Progress and future view of silicon space solar cells in Japan

The progress and the future view of silicon (Si) space solar cells in Japan are reviewed. In 1991, two types of the high-efficiency silicon (HES) cell were developed: (1) NRS/LBSF cell; (2) NRS/BSF cell. The former shows a conversion efficiency of 18.0% (AM0, 28°C) at beginning-of-life (BOL), the latter shows superior radiation tolerance. In 1998, the radiation tolerance of the NRS/BSF cell was improved; moreover, the advanced high-efficiency silicon-1 (AHES-1) cell was accomplished. It shows 13.1% at end-of-life (EOL). The development has progressed to make the 13.7% EOL cell: AHES-2 cell. In 1994, the integrated bypass function (IBF), which prevents failures due to reverse biasing of cells, was proposed. The NRS/BSF cells with IBF have been used already on several satellites. The structures, performance, and radiation tolerances of these cells are introduced. New approaches for further improvement are proposed