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20 August 2009 Extraction of carrier transport parameters from hydrogenated amorphous and nanocrystalline silicon solar cells
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Transport properties are very important for solar cells. The efficiency of solar cells is determined by the competition of carrier collection and recombination. The most important parameter is the carrier mobility-lifetime product. However, methods commonly used for measuring transport parameters require specially designed samples. The results are often not easily correlated to solar cell performance. In this paper, we present our studies of extraction of material properties from conventional current-voltage characteristics and quantum efficiency curves. First, we carried out analyses of shunt resistance as a function of the light intensity. For solar cells with no clear parasitic shunt resistance, the shunt resistance is inversely proportional to the short-circuit current, and its proportionality coefficient is related to the effective carrier mobility-lifetime product. For an a-Si:H solar cell made under an optimized condition with high hydrogen dilution, the effective mobility-lifetime product was estimated to be 1.2x10-8 cm2/V. For a-SiGe:H solar cells, the effective mobility-lifetime product depends on Ge content. For optimized a-SiGe:H bottom cells used in high efficiency a-Si:H/a-SiGe:H/a-SiGe:H triple-junction structures, their values are ~5.0x10-9 cm2/V. For high efficiency nc-Si:H solar cells, the effective mobility-lifetime product is ~5.0x10-7 cm2/V. Second, we measured the quantum efficiency as a function of electrical bias and developed an analytical model to deduce the effective mobility-lifetime product. The results obtained from the second method are consistent with the values from the first method. We will present detailed analyses and interpretations of the transport parameters and their correlation to solar cell performance.
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Baojie Yan, Guozhen Yue, Laura Sivec, Jeffrey Yang, and Subhendu Guha "Extraction of carrier transport parameters from hydrogenated amorphous and nanocrystalline silicon solar cells", Proc. SPIE 7409, Thin Film Solar Technology, 74090H (20 August 2009);

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