Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session A36: Focus Session: Scalable Technologies for Terawatt Photovoltaics |
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Sponsoring Units: DMP GERA Chair: Wladek Walukiewicz, Lawrence Berkeley National Laboratory Room: C142 |
Monday, March 21, 2011 8:00AM - 8:36AM |
A36.00001: Film Si photovoltaics from high quality c-Si layers on inexpensive substrates Invited Speaker: We develop crystalline silicon film photovoltaic (PV) technology to approach the efficiency of wafer silicon PV at thin-film manufacturing costs. Epitaxial c-Si layers can be grown by a fast, scalable hot-wire CVD technique at rates that exceed those of amorphous and nanocrystalline thin film PV by factor of 20, with quality approaching that of the crystalline Si wafer. This approach greatly reduces the absorber material costs that today account for about half the cost of a Si wafer PV module while bypassing the low growth-rate bottleneck that dominates thin film Si PV economics. As part of this equation, devices must also be fabricated on inexpensive substrates. To this end, we explore homo- and hetero-epitaxy at display glass-compatible temperatures as well as collaborate with several groups on promising high crystal quality seed layer technology. In the talk, we discuss key physics issues associated with film Si PV and describe recent experimental results, including: 1) device physics showing feasibility of 2 -10 microns thick c-Si PV absorber layers and their relative tolerance to defects and impurities; 2) demonstration of epitaxial cells on Si wafers with open-circuit voltages up to 600 mV; 3) understanding of high-rate, high-quality epitaxial growth in the temperature range 620 to 760C; 4) growth on seed layers on display glass and metal foils; 5) novel light trapping schemes that result in improved spectral response without texturing the growth template or etching away valuable absorber layer material. [Preview Abstract] |
Monday, March 21, 2011 8:36AM - 9:12AM |
A36.00002: CdTe Solar Cells Scaling to Grid Parity Invited Speaker: CdTe thin-film solar cells are leading the technology race to deliver low-cost and sustainable photovoltaics. The technology has an inherent cost advantage over c-Si, and has achieved volume manufacturing ahead of any other thin-film technology. TF-CdTe is also more sustainable than other approaches, with a lower carbon-footprint and far faster energy-payback than c-Si. Having achieved the long-standing target of {\$}1/W module and well over 1GW/year in volume, the technology is continuing to drive down costs towards a levelised cost of electricity comparable to fossil fuels. [Preview Abstract] |
Monday, March 21, 2011 9:12AM - 9:48AM |
A36.00003: Challenges to Scaling CIGS Photovoltaics Invited Speaker: The challenges of scaling any photovoltaic technology to terawatts of global capacity are arguably more economic than technological or resource constraints. All commercial thin-film PV technologies are based on direct bandgap semiconductors whose absorption coefficient and bandgap alignment with the solar spectrum enable micron-thick coatings in lieu to hundreds of microns required using indirect-bandgap c-Si. Although thin-film PV reduces semiconductor materials cost, its manufacture is more capital intensive than c-Si production, and proportional to deposition rate. Only when combined with sufficient efficiency and cost of capital does this tradeoff yield lower manufacturing cost. CIGS has the potential to become the first thin film technology to achieve the terawatt benchmark because of its superior conversion efficiency, making it the only commercial thin film technology which demonstrably delivers performance comparable to the dominant incumbent, c-Si. Since module performance leverages total systems cost, this competitive advantage bears directly on CIGS' potential to displace c-Si and attract the requisite capital to finance the tens of gigawatts of annual production capacity needed to manufacture terawatts of PV modules apace with global demand growth. [Preview Abstract] |
Monday, March 21, 2011 9:48AM - 10:24AM |
A36.00004: CZTSSe: Materials and Physics Challenges Invited Speaker: Thin-film photovoltaic (PV) technologies led by CdTe and Cu(In,Ga)Se$_{2}$ (CIGS) are enjoying growing market share, due to their high performance and cost competitiveness, in the quest for renewable energy for the future. However the reliance on non-earth abundant elements tellurium and indium in these technologies presents a potential obstacle to ultimate terawatt deployment. We recently demonstrated kesterite Cu$_{2}$ZnSn(Se,S)$_{4}$ (CZTSSe) solar cells, comprised of the earth abundant metals copper, zinc and tin, with world record efficiency of 9.7{\%}. In this talk we present a comprehensive device characterization study that pinpoints the key performance bottlenecks in these cells. We find strong buffer-absorber interface recombination and low minority carrier lifetimes that limit the open circuit voltage and a high and diverging device series resistance at lower temperature that suggests a blocking back contact that may limit the fill factor. These findings help to identify key areas for improvement for these CZTSSe cells in the pursuit of a high performance terawatt-scalable PV technology. [Preview Abstract] |
Monday, March 21, 2011 10:24AM - 10:36AM |
A36.00005: Screening of inorganic wide-bandgap p-type semiconductors for high performance hole transport layers in organic photovoltaic devices David Ginley, Andriy Zakutayev, Andreas Garcia, Nicodemus Widjonarko, Paul Ndione, Ajaya Sigdel, Phillip Parilla, Dana Olson, John Perkins, Joseph Berry We will report on the development of novel inorganic hole transport layers (HTL) for organic photovoltaics (OPV). All the studied materials belong to the general class of wide-bandgap p-type oxide semiconductors. Potential candidates suitable for HTL applications include SnO, NiO, Cu2O (and related CuAlO2, CuCrO2, SrCu2O4 etc) and Co3O4 (and related ZnCo2O4, NiCo2O4, MgCo2O4 etc.). Materials have been optimized by high-throughput combinatorial approaches. The thin films were deposited by RF sputtering and pulsed laser deposition at ambient and elevated temperatures. Performance of the inorganic HTLs and that of the reference organic PEDOT:PSS HTL were compared by measuring the power conversion efficiencies and spectral responses of the P3HT/PCBM- and PCDTBT/PCBM-based OPV devices. Preliminary results indicate that Co3O4-based HTLs have performance comparable to that of our previously reported NiOs and PEDOT:PSS HTLs, leading to a power conversion efficiency of about 4 percent. The effect of composition and work function of the ternary materials on their performance in OPV devices is under investigation. [Preview Abstract] |
Monday, March 21, 2011 10:36AM - 10:48AM |
A36.00006: A New Paradigm for Multijunction Solar Cells Marina Leite, Robyn Woo, Emily Warmann, Daniel Law, Harry Atwater We propose an approach for a multijunction solar cell (MJSC) based on direct band gap InAlAs/InGaP/InGaAsP/InGaAs alloys. Device simulations indicate that the proposed design can achieve over 50 {\%} efficiency at 100-suns illumination by using an alloy combination with lattice parameter of 5.80 {\AA}. For that, we created a virtual substrate for epitaxial growth. By relieving 40nm thick coherently-strained In$_{x}$Ga$_{1-x}$As films from InP substrates, full relaxation occurs preserving the crystalline quality of the films, as confirmed by X-ray diffraction, transmission electron microscpy and photoluminescence measurements. Once these films are transferred to a cheap support they can be used as a template for epitaxial growth with specifically chosen lattice parameter and therefore band gap energy. Our realization demonstrates the ability to control the lattice parameter and energy band structure of single layer crystalline alloy semiconductors in an unprecedented way. For the top subcell, we fabricated InAlAs solar cells with efficiencies $>$ 14 {\%} and Voc = 1 V. These results indicate that the novel MJSC design is feasible. Future directions and subcells performance will be presented. [Preview Abstract] |
Monday, March 21, 2011 10:48AM - 11:00AM |
A36.00007: Resonant TCO nanostructures for improved light trapping in thin-film photovoltaics Alok Vasudev, Mark Brongersma The desire for widespread photovoltaic (PV) adoption has motivated many recent efforts in advanced photon management in thin-film solar cells. Approaches to enhance PV optical absorption by exploiting surface plasmon resonances in metallic nanostructures, in particular, have been extensively studied. Here we present an alternative means to improve light trapping in thin-film solar cells using resonant transparent conductive oxide (TCO) nanostructures. Dielectric nanowires support leaky mode resonances, which, in poorly absorbing media, can scatter light efficiently. This resonant scattering can enhance optical absorption in a nearby photoabsorber. Using finite difference frequency domain (FDFD) techniques we show that an optimized planar solar cell's performance is improved by patterning the TCO into resonant scatters. Unlike their plasmonic counterparts, these resonators do not suffer large absorption losses, depend strongly on polarization or force a radical change in processing. We will discuss scalability, future improvements and application to a variety of solar cell configurations. [Preview Abstract] |
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