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We have been developing InGaP/GaAs/InGaAs inverted triple junction solar cells for a concentrator application with a target efficiency of 45%. We reduced the series resistance in the cells. As a result we improved the maximum concentration ratio up to around 300-suns and obtained an efficiency of 43.5% as an official value measured by Fraunhofer Institute for Solar Energy Systems. Recently we achieved an efficiency of around 44% in house measurement by improving short current density (Jsc) in a cell by reduction of shadow loss. We performed reliability tests on receivers with inverted triple junction solar cells. No obvious degradation was observed in open circuit voltage and fill factor measured under 150-suns after 1,500h exposure to 85 degree Celsius and 85% humidity atmosphere. In addition improvement of 1-sun efficiency up to 37.7% was confirmed in a cell with 1.047cm2 aperture area.
SASAKI et al. (Tue,) studied this question.