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12 October 2012 Nanowire tandem solar cells
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Amorphous silicon (a-Si) is a promising material to serve as the top absorbing layers in tandem solar cells. However, due to its intrinsic high defect density, the thicknesses of a-Si layers are limited to a few hundred nanometers. This severely restricts the top cell current density, and therefore the total current density. In this research, we propose a novel structure that utilizing a-Si and crystalline silicon (c-Si) nanowire arrays to serve as top and bottom cells in a tandem solar cell. Two configurations of nanowire tandem solar cells (NWTCs) - a-Si nanowires (NWs) are aligned with c-Si ones (NWTC B) and are horizontally shifted relative to c-Si ones (NWTC A) - are respectively investigated. Numerical analyses present that NWTC A leads to a remarkable photocurrent enhancement of 15.7% and 21.3% when respectively compared with the reference cell (planar tandem cell with c-Si top cell and a-Si bottom cell) with and without optimal IRL, while the performance of NWTC B is similar to that of the reference cell with optimal IRL. Additionally, the usage of c-Si in NWTC A is reduced by 44% compared with the reference cell with IRL. The priorities of NWTC A are mainly attributed to the dielectric (air) attached to the back side of its top cell, causing light to reflect back. In contrast, the back side of NWTC B is mainly attached to c-Si, causing little reflection. The compatibility of intermediate reflecting layers (IRLs) and our proposed structure is studied.
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Renze Wang and Zhiping Zhou "Nanowire tandem solar cells", Proc. SPIE 8471, Next Generation (Nano) Photonic and Cell Technologies for Solar Energy Conversion III, 84710T (12 October 2012);

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