Paddy K. L. Chan, The University of Hong Kong
Oana Jurchescu, Wake Forest University
Ioannis Kymissis, Columbia University
Brendan T. O'Connor, North Carolina State University
BB2: Systems and Integration
Monday PM, November 30, 2015
Hynes, Level 2, Room 203
2:30 AM - *BB2.01
Stretchable and Ultraflexible Electronics for E-Textile and Wearable Devices
Takao Someya 1 Naoji Matsuhisa 1 Tsuyoshi Sekitani 1 2 Tomoyuki Yokota 1
1University of Tokyo Tokyo Japan2Osaka University Osaka JapanShow Abstract
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.
3:00 AM - BB2.02
Large Area Organic Temperature Sensor Array: From Thermal Conductivity Measurements to Device Fabrication
Paddy K. L. Chan 1 Xiaochen Ren 1 Xinyu Wang 1
1Univ of Hong Kong Hong Kong Hong KongShow Abstract
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 (AlOx) 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.
3:15 AM - BB2.03
High Detectivity All-Printed Organic Photodiodes
Adrien Pierre 1 Igal Deckman 1 Pierre Balthazar Lechene 1 Ana Claudia Arias 1
1Univ of California-Berkeley Berkeley United StatesShow Abstract
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;Hz0.5middot;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.
3:30 AM - BB2.04
Hierarchical Photonic Surfaces Using Template Stripping of Colloidal Quantum Dot Films
Ferry Prins 1 David K. Kim 1 Eva De Leo 1 Kevin McPeak 1 David J. Norris 1
1ETH Zurich Zurich SwitzerlandShow Abstract
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.
(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.
3:45 AM - BB2.05
Highly-Aligned, Invisible, Printed Ag Nanofiber Electrode Array
Yeongjun Lee 1 Sung-Yong Min 1 Su-Hun Jeong 1 Tae-Sik Kim 1 Juyeon Won 2 Hobeom Kim 1 Jae Kyeong Jeong 2 Tae-Woo Lee 1
1POSTECH Pohang Korea (the Republic of)2Inha University Incheon Korea (the Republic of)Show Abstract
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.
4:30 AM - *BB2.06
High Performance Digitally Printed Electronic Systems
Gregory Lewis Whiting 1 David Schwartz 1 Tse Nga Ng 1 Ping Mei 1 Brent Krusor 1 Eugene Chow 1 JengPing Lu 1
1Palo Alto Research Center Palo Alto United StatesShow Abstract
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.
5:00 AM - BB2.07
Solution-Processed Radio Frequency Diodes Based on Co-Planar Asymmetric Nanogap Electrode Architectures
James Semple 1 Stephan Rossbauer 1 Dimitra Georgiadou 1 Thomas Anthopoulos 1
1Imperial College London London United KingdomShow Abstract
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.
5:15 AM - BB2.08
Direct Printing of Sub-10mu;m Metallic Features Using Engineered Nanoporous Stamps
Sanha Kim 1 Hossein Sojoudi 1 2 Hangbo Zhao 1 Gareth McKinley 1 Karen Gleason 2 A. John Hart 1
1Massachusetts Institute of Technology Cambridge United States2Massachusetts Institute of Technology Cambridge United StatesShow Abstract
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.
5:30 AM - BB2.09
Printing Organic Semiconductors for Logic Circuits with Low Patterning Errors and Electrical Variability
Gaurav Giri 1 Steve Jeung Hoon Park 2 Zhenan Bao 3
1MIT Cambridge United States2Columbia University New York United States3Stanford University Stanford United StatesShow Abstract
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.
5:45 AM - BB2.10
High Mobility Low-Voltage Organic Transistors and Unipolar and Complementary Ring Oscillators on Plastic and Paper Substrates
Ulrike Kraft 1 2 Kazuo Takimiya 3 Florian Letzkus 4 Tarek Zaki 4 Joachim Burghartz 4 Edwin Weber 2 Hagen Klauk 1
1Max Planck Institute for Solid State Research Stuttgart Germany2TU Bergakademie Freiberg Freiberg Germany3RIKEN Advanced Science Institute Wako, Saitama Japan4Institute for Microelectronics (IMS Chips) Stuttgart GermanyShow Abstract
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 AlOx layer and a self-assembled monolayer of either an alkylphosphonic acid or a fluoroalkyphosphonic. 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.
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.
 U. Kraft et al., Adv. Mater., 2015, 27, 207
 U. Kraft et al., DRC, Santa Barbara, USA, 2014,
 F. Ante et al., Small, 2012, 8, 73
 F. Letzkus et al., Microelectron. Eng., 2000, 53, 609
Monday AM, November 30, 2015
Hynes, Level 2, Room 203
9:00 AM - *BB1.01
Oxide and Organic TFTs on Thin Solution Cast Polymeric Substrates
Thomas N. Jackson 1
1Pennsylvania State Univ University Park United StatesShow Abstract
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).
BB3: Poster Session I
Monday PM, November 30, 2015
Hynes, Level 1, Hall B
9:00 AM - BB3.01
Orthogonal Hydrofluoroethers Enable Photo-Patterning of State-of-the-Art Phosphorescent Small Molecule OLEDs and Deposition of Outcoupling Enhancement Structures
Simonas Krotkus 2 Tim Schaefer 2 Tobias Schwab 2 Fabian Ventsch 2 Daniel Kasemann 2 Alexander A. Zakhidov 2 Simone Lenk 2 Karl Leo 2 Malte C Gather 2 1
1University of St Andrews St Andrews United Kingdom2Technische Universitauml;t Dresden Dresden GermanyShow Abstract
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 t0.75 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.
 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)
 T. Schaefer, T. Schwab, S. Lenk, M. C. Gather, “White top-emitting OLEDs with solution-processed nano-particle scattering layers”, submitted
9:00 AM - BB3.02
New Organic/Inorganic Hybrid Films for Lighting Applications
Sara El Hanbali 1 Jennifer Weimmerskirch-Aubatin 2 Christophe Labbe 2 Nathalie Bar 3 Didier Villemin 3 Nicolas Barrier 1 Alain Pautrat 1 Ulrike Lueders 1 Vincent Caignaert 1 Olivier Perez 1 Sophie Boudin 1
1CRISMAT, CNRS/ENSICAEN/UCBN Caen France2CIMAP, CNRS/CEA/ENSICAEN/UCBN Caen France3LCMT, CNRS/ENSICAEN/UCBN Caen FranceShow Abstract
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.
9:00 AM - BB3.03
Transparent Ag-Free OLED Fabricated by OVPD Using Thin Au Contacts
Pascal Pfeiffer 1 Dominik Stuemmler 1 Sofia Loginkin 1 Michael Heuken 1 2 Andrei Vescan 1 Holger Kalisch 1
1RWTH Aachen Univ Aachen Germany2AIXTRON SE Herzogenrath GermanyShow Abstract
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 MoOx 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.
9:00 AM - BB3.04
Evaporation-Driven Assembly of Nanomaterials in a Confined Cylindrical Geometry
Yong Lin Kong 1 Francois Boulogne 1 Hyoungsoo Kim 1 Janine K. Nunes 1 Jie Feng 1 Howard Stone 1
1Princeton University Princeton United StatesShow Abstract
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.
9:00 AM - BB3.05
A Novel Fabrication Method for Passivation of Large-Area OLED Anode Grid Lines
Donald Lupo 1 Marika Janka 1
1Tampere University of Technology Tampere FinlandShow Abstract
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. 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.
 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).
 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).
 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).
9:00 AM - BB3.06
Controlling Vertical Composition Profile in Organic Photovoltaic Active Layers through the Photoprecursor Approach
Mitsuharu Suzuki 1 Yuji Yamaguchi 2 Ken-ichi Nakayama 2 3 Hiroko Yamada 1 3
1Nara Institute of Science and Technology Ikoma Japan2Yamagata University Yonezawa Japan3CREST, JST Kawaguchi JapanShow Abstract
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%) . 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.
 Y. Yamaguchi et al. Sci. Rep.4 (2014), 7151.
9:00 AM - BB3.07
A New Facile Method to Pattern a Conductive Polymer
Namchul Cho 1 Justin Diekhans 1 Malia Steward 1 seungkeun Choi 1
1University of Washington Bothell United StatesShow Abstract
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 c