Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D3: Materials for Solar to Electricity Conversion: Status and Future |
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Sponsoring Units: DMP GERA Chair: Ramamoorthy Ramesh, University of California, Berkeley Room: Oregon Ballroom 203 |
Monday, March 15, 2010 2:30PM - 3:06PM |
D3.00001: Physics of Multijunction and Multiband Solar Cells Invited Speaker: In the presentation I will discuss research on semiconductor materials for high efficiency solar power conversion devices. After reviewing the fundamentals of different types of cells, I will present our work on searching for new materials for multijunction and multiband devices. The work on the multijunction cells is based on the discovery that the band gaps of Ga$_{x}$In$_{1-x}$N alloys span an energy range from 0.7 to 3.4 eV. This provides an almost perfect match to the solar spectrum and an interesting possibility of using this alloy system for the fabrication of high efficiency multijunction solar cells. In the second part of the talk I will present recent progress on the utilization of multiband semiconductors for high efficiency solar cells. We have synthesized group II-VI (ZnOTe) and group III-V (GaNAsP) alloys with a mid gap intermediate band. The intermediate band serves as a ``stepping stone,'' allowing pairs of sub- bandgap photons to contribute to the current of the cell, leading to better utilization of the full solar spectrum. Ongoing efforts to produce simple, single junction multiband photovoltaics will be discussed. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:42PM |
D3.00002: Interfacial Modification for Enhanced Performance of OPV Devices Invited Speaker: Organic Photovoltaics (OPV) represent a potentially low cost, scalable approach to produce renewable energy at near the Terrawatt scale. Their low temperature solution based processing potentially leads to cost/per watt well below \$0.50. Over the last year OPV has seen a rapid evolution in efficiency to a now certified 7.9\% for Solarmer. As important module efficiencies are nearing 4\% supporting scalability. There is now a pretty clear pathway for developing acceptors and donors so as to achieve 10\% or greater. One of the key questions remaining is that of the stability of OPV devices and the potential for their lifetime to be sufficient for commercial viability. Critical to this is both the intrinsic stability of the donor/acceptor phase separated mixture and the stability of the interfaces especially those between the inorganic and organic phases. We will report on a number of recent studies beginning to look at the mechanisms of degradation in OPV device structures and on their potential resolution through new materials, new device configurations and enhanced encapsulation. Current data indicates that there is no inherent instability in the bulk heterojunction and that solving the interfacial issues may lead to devices of sufficient stability for commercial viability.\\[4pt] In collaboration with Joseph Berry, Matthew Lloyd, Matt White, Nikos Kopidakis, Xerxes Steires, Ajaya Sigdel, Nicodemus Widjonarko, Matthew Reese and Sean Shaheen, and Dana Olsen, National Renewable Energy Laboratory. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 4:18PM |
D3.00003: The Physics of Organic Solar Cells Invited Speaker: The best polymer bulk heterojunction solar cells now have efficiency exceeding 7{\%}. Attaining even higher efficiency will require a detailed understanding of how the cells operate and what limits their performance. There is controversy regarding what limits the performance of one of the most studied systems, P3HT-PCBM. The primary limitation has been attributed to geminate recombination, bimolecular recombination, recombination near electrodes, formation of a region in the film with no electric field due to the semiconductors being doped, and series resistance. We will compare these different theories and demonstrate cases in which each one can be correct. We will show that some of the loss as a result of excitons in the PCBM recombining before they reach the interface with the polymer. Finally we will examine the nanostructures that form when various polymers are mixed with fullerenes and other electron acceptors, highlighting the important consequences of the acceptor molecules intercalate in between the sidechains of the polymer. [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:54PM |
D3.00004: Organic Photovoltaics Invited Speaker: I will describe the discovery of ultrafast photoinduced electron transfer as the scientific foundation for the creation of a technology for low cost ``plastic'' solar cells. This initial charge separation occurs at a time scale two orders of magnitude faster than the first step in photo-synthesis in green plants. Charge collection at the electrodes is accomplished through self-assembly of bulk heterojunction (BHJ) nano-materials by spontaneous phase separation. I will focus on the details of the operating mechanism; the origin of the open circuit voltage (V$_{\textrm{oc}}$), the role of morphology on the charge separation and charge collection at the electrodes, the need for charge selective buffer layers and the origin of the limitations on the fill factor (FF). [Preview Abstract] |
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