Effect of SRH recombination rate coefficient on internal luminescence efficiency and conversion efficiency of space solar cells
Tetsuya Nakamura1,2, Mitsuru Imaizumi1, Hidefumi Akiyama3,4, Yoshitaka Okada2
1Japan Aerospace Exploration Agency, Tsukuba, Inaraki, Japan
/2Research Center for Advanced Science and Technology, University of Tokyo, Meguro-ku, Tokyo, Japan
/3Institute for Solid State Physics. University of Tokyo, Kashiwa, Chiba, Japan
/4AIST-UTokyo OPERANDO-OIL, University of Tokyo, Kashiwa, Chiba, Japan

The ABC model used for light-emitting diodes is applied to the current triple-junction space solar cells to analyze the internal luminescence efficiency of the depletion region which greatly affects the conversion efficiency. The ABC model can determine the recombination current dependency of the the internal luminescence efficiency of the depletion region using the recombination rate equation. As a result of the analysis, in the low recombination current region including the maximum power point (MPP) condition, the measured internal luminescence efficiency of the solar cells can be explained by the ABC model. This indicates that the internal luminescence efficiency of the solar cells under MPP operating condition depends on that of the depletion region in these solar cells. Furthermore, we obtained the values of Shockley-Read-Holl (SRH) recombination rate coefficient (A) normalized with the radiative recombination rate coefficient (B) (A/B) through the fitting process. We found that the A/B values is an important parameter that determines not only the internal luminescence efficiency of the depletion region but also the conversion efficiency in these solar cells. Our analysis on A/B value clarified the practical value of A/B to realize the conversion efficiency close to the theoretical limit.