Change in I–V characteristics of subcells in a multi-junction solar cell due to radiation irradiation

Roensch et al. recently proposed a new method of estimating the current-voltage (IV) characteristics of subcells in a multi-junction (MJ) solar cell by using electroluminescence (EL). The estimated IV characteristics of a proton-irradiated MJ solar cell from the IV curve obtained from each subcell agreed well with the actual dark IV (DIV) and light IV (LIV) characteristics, except for series resistance (R_s) and shunt resistance (R_sh). This method can also clarify R_s of a MJ cells and R_sh of subcells through circuit simulation program. In this work, we applied this method to InGaP/GaAs dual-junction (2J) solar cells in order to obtain the IV characteristics of the InGaP top subcells and GaAs bottom subcells before and after proton irradiation with various fluences. In addition, we succeeded to predict the degradation curve of maximum power (P_max) of the 2J solar cell where the current-limiting subcell changes from InGaP to GaAs subcell.