Development of Nanocrystalline Silicon Based Multi-junction Solar Cell Technology for High Volume Manufacturing
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Development of Nanocrystalline Silicon Based Multi-junction Solar Cell Technology for High Volume Manufacturing Xixiang Xu1, Jinyan Zhang1, Anhong Hu1, Cao Yu2, Minghao Qu1,3, Changtao Peng1, Xiaoning Ru1, Jianqiang Wang2, Furong Lin2, Hongqing Shan1, Yuanmin Li1, and Hui Yan3 1 Apollo Precision Equipment Limited Company, R&D Center, Shuangliu, Sichuan, China 2 Hanergy Holding Group Limited, Beijing, China 3 Colleage of Materials Sci., Beijing Univ. of Technology, Beijing, China ABSTRACT We conduct a comparative study mainly on two types of nc-Si based solar cell structures, a-Si/a-SiGe/nc-Si triple-junction and a-Si/nc-Si double-junction. We have attained comparable initial efficiency for the both solar cell structures, 10.8~11.8% initial total area efficiency (85 95W over an area of 0.79 m2). For better compatibility to our installed manufacturing equipment, we deposit a-Si and a-SiGe component cells with the existing deposition machines. Only nc-Si bottom component cells are prepared in separate deposition machines tailored for nc-Si process. Material properties of nc-Si and TCO films are also studied by Raman spectra, SEM, and AFM. INTRODUCTION Thin film silicon, amorphous silicon (a-Si) and nanocrystaline silicon (nc-Si), has evolved into an important technology for photovoltaic industry in the last decade. Over 2 GW capacities of amorphous silicon and silicon-germanium (a-SiGe) multijunction solar cell manufacturing lines using Apollo/Hanergy’s turn-key technology have been installed in Hanergy Group and GS-Solar factories. However, compared with other thin film PV technologies, such as CdTe and CIGS with 11-14% product efficiency, most of thin film Si product’s efficiency is still significantly lower, in the range of 8-10%. Therefore, evolution of thin film silicon PV technology shows a trend moving from a-Si and a-SiGe multi-junction structures, showing light-induced degradation in range of 10-20%, to a more stable nc-Si based ones with typical ~10% or less light-induced degradation [1-4]. Hybridizing a-Si and a-SiGe with nc-Si, Yan et al. reported 16.3% initial efficiency for a small area a-Si/a-SiGe/nc-Si triple-junction cell (0.25 cm2) [5]. In order to increase cell conversion efficiency of our thin film Si PV products, we have focused our effort on development of compatible nc-Si technology. We have conducted our experiments mainly on two types of nc-Si based solar cell structures, a-Si/a-SiGe/nc-Si triplejunction and a-Si/nc-Si double-junction device, with schematic cell structures illustrated in Fig. 1. Currently we are attaining slightly higher initial efficiency for the a-Si/nc-Si double-junction than a-Si/a-SiGe/nc-Si triple-junction structure, 93W vs. 85 W, corresponding to 11.8% and 10.8% initial total area (0.79 m2) efficiency. Other experimental results, including study of volume fraction of crystalline (Raman spectroscopy) along nc-Si growth, individual component cell optimization and current match assisted by QE (quantum efficiency), and development of superior tunnel-junction and contact laye
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