Interdigitated Back Contact Silicon Heterojunction (IBC-SHJ) Solar Cell
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0989-A24-05
Interdigitated Back Contact Silicon Heterojunction (IBC-SHJ) Solar Cell Meijun Lu1,2, Stuart Bowden1, Ujjwal Das1, Michael Burrows1, and Robert Birkmire1,2 1 Institute of Energy Conversion, University of Delaware, Newark, DE, 19716 2 Department of Physics and Astronomy, University of Delaware, Newark, DE, 19716
ABSTRACT Interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells have been developed. This structure has interdigitated p/n amorphous silicon (a-Si:H) films deposited by plasma enhanced chemical vapor deposition (PECVD) on the backside of crystalline silicon (cSi) wafers, with light irradiating the front surface. IBC-SHJ cells possess advantages over front junction a-Si:H/c-Si heterojunction cells due to minimized current losses in the illuminating side, and over traditional diffused back-junction cells due to low temperature processing combined with the potential of high voltages for the heterojunction. Current-voltage curves, spectral response and laser beam induced current maps have been used to characterize the IBC-SHJ cells. It was found that the IBC-SHJ cell has non-linear illumination level dependence that correlates with measured minority-carrier lifetime. As the performance of these cells is very sensitive to the quality of passivation on front surface, they are ideally suited as a diagnostic tool for detailed characterization of surface passivation. Initial cell structures have achieved independently confirmed cell efficiencies of 11.8% under AM1.5 illumination. Device simulation shows that an efficiency of higher than 20% can be expected after optimizing the IBC-SHJ cells. INTRODUCTION Presently, 95 percent of solar cells are fabricated on crystalline silicon wafers and the rapid market growth has resulted in a shortage of silicon feedstock. Further cost reductions in photovoltaics require a thin, high efficiency cell to reduce the cost per watt generated. The ìInterdigitated Back Contact Si HeteroJunctionî (IBC-SHJ) solar cell introduced in this paper is aimed to achieve these requirements. The IBC-SHJ solar cell is based on amorphous-silicon (a-Si) / crystalline-silicon (c-Si) heterojunction (SHJ) [1], rather than the high temperature (~800oC) diffusions used to form conventional homojunction cells. By using deposited amorphous silicon (a-Si:H) as an emitter layer, SHJ solar cells can be produced at low temperature (~200oC). The SHJ also achieves a high open-circuit voltage (Voc) due to the excellent surface passivation by a-Si:H layer on both sides of Si wafer. The high Voc together with non-detrimental low-temperature processes allows SHJ solar cells to achieve high efficiency. Efficiencies of 21% have been reported [2], and Sanyo has started mass production of SHJ solar cells. Based on SHJ structure, the uniqueness of IBC-SHJ solar cells is that it combines the performance advantages of the SHJ with an IBC technique. IBC was first developed for concentrator systems about 30 years ago [3]. Recently, its application at one sun has been introduced to diffused juncti
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