Improved metastability and performance of amorphous silicon solar cells
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Improved metastability and performance of amorphous silicon solar cells Takuya Matsui1, Adrien Bidiville1, Hitoshi Sai1, Takashi Suezaki2,3, Mitsuhiro Matsumoto2,4, Kimihiko Saito2,5 , Isao Yoshida2 and Michio Kondo1 1
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568 Japan 2 Photovoltaic Power Generation Technology Research Association (PVTEC), 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568 Japan 3 Kaneka Corporation, 157-34 Kamiyoshidai, Toyooka, Hyougo, 668-0831 Japan 4 Panasonic Corporation, 3-4 Hikaridai, Seika-cho, Soraku-gun, Kyoto, 619-0237 Japan 5 Fukushima University, 1 Kanayagawa, Fukushima, Fukushima, 960-1296 Japan
ABSTRACT We show that high-efficiency and low-degradation hydrogenated amorphous silicon (a-Si:H) p-in solar cells can be obtained by depositing absorber layers in a triode-type plasma-enhanced chemical vapor deposition (PECVD) process. Although the deposition rate is relatively low (0.01-0.03 nm/s) compared to the conventional diode-type PECVD process (~0.2 nm/s), the light-induced degradation in conversion efficiency of single-junction solar cell is substantially reduced (Δη/ηini~10%) due to the suppression of light-induced metastable defects in the a-Si:H absorber layer. So far, we have attained an independently-confirmed stabilized efficiency of 10.11% for a 220-nm-thick a-Si:H solar cell which was light soaked under 1 sun illumination for 1000 hours at cell temperature of 50°C. We further demonstrate that stabilized efficiencies as high as 10% can be maintained even when the solar cell is thickened to >300 nm. INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) films grown by plasma-enhanced chemical vapor deposition (PECVD) are extensively employed as light absorbers in thin-film silicon solar cells. Although the high-efficiency (~14-15%) tandem devices have been demonstrated in the initial state [1,2], the stabilized efficiencies after prolonged illumination are limited to ~12% [3-7] due to the light-induced degradation of a-Si:H, known as the Staebler-Wronski effect [8]. Because of this adverse effect, the performance of thin-film silicon solar cells remains nearly half of that of high-efficiency crystalline silicon solar cells. So far, a variety of deposition techniques have been proposed to improve the light-soaking stability of a-Si:H. Nevertheless, the substantial reduction of the light-induced degradation has not been satisfactorily demonstrated, particularly for the cells exhibiting high initial efficiency. In our previous studies [9,10], we have shown that high-efficiency and low-degradation aSi:H solar cells can be obtained when the a-Si:H absorber layer is deposited by the triode
PECVD technique. Although the deposition rate is relatively low (0.01-0.03 nm/s) compared to the conventional diode-type PECVD process (~0.2 nm/s), the light-induced degradation in conversion efficiency (Δη/ηini) of single-junction solar cell is substantially reduced. A stabilized efficiency of 9.6
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