Thin high efficiency defect-tolerant homo-type GaAs tandem design

Abstract

Crystalline defects (e.g. dislocations or grain boundaries) or/and radiation defects cause reduction of minority carrier diffusion length which in turn results in the degradation of solar cell efficiency. We have previously shown that by optimizing the device design (emitter-base thickness, doping) efficiency of highly dislocated (or irradiated) single junction solar cells can be significantly improved thus relaxing the need for excessive defect filtering in metamorphic solar cells. For hetro-epitaxial or metamorphic solar cells with high dislocation density (>5×107 cm−2), here a novel device design is devised where a carefully crafted tandem made through a series connection of two homo-type GaAs sub solar cells is shown as capable of achieving efficiencies higher than single junction GaAs solar cell. The proposed device is shown to be particularly attractive for space operations in harsh radiation environments as it offers higher end-of life efficiencies and flatter power response than conventional single junction counterparts.