Improvement in Performance of a-SiGe:H Solar Cells for Multi-Junction Cells
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IMPROVEMENT IN PERFORMANCE OF A-SiGe:H SOLAR CELLS FOR MULTI-JUNCTION CELLS E. MARUYAMA, Y. YOSHIMINE, A. TERAKAWA, K. SAYAMA, K. NINOMIYA, Y. HISHIKAWA, H. TARUI, S. TSUDA, S. NAKANO AND Y. KUWANO Functional Materials Research Center, Sanyo Electric Co., Ltd. 1-18-13 Hashiridani, Hirakata, Osaka, Japan ABSTRACT The quality of a-SiGe:H film was improved by considering the effects of substrate temperature and deposition rate on film properties. Accurate measurement of the optical gap and the film composition of Si, Ge and H made it possible to formulate the optical gap using a linear function of bonded H content (C11) and Ge content (CG,). It was found for the first time that, when the optical gap is fixed to a certain value, the optimum compositions of C11 and CGe exist for high-quality a-SiGe:H. Based on these, we obtained the world's highest conversion efficiency of 3.7% under red light (AM-1.5, 100mW/cm 2 through an R65 filter which allows passage of longer wavelength (>650nm) light) for a 1cm 2 a-SiGe singlejunction cell. Long-term stability of the cell was also improved. INTRODUCTION We have obtained the world's highest total area conversion efficiency of 12.0% for a 100 cm 2 integrated-type single-junction a-Si solar cell submodule (Fig. 1) by combining a high-quality i-layer, a high-quality buffer layer treated by hydrogen plasma, and other successful techniques. Multi-junction cells have also been studied in order to improve conversion efficiency and long-term stability. A-SiGe:H is a promising material for the bottom cell of high-performance multi-junction cells because its optical gap can be easily narrowed by changing its composition. There are many studies focusing on the influence of film composition on the optical gap [1-3], however, most of them mentioned the relationship between the optical gap (EPt) and only CG,. On the other hand, the optical gap of a-Si:H is well known to have strong correlation with CH. Our recent study 150 Module size (10X10c clarified that the properties (Eopt, a ph, C11, Inie rated-type celsin series) etc.) of "device quality" a-Si deposited by a plasma CVD method from 100% SiH 4 are Z100 mostly determined by the deposition rate 2 AM-1.5, 100 mW/cm and substrate temperature [4,5]. 50 In this study, the improvement of film quality of a-SiGe:H is investigated by considering the effects of the deposition parameters, such as substrate temperature 0 0 5 10 15 and deposition rate. The relationship Voltage(V) between the optical gap and both CGe and C11 is also studied for the first time. Film Fig. I Illuminated I-V characteristics of an integrated-type a-Si solar cell properties were carefully studied with submodule measured at JMI. Mat. Res. Soc. Symp. Proc. Vol. 297. @1993 Materials Research Society
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regard to their composition (CGe and C11) using a-SiGe:H which had the same optical gap and different compositions. EXPERIMENTAL The a-SiGe:H films were deposited by RF glow discharge using the super chamber method[6] to reduce impurity concentration. Typical impurity contents
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