The radiation response of In_0.5Ga_0.5P, GaAs, In_0.2Ga_0.8As, and In_0.3Ga_0.7As 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. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

Japan's Research and Development (R&D) activities on high‐performance III–V compound space solar cells are presented. Studies of new CuInGaSe₂ thin‐film terrestrial solar cells for space applications are also discussed. Performance and radiation characteristics of a newly developed InGaP/GaAs/Ge triple‐junction space solar cell, including radiation response, results of a flight demonstration test of InGaP/GaAs dual‐junction solar cells and CuInGaSe₂ thin‐film solar cells, and radiation response of three component sub‐cells are explained. This study confirms superior radiation tolerance of InGaP/GaAs dual‐junction cells and CuInGaSe₂ thin‐film cells by space flight experiments. Copyright © 2005 John Wiley & Sons, Ltd.

The conversion efficiency of a solar cell depends on the degree of non-radiative recombination, and thus efficiency improvements can also be achieved by reducing Shockley–Read–Hall (SRH) recombination losses. This type of loss depends not only on the crystal quality, but also on the device structure. A clear separation of the contributions of these factors would improve our understanding of the control of non-radiative recombination. In this work, we discuss the reduction of the integrated SRH recombination rate in the depletion region ($U_{\mathrm{SRH}}^{\mathrm{dep}}$ ) by changing the emitter material, instead of fabricating a base layer with a higher crystal quality. First, we theoretically show that, by employing a suitable n-InGaP/p-GaAs heterojunction structure instead of a GaAs p–n homojunction, the integrated $U_{\mathrm{SRH}}^{\mathrm{dep}}$ can be reduced, because a significant part of the depletion region in the heterojunction is located in the wide-gap emitter material, which has a lower intrinsic carrier density. Then, the effective SRH recombination coefficient in the depletion region ($\overline{A^{\mathrm{dep}}}$ ) is obtained from experiments, and the effect of the structural modification on $U_{\mathrm{SRH}}^{\mathrm{dep}}$ is analyzed. We are able to clearly assess the effect of the heterojunction structure on the non-radiative recombination because the grown samples exhibit the same radiative recombination loss. The analysis reveals that, in suitable heterojunction solar cells with an emitter layer containing a low intrinsic carrier concentration, $\overline{A^{\mathrm{dep}}}$ (and thus also $U_{\mathrm{SRH}}^{\mathrm{dep}}$ ) is effectively reduced.

3 MeV proton irradiation effects on ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ single junction and ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ tandem solar cells have been investigated for the fluence range from ${\text{1×10}}^{11}$ to ${\text{1×10}}^{13}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}.$ The overall radiation degradation of ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ tandem cells was higher than ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ single junction cells. It was observed that the spectral response of the GaAs bottom cell degrades more than the InGaP top cell. Proton irradiation decreases the longer wavelength spectral response more significantly than the shorter wavelength in both ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ and ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ cells. The difference in the degradation properties of $n^{+}p$ and $p^{+}n$ polarity InGaP solar cells is discussed. The radiation response of a tandem $n^{+}p$ InGaP/GaAs cell is very nearly that which is predicted from the information of these two cells independently. The minority-carrier diffusion length in the base layer was determined from the spectral response data. The minority-carrier diffusion length damage coefficient $K_L$ was analyzed for ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ and GaAs cells. The minority-carrier injection-enhanced annealing of radiation-induced defects in ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}$ and ${\mathrm{In}}_{\text{0.5}}{\mathrm{Ga}}_{\text{0.5}}\mathrm{P}/\mathrm{GaAs}$ cells were also observed.