Radiation degradation characteristics of component subcells in inverted metamorphic triple-junction solar cells irradiated with electrons and protons

The radiation response of In0.5Ga0.5P, GaAs, In0.2Ga0.8As, and In0.3Ga0.7As single-junction solar cells, whose materials are also used as component subcells of inverted metamorphic triple-junction (IMM3J) solar cells, was investigated. All four types of cells were prepared using a simple device layout and irradiated with high-energy electrons and protons. The essential solar cell characteristics, namely, light-illuminated current-voltage (LIV), dark current-voltage (DIV), external quantum efficiency (EQE), and two-dimensional photoluminescence (2D-PL) imaging were obtained before and after irradiation, and the corresponding changes due to the irradiations were compared and analyzed. The degradation of the cell output parameters by electrons and protons were plotted as a function of the displacement damage dose. It was found that the radiation resistance of the two InGaAs cells is approximately equivalent to that of the InGaP and GaAs cells from the materials standpoint, which is a result of different initial material qualities. However, the InGaAs cells show relatively low radiation resistance to electrons especially for the short-circuit current (Isc). By comparing the degradation of Isc and EQE, data, It was confirmed that the greater decrease of minority-carrier diffusion length in InGaAs compared with InGaP and GaAs causes severe degradation in the photo-generation current of the InGaAs bottom subcells in IMM3J structures. Additionally, it was found that the InGaP and two InGaAs cells exhibited equivalent radiation resistance of Voc, but radiation response mechanisms of Voc are thought to be different. Further analytical studies are necessary to interpret the observed radiation response of the cells. (c) 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.