Symposium Organizers
Maikel F. A. M. van Hest National Renewable Energy Laboratory
Patrick J. Smith The University of Sheffield
David B. Mitzi IBM T. J. Watson Research Center
Aoife Morrin Dublin City University
S3: Poster Session: Solution-Processed PV, TCOs, TFTs
Session Chairs
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
S1: Solution-Processed Chalcogenides for Thin Film Photovoltaic Devices
Session Chairs
David Mitzi
Maikel van Hest
Tuesday PM, November 29, 2011
Room 310 (Hynes)
9:30 AM - **S1.1
Nanocrystal-Ink Routes and High-Yield Molecular Precursor Routes to Chalcopyrite and Kesterite Thin Film Solar Cells.
Hugh Hillhouse 1
1 Chemical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractThe presentation will briefly summarize recent progress on nanocrystal-ink based routes to CIGS. However, given the terawatt scale of future energy needs, the most promising future photovoltaic materials should be Earth abundant with their primary mineral resources distributed across several geographic regions and their supply chains robust to reduce concerns of price volatility. In addition, the process of forming the solar cell should be scalable, low-cost, and not utilize dangerous or toxic materials. The strongest initial candidate appears to be Cu2ZnSnS4 (CZTS). Up until 2009, CZTS thin film solar cells were synthesized primarily by evaporating or sputtering metals (Cu, Zn, & Sn) followed by sulfurization. More recently, two potentially low-cost high-throughput approaches have been demonstrated that form the quaternary or pentenary chalcogenide directly from solution-phase processes. One is based on first synthesizing multinary sulfide nanocrystals and then sintering them to form a dense layer. The other approach utilizes molecular precursors dissolved in hydrazine. Both new approaches reach their highest device efficiencies by incorporating Se to form Cu2ZnSn(Sx,Se1-x)4 devices, and each has yielded substantially higher efficiency devices than the best vacuum deposited absorbers. The hydrazine route has yielded the most efficient CZTS-based devices thus far. The presentation will focus on our recent progress in CZTS-based nanocrystal-ink devices. In particular, we have shown that germanium may be alloyed with CTZS (at least up to Ge/(Sn+Ge) ratios of 0.7) to form Cu2Zn(Sn,Ge)S4 nanocrystals that have an increased bandgap [1]. The defect chemistry is serendipitous, and allows for at least 6.8% efficient devices at high germanium content. This exciting prospect may be used to create a back surface field and direct carriers in a similar manner to how gallium is used in high efficiency CIGS devices. In addition, we will report recent results on a scalable chemical route to Earth abundant element thin film solar cells by coating a solution of highly soluble, inexpensive, and commercially available precursors in an environmentally friendly non-toxic solvent to form device quality films (without using nanocrystals or hydrazine). [1] Ford, G.M., Guo, Q., Agrawal, R., and Hillhouse, H.W., “Earth Abundant Element Cu2Zn(Sn1-xGex)S4 Nanocrystals for Tunable Band Gap Solar Cells: 6.8% Efficient Device Fabrication,” Chemistry of Materials 23 (10), 2626–2629 (2011).
10:00 AM - **S1.2
Advances in Kesterite Solar Cells by Solution-Nanoparticle Ink Processing.
Teodor Todorov 1 , David Aaron Barkhouse 1 , Santanu Bag 1 , Oki Gunawan 1 , Tayfun Gokmen 1 , Goislard de Monsabert Thomas 1 , S. Jay Chey 1 , David Mitzi 1
1 Photovoltaic Science and Technology, IBM T. J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractFuture terawatt-scale solar electricity requires lower photovoltaic (PV) module fabrication costs, reliance on more abundant materials and efficiency equal to or greater than current commercial technologies. Thin-film indium-based chalcopyrite devices have one of the fastest growth potentials and also highest efficiencies among thin-film PV technologies. Replacement of the scarce indium element is viewed as a strategic step towards unlimited growth of chalcogenide PV production beyond 100GWp/year. A strong candidate in this category is the kesterite family, including Cu2ZnSnS4 and Cu2ZnSn(S,Se)4 (CZTS and CZTSSe). We have developed kesterite solar cells operating in the 10% efficiency range. This performance is achieved by a simple low-cost liquid-based deposition approach based on chalcogenide solutions in combination with particle-based precursors that yield homogeneous CZTS and CZTSSe phases after thermal treatment. Here we will present recent advances in this field.
10:30 AM - S1.3
Air-Stable Hybrid Inks for Low-Cost CZTS Solar Cells.
Kyoohee Woo 1 , Youngwoo Kim 1 , Joosun Kim 2 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of), 2 Principal Research Scientist Center for Energy Materials Research, Korea Institute of Science & Technology (KIST), Seoul Korea (the Republic of)
Show Abstract Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is a very promising material as a low cost absorber alternative to other chalcopyrite-type semiconductors based on Ga or In because it is only composed of abundant and economical elements. In addition, CZTS has a direct band-gap energy of 1.0~1.5 eV and large absorption coefficient over ~104 cm-1, which are similar to those of Cu(In,Ga)Se2(CIGS) that is regarded as one of the most successful absorber materials. Typically, metal chalcogenide films such as CIGS and CZTS are deposited by vacuum process such as evaporation or sputtering. However, this vacuum deposition suffers from relatively low throughput, low material utilization, and difficulties associated with large-scale production. In this regard, solution-based deposition methods are being developed because they have advantages including suitability for large-area substrates, higher throughput, and more efficient materials usage. Various solution based approaches for producing absorber layer have been reported including sol-gel and nanocrystal dispersion, but they are still facing some limitations; sol-gel method is vulnerable to the contamination of carbon, oxygen, and other impurities from the precursor solution and inevitably leads to the formation of porous structure. Nanocrystal dispersion method needs the complex synthesis of nanocrystals. Recently, Todorov et al. reported the fabrication of CZTS thin film solar cells with 9.6% power conversion efficiency using a hydrazine based approach. However, hydrazine is a highly toxic and very unstable compound that requires extreme caution during handling and strorage. Furthermore, due to the reactive nature of this solvent, all processings for slurry and film preparations must be performed under inert atmospheric conditions and thus it would not be easily adapted for large-scale solar cell fabrication. With these considerations, it is highly desirable to develop a robust, easily scalable and relatively safe solution-based process for the fabrication of high quality CZTS absorber layer. Here, we devise the air-stable hybrid solution-particle approach for the fabrication of dense CZTS absorber layer. Our air-stable ink comprises of commercially available powder mixture of Zn, Sn, and S dispersed in an environmentally benign solvent in which Cu and Zn precursors are dissolved. The metal precursor solution is vulcanized by sulphur element to create a rubberlike polymer, providing the viscosity and wetting that allows us to prepare highly stable hybrid ink containing heavy metallic powders. Our readily achievable hybrid ink, without the involvements of complex particle synthesis and high toxic solvent, enables a convenient access to fabricate uniform, dense, contaminant-free, large-grained CZTS absorber layer. Our simple approach reported here will be the first step in realizing the low-cost and large-area solar cells with high efficiency.
10:45 AM - S1.4
Sonication Assisted Phase and Microstructure Evolution of CuInSe2 by Elemental Cu,In,Se Precursors.
Emre Yassitepe 1 , William Shafarman 2 , S. Ismat Shah 1 3
1 Material Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Institute of Energy Conversion, University of Delaware, Newark, Delaware, United States, 3 Physics and Astronomy, University of Delaware, Newark, Delaware, United States
Show AbstractNon toxic chemical routes that enable formation of high quality CuInSe2 thin films with high materials utilization are desired for low production cost of solar cells. We will present results on the effects of ultrasound on Cu,Se and In,Se elemental precursors with different solvents. Depending on the solvent, the reaction between these elemental precursors facilitates binary selenide phases. These crystalline phases are compared with the effective heat of formation model of Cu-Se and In-Se compounds. The formed binary selenide phases gave an exact match with the predicted effective heat of formation model. However, sonication of Cu,In and Se elemental particles for short times did not yield any single phase CuInSe2 due to the unfavored reaction pathways between CuSe2 and In4Se3 phases. Further annealing these binary phases led to the single phase formation of CuInSe2 at 350C. SEM studies revealed upon sonication above one micron sized Cu,In,Se elemental particles are broken to smaller particles during sonication and moreover upon completion of the reaction CuInSe2 nanocrystals are obtained.
11:30 AM - **S1.5
Understanding Hydrazine Solution Processed CuIn(Se,S)2 Solar Cells.
Yang Yang 1 , Choong-Heui Chung 1 , Bao Lei 1
1 Materials Science and Engreeing, Univ. of California Los Angeles, Los Angeles, California, United States
Show AbstractCuIn(Se,S)2 and other chalcopyrite-based solar cells have received substantial research interest owing to their high optical absorption coefficient, a tunable band gap and demonstrated the highest power conversion efficiency among thin film solar cells. However, the use of vacuum technique in the preparation of absorber layers imposes hurdles in the the production of low cost and large area photovoltaic modules. Solution-based absorber deposition approaches offer an alternative to many of these issues, and have thus been extensively pursued for more than a decade. Recently, a hydrazine solution based processing method has demonstrated copper chalcopyrite based thin film solar cells with efficiencies of up to 13.6% despite the early developmental stage of this technique. In order to further improve this approached solar cells performance, deeper understanding on dissolving mechanism, the structure of molecular precursors, phase formation, defect physics and recombination mechanisms in such devices would be necessary. In this talk, we present the molecular structures present in solutions containing Cu2S, In2Se3, or mixtures of the two, and the CuIn(Se,S)2 phase formation after annealing the solution-processed precursor films. We also examine the effects of introducing an additional Cd ion solution soaking step into our device fabrication process on the defect energy levels and carrier concentration which in turn consistently improves the open circuit voltage of solar cell devices.
12:00 PM - S1.6
Studies of Carrier Recombination in CuIn(S,Se)2 through Photoluminescence Spectroscopy.
Hsin-Sheng Duan 1 , Wan-Ching Hsu 1 , Kuo-Chun Tang 2 , Bao Lei 1 , Pi-Tai Chou 2 , Yang Yang 1
1 , University of California, Los Angeles, Los Angeles, California, United States, 2 , National Taiwan University, Taipei Taiwan
Show AbstractSolution-processed CuIn(S,Se)2 has shown considerable promise as an absorber material in the fabrication of high performance solar cells. However, it is crucial to indentify the primary factors limiting photovoltaic performance. In this study, photoluminescence spectroscopy is employed to investigate the carrier recombination in CuIn(S,Se)2 with emphasis on the effect of cadmium sulfide (CdS) deposition. In steady state photoluminescence, it has been found that CdS deposition (1) leads to an altered photoluminescence profile due to cadmium diffusion into the CuIn(S,Se)2 layer as well as defect passivation at the absorber surface. (2) CdS deposition helps to protect the CuIn(S,Se)2 film from chemical degradation, and also (3) the shallow defects in CuIn(S,Se)2 film at roughly 31 meV above the valence band and with density about 1015cm-3 are estimated through temperature-dependent photoluminescence measurements. These effects have been studied quantitatively, and the results are presented along with suggestions for how future devices can be optimized with respect to material parameters and fabrication strategies.
12:15 PM - S1.7
Solution-Processed Sintered Nanocrystal Solar Cells and Semiconductor Quantum Dot Energy Levels.
Scott Watkins 1 , Jacek Jasieniak 1 , Brandon MacDonald 1 2 , Paul Mulvaney 2
1 Materials Science and Engineering, CSIRO, Melbourne, Victoria, Australia, 2 Chemistry, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractThe use and characterisation of solution processable inorganic semiconductors is highly relevant to the development of low-cost electronic devices such as solar cells. In this paper we will report on two aspects of our work in this area. Firstly, we will describe our layer-by-layer process that enables the fabrication of totally solution processable solar cells from inorganic nanocrystal inks in air at temperatures as low as 300 degrees Celsius. Focusing on a CdTe/ZnO thin-film system we report solar cells that achieve power conversion efficiencies of over 7% with greater than 90% internal quantum efficiency (IQE). We will describe the characterisation of the devices and, through capacitance-voltage measurements, demonstrate that the CdTe layer is fully depleted which enables charge carrier collection to be maximized. Finally, we also discuss the use of photoelectron spectroscopy in air (PESA) to investigate the size-dependent valence and conduction band-edge energies of CdSe, CdTe, PbS and PbSe semiconductor quantum dots (QDs). We will compare the results to those of previous studies, based on differing experimental methods, and to theoretical calculations based on k-p theory and state-of-the-art atomistic semi-empirical pseudopotential modelling.
12:30 PM - S1.8
Improved Efficiency in a PbS Nanocrystal Heterojunction Solar Cell by Employing a Thin TiO2 Film and a Hole Transporting Polymer Layer.
Jangwon Seo 1 , Dongho Lee 1 , Alexander Cartwright 1 , Paras Prasad 1
1 , University at Buffalo, Buffalo, New York, United States
Show AbstractWe report a highly efficient hybrid nanostructured solar cell consisting of a densely-packed TiO2 film; a PbS nanocrystal film; a hole transporting polymer layer (HTL); and metal contacts. The TiO2 film was spray deposited on an ITO coated glass slide. Subsequently, a PbS nanocrystal film was deposited, layer-by-layer, on the TiO2 film to establish a planar donor-acceptor heterojunction. Two device geometries were fabricated on this structure by subsequently depositing either: i) a single Au contact layer or ii) a HTL followed by the Au contact layer. Drastic increases in the photocurrent, and stability in ambient air, was observed in the device with the HTL, relative to the device without the HTL. The device with the HTL layer had a power conversion efficiency of more than 5% under AM1.5G (100 mW/cm2). Moreover, the external quantum efficiencies of this device was very high (~90% in the visible range [400~600 nm] and ~30% in the near infrared range). The dependence of photovoltaic performance of the device on the thickness of the PbS nanocrystal film and the TiO2 film will be presented.
12:45 PM - S1.9
Adhesion Study of CZTS Layer Deposited from Ink Type Precursor onto Back Contact for Photovoltaic Applications.
Prashant Sarswat 1 , Michael Free 1
1 Metallurgical Engineering, University of Utah, Salt Lake city, Utah, United States
Show AbstractCZTS (Cu2ZnSnS4) based ink has been emerged as a potential candidate for high throughput production of p-type layer on a back contact. An ink based absorber material can simplify device production process because of fast printing technology. The pre-synthesized liquid can also be used as a spray to get faster output. Although this technique is very fast, some issues such as adhesion of ink on back contact need to be addressed. A systematic study of adhesion of ink on different substrates using various solvents, binders and annealing temperatures is discussed. Some techniques for improved adhesion were proposed and demonstrated.
S2: Solution-Processed Oxides
Session Chairs
David Mitzi
Maikel van Hest
Tuesday PM, November 29, 2011
Room 310 (Hynes)
2:30 PM - **S2.1
Electrodeposition and Chemical Bath Deposition of Zinc Oxide Semiconducting Films and Nanostructures: A Case Example of a Potential Alternative to Classical Vacuum Deposition Routes.
Daniel Lincot 1
1 , Institute of Research and Development of Photovoltaic Energy (IRDEP), Joint Laboratory CNRS-EDF-Chimie Paristech, Chatou France
Show AbstractZinc oxide has become in recent years one of the key materials in the search for advanced applications in optoelectronics, photovoltaics, sensing and magnetic applications, as a low cost alternative to existing state of the art materials. ZnO, in contrast with many other key wide gap semiconductors has the unique advantage to be easily prepared in high quality from solution routes. This allows low temperature cost effective deposition processes (mostly <100°C) and also to take the advantage of the solution environment to promote highly-selective self-assembling processes to generate a wide range of structures from classical thin films to nanostructures [1]. This explains why tremendous attention is now paid, mostly since 2000, to these new solution synthetic approaches. Three main approaches are Chemical bath deposition (CBD), also named chemical solution deposition (CSD), Hydrothermal deposition and electrodeposition (ED). All these methods, even if they are often presented separately, possess common roots based on solution chemistry, interfacial reactions and general concepts of heterogeneous nucleation and growth. The aim of this presentation is first to highlight these aspects. Then recent advances in the electrodeposition of ZnO thin films for TCO applications for thin film CIGS solar cells will be presented which may represent a breakthrough for replacing sputtering deposition. The deposition of nanostructures consisting in nanocolumns and nanoporous will be presented with possible applications in nanostructured solar cells. Recent results on epitaxial growth will be highlighted. Next avenues for research will be discussed.[1] D. Lincot, MRS Bulletin, 35(2010)778-788 and references therein.
3:00 PM - S2.2
A Unifying Modular Approach to Solution Processed Dielectric Semiconducting and Conducting Mixed Metal Oxides: Synthesis, Characterization and Electronic Performance.
Joerg Schneider 1
1 , TU Darmstadt, Darmstadt Germany
Show AbstractTransparent metal oxides are promising materials for applications in thin film electronic transisistors (TFTs)[1]. Due to their variable dopant content, their tunable properties their electronic performance can sometimes be tailored from insulating dielectric, to semiconducting to metallic behaviour. Especially, amorphous metal oxides of Zn, Al, Ga, In, and Sn for semiconducting and conducting oxides, and Zr and Hf for dielectric transparent oxides are interesting and thus have been studied extensively over the last couple of years worldwide. However, solution processing of such metal oxides under ambient conditions is still a major challenge since processing conditions under ambient conditions are necessary e.g. to use soft substrates, e.g. polymers for the thin film deposition. We report on a solely molecular based, modular approach which allows to tailor the elemental composition of resulting metal oxide films with respect to composition and performance obtained from such precursors as single, binary or ternary phases. This offers a synthetic route to dielectric, semiconducting and electrically conducting thin films under very similar processing conditions.[1] T. Minami, New n-type transparent conducting oxides, MRS Bull. 25, 2000, 38-44
3:15 PM - S2.3
Solution Processing of Nb-Doped TiO2 and Ti-Doped In2O3 Transparent Conductors.
Robert Pasquarelli 1 , Maikel van Hest 2 , Alexander Miedaner 2 , Calvin Curtis 2 , Joseph Berry 2 , John Perkins 2 , Ryan O'Hayre 1 , David Ginley 2
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractTransparent conducting oxide (TCO) thin-films play a critical role in many current and emerging opto-electronic devices due to their combination of high transparency in the visible region of the spectrum and tunable electronic conductivity. Nb-doped anatase TiO2 deposited by physical vapor deposition methods and on lattice-matched substrates has demonstrated potential as a replacement for indium-based TCOs such as indium tin oxide. Atmospheric-pressure solution deposition is an attractive alternative to these conventional vacuum-based TCO deposition techniques due to its ease and potential to lower device manufacturing costs. Here we report on 5 at% Nb-doped TiO2 films deposited from solutions of Ti(OEt)2(acac)2 and Nb(OEt)5. The desired anatase phase formed from an amorphous state on glass substrates at 500°C without the need of lattice-matching or a seed layer. Films demonstrated conductivities of 20-60 S/cm with mobilities ranging 0.1-0.6 cm2/Vs and a carrier concentration of 5x1020 /cm3. Processing conditions had a significant effect on the final electronic properties and will be presented. The Ti precursor was also used in combination with the novel low-temperature In precursor, In5O(OPr)13, to prepare 3 at% Ti-doped In2O3 films. Undoped films have demonstrated conductivities of 60-100 S/cm with mobilities as high as 10 cm2/Vs.
3:30 PM - S2.4
Electrochemically Triggered Deposition of Porous Zinc Oxide from Aqueous Precursor Solutions on Textile- Compatible Microelectrodes on the Way towards Textile-Based Photovoltaics.
Derck Schlettwein 1
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany
Show AbstractOver the last years electronics have been more and more integrated into textiles, mainly for sensing purposes. Interest rose to also integrate photovoltaics as an independent energy supply. Preparation of semiconductor films from precursor solutions represents the most promising approach because of good compatibility of the processes to a low thermal stability of textiles and to the need of a three- dimensional coating process. Water as solvent is optimum because of perfect environmental and textile chemical compatibility. Dye-sensitized solar cells represent a suitable photovoltaic cell technology since electrolytes are capable to bridge an insulating gap between the active electrodes of typically 10 - 100 µm in most finely woven fabrics.Thin porous films of ZnO were electrochemically deposited on silver- coated polyamide (ELITEX®) threads, filaments and knitted fabrics and subsequently sensitized by appropriate dyes. Such textiles had been established earlier as quite well conducting textiles, stable under environmental conditions. They were therefore chosen in a first step towards textile- integrated photovoltaics. Electrodeposition of zinc oxide from oxygen-saturated aqueous solutions was presented as a successful strategy to realize semiconductor structures on textiles and detailed control and influence of the deposition conditions was discussed [1]. The role of microelectrode effects at such threads, options of forced convection, deposition under pulsed potential, alternative deposition baths and different substrate metals were investigated [2]. However, corrosion problems in the typically used iodine- containing electrolyte hampered the use of ELITEX® in dye-sensitized cells. Thin tungsten wires served as model for a passivated surface. ZnO could still be deposited electrochemically but the active electrode structure was protected against corrosion. Recent work therefore concentrated on utilization of corrosion- resistant micro-fibers of stainless steel which are compatible to textile technologies. Structures with conversion efficiency close to 1 % under AM 1.5 conditions could be realized and thereby open the door towards devices of technical interest [3].1. T. Loewenstein, A. Hastall, M. Mingebach, Y. Zimmermann, A. Neudeck and D. Schlettwein, "Textile electrodes as substrates for the electrodeposition of porous ZnO," Phys. Chem. Chem. Phys. 10(14), 1844-1847 (2008).2. M. Rudolph, T. Loewenstein, E. Arndt, Y. Zimmermann, A. Neudeck and D. Schlettwein, "Pulsed electrodeposition of porous ZnO on Ag-coated polyamide filaments," Phys. Chem. Chem. Phys. 11(17), 3313-3319 (2009).3. T. Loewenstein, M. Rudolph, M. Mingebach, K. Strauch, Y. Zimmermann, A. Neudeck, S. Sensfuss and D. Schlettwein, "Textile-Compatible Substrate Electrodes with Electrodeposited ZnO-A New Pathway to Textile-Based Photovoltaics," Chemphyschem 11(4), 783-788 (2010).
3:45 PM - S2.5
Thin Film Formation of Transparent Conductive Oxides and Organic Materials by Solution-Based Mist Deposition Method toward Hybrid Device Applications.
Takumi Ikenoue 1 2 , Shizuo Fujita 2
1 Department of Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 Photonics and Electronics Science and Engineering Center, Kyoto University, Kyoto Japan
Show AbstractSolution processable organic devices such as solar cells and light emitting diodes have attracted increasing interest due to its rapid efficiency-improvement, ease of processing, and cost-effective large-area processability. Many of organic devices have generally been fabricated by spin-coating technique, but material efficiency of this method is low and it is not suitable for large area fabrication. In addition, indium-tin oxide (ITO), which is used as a transparent electrode, is fabricated by vacuum processes, therefore it cannot take full advantages of the solution based processes. We report, in this presentation, a novel vapor-like-deposition technique based on a solution process, namely ultrasonic spray assisted mist deposition technique. Transparent conductive oxides such as ITO and zinc oxide can be fabricated by this technique without any vacuum systems. Additionally, this technique offers many advantages, for example, (i) it is possible to grow high quality thin organic films, (ii) this technique is suitable for large area substrates and roll-to-roll processes, (iii) source materials can be formed into films without many wastes, and (iv) owing to a vapor-deposition technique this deposition method allows hard-mask patterning without photolithography, which can simplify device fabrication processes, and easy formation of multilayer structures. In the mist deposition technique, the source solution is ultrasonically atomized and the aerosol particles formed are supplied onto a substrate using nitrogen carrier gas to form thin films. To fabricate ITO thin films, we used indium acetylacetonate and tin acetate as a starting source, which were diluted in methanol and deionized water with concentrations of 0.020 and 0.002 mol/L, respectively. A flow rate of nitrogen carrier gas and the substrate temperature were set at 5 L/min and 400 degrees centigrade, respectively. The ITO films were indicated the high transmittance and sheet resistance of less than 10 Ω/square, which was reasonable to be applied as a transparent electrode. Similarly, by optimizing the deposition conditions of organic thin film formation, thicknesses of organic thin films have been well controlled and the properties such as conductivity values and roughness of those were comparable to those deposited by spin-coating. The detailed properties of the films and some examples of device applications such as solar cells will be demonstrated at the presentation.
4:30 PM - **S2.6
Solution Based Processing for Cost Effective Smart Windows.
Robert Tenent 1 , Chi-Ping Li 2 , Feng Lin 4 , David Alie 3 , Colin Wolden 2 , Ryan Richards 4 , Sean Shaheen 3 , Anne Dillon 1
1 Chemical and Materials Sciences, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Materials Science, Colorado School of Mines, Golden, Colorado, United States, 4 Chemistry, Colorado School of Mines, Golden, Colorado, United States, 3 Physics, University of Denver, Denver, Colorado, United States
Show AbstractInternal environmental control in buildings is the largest source of electrical energy use in the United States. “Smart” windows which dynamically control the transmission of both heat and visible light could potentially save roughly 30% of this energy amounting to almost $40 billion in total energy savings annually. At present, the smart windows market is dominated by vacuum processed metal oxide-based electrochromic devices. These devices typically consist of a five layer structure that includes two electrode materials separated by an ion conductor with these three layers sandwiched between transparent, but electrically conducting contacts. These devices change tint upon applying a small voltage (~1V) and act via an ion intercalation mechanism similar to battery materials. A consensus based on energy efficiency modeling as well as windows industry input has determined that prices must drop to between $20-$25/ft2 in order for this technology to be market viable. Present market prices vary from $50 to $100/ft2.Here we will present what we believe to be fruitful routes toward low-cost production of multilayer electrochromic devices. Our work is focused on solution processing of electrochromic metal oxide layers as well as ion conductors using the ultrasonic spray deposition method. Two possible manufacturing options will be presented. The first will be deposition on flat glass substrates and possible integration with the well known float glass process. We will also present work aimed at the development of roll-to-roll (R2R) processing methods using inexpensive flexible plastic substrates. To date we have demonstrated a high temperature deposition of lithium-doped nickel oxide1 material that is likely compatible with float glass processing as well as a low temperature deposition of tungsten oxide2 that may be suitable for R2R methods. We will touch briefly on these results and primarily discuss further work toward deposition of ion conductor materials and initial demonstrations of integrated device structures. Ion conductor work will primarily focus on development of gel electrolyte materials that may be compatible with atmospheric pressure deposition onto flexible substrates.1.Tenent, R. C.; Gillaspie, D. T.; Miedaner, A.; Parilla, P. A.; Curtis, C. J.; Dillon, A. C., Fast-Switching Electrochromic Li+Doped NiO Films by Ultrasonic Spray Deposition. Journal of the Electrochemical Society 2010, 157 (3), H318-H322.2.Li, C.-P.; Tenent, R. C.; Wolden, C.; Dillon, A. C., Electrochromic Films Produced by Ultrasonic Spray Deposition of Tungsten Oxide Nanoparticles. Solar Energy Materials and Solar Cells, 2011, in press, doi:10.1016/j.solmat.2011.03.034
5:00 PM - S2.7
Structure, Sodium Ion Role, and Practical Issues for β-Alumina as a High-K Solution-Processed Gate Layer for Transparent and Low Voltage Electronics.
Bo Zhang 1 , Yu Liu 1 , Howard Katz 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show Abstractβ-alumina (SBA) has been discovered as a promising high dielectric constant gate material for solution processed, transparent and low voltage transistor devices. Some experimental evidence indicates that the mobile Na ion within two spinel blocks made by Al and O is responsible for the high dielectric constant. Transistors (W/L ratio 10) using SBA as gate layer and sol-gel-processed zinc tin oxide (ZTO) as active layer only need 2V to obtain 0.7mA output current. The calculated field driven mobility for the devices is 22cm2/Vs. SBA material is compatible with organic semiconductors such as NTCDI and pentacene as well. Some key issues regarding using SBA for real applications, such as device stability in the ambient atmosphere, response under high frequency, and threshold voltage shift under gate bias have also been studied. It is found that encapsulating the device with CYTOP fluorinated polymer is an effective way to increase the operational stability of the devices in the ambient environment.
5:15 PM - S2.8
Solution-Processed Oxide Thin-Film Transistors Using La-Ta-O/Bi-Nb-O Stacked Gate Insulator.
Takaaki Miyasako 1 3 , Masatoshi Onoue 1 , Eisuke Tokumitsu 1 3 , Tatsuya Shimoda 1 2
1 ERATO SHIMODA Nano-Liquid Process Project, JST, Nomi, Ishikawa, Japan, 3 Precision and Intelligence Laboratory, Tokyo institute of Tecnology, Yokohama, Kanagawa, Japan, 2 School of Material Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan
Show Abstract