Bay Area Photovoltaic Consortium

The Bay Area Photovoltaic Consortium (BAPVC) is conceived to create a vibrant forum for interaction among Photovoltaic (PV) industry and academic experts to address the critical challenges in converting the U.S. leadership in PV R&D into leadership in PV Manufacturing. The U.S. faces substantial challenges in building such a PV manufacturing base as many of our competitors benefit from fewer manufacturing restrictions, faster permitting processes, lower cost labor and substantial financial incentives. In this environment, U.S. manufacturing leadership must be built upon superior, more innovative technologies delivered at all stages of the value chain. The industry leaders who have founded the numerous PV start‐ups or launched internal development in larger firms are highly creative people. Certainly they are guiding their own companies toward excellent results. Providing this input to guide additional research in universities will add significant value. However, great innovation is possible if this expertise is engaged interactively with their counterparts in the academic realm. BAPVC will provide the forum for great innovation. Introduction BAPVC is led by Stanford University and University of California Berkeley. BAPVC is funded by the U.S. Department of Energy with additional support from industry, universities and GCEP. DOE is providing $25 million over five years (2011–2016) as part of the SunShot Photovoltaic Manufacturing Initiative (PVMI) to provide a source of research funding for all universities across the United States. BAPVC conducts industry‐relevant research and development that will impact high‐ volume PV manufacturing, produce a highly trained workforce, and speed up commercialization of cutting‐edge PV technologies. BAPVC will develop and test innovative new materials, device structures, and fabrication processes necessary to produce cost‐effective PV modules in high volumes. The research aims to find technologies which can increase photovoltaic conversion efficiencies and simultaneously reduce manufacturing cost. Success in research is measured by transfer of the technologies for development in industry. Background The heart of the BAPVC is the Industry Board that includes all of the member companies. The Industry Board identifies research priorities, informs the scope of RFPs, reviews and ranks proposals, and monitors the progress of research. Industry members are the first to learn of inventions and will be in the best position, potentially in partnership with other member companies, to adopt and build on those inventions in their own laboratories and factories. In addition to GCEP members, current members include First Solar, Alta Devices, BASF, EpiSolar, Total American Services, and 3SUN. BAPVC launched thirty five projects which are coordinated in the following thrusts: 1) High performance and multijunction cells; 2) Silicon absorbers and cells; 3) Thin film absorbers and cells; 4) Photon management and transparent conductors; and, 5) Encapsulation and reliability. The high performance and multijunction thrust explores new growth processes, material systems, and device architectures offering high device efficiencies at low processing costs. In particular, two parallel approaches are being explored, one relying on reducing the processing costs of III-V single junction solar cells and the other exploring tandem device architectures based on Si bottom cells. The highest performance for single-junction cells, currently at 28.8% efficiency, has been demonstrated in III-Vs. However, their module costs have been estimated by NREL to be currently >10x of those of Si cells. This high cost mainly arises from the initial substrate and epi-growth by the MOCVD process. Thus, BAPVC is developing disruptive growth and processing technologies that will drastically lower the cost without sacrificing the device efficiencies. The second path is exploring tandem cells based on Si (or CIGS, CdTe, or III-V) bottom cells to enhance the efficiency of the existing PV technologies. Cost analysis, device modeling, and experiments are being performed in parallel in a collaborative manner to ensure success. The projects are shown in Table 1. Table 1. High Performance and Multijunction Cells Thrust Ali Javey Berkeley High Performance, Low Cost, III‐V Photovoltaics on Metal Foils James S. Harris Stanford Ultra high efficiency thin film multi-junction solar cell Paul McIntyre Stanford Thin Film Compound Semiconductor Solar Cells via Templated Growth Michael McGehee Stanford Low-Cost Tandem Solar Cells With Greater than 20% Power Conversion Efficiency Eli Yablonovitch Berkeley High Voc Solar Absorbers for High-Efficiency, SpectralSplitting, Solar Cells Y.-H. Zhang ASU Si/II-VI double-heterostructure solar cells Tonio Buonassisi MIT Design principles and defect tolerances of silicon / III-V multijunction interfaces Peter Bermel Purdue Exploratory Photovoltaic Modeling and Simulation Silicon-based solar cells are the dominant PV technology today with more than 80% market share. While the Si cost component has been decreasing steadily (from over 40% to 19% over the last decade) it is still a significant cost at the module level. Thinner Si cells can reduce the module cost further and leverage the potential higher efficiency and form factor to reduce balance-of-system costs. In this thrust, the key problems which are being addressed to enable high volume manufacturing of high efficiency Si cells include: 1) Commercially viable manufacturing of thin crystalline Si below 50um; 2) Passivation of thin crystalline Si to meet the high efficiency targets; 3) Absorption of all available light within a reduced absorber volume; and, 4) Metallization and packaging of thin Si cells into lightweight modules. Project in Silicon are shown in Table 2. Table 2. Silicon Absorbers and Solar Cells Yi Cui Stanford High Efficiency Ultrathin Silicon Solar Cells Sanjay Banerjee Texas Thin Crystalline RPCVD Back Contact Cells Stuart Bowden ASU Laser Wafering Maikel van Hest NREL Module Interconnects and Crystalline Film Silicon by Atmospheric Pressure Processing Vivek Subramanian Berkeley High-resolution, high-speed printing of PV contacts Thin Film PV technologies are now established in commercial markets. As the global market continues to expand, the competitiveness of thin film solutions faces four significant Grand Challenges: (1) increasing efficiency of modules; (2) reducing direct materials costs; (3) reducing capital intensity of manufacturing; and, (4) design and validation for long-term field reliability. BAPVC projects in thin film photovoltaics are shown in Table 3. Table 3. Thin Film Photovoltaics Bruce Clemens Stanford Bandgap Grading in Cu2ZnSn(S,Se)4 Solar Cells Stacey Bent Stanford SnS based Photovoltaics Michael Toney SLAC Advanced Materials Characterization Greg Hanket Delaware Advanced Evaporation Source Design Hugh Hillhouse Washington Development of Multicolor Lock-in PL Method Scott Dunham Washington Fundamental Modeling of Chalcopyrite Solar Cells Mark Lonergan Oregon Identifying Problem Areas in CIGS and CdTe Based Photovoltaic Devices Colin Wolden CSM Non-Equilibrium Processing of CdTe Absorbers Mike Scarpulla Utah Laser Processing CdTe: Efficiency & Manufacturing Chris Ferekides USF CdTe Absorbers Delia Milliron Texas In situ characterization of grain growth in thin film semiconductors Peidong Yang Berkeley Applying Cation-Exchange Chemistry to Nanowire Arrays for Efficient Solution-Processed Solar Cells The Photon Management and Transparent Conductors thrust attacks several grand challenges including: 1) develop materials and structures to couple maximum sunlight into the solar cells and to control the above bandgap photon distribution for complete absorption with significantly reduced absorber materials; 2) use photon management to enhance the solar cells parameters including short circuit current and open circuit voltage; 3) Develop low-cost highly transparent (~95%) and low sheet resistance electrodes (<5 ohm/sq) for solar cells with nand p-type contact capability; and, 4) develop processes to implement the above materials and structures in practical, scalable solar cell manufacturing. Table 4. Photon Management and Transparent Conductors Mark Brongersma Stanford Percolating Transparent Metallic Electrodes for Solar Cells Shanhui Fan Stanford Theory and simulation of photon management in nanostructured solar cells Wladek Walukiewicz LBNL Ideal Transparent Conductors for Full Spectrum Photovoltaics Joel Ager LBNL New P-type Transparent Conductors Harry Atwater Cal Tech Solar Cell Efficiency Enhancement via Light Trapping in Resonant Dielectric Sphere Arrays Kaustav Banerjee U.C.S.B. Graphene Electrode Eng. for Photovoltaic Application Ning Wu CSM Large-Area, Fast, and Electric-Field Assisted Continuous Coating for Nanostructured Photon Management The impact of high‐volume and cost-effective PV technologies depends critically on their reliability and durability over extended operating lifetimes. Successful commercialization also requires accurate PV lifetime predictions and related product warranties. Ironically, despite optimistic forecasts for the impact of cost-effective PV technologies, uncertain degradation mechanisms, the lack of testing metrologies, poor accelerated testing protocols, the almost complete lack of science-based kinetic degradation models, and uncertain lifetimes currently present significant barriers for success. BAPVC’s projects to address these issues are listed in Table 5. Characterizing the stability and reliability of PV materials, including barrier-films and encapsulants, is necessary not only to design accelerated testing protocols to standardize PV module requirements, but also to provide the fundamentals for the design of improved PV materials and product designs. The encapsulation and reliability thrust attacks these barriers to develop understanding of the coupled thermo-mechanical, electro-chemical, and photo-chemical degradation mechanisms that determine the reliability and operational lifetimes of PV technologies. Table 5. Reliability, Encapsulation & Barrier layers Reinhold Dauskardt Stanford Reliability and Operational Lifetimes for BAPVC Technologies Roger French Case Western PV Module Performance & Lifetime Prediction: Inserting New Technologies Without Lifetime Penalty Jeffrey Urban Berkeley Novel polymer-nanocrystal composite barrier layers Bernard Kippelen, Samuel Graham GIT Tailoring Electrostatic Interactions to Produce Hybrid Barrier Films for Photovoltaics Results BAPVC holds meetings bi-annually to stimulate interaction among the industry members and researchers. These were held May 12-13, 2014 at Stanford and October 67, 2014 at Berkeley. We are currently preparing a full report of progress and plans for future work that is available in the Bay Area Photovoltaic Consortium Project Catalogue 2015. Here we will describe some of the most significant highlights from a few of the projects. A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction: In an exciting example of collaboration among several BAPVC research teams, research to develop a top-cell partner for silicon solar cells delivered a first-of-a-kind tandem solar cell. The publication in Applied Physics Letters was cited for “the most read this month” in January 2015. Led by Michael McGehee from Stanford and Tonio Buonassisi from the Massachusetts Institute of Technology, the team addressed what is recognized as the most important challenge for next-generation photovoltaics. Silicon based photovoltaic modules constitute about 90% of the total solar electric energy market. Solar-to-electricity conversion efficiency is the technical variable that most strongly influences silicon (Si) photovoltaic (PV) module costs. The record efficiency of crystalline silicon (c-Si) single-junction PV devices has only increased from 25% to 25.6% during the last fifteen years, asymptotically approaching the 29.4% Augerrecombination-constrained Shockley-Queisser limit. To make PV modules with higher efficiency than market-leading c-Si while leveraging existing c-Si manufacturing capacity, Si-based tandem approaches have been proposed. The top sub-cell in a siliconbased tandem should have a band gap between 1.6 and 1.9eV. However, very few materials exhibit high open-circuit voltages (VOC) within this band gap range. Recently, the methylammonium-lead-halide perovskite has demonstrated a rapid efficiency increase with a VOC of 1.15 V. The methylammonium-lead-halide perovskite has a tunable band gap, ranging from 1.6 to 2.3eV depending on halide composition, though not all compositions are currently stable under illumination. Methods to optically transmit longer-wavelength light through a top perovskite sub-cell in a mechanically stacked tandem configuration have been developed recently. A perovskite/Si multijunction solar cell may also be constructed via monolithic integration where a thin film perovskite sub-cell is deposited directly onto the c-Si subcell. Monolithic integration requires electrical coupling between sub-cells and transmission of infrared light to the bottom sub-cell. The BAPVC team used an interband tunnel junction to facilitate electron tunneling from the electron-selective contact of the perovskite sub-cell into the p-type emitter of the Si sub-cell. This approach stands in contrast to the recombination layer used in other perovskite tandem systems and is the one widely used in III-V and micromorph (a-Si/c-Si) tandem solar cells. Unlike the tunnel junction in III-V multi-junction solar cells, the tunnel junction for connecting the perovskite cell is made of silicon with an indirect band gap, enabling electrical coupling with minimal parasitic absorption. The conduction-band alignment between Si and the perovskite sub-cell’s electron-selective contact (TiO2) enables bypassing the usage of a transparent conducting oxide (TCO) recombination layer, an alternative option with greater parasitic absorption. This work used the methylammonium-lead(II)-iodide perovskite (CH3NH3PbI3), which has a 1.61eV band gap. The schematic, micrograph and band structure are shown in Figure 1. Figure 1. The device structure of a 2-terminal monolithically grown perovskite/Si multijunction solar cell with an n-type Si base. The polished SEM image is taken at 45 tilt to show the Ag nanowire mesh (500nm scale bar). Band diagram of the perovskite/silicon cell interface showing the charge-transport mechanism around the Si tunnel junction. Rapid Thermal Processing of ZnTe:Cu Contacted CdTe Solar Cells: Cadmium telluride (CdTe ) is a leading absorber for thin-film solar cells. However, state-of-the art open circuit voltages (Voc) of CdTe thin film solar cells fall ~350 mV below the value expected based on the band gap of CdTe. One of the reasons is due to barriers at the back contact. A BAPVC Team at Colorado School of Mines headed by Colin Wolden has developed a process for forming the back contact that employs rapid thermal annealing to form a ZnTe:Cu contact. This process precisely controls the activation and distribution of copper. A 30 s annealing steps significantly improve fill factor and Voc without compromising the current density. Devices with >14% efficiency and >825 mV Voc are obtained under optimal conditions. It is notoriously difficult to make good ohmic contact with CdTe using conventional metals, because this requires a work function of greater than 5.7 eV. The most common method to solve this problem is by etching the CdTe surface to make its surface heavily p-doped and contacting it with a buffer layer before metallization. Wet chemical etching using solutions such as Br2/methanol or nitric acid/phosphoric acid mixtures are most common. An alternative preparation is through ion beam milling, which also produces a Te–rich surface. Copper-doped zinc telluride (ZnTe:Cu) is one of the most commonly employed buffer layers. ZnTe was identified due to its valence band alignment and compatibility with CdTe. Copper is commonly used to degenerately dope this layer, which narrows the barrier width and permits electron tunneling, creating a quasi-ohmic contact. First Solar has integrated ZnTe:Cu into its product line, crediting this layer for improvements in both champion cell efficiency and module reliability. Small amounts of copper are also beneficial for doping CdTe. However the free carrier concentration is typically several orders lower than the total Cu concentration, suggesting that significant charge compensation takes place during Cu incorporation. Excessive copper has also been implicated in the formation of deep level defects, which have been correlated with reduced carrier lifetimes. Copper is highly mobile, and has been observed to preferentially accumulate at both the back contact interface and in the CdS window layer after thermal processing. With copper having both positive and deleterious effects it is critical to precisely control both its amount and spatial distribution in order to obtain high efficiency. The most common approach to apply ZnTe:Cu is through thermal evaporation or sputtering at elevated temperature. A typical process in research laboratories employs temperatures between 240 360 oC, and process times on the order of hours which accounts for sample heating, deposition, and cool down. The amount of copper introduced is controlled by either the target composition (1 – 5 wt %), or by using a fixed composition and altering the total thickness of the buffer layer. One drawback of this procedure is that deposition and diffusion occur simultaneously, with substantial diffusion continuing to occur during the subsequent cool down. The BAPVC team developed an RTP-based process for back contact preparation that de-couples Cu deposition from its re-distribution. The ZnTe:Cu back contact is co-evaporated at low temperature, with little or no interdiffusion. The sample is then subjected to short RTP treatment(s) to activate the junction. Figure 2 shows I-V curves of four representative devices exposed to different RTP treatments. The original sample was the as-deposited device which wasn’t treated by RTP. The as-deposited device showed good current collection, but the open circuit voltage was only 676.3 mV. In addition, the sample showed significant roll-over, which attributed to the presence of barriers at the back contact. The highest efficiency device was obtained after subsequent RTP treatments at 320/330 oC. In this case the Jsc value remains essentially unchanged, but the VOC and FF increase significantly to 826.4 mV and 71.1 %, respectively, and the rollover in the J-V was eliminated. Very similar results could also be obtained from devices processed using just one 30 s RTP step, and here it was found that a setpoint of 360 oC provided optimal results. Finally the device treated at 450 oC is characteristic of overcooked samples. Here all the parameters decreased significantly, and it is inferred that Cu had diffused to the CdS layer, degrading the quality of the junction and leading to shunting. The team at Colorado School of Mines demonstrated that thermal evaporation combined with RTP processing is an effective approach for fabricating back contacts for CdTe solar cells. RTP provides low thermal budgets and precise control over time-temperature trajectories, which is very applicable to CdTe solar cell fabrication. The work showed that the fraction of Cu in the ZnTe buffer was critical, but its initial distribution or the thickness of the buffer layer was not critical. Sequential RTP treatments were refined to optimize the process. By using appropriate RTP treatments, the efficiency of the devices increased from about 9% to 14.5%, increasing the Voc to >825 mV. Figure 2. J-V curves of devices with different RTP treatments Future Plans BAPVC selected the initial sub-awards on the basis of the individual merit of the ideas and capabilities of the proposing teams. As work advanced, we have identified additional specific technologies that can support the BAPVC technologies accelerating progress toward industrial adoption. During the coming year we will fund this next phase of research as selected through a competitive procurement in 2014. These new projects will support BAPVC’s core technologies either by increasing the level-of-effort or duration of existing projects or by funding new projects addressing topics needed to accelerate progress of the existing technologies toward industrial adoption. References 1. Jonathan P. Mailoa, Colin D. Bailie, Eric C. Johlin, Eric T. Hoke, Austin J. Akey, William H. Nguyen, Michael D. McGehee, and Tonio Buonassisi, “A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction” Applied Physics Letters 106, 121105 (2015) 2. Jiaojiao Li, Joseph D. Beach, and Colin A. Wolden, “Rapid Thermal Processing of ZnTe:Cu Contacted CdTe Solar Cells” Proc.40 IEEE PV Specialists Conf., pp. 2436-2438 (2014) Contacts John P. Benner, Executive Director BAPVC, [email protected] Bay Area Photovoltaic Consortium (BAPVC) List of Publications 1 PI: Harry Atwater California Institute of Technology "Scanning Laser-Beam-Induced Current Measurements of Lateral Transport Near-Junction Defects in Silicon Heterojunction Solar Cells”, M.G. Deceglie, H.S. Emmer, Z.C.Holman, A. Descoeudres, S. De Wolf. C. Ballif, and H.A. Atwater, IEEE JOURNAL OF PHOTOVOLTAICS, 4 pp 154-159 (2014). "Silicon Solar Cell Light-Trapping Using Defect Mode Photonic Crystals", K.A. Whitesell, D.M. Callahan, H.A.Atwater. "Physics, Simulation, and Photonic Engineering of Photovoltaic Devices II", edited by Alexandre Freundlich, Jean-Francois Guillemoles, Proc. of SPIE Vol. 8620, 86200D, CCC code:0277786X/13/$18 · doi: 10.1117/12.2005450 (2013). "Light trapping in ultrathin silicon photonic crystal superlattices with randomly-textured dielectric uncouplers", D.M. Callahan, K.A.W. Horowitz, and H. A. Atwater, OPTICS EXPRESS 21 pp: 30315-30326 DOI: 10.1364/OE.21.030315 (2013). PI: Stacey Bent Stanford University “Vapor transport deposition and epitaxy of orthorhombic SnS on glass and NaCl substrates,” A. Wangperawong, S. M. Herron, R. R. Runser, C. Hägglund, J. Tanskanen, H.B. R. Lee, B. M. Clemens, and S. F. Bent, Appl. Phys. Lett, 103 (2013) 052105, http://dx.doi.org/10.1063/1.4816746. “Bifacial solar cell with SnS absorber by vapor transport deposition,” A. Wangperawong, P. C. Hsu, Y. Yee, S. M. Herron, B. M. Clemens, Y. Cui, and S. F. Bent, Appl. Phys. Lett., 105 (2014) 173904:1-4, 10.1063/1.4898092. PI: Peter Bermel Purdue University R. V. K. Chavali, J. E. Moore, X. Wang, M. A. Alam, M. S. Lundstrom, J. L. Gray, "Frozen Potential Approach to Separate the Photo-Current and Diode Injection Current in Solar Cells," IEEE J. Photovoltaics, 2015 (In Press). R. V. K. Chavali, S. Khatavkar, C. V Kannan, V. Kumar, J. L. Gray, and M. A. Alam, “Multi-Probe Characterization of Inversion Charge for Self-Consistent Parameterization of HIT Cells,” IEEE J. Photovoltaics, 2015 (In Press). Z. Zhou, Q. Chen, P. Bermel, "Prospects for high-performance thermophotovoltaic conversion efficiencies exceeding the Shockley-Queisser limit," J. Energy Conversion Manag., 2015 (In Press). Bay Area Photovoltaic Consortium (BAPVC) List of Publications 2 W. Nie, H. Tsai, R. Asadpour, J.-C. Blancon, A. J. Neukirch, G. Gupta, J. J. Crochet, M. Chhowalla, S. Tretiak, M. A. Alam, H.-L. Wang, and A. D. Mohite, “High-efficiency solution-processed perovskite solar cells with millimeter-scale grains,” Science, vol. 347, no. 6221, pp. 522–525, Jan. 2015. X. Sun, R. Asadpour , W. Nie , A. Mohite , and M. Ashraful , “A Physics-based Analytical Model for Perovskite Solar Cells: A Simple Approach for Characterization and Optimization,” Appl. Phys. Lett., 2015. (Submitted) M. Ryyan Khan, Xufeng Wang, and Muhammad A. Alam, "Practical Constraints in Efficiency Gain for Angular Restricted Solar Cells", Journal of Applied Physics, 2015 (Submitted) Zhiguang Zhou, Omar Yehia, Peter Bermel, “Integrated photonic-crystal selective emitter for thermophotovoltaic systems,” Physical Review Applied, 2015 (submitted, authors revision). Xufeng Wang, Jayprakash Bhosale, James Moore, Rehan Kapadia, Peter Bermel, Ali Javey, and Mark Lundstrom, "Photovoltaic Material Characterization with Steady-State and Transient Photoluminescence," IEEE Journal of Photovoltaics 5(1), 282-287 (2015). M. Ryyan Khan, Xufeng Wang, Peter Bermel, and Muhammad A. Alam, "Enhanced light trapping in solar cells with a meta-mirror following Generalized Snell's law," Opt. Express 22, A973-A985 (2014). Peter Bermel, Xufeng Wang, and Gary J. Cheng, "Photonic Systems for Crystalline Silicon and ThinFilm Photovoltaic Manufacturing," Shimon Nof and Andrew M. Weiner, Eds., Laser and Photonic Systems: Design and Integration (Boca Raton: Taylor & Francis, 2014). R. V. K. Chavali, J. R. Wilcox, B. Ray, J. L. Gray, and M. A. Alam, “Correlated Nonideal Effects of Dark and Light I--V Characteristics in a-Si/c-Si Heterojunction Solar Cells,” IEEE J. Photovoltaics, vol. 4, no. 3, pp. 763 – 771, 2014. Enas Sakr, Zhiguang Zhou, and Peter Bermel, "High Efficiency Rare-Earth Emitter for Thermophotovoltaic Applications," Applied Physics Letters 105, 111107 (2014). M. Ryyan Khan, X. Wang, P. Bermel, and M. A. Alam, “Enhanced light trapping in solar cells with a meta-mirror following generalized Snell’s law,” Opt. Express, vol. 22, no. S3, pp. A973–A985, May 2014. H. Chung, K-Y. Jung, X. T. Tee, and P. Bermel, "Time domain simulation of tandem silicon solar cells with optimal textured light trapping enabled by the quadratic complex rational function," Opt. Express 22, A818-A832 (2014). X. Wang, M. Khan, M. Lundstrom, and P. Bermel, "Performance-limiting factors for GaAs-based single nanowire photovoltaics," Opt. Express 22, A344-A358 (2014). P. Bermel, "Photon management and beyond for photovoltaics," Optics Communications, corrected proof available online, October 25, 2013. Leo T. Varghese, Yi Xuan, Ben Niu, Li Fan, Peter Bermel, Minghao Qi, "Enhanced photon management of thin-film silicon solar cells using inverse opal photonic crystals with 3D photonic bandgaps," Advanced Optical Materials, early view online, July 19, 2013. Bay Area Photovoltaic Consortium (BAPVC) List of Publications 3 PI: Mark Brongersma Stanford University “Transparent Metallic Fractal Electrodes for Semiconductor Devices,” Farzaneh Afshinmanesh, Alberto G. Curto, Kaveh M. Milaninia, Niek F. van Hulst, and Mark L. Brongersma Nano Letter, 14, 5068–5074 (2014). PI: Tonio Buonassisi Massachusetts Institute of Technology Colin D. Bailie, M. Greyson Christoforo, Jonathan P. Mailoa, Andrea R. Bowring, Eva L. Unger, William H. Nguyen, Julian Burschka, Norman Pellet, Jungwoo Z. Lee, Michael Grätzel, Rommel Noufi, Tonio Buonassisi, Alberto Salleo, Michael D. McGehee, "Semi-transparent perovskite solar cells for tandems with silicon and CIGS,” Energy & Environmental Science 8, 956–963 (2015) — DOI: 10.1039/c4ee03322a, http://dx.doi.org/10.1039/c4ee03322a Featured in Science magazine: http://www.sciencemag.org/content/347/6219/225.full Most downloaded paper in Energy & Environmental Science during mid to late January and early February 2015. Jonathan P. Mailoa, Colin D. Bailie, Eric C. Johlin, Eric T. Hoke, Austin J. Akey, William H. Nguyen, Michael D. McGehee, Tonio Buonassisi, "A 2-Terminal Perovskite/Silicon Multijunction Solar Cell Enabled by a Silicon Tunnel Junction,” accepted to Applied Physics Letters (2015). PI: Bruce Clemens Stanford University “Bifacial solar cell with SnS absorber by vapor transport deposition, Wangperawong, A., Hsu, P., Yee, Y., Herron, S. M., Clemens, B. M., Cui, Y., Bent, S. F., Appl. Phys. Lett., 105 (17), 2014. “Rapid liftoff of epitaxial thin films,” G.J. Hayes and B.M. Clemens, Journal of Materials Research, 28, 2564-2569, (2013). “Vapor transport deposition and epitaxy of orthorhombic SnS on glass and NaCl substrates,” A. Wangperawong, S.M. Herron, R.R. Runser, C. Haegglund, J.T. Tanskanen, H.-B.-R. Lee, B.M. Clemens, S.F. Bent, Applied Physics Letters, 103, 052105 (2013). “Investigating the Role of Grain Boundaries in CZTS and CZTSSe Thin Film Solar Cells with Scanning Probe Microscopy,” J. B. Li, V. Chawla, and B. M. Clemens, Adv. Mater., vol. 24, no. 6, pp. 720–723, Jan. 2012. “Biaxially-textured photovoltaic film crystal silicon on ion beam assisted deposition CaF2 seed layers on glass,” J. R. Groves, J. B. Li, B. M. Clemens, V. LaSalvia, F. Hasoon, H. M. Branz, and C. W. Teplin, Energy Environ. Sci., vol. 5, no. 5, p. 6905, 2012. “Understanding the role of grain boundaries in sulfide thin film solar cells with scanning probe microscopy,” J. B. Li, V. Chawla, and B. M. Clemens, 2012 38th IEEE Photovoltaic Specialists Conference (PVSC) Published: 2012. Bay Area Photovoltaic Consortium (BAPVC) List of Publications 4 PI: Yi Cui Stanford University S. Jeong, M. D. McGehee, and Y. Cui, "All-back-contact ultra-thin silicon nanocone solar cells with 13.7% power conversion efficiency," Nature Communications 4, 2950 (2013). S. Wang, B. Weil, Y. Li, K. X. Wang, E. Garnett, S. Fan, and Y. Cui, "Large-Area Free-Standing Ultrathin Single-Crystal Silicon as Processable Materials," Nano Letters, 13, 4393 (2013). PI: Reinhold Dauskardt Stanford University F.D. Novoa, D.C. Miller, R.H. Dauskardt, Environmental mechanisms of debonding in photovoltaic backsheets, Sol. Energy Mater. Sol. Cells. (2013) 1–7. Stephanie R. Dupont, Fernando Novoa, Eszter Voroshazi, Reinhold H. Dauskardt, “Decohesion Kinetics of PEDOT:PSS Conducting Polymer Films,” Advanced Functional Materials, 24[9], 1325–1332, 2014. Christopher Bruner, Fernando Novoa, Stephanie Dupont and Reinhold H. Dauskardt, “Decohesion Kinetics in Polymer Organic Solar Cells,” ACS Applied Materials and Interfaces, 10;6(23), 21474-83, 2014. F. D. Novoa and R. H. Dauskardt, “Debonding Kinetics of Photovoltaic Encapsulation in Moist Environment,” Prog. Photovoltaics, 2015. In press. PI: Scott Dunham University of Washington D. Mutter and S. T. Dunham, “Calculation of defect concentrations in Cu2ZnSnS4 from stoichiometry” in Photovoltaic Specialist Conference (PVSC), 2014 IEEE 40th, 2014, p. 2384. (Publisehd) D. Mutter and S. T. Dunham, “Formation energies of carbon related defects in Cu2ZnSnS4” in Photovoltaic Specialist Conference (PVSC), 2014 IEEE 40th, 2014, p. 2390. (Published) D. Mutter and S. T. Dunham, “Calculation of Defect Concentrations and Phase Stability in Cu2ZnSnS4 and Cu2ZnSnSe4 from Stoichiometry", submitted to the IEEE Journal of Photovoltaics (2015) (Under Review) D. Mutter and S. T. Dunham, “Ab initio study of Carbon Impurities in Cu2ZnSnS4", submitted to the IEEE Journal of Photovoltaics (2015) (Under Review) Bay Area Photovoltaic Consortium (BAPVC) List of Publications 5 PI: Shanhui Fan Stanford University K. X. Wang, Z. Yu, S. Sandhu and S. Fan, “Fundamental Bounds on Decay Rates in Asymmetric SingleMode Optical Resonators”, Optics Letters, vol. 38, pp. 100-102 (2013). S. Sandhu, Z. Yu and S. Fan, “Detailed balance analysis of nanophotonic solar cells”, Optics Express, vol. 21, pp. 1209-1217 (2013). S. Wang, B. D. Weil, Y. Li, K. X. Wang, E. Garnett, S. Fan and Y. Cui, “Large area free-standing ultrathin single-crystal silicon as processable materials”, Nano Letters, vol. 13, pp. 4393-4398 (2013). Z. Yu, S. Sandhu and S. Fan, “Achieving efficiency above the Shockley-Queisser limit using a single band gap material in a tandem configuration”, Nano Letters, vol. 14, pp. 66-70 (2014). S. Sandhu, Z. Yu, and S. Fan, “Detailed balance analysis and enhancement of open circuit voltage in single nanowire solar cells”, Nano Letters, vol. 14, pp. 1011-1015 (2014). K. Wang, J. R. Piper and S. Fan, “Optical impedance transformer for transparent conducting electrodes”, Nano Letters, vol. 14, pp. 2755-2758 (2014). K. Wang, Z. Yu, V. Liu, A. Raman, Y. Cui and S. Fan, “Light trapping in photonic crystals”, Energy and Environmental Science, vol. 7, pp. 2725-2738 (2014). K. Wang, Z. Yu, S. Sandhu, V. Liu, and S. Fan, “Condition for perfect antireflection by optical resonance at material interface”, Optica, vol. 1, pp. 388-395 (2014). I. Karakasoglu, K. X. Wang and S. Fan, “Optical-Electronic Analysis of the Intrinsic Behaviors of Nanostructured Ultrathin Crystalline Silicon Solar Cells”, ACS Photonics (submitted) PI: Chris Ferekides University of South Florida Pulsed laser induced ohmic back contact in CdTe solar cells Brian J. Simonds, Vasilios Palekis, Brian Van Devener, Christos Ferekides and Michael A. Scarpulla Appl. Phys. Lett. 104, 141604 (2014); http://dx.doi.org/10.1063/1.4870838 Pulsed UV laser annealing of polycrystalline CdTe Brian J. Simonds ; Vasilios Palekis ; M. I. Khan ; Chris S. Ferekides ; Michael A. Scarpulla Proc. SPIE 8826, Laser Material Processing for Solar Energy Devices II, 882607 (September 16, 2013); doi:10.1117/12.2024437 Sub-bandgap laser annealing of room temperature deposited polycrystalline CdTe Brian J. Simonds ; Sudhajit Misra ; Naba Paudel ; Koen Vandewal ; Alberto Salleo ; Christos Ferekides ; Michael A. Scarpulla Proc. SPIE 9180, Laser Processing and Fabrication for Solar, Displays, and Optoelectronic Devices III, 91800F (October 8, 2014); doi:10.1117/12.2062178 Bay Area Photovoltaic Consortium (BAPVC) List of Publications 6 Surface stoichiometry of pulsed ultraviolet laser treated polycrystalline CdTe Brian J. Simonds, Vasilios Palekis, Brian Van Devener, Christos Ferekides and Michael A. Scarpulla1 J. Appl. Phys. 116, 013506 (2014); http://dx.doi.org/10.1063/1.4887079 Laser processing for thin film chalcogenide photovoltaics: a review and prospectus Brian J. Simonds ; Helene J. Meadows ; Sudhajit Misra ; Christos Ferekides ; Phillip J. Dale ; Michael A. Scarpulla J. Photon. Energy. 5(1), 050999 (Jan 19, 2015). doi:10.1117/1.JPE.5.050999 History: Received October 15, 2014; Accepted December 8, 2014 Laser Treatment as Surface Modification Technique for CdTe Solar Cells V. Palekis, B. J. Simonds, V. Evani, M. Khan, P. Bane, M. A. Scarpulla,and C. Ferekides Proc. EMRS 2014, May27-29, Lille, France PI: Roger French Case Western Reserve University Bruckman, Laura S., Nicholas R. Wheeler, Ian V. Kidd, Jiayang Sun, and Roger H. French. “Photovoltaic Lifetime and Degradation Science Statistical Pathway Development: Acrylic Degradation.” In SPIE Solar Energy+ Technology, 8825:88250D – 8. International Society for Optics and Photonics, 2013. doi:10.1117/12.2024717. French, Roger H., Rudolf Podgornik, Timothy J. Peshek, Laura S. Bruckman, Yifan Xu, Nicholas R. Wheeler, Abdulkerim Gok, et al. “Degradation Science: Mesoscopic Evolution and Temporal Analytics of Photovoltaic Energy Materials.” Current Opinion in Solid State and Materials Science. Accessed February 28, 2015. doi:10.1016/j.cossms.2014.12.008 Hu, Yang, Yifan Xu, Timothy J. Peshek, Wenyu Du, Jiayang Sun, and Roger H. French. “A Data Science Procedure for Forecasting Brand-Dependent Regression Model to Predict Photovoltaic Performance.” Submitted to: Progress in Photovoltaics, 2015. Lemire, Heather M., Kelly A. Peterson, Samuel Sprawls, Kenneth Singer, Ina T. Martin, and Roger H. French. “Degradation of Transparent Conductive Oxides: Mechanistic Insights across Configurations and Exposures.” In Proceedings of SPIE, 8825:882502–1 – 8, 2013. doi:10.1117/12.2024691. Lemire, Heather M., Kelly A. Peterson, Mona S. Breslau, Kenneth D. Singer, Ina T. Martin, and Roger H. French. “Degradation of Transparent Conductive Oxides, and the Beneficial Role of Interfacial Layers.” In MRS Online Proceedings Library, 1537:null – null, 2013. doi:10.1557/opl.2013.695. Lemire, H.M. “Degradation of Transparent Conductive Oxides: Mechanistic Insights and Interfacial Engineering.” Master of Science Thesis, Case Western Reserve University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1386325661. Mirletz, Heather M., Kelly A. Peterson, Ina T. Martin, and Roger H. French. “Degradation of Transparent Conductive Oxides: Interfacial Engineering and Mechanistic Insights.” Submitted to: Solar Energy Cells and Materials, 2014. Bay Area Photovoltaic Consortium (BAPVC) List of Publications 7 Wheeler, Nicholas R, Yifan Xu, Abdulkerim Gok, Ian V. Kidd, Laura S. Bruckman, Jiayang Sun, and Roger H French. “Data Science Study Protocols for Investigating Lifetime and Degradation of PV Technology Systems.” In IEEE PVSC 40. Denver, Colorado, 2014. Wheeler, N.R., L.S. Bruckman, Junheng Ma, E. Wang, C.K. Wang, I. Chou, Jiayang Sun, and R.H. French. “Statistical and Domain Analytics for Informed Study Protocols.” In 2013 IEEE Energytech, 1–7, 2013. doi:10.1109/EnergyTech.2013.6645354. Wheeler, N.R., L.S. Bruckman, Junheng Ma, E. Wang, C.K. Wang, I. Chou, Jiayang Sun, and R.H. French. “Degradation Pathway Models for Photovoltaics Module Lifetime Performance.” In Photovoltaic Specialists Conference (PVSC), 2013 IEEE 39th, 3185–90, 2013. doi:10.1109/PVSC.2013.6745130. PI: Gregory Hanket University of Delaware Began outlining a manuscript for publication relating to the engineering of high rate vacuum evaporation sources. PI: James Harris Stanford University Dong Liang, Anjia Gu, Yijie Huo, Jingzhou Yan, Shuang Li, Erik Garnett, Evan Pickett, Yangsen Kang, Meiyueh Tan, Antonio Xavier Cerruto, Jia Zhu, Ching-Mei Hsu, Yan Yao, Majid Riaziat, Yi Cui, and James S. Harris, “A novel nano-structured GaAs solar cell,” Proc. American Physical Society March Meeting 56 (1), D36.00009, Dallas, Texas, USA, March 21-25, 2011 D. Liang, Y. Huo, Y. Kang, K. X. Wang, A. Gu, M. Tan, Z. Yu, S.Li, J. Jia, X. Bao, S. Wang, Y. Yao, S. Fan, Y. Cui, J. S.Harris, “GaAs Thin Film Nanostructure Arrays for III-V Solar Cell Applications”, Proceedings of SPIE 8269, 82692M, 2012 D. Liang, Y. Huo, Y. Kang, K. Wang, A. Gu, M. Tan, Z. Yu, S. Li, J. Jia, X. Bao, S. Wang, Y. Yao, H.-S. P. Wong, S. Fan, Y. Cui, J. S. Harris, “Optical absorption enhancement in freestanding GaAs thin film nanopyramid arrays”, Adv. Energy Matls. 2 (10), pp 1254-1260, October 2012 Yangsen Kang, Dong Liang, Yijie Huo, Anjia Gu, Shuang Li, Yusi Chen, James Harris, “Design and Fabrication of Nano-pyramid GaAs Solar Cell” Proc. 39th IEEE Photovoltaic Specialists Conference (PVSC), Tampa, FL, 2013 Dong Liang, Yangsen Kang, Yijie Huo, Yusi Chen, Yi Cui, and James S. Harris “High-Efficiency Nanostructured Window GaAs Solar Cells”, Nano Letters 13 (10), 4850-4856, September 2013 Yusi Chen, Yangsen Kang, Yijie Huo, Dong Liang, Li Zhao, Jieyang Jia, Jeremy Kim, Leon Yao, Jeremy Bregman, James S. Harris, “Nanostructured Dielectric Layer A New Approach to Design Nanostructured Solar Cells” Proc. 40th IEEE Photovoltaic Specialists Conference (PVSC), Denver, CO, June, 2014 Yangsen Kang, Yusi Chen, Yijie Huo, Li Zhao, Jieyang Jia, Huiyang Deng, James S. Harris, “Ultra-thin Film Nanostructured Gallium Arsenide Solar Cells” 2014 Proc. SPIE Photonics Asia, Beijing, China, 2014 Bay Area Photovoltaic Consortium (BAPVC) List of Publications 8 Y. Miao, J. Jia, Y. Kang, Y. Huo, M. Mazouchi, Y. Chen, H. Deng, P. Supaniratisai, S. AlQahtani, L. Zhao, and J. Harris, "Dependency of Luminescent Coupling Efficiency on Bias Voltage and Illumination Intensity," Proc. OSA Conf. Light, Energy and the Environment, Sydney, Australia, October, 2014), paper PTu3C.3. PI: Kaustav Banerjee UC Santa Barbara W. Liu, S. Krämer, D. Sarkar, H. Li, P. M. Ajayan, and Kaustav Banerjee, "Controllable and Rapid Synthesis of High-Quality and Large-Area Bernal Stacked Bilayer Graphene using Chemical Vapor Deposition," Chemistry of Materials, Vol. 26, No. 2, pp 907-915, 2014. Y. Khatami, H. Li, W. Liu and K. Banerjee, "On the Electrostatics of Bernal-Stacked Few-Layer Graphene on Surface Passivated Semiconductors," IEEE Transactions on Nanotechnology, Vol. 13, No. 1, pp. 94-100, 2014. H. Li, C. C. Russ, W. Liu, D. Johnsson, H. Gossner and K. Banerjee, "On the Electrostatic-Discharge Robustness of Graphene," IEEE Transactions on Electron Devices, Vol. 61, No. 6, pp. 1920-1928, 2014. Y. Khatami, W. Liu, J. Kang and K. Banerjee, "Prospects of Graphene Electrodes in Photovoltaics," Proc. SPIE 8824, Next Generation (Nano) Photonic and Cell Technologies for Solar Energy Conversion IV, 88240T, September 25, 2013 (INVITED). PI: Bernard Kippelen Georgia Institute of Technology “Engineering the mechanical properties of ultrabarrier films grown by atomic layer deposition for the encapsulation of electronics,” A. Bulusu, A. Singh, C.-Y. Wang, A. Dindar, C. Fuentes-Hernandez, H. Kim, D. Cullen, B. Kippelen, and S. Graham, submitted to BAPVC for internal clearance (2015). PI: Mark Lonergan University of Oregon J.W. Boucher, D.W. Miller, C.W. Warren, J.D. Cohen, B.E. McCandless, J.T. Heath, M.C. Lonergan, S.W. Boettcher "Optical response of deep defects as revealed by transient photocapacitance and photocurrent spectroscopy in CdTe/CdS solar cells" Solar Energy Materials and Solar Cells 129, 57-63 (2014). C.W. Warren, D.W. Miller, F. Yasin, J.T. Heath, “Characterization of bulk defect response in Cu(In, Ga)Se2 thin-film solar cell using DLTS,” 2013 IEEE 39th Photovoltaic Specialists Conference (PVSC) 16-21, 170-173 (2013). J. Li, D.R. Diercks, T.R. Ohno, C.W. Warren, M.C. Lonergan, J.D. Beach, C.A. Wolden, "Controlled activiation of ZnTe:Cu contacted CdTe solar cells using rapid thermal processing" 133, 208 (2015) Bay Area Photovoltaic Consortium (BAPVC) List of Publications 9 Charles W. Warren, Jiaojiao Li, Colin A. Wolden, Daniel M. Meysing, Teresa M. Barnes, D. Westley Miller, Jennifer T. Heath, and Mark C. Lonergan, "Sub-bandgap density of states in CdTe solar cells: optical transitions and the influence of Cu,” Applied Physics Letters, submitted PI: Mike McGehee Stanford University “Spray Deposition of Silver Nanowire Electrodes for Semitransparent Solid-State Dye-Sensitized Solar Cells,” G.Y. Margulis, M.G. Christoforo, D. Lam, Z.M. Beiley, A.R. Bowring, C.D. Bailie, A. Salleo, M.D. McGehee, Advanced Energy Materials, 3 (2013) p. 1657-1663. “Semi-Transparent Polymer Solar Cells with Excellent Sub-Bandgap Transmission for Third Generation Photovoltaics,” Z.M. Beiley, M.G. Christoforo, P. Gratia, A.R. Bowring, P. Eberspacher, G.Y. Margulis, C. Cabanetos, P. Beaujuge, A. Salleo, M.D. McGehee, Advanced Materials, 25 (2013) p. 7020-7026. "Semi-transparent perovskite solar cells for tandems with silicon and CIGS," C. D. Bailie, M. G. Christoforo, J. P. Mailoa, A. R. Bowring, E. L. Unger, W. H. Nguyen, J. Burschka, N. Pellet, J. Z. Lee, M. Grätzel, R. Noufi, T. Buonassisi, A. Salleo, M. D. McGehee, Energy and Environmental Science 23, 480–484 (2015) "A 2-Terminal Perovskite/Silicon Multijunction Solar Cell Enabled by a Silicon Tunnel Junction," J. P. Mailoa, C. D. Bailie, E. C. Johlin, E. T. Hoke, A. J. Akey, W. H. Nguyen, M. D. McGehee, T. Buonassisi, Applied Physics Letters, In press (2015). PI: Paul McIntyre Stanford University Y.Y. Li, Y. Kang, J.S. Harris and P.C. McIntyre, GaAs/Ge Absorbers Synthesized on SiO2 by MetalInduced Crystallization Templating, manuscript in preparation 2015. Y.Y. Li, PC McIntyre, Nanostructured Templates for Thin Film Absorber Growth on Various Substrates, Bay Area Photovoltaic Consortium (BAPVC) Bi-annual Meeting, Oct 2014. PI: Delia Milliron University of Texas, Austin A Singh, C Coughlan, DJ Milliron, KR Ryan, “Solution Synthesis and Assembly of Wurtzite derived CuIn-Zn-S Nanorods with Tunable Composition and Band Gap,” Chem. Mater., in press. doi: 10.1021/cm5035613. http://pubs.acs.org/doi/abs/10.1021/cm5035613 EL Rosen, AM Sawvel, DJ Milliron, BA Helms*, "Influence of surface composition on electronic transport through naked nanocrystal networks," Chem. Mater. 26 (2014), 2214. http://pubs.acs.org/doi/abs/10.1021/cm404149u Bay Area Photovoltaic Consortium (BAPVC) List of Publications 10 Richa Sharma, April Sawvel, Bastian Barton, Angang Dong, Raffaella Buonsanti, Jeffrey J. Urban, Christian Kisielowski, Delia J. Milliron, "Fabrication of ultrathin inorganic nanocomposites by nanocrystal ligand exchange at a liquid surface,"Chem. Mater., in review. PI: Sanjay Banerjee University of Texas, Austin S. Saha, M. M. Hilali, E. U. Onyegam, S. Sonde, R. A. Rao, L. Mathew, A. Upadhyaya, S. K. Banerjee, Improved Cleaning Process for Textured ~25μm Flexible Mono-crystalline Silicon Heterojunction Solar Cells with Metal Backing, J. Solid State Sc. And Tech, Vol. 3 (7) Q1-Q4 (2014). E. U. Onyegam, D. Sarkar, M. Hilali, S. Saha, L. Mathew, R. A. Rao, R. S. Smith, D. Xu, D. Jawarani, R. Garcia, M. Ainom, S. K. Banerjee, Realization of dual-heterojunction solar cells on ultra-thin ∼25 μm, flexible silicon substrates, Appl. Phy. Lett., Vol. 104, pp. 153902, April, 2014. M. Hilali, S.Saha, Onyegam, Emmanuel; Rao, Rajesh; Mathew, Leo; Banerjee, SK, Light trapping in ultrathin 25 mu m exfoliated Si solar cells , APPLIED OPTICS Volume: 53 Issue: 27 Pages: 61406147 SEP 2