Jaxa´s strategy for development of high-performance space photovoltaics

JAXA´s approach to realizing a high specific power solar paddle by utilizing thin-film III-V multi-junction solar cells is introduced. Thin-film cells laminated with thin and transparent sustaining materials have been named “Space Solar Sheet (SSS).” Development of a first-generation SSS (SSS-1) was completed in the beginning of 2010. Thin-film InGaP/GaAs dual-junction (TF2J) cells are used as solar cells in SSS-1. The AM0 efficiency of TF2J cells is ~25%. Two types of lamination structure for the active side are employed: one uses transparent resin films with UV coating, and the other is a conventional configuration using a thin coverglass. Qualification tests have confirmed their life at more than 5 years in the LEO environment (the resin film type) and 10 years in the GEO environment (the thin coverglass type). Second-generation SSS (SSS-2) development has started this year (2010). The major improvement from SSS-1 to SSS-2 will be cell efficiency, achieved by adopting an inverted metamorphic triple-junction (IMM-3J) structure cell. The target efficiency is 32% at BOL under AM0, 1sun. A cost reduction study involving GaAs substrate recycling will also be carried out in this development. As well, the lamination technology will be modified to improve specific power from 0.5 W/g to 0.7 W/g. The achievement of such a SSS will enable us to realize lightweight solar paddles with specific power of 150 W/kg or greater.