characteristics of the channel material) to structural changes observed by XRD in the material, as well as to an anomalous shape of the transistor transfer characteristics (i.e. the electronic characteristics of the
channel materials). A charge density of ca. 10¹⁴-10¹⁵ cm² (Vg=1.2 V, Vds= 0.3 V), and electron mobility of 0.2 cm²/Vs (Vg=1.2 V, Vds=1 V) were extracted from transistor measurements. These results enrich the current understanding of electron/ionic electroactivity at metal-oxides and electrolytes interfaces, promoting their applications in optoelectronic devices for energy conversion and energy conservation.
[1] Cazzanelli, E., et al., Solid State Ionics 1999, 123, 67-74. [2] Kobrak, M. N., Green Chemistry 2008, 10, 80-86. [3] Hepel, M.; Redmond, H., Central European Journal of Chemistry 2009, 7, 234-245.

Yoon et al. reported on room temperature negative differential resistance (NDR) in an organic diode with a few nanometer thick interfacial TiO₂ layer juxtaposed between indium tin oxide (ITO) and a MEH-PPV active layer [1]. They proposed that the NDR arose due to defect assisted tunneling through an oxygen vacancy at a localized energy below the TiO₂ conduction band in a plasma oxidized Ti metal layer and its alignment with the MEH-PPV LUMO density of states. Thus, TiO₂ defect characteristics greatly affect the operation of tunnel diodes exhibiting NDR. More recently, the growth method was extended beyond anodic oxidation of Ti [2] to non-stoichiometric atomic layer deposition (ALD) [3] to fabricate thin TiO₂ interfacial layers with a high amount of defects suitable for room temperature NDR [2].
In this work, we compare a variety of potential high volume, roll-to-roll compatible TiO₂ fabrication methods to produce thin TiO₂ layers with varying defect densities used in hybrid oxide/organic tunnel diodes. In addition to the results obtained using anodic oxidation, ALD has proven to be another viable way to fabricate candidate TiO₂ interfacial layers. A variety of ALD deposition temperatures and precursors are investigated to correlate their effect on TiO₂ layer properties and associated device performance. Electrochemical impedance spectroscopy (EIS), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) are used to characterize the layer properties. Furthermore, C-V measurements were performed to understand the defect characteristics of hybrid oxide/organic NDR diodes and it&’s correlation to the NDR phenomena. The results give insight into NDR diode operation and help to deepen the understanding of this hybrid inorganic/organic device.
[1] W.-J. Yoon, S.-Y. Chung, P. R. Berger, S. M. Asar, Room-temperature negative differential resistance in polymer tunnel diodes using a thin oxide layer and demonstration of threshold logic, Appl. Phys. Lett. 87 (2005) 203506.
[2] P. S. Heljo, K. Wolff, K. Lahtonen, M. Valden, P. R. Berger, H. S. Majumdar, and D. Lupo, Anodic oxidation of ultra-thin Ti layers on ITO substrates and their application in organic electronic memory elements, Electrochimica Acta, in press.
[3] http://www.picosun.com/en/products/roll-to-roll+ald+chamber/

Polymers are important components in the formulation of solution based inks as stabilizing and thickening agents, and they are also used to promote adhesion of such inks to flexible substrates.
In this work, we investigate the effect of UV sensitive polymer addition to metal-organic precursor inks and its relation to ink manipulation and direct writing deposition behavior. Specifically, titanium-organic and zinc-organic systems are transformed into TiO2 and ZnO crystalline compounds. We study the effect of UV intensity, wavelength and exposure time on the printed material accompanied by moderate heat treatments, and the effect of residual polymer after UV exposure on the resulting electrical properties.
Ink characterization includes viscosity and dynamic stability studies under ambient conditions. Direct writing of the inks on ITO/PET substrates is done by nozzle based robotic deposition. The microstructure and compositional changes are studied in relation to the UV parameters employed. Additionally, the electrical, mechanical and optical properties of the directly written patterns are investigated.
The stabilization role of the polymer as additive for inks is shown to be of paramount importance in establishing the range of possible ink composition-processing conditions that allow for minimum compromising of the resulting materials performance. The associated microstructural changes are dependent on the amount of polymer as well as the UV exposure conditions and suggest partial crystallization of the metal-organic inks.
It is believed that the integration of chemical and physical phase transformation routes is pivotal for further advances in flexible printed photoelectric device manufacturing. UV photo-decomposition of organics may hold the key for low temperature crystallization of amorphous materials on heat-sensitive substrates.

This study systematically demonstrates the effects of the grain structure of crystalline self-assembled monolayers (SAMs) on the growth of organic semiconductor thin films on such monolayers, as well as the electrical characteristics of the resulting semiconductor films. The grain structure of the octadecyltrichlorosilane (OTS) monolayers could be tailored by constructing the monolayers at three different temperatures: -30 °C (-30 °C OTS), -5 °C (-5 °C OTS) and 20 °C (20 °C OTS). Among the three layers, -30 °C OTS exhibited the largest crystalline grains and longest-range homogeneity of alkyl chain arrays. We found that pentacene films deposited on -30 °C OTS monolayers show larger crystalline grains with higher degrees of crystallinity and lateral alignment compared to films deposited on -5 °C OTS or 20 °C OTS monolayers, following the surface characteristics of the underlying OTS monolayers. Furthermore, pentacene field-effect transistors fabricated with -30 °C OTS monolayers showed lower charge trap densities and higher field-effect mobility values than devices fabricated using -5 °C or 20 °C OTS monolayers. These results are explained in terms of enhanced quasi-epitaxial growth of pentacene films on OTS monolayers with large grains.

Printing technologies are instrumental to the fabrication of low-cost lightweight flexible electronic devices and circuits, which are necessary to produce wearable electronic applications. However, attaining fully printed devices on flexible films over large areas has typically been a challenge. Here, we demonstrate the fabrication of fully drawn all-organic field-effect transistor (FET) arrays on mechanically flexible substrates using a capillary-pen printing method. A highly crystalline organic semiconductor (active layer), a smooth insulating polymer (dielectric layer), and a conducting polymer (source, drain, and gate electrodes) were deposited from solution sequentially. The bottom-gate bottom-contact FETs drawn onto flexible substrates exhibit superior field-effect mobilities of up to 0.54 cm² V^-1 s^-1, good reproducibility, operational stability, and mechanical bendability. Furthermore, to emphasize the methodological advantages of the capillary-pen printing, we demonstrate an OFET array on a curvilinear substrate of a plastic straw and the repairing concept for a broken electrical circuit. These results indicate that capillary pen printing shows promise as a manufacturing technique for a wide range of large-area electronic applications.

In the past two decades, block copolymer nanolithography draws growing attention as a potential powerful toolset for the fabrication of nanoscale features. Self-assembly of block copolymer can give highly ordered nanostructure with varying morphology on sub-10nm scale. However, pattern transfer process by such method is seldom demonstrated. There is still a need for a facile and versatile approach using high-chi; block copolymer with large etching contrast, orientation control and substrate independence to succeed in lithography process. Here, we demonstrate a simple and efficient solvent annealing method to manufacture highly ordered PS-PDMS masks with various length scales. The inclusion of selective solvent shifts the morphology from cylinder to sphere phase during which the perpendicular orientation can be trapped. Only a simple dry etch process enables formation of the hard mask, removal of one block and patterning on substrate simultaneously. And thus several pattern transfers are presented including common polymers, silicon and graphene. This approach shows unparalleled simplicity and applicability in block copolymer nanolithography,which could enable practical, large-area, manufacturable application of two-dimensional layered materials, such as semiconducting transition metal dichalcogenides (TMDs), insulating hexagonal boron nitride (hBN).

Electroplating is a cost-effective and high-throughput process, and is used in a wide range of applications, such as electronics, printed circuit boards, and semiconductor industries. In this work, we aim to tackle a remaining important issue in electroplating process, which is the poor surface coverage and interfacial adhesion between electroplated metal and low surface-energy substrate, such as indium tin oxide polyethylene naphthalate (ITO-PEN). We present to use 3-mercaptopropyl-trimethoxysilane (MPS) as an effective promoter to enable uniform electroplated Ag on ITO-PEN with strong adhesion. The MPS layer on the substrate provides the bridging-link between the sulfur functional groups and the Ag ions in the electrolyte, facilitating the electroplating nucleation process. To understand the significance of bridging-link effect on strong adhesive electroplating, rate constants of electron transfer on blank and MPS-grafted substrates were evaluated quantitatively by applying alternating current voltammetry and nucleation mechanisms of Ag by MPS pre-treatment was compared and identified by fitting into nucleation models, like Shariker-Hills model. With proof, it is confident that this cost-effective and reliable electroplated metallization process would be applicable in the manufacturing of various metals on ITO-PEN beneficial for the flexible and rollable devices.

Various lithography techniques for fabricating micro/nano scale patterns are two sides of the same coin. A conventional photolithography with an advantage of mass production has a limited resolution of 100 nm due to a diffraction of light. Meanwhile, different patterning techniques such as Electron-beam (E-beam), X-ray and Scanning Probe Microscope (SPM) lithography which realize the much higher resolution than that of the photolithography are widely adopted as competitive alternative technologies. However, they demands laborious and time-consuming steps. Moreover, these are rather expensive and have restriction to use flexible plastic substrate and organic materials in the process. Thus, to overcome these drawbacks, we suggest a simple but robust strategy for an elaborately temperature-controllable molding device that achieves direct prints like a stamp with high resolution and site-specific accuracy. A surface of rigiflex polymeric mold composed of Polyurethane-acrylate (PUA) is coated with thin metallic film and self assembly monolayer (SAM) of 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (FOTS) in the order stated. When electric power is applied, a temperature of the device changes in a remarkably accurate and uniform manner in the whole surface. We enable to generate site-selective dewetting patterns on a Polystyrene (PS) thin film and manipulate the nanoscale pattern width of the polymeric layer. In particular, compared with other printing techniques, our device indicates a high-potential for step & repeat and hierarchically structured patterning process due to the localized heating. The proposed strategy is anticipated to widen its patterning related applications including semi-conductor electronics, transparent electrodes, pressure sensors and micro/nano scale reactors.

The discovery of electrically conducting polymers has attracted a lot of attention mainly because of their potential for diverse applications. These polymers can also be used as beam splitters or wave-plates at terahertz (THz) frequencies; therefore, it is important to understand their response in THz frequency regime. With the development of intense THz sources, it has now become possible to investigate the intense THz electric field dependent nonlinear response of various materials. In this work, we investigated the THz electric field induced birefringence in four different conducting polymer samples using the intense THz electric field of 100kV/cm. This THz electric field induced birefringence effect may reveal polarizability dynamics associated with electronic, vibrational, and structural responses in conducting polymer samples. Detailed experimental and theoretical characterization of these conducting polymers at THz frequencies will be presented.

Printed electronics is a fast moving field that promises applications such as flexible displays and low-cost sensor networks. Printed transistors will play a key role to drive these electronic systems. These transistors will have to operate at low voltages below 5V to be compatible with printed portable power sources and other system requirements. Tremendous progress has been made in the past to improve both printable materials as well as printing methods to improve transistor performance. However, it has proven challenging to combine high performance materials with high performance printing whilst achieving low operating voltages. Here we demonstrate such transistors fully printed using gravure printing to deliver high performance at low operating voltage while simultaneously realizing small device-to-device variation.
Gravure printing is a high performance printing technique that allows printing at high speeds with very high resolution. All transistor layers were printed at printing speeds on the order of 1m/s. This is significantly faster than other printing techniques such as inkjet printing. The source and drain electrodes were scaled down to sub-5µm linewidth as well as sub-5µm channel length. One difficulty with gravure printing is alignment accuracy, which lags behind the aggressive scaling of feature size. A fully overlapped top gate architecture was thus employed to achieve alignment tolerant fabrication. The fine linewidth of the source and drain electrodes ensures that AC performance is not affected significantly by the fully overlapped gate architecture.
Such aggressive scaling of the channel dimensions also requires similar scaling of the semiconductor and dielectric layers. The semiconductor SP400 and matched dielectric were supplied by EMD Performance Materials Corp. (an affiliate of Merck KGaA, Darmstadt, Germany). This semiconductor is an amorphous polymer material that does not require crystallization, which reduces device-to-device variations. Saturation mobilities around 0.4cm²/V-s could be achieved, which is comparable to state-of-the-art polycrystalline semiconductors when employed in such short channel fully printed transistors. The semiconductor was patterned by gravure printing in order to isolate devices electrically. The effect of ink rheology on pattern fidelity, semiconductor thickness and electrical performance and trade-offs were studied. By scaling both the semiconductor and dielectric carefully, performance was optimized and operation voltage minimized. Devices could be operated at less than 4V. This is mainly due to a subthreshold swing below 500mV/decade and a threshold voltage of approximately -1V.
In summary these devices exhibit superior performance both in the on- and the off-state, superior variability, low-voltage operation and are fully printed at printing speeds of approximately 1m/s, thus providing a promising path for realization of functional printed systems.

We present a novel design technique for the production of self-aligned diodes on flexible substrates using additive methods with micron-level precision. Liquid inks are sequentially deposited into a network of overlapping, vertically stacked channels, utilizing capillary force to drive materials registration. Self-assembled monolayers applied over the printed electrode subsequently tune the energy barrier at the electrode/semiconductor interface through dipole alignment. Using this approach, and device design based on complementary material selection, we create all ink-jet printed flexible organic Schottky diodes in an open-air environment with control over the overlap area, current, threshold voltage, and on/off ratio without the necessity of pre-patterned electrodes.

In printed electronics, electronic inks are patterned onto flexible substrates using roll-to-roll (R2R) compatible graphic arts printing methods. The most significant problem of printed electronics manufacturing is to achieve alignment of multiple layers of disparate materials with micron-level tolerances on deformable, moving substrates. Here, we present a self-aligned manufacturing strategy for printed electronics that relies on capillary flow of inkjet-printed inks within open micro-channels. Materials registration is achieved automatically by sequential deposition of liquid inks into multi-level trench networks on the substrate surface. By creating suitable multi-tier capillary networks, we demonstrate fully self-aligned fabrication of all the major building blocks of an integrated circuit, including resistors, capacitors, transistors, and crossovers, with excellent yields and performance metrics. Concurrent with the ongoing developments in inkjet printing and imprint lithography, this self-aligned manufacturing strategy has the potential of achieving unprecedented resolution and device integration densities for R2R printed electronics.

The combination of printing with more conventional electronics processing is one of the most promising methods to enable new forms of flexible and distributed electronics, but leveraging the advantages of printing and coating as a cost-effective process for large areas with the strength of CMOS electronics for data processing and communication. In particular, we will focus on advances in our group in the following fields
- printed energy harvesters, especially RF rectennas
- novel non-toxic hydrogel electrolytes for supercapacitors
- integration of printed energy harvesters with solution coated non-toxic
Supercapacitors with power-efficient ASICs to enable energy autonomous distributed
Sensors
- Scalable processes for fabrication of organic tunnel diodes
- Joule heating for self-aligned passivation of current distribution grids in OLEDs.

We report on the latest progress on oligomer based vacuum deposited tandem and triple junction solar cells. Efficiencies above 12% together with excellent durability are now routinely achieved for lab scale triple junction cells. The world&’s first fully integrated roll-to-roll-production tool for organic tandem junction solar cells on PET substrate film has been successfully ramped-up and delivers high quality solar films with efficiencies above 7% on the active area. The cells and modules show efficiencies that increase with increasing temperature and excellent low light behavior. These two factors suggest a superior harvesting factor (harvested kWh per installed kWp) which is confirmed by outdoor measurements.

Organic and printed photovoltaics (OPVs) onto flexible substrates have attracted an enormous interest, due to their several advantages that include conformability to curved surfaces and fabrication by low-cost production processes, such as roll-to-roll (r2r) printing. Roll-to-roll (r2r) manufacturing processes enable the low-cost and large area production of OPVs on flexible substrates. The optimization of the quality of the OPV printed nanomaterials (organic semiconductors, transparent electrodes, barrier nano-layers etc.) is a prerequisite for the achievement of the required performance, efficiency and lifetime of OPVs to allow their market exploitation. In-line optical monitoring is of paramount importance for the robust quality control of the printed OPV nanomaterials and for the optimization of the blend morphology of the photoactive layer (blend of a polymer electron donor and a fullerene-based electron acceptor) that will result to the achievement of the desired efficiency and lifetime of the printed OPVs.
In this work, we report on an innovative methodology for the ultra-fast in-line optical monitoring and quality control of r2r printed OPV nanomaterials and devices by the adaptation of in-line Spectroscopic Ellipsometry and Raman Spectroscopy on a r2r printing pilot line. These optical techniques are combined with sophisticated modelling procedures and methodologies in order to obtain significant information on the optical properties, homogeneity, thickness, and quality of bulk heterojunction (BHJ) photoactive layers for OPVs that consist of state-of-the-art electron donors (e.g. polythiophenes) and acceptors (e.g. fullerene derivatives, PC₆₀BM, PC₇₀BM, ICBA, etc.).
This innovative methodology establishes the importance and applicability of optical monitoring tools to be used as standard components for r2r pilot lines for the ultra-fast quality control and determination of thickness, optical and structural properties and the quality of novel organic and inorganic nanolayers for several Organic and Printed Electronics applications.

Self-assembled monolayer (SAM) is usually applied to tune interfaces properties of the thin film layers in organic electronics such as organic transistors, organic light emitting diodes and others. Till now, most of the SAM deposition is done by immersing the substrate into SAM solution for a relatively long period of time to allow the molecules to be attached onto the sample. There are a few major drawbacks in the immersion approach such as time consuming, difficult in patterning the deposited SAM and difficult to apply in large area substrate for mass production. As a result, there is a strong desire to develop a time saving, patternable SAM deposition method which can also be used in large area fabrication. In the current work, we develop a fast stamp printing method for SAM compatible with large area roll-to-roll process. We utilize paraffin stamps consist of hydrocarbon molecules to transfer a well oriented and crystalized SAM layer onto the dielectric surface of organic field-effect transistors (OFETs).The DNTT OFETs based on stamped SAM show mobility as high as 3 cm²V^-1s^-1 which is significantly better than devices fabricated by traditional immersion method. This stamp printing method can also be used for SAMs with different terminal groups like SAM ended with fluorine atoms, as long as suitable stamps of different components are applied. Fluoroalkyl SAMs are printed for instance by using a paraffin stamp blended with fluorides, and mobility of OFETs based on n-type F₁₆CuPc can reach 0.018 cm²V^-1s^-1. Other than usual substrates like silicon wafer or glass, this approach is also suitable for green substrates such as paper, which may not be suitable for other solution processes due to the strong soaking properties of cellulose fiber in paper substrate. However, since immersion is not required in our current paraffin stamping method, OFETs on paper substrate can be fabricated without making damage to the substrate and the performance is also very competitive.

Adhesion lithography (a-Lith) is a novel patterning technique for manufacturing of large aspect ratio metal nano-junctions on a variety of substrate types and sizes [1]. The low temperature process requirements posed by this versatile patterning method allows the high throughput fabrication of asymmetric coplanar electrodes, featuring inter-electrode nanogap distances smaller than 50 nm on glass or plastic flexible substrates. This enables the development of high performance optoelectronic devices, such as radio frequency (RF) co-planar rectifying Schottky diodes, photodetectors and nano-scale light emitting diodes (LEDs), with architectures and dimensions that would be difficult or far too expensive to obtain with alternative patterning techniques (e.g. e-beam lithography).
Here, we describe the key processing steps of a-Lith and discuss its manufacturing scalability via development of a semi-automated large-area process system. The latter allows accurate control of the a-Lith critical steps and manipulation of key process parameters and, therefore, carries the prospect of realising the industrial manufacturing of a plethora of devices previously not considered in the realm of large-area, plastic optoelectronics technology.
On that basis we exploit the fabrication of dissimilar (i.e. cathode/anode) electrode nanogaps with lateral inter-electrode distances in the range of 5-30 nm for the development of co-planar large aspect ratio (>10,000) organic LEDs (OLEDs). As-prepared devices emit light from a narrow active region that is defined by the nanogap geometry and specifically the electrodes thickness and the nanogap length/width. Despite the low-dimensional nature of these nano-OLEDs, the unique large aspect ratio geometry leads to high performance devices due to extreme confinement of charge carriers and suppressed Joule heating [2], while at the same time new physical phenomena can be unveiled at these nanoscopic metal/semiconductor/metal systems.
The successful demonstration of fully functional nano-OLEDs over large area substrates with unprecedented manufacturing simplicity paves the way to a number of applications such as ultra-fast photo-detectors, OLEDs for next generation ultra-high definition displays as well as electrically pumped organic semiconductor laser diodes, whereas the facile manufacturing protocol expands the capabilities of de novo design of innovative device concepts.
[1] David J. Beesley, James Semple, Lethy Krishnan Jagadamma, Aram Amassian, Martyn A. McLachlan, Thomas D. Anthopoulos and John C. deMello, Nature Communications5, 3933 (2014).
[2] Kyohei Hayashi, Hajime Nakanotani, Munetomo Inoue, Kou Yoshida, Oleksandr Mikhnenko, Thuc-Quyen Nguyen and Chihaya Adachi, Applied Physics Letters106, 093301 (2015).

The mechanical properties of organic semiconductors and the mechanical failure mechanisms of devices play critical roles in the yield of modules in roll-to-roll manufacturing and the operational stability of organic solar cells (OSCs) in portable and outdoor applications. This talk begins by reviewing the mechanical properties— principally stiffness and brittleness—of pure films of organic semiconductors. It identifies several determinants of the mechanical properties, including molecular structures, polymorphism, and microstructure and texture. Next, a discussion of the mechanical properties of polymer-fullerene bulk heterojunction blends reveals the strong influence of the size and purity of the fullerenes, the effect of processing additives as plasticizers, and the details of molecular mixing—i.e., the extent of intercalation of fullerene molecules between the side chains of the polymer. Mechanical strain in principle affects the photovoltaic output of devices in several ways, from strain-evolved changes in alignment of chains, degree of crystallinity, and orientation of texture, to debonding, cohesive failure, and cracking, which dominate changes in the high-strain regime. The active materials and electrodes, however, comprise a small fraction of the total mass of a roll-to-roll processed OSC, and thus we also consider the substrate and barrier materials. We are investigating ultra-flexible and stretchable barrier films based on high-quality single-layer graphene fabricated using an inexpensive technique based on mechanical exfoliation from a copper growth substrate, which can be recycled. Our conclusions highlight the importance of mechanical properties and mechanical effects on the viability of OSCs during manufacture and in operational environments.

Solution processes are attractive in depositing electronic materials at a low-cost. The versatile solution processes lend new controlling of solid film formation by multiple channels, and the electronic properties and associated device performance are extremely sensitive to the process. Here I will present our recent progress in manipulating the crystal alignment and crystallinity of the grains by several novel solution processes and interface engineering. Their applications in electronic devices including high efficiency, vivid colorful perovskite solar cells and high mobility organic field effect transistors, high gain and low noise detectors will be presented.

Hybrid inorganic-organic perovskite materials, most commonly methylammonium lead triiodide (MAPbI₃), have garnered significant interest in the thin film optoelectronics community due to their outstanding optical and electrical properties. With certified photovoltaic efficiencies exceeding 20%, hybrid perovskites are already competitive with well-established technologies like poly-Si and CIGS. However, solution processed perovskites commonly suffer from poor thin film quality, reproducibility, stability, and scalability. Our work has determined that the fabrication of MAPbIshy;₃ thin films displays all of the hallmarks of sol-gel processing. Solutions actually begin as colloidal dispersions with particle size distributions which were characterized by dynamic light scattering. The dispersions gel during spin coating which produces a dense perovskite film after further drying and annealing. We directly correlate experimental observations with basic sol-gel theory to elucidate the critical steps and specifically target these steps to improve the quality of spin coated thin films. We show that well established concepts from the sol-gel community can be applied to MAPbI₃ processing including the impacts of sol stabilization, pH, gel aging, and sintering. In particular, we were able to fabricate films by several different methods achieving low RMS surface roughness (< 10 nm), nearly full surface coverage, and high crystallinity as measured by XRD. We conclude that the large number of seemingly distinct processing methods of perovskites can be reduced to a single sol-gel process with slightly different conditions that each require optimization.

Matrix-assisted pulsed laser evaporation (MAPLE) was developed for thin-film deposition of polymeric materials[1]. In the ideal process, the organic material is dissolved in a solvent and frozen inside a deposition chamber. The incident laser energy density in the target sublimates the solvent host matrix so it is pumped away, while the relatively dry, organic material is transferred to the substrate. The approach is unique because it combines features of solution-processing and physical vapor deposition. Resonant infrared MAPLE (RIR-MAPLE) uses infrared laser radiation that is resonant with solvent-specific bond energies to minimize degradation of organic materials[2]. The emulsion-based approach (i.e., frozen host matrix comprises uniformly mixed solvent and water) takes advantage of hydroxyl bond vibrational modes in water to resonantly absorb 2.94 mu;m radiation from an Er:YAG laser[3].
Emulsion-based RIR-MAPLE is versatile because the organic material and compatible solvent are completely decoupled from the absorption of laser energy. As such, the technique is appropriate for many polymers, small molecules, nanoparticles, and hybrid nanocomposites. Despite demonstrating nanoscale domain sizes[4] and independence from solubility in multi-layer films[5], the fundamental growth mechanisms for this technique are unknown and must be determined empirically because the laser-target interaction is not thermally-confined (laser pulse width ~ 90 µs).
We will present empirical growth mechanisms of emulsion-based RIR-MAPLE that are influenced by several parameters, such as the laser fluence and repetition rate, growth rate, and substrate temperature. In addition, the growth mechanisms related to the target emulsion composition will be described. For example, the material is deposited from the emulsion as discrete clusters, as opposed to discrete molecules; therefore, the key to achieving smooth films is to reduce the cluster size in the film, which requires reducing the cluster size in the emulsion. The typical emulsion target comprises the guest material, primary solvent, secondary solvent, deionized (DI) water, and surfactant. Proper selection of the emulsion components has the most significant and direct impact on film properties. In addition to basic materials properties, the performance of organic solar cells featuring active regions grown by RIR-MAPLE will be presented to determine the impact of different growth conditions.
This work is supported in part by the Office of Naval Research (N00014-10-1-0481) and the NSF Research Triangle MRSEC (DMR-1121107).
References
1. Pique, A., et al., Thin Solid Films, 1999. 355: p. 536-541.
2. Toftmann, B., et al., Thin Solid Films, 2004. 453: p. 177-181.
3. Pate, R. and A.D. Stiff-Roberts, Chemical Physics Letters, 2009. 477(4-6): p. 406-410.
4. Ge, W. Y., et al., Organic Electronics, 2015. 22:p. 98-107.
5. Pate, R., et al., Applied Physics A: Materials Science and Processing, 2011. 105: p. 555-563.

Polymeric semiconductors have received considerable attentions since their discovery in 1970s due to their low-cost, light-weight and easy solution fabrication. To realize their real applications, exploring the fundamentals of charge transport is important for understanding one-dimensional conjugated polymers and constructing next generation of two-dimensional conjugated polymers as well as their application in plastic electronics.
Highly ordered single crystals of organic semiconductors are the best candidates for charge transport investigations because there are no grain boundaries and no defects. However, it has remains a big challenge in polymer science to grow high quality polymeric crsytals. Here we demonstrate a fundamental breakthrough in generating high quality conjugated polymer micro- and nanocrystals with extended conjugation and exceptionally high order of chains using a surface supported topochemical polymerization method.
In the crystal the conjugated polymer chain backbones are extended along the long axis of the crystal with the side chains perpendicular to the long axis. Anisotropic charge transport, based on individual polymer microcrystal, demonstrate that the intrachain mobility is about two orders of magnitude higher than that of interchain mobility (π-π stacking direction), and is 5~8 orders of magnitude greater than conventional disorder thin films, revealing the importance of intrachain charge transport in plastic electronics.
References:
[1] Dong, H. L., Fu, X. L., Liu, J., Wang, Z. R. and Hu, W. P. Adv. Mater. 25, 6158-6183 (2013)
[2] Dong, H. L., Jiang, S. D., Jiang, L. Liu, Y. L., Li, H. X., Hu, W. P., Wang, E. J., Yan, S. K., Wei, Z. M., Xu, W. and Gong, X. J. Am. Chem. Soc. 131, 17315-17320 (2009)
[3] Yao, Y. F., Dong, H. L. and Hu, W. P. Poly. Chem. 4, 5197-5205 (2013)

Recording and stimulation of neural and muscle activity is critical for clinical and fundamental electrophysiology applications ranging from functional brain mapping and brain-machine interfacing to clinical diagnosis/rehabilitation. Organic electronic materials, especially those based on conducting polymers, offer a unique set of characteristics that allow for mechanically matched and conformal devices and that enable enhanced signal transduction and stimulation at the biotic/abiotic interface. Electrochemical transistors, for example, show good ionic-to-electronic signal transduction, robustness to mechanical deformation, and compatibility with living neural tissue. The operation and device physics of such transistors are understood by modification of physical device geometry and materials properties, where thickness and volumetric capacitance are found to play a critical role. Varying the active layer thickness of these transistors can enhance recordings of low frequency physiological and pathological rhythms with high content of signal. Furthermore, this work highlights the materials and processing requirements necessary for developing medical tools based on conducting polymer devices ranging from flexible and conformal neural probes to wearable sensors for clinical diagnosis and health monitoring.

We demonstrate a novel metal-organic framework nanocrystals memristor. Gradual resistance tuning between high resistance states and low resistance states is realized during set/reset switching process, which is caused by gradual formation and dissolution of conductive fiaments in native switching interface layer. Moreover, based on gradual resistance tuning and organic feature of metal-organic framework memristor, synapse-like functions such as short-term potentiation, long-term potentiation and synapse depression process and flexible memristive devices with excellent bending durability over 10⁴ cycles are demonstrated, indicating their potential applications in flexible adaptive networks.

The new paradigm of transparent electronics has attracted great attention in the next generation consumer electronics, including ‘see-through&’ or ‘invisible&’ devices such as transparent sensors or displays. In these transparent electronic devices, high performance, low manufacturing cost and low driving voltage transistors are essential and important elements that govern the overall performance of the devices. Here we utilize highly transparent, junction-free metal network as gate electrode developed by polymer crack template method and further integrate the electrode with anodization growth of high-k metal oxide network dielectric layer, for the first time, to develop low cost and low operating power transparent organic field effect transistors (OFETs) where metal network (50 nm) and DNTT (50 nm) are employed as bottom-contact source drain electrodes and semiconductor, respectively. The metal network electrodes exhibit high transmittance (~85% at 550 nm) and low sheet resistance (~5 ohm/sq). The obtained transparent OFETs showed transmittance ~70% over the whole visible spectrum, field effect mobility of 0.1 cm²V^-1s^-1, and on/off ratio higher than 10⁴. The proposed low cost and low operating power fully transparent OFETs is an important step towards next generation portable transparent electronics.

While organic light emitting diodes are a multibillion dollar industry, their continued development relies on the use of materials compatible with low-cost, large-scale processing techniques. These include solution-processed materials, such as the methylammonium lead halide perovskites, which have recently demonstrated astonishing potential as efficient photovoltaics. Hybrid perovskites can also exhibit high PLQEs, and the first demonstration of room-temperature electroluminescence was made in August 2014. These perovskite light emitting diodes (PeLEDs) are limited by the use of fluorene cathode interlayers, which are unstable in air and have a low barrier to hole injection, resulting in them co-emitting with the perovskite.^[1] To address these limitations, we developed an atmospheric pressure chemical vapor deposition (AP-CVD) reactor that rapidly synthesizes high quality oxides at low temperatures under ambient conditions. Our AP-CVD reactor consists of a manifold, which is fixed in position, while the substrate oscillates repeatedly through the alternating channels of metal precursor and oxidant gases.^[2] With the ability to co-inject different metal precursors, ternary compounds, such as Zn_1-xMg_xO can be synthesized. By controlling the Mg content, we were able to finely tune the electron-affinity of ZnO from -3.6 eV to -3.35 eV. We deposited Zn_1-xMg_xO onto methylammonium lead tribromide (CH₃NH₃PbBr₃) perovskite at 60 °C, achieving complete coverage after 3 min of oxide growth without damaging the perovskite. Using Zn_1-xMg_xO as the cathode interlayer, we overcame the problem of parasitic emission because our oxide forms a large hole-injection barrier. By doing so, we achieved color-pure PeLEDs that had only one electroluminescence peak. This was at a wavelength of 525 nm, was air-stable and had a full width half maximum of 25 nm, making the emission twice as sharp as industry standard InGaN light emitting diodes.^[1] Our ability to tune the electron-affinity of the Zn_1-xMg_xO also allowed us to reduce the turn-on voltage by 20%. Our highest performing PeLEDs had a turn-on voltage of 2 V and 50% higher luminance than previously reported. These PeLEDs are promising for ultrahigh definition displays. The scalable, roll-to-roll compatible reactor we have developed for synthesizing the oxide injectors will play a crucial role in enabling these PeLEDs, and also other organic light emitting diodes, to fulfil their potential for widescale deployment.
[1] R. L. Z. Hoye, et al., Adv. Mater., 27, 1414 (2015)
[2] R. L. Z. Hoye, et al., ACS Appl. Mater. Interfaces, 7, 10684 (2015)

Organic field-effect transistors (OFETs) with high carrier mobility, low operating voltage, ease of fabrication and compatibility with large-area processing are crucial for further mass productions of flexible displays, wearable electronics and biosensors. Compared with the conventional organic semiconductor materials used in OFETs, solution-processed organic semiconductor crystals (OSCs) stand out with their unique advantages including high carrier mobilities, less grain boundary effects, and controllable orientation of the active layers. Until now, most of reported OSC-based OFET devices are developed on silicon/silicon dioxide substrates, but the investigation of crystal growth mechanism and the crystallinity of OSCs on high-k dielectric with small operating power are rarely reported. In this work, we focus on studying the solution-shearing method to afford C10-DNTT OSC on a solution-processed Ba_0.7Sr_0.3TiO₃ (BST) dielectric with a high dielectric constant. The high areal capacitance (~300 nF/cm²) of the BST layer allows the OFET to work at a low voltage regime (less than 4 V). After modified by self-assembled monolayers, the BST surface energy is further improved to be compatible with solution-shearing method and the interface trap density is significantly decreased. The optimized OFET device shows a subthreshold swing of 120 mV/decade and a mobility of 4.1 cm²V^-1s^-1, which is outstanding among the OFETs with solution-processed semiconductor and high-k dielectric layers. We also performed various thermal-electrical characterizations and crystal analysis measurements such as selected area electron diffraction (SAED) and grazing incident small angle x-ray scattering (GISAXS). Based on the characterizations results, the theoretical limit of carrier mobility can be evaluated by calculating the transfer integrals of the C10-DNTT OSC in (100) and (110) directions. The current finding can provide not only valuable information of the carrier transport and its relationship with molecular packing of the single crystal, but also applications of solution-shearing method in high performance low-voltage OFETs.

The development of next generation large-area organic/hybrid optoelectronics relies not only on the availability of well-performing semiconductors but also on the development of innovative and highly scalable manufacturing methods. This presentation is divided into two parts. In the first part I will discuss the development of solution-processable transparent hole & electron transporting inorganic semiconductors and their implementation in various opto/electronic devices including; thin-film transistors, organic light-emitting diodes and organic solar cells. In the second part of my talk I will describe the development and application of a novel, high-throughput patterning method that enables facile manufacturing of nano-gap electrodes onto large-area arbitrary substrates including plastic. Emphasis will be placed on the combination of these novel materials and nano-gap electrode structures for the development of wireless energy harvesting devices and systems.