Accelerated aging of unencapsulated flexible GaInP/GaAs/InGaAs solar cells by means of damp heat and thermal cycling tests.

The extended damp heat and thermal cycling tests were performed on unencapsulated flexible thin-film GaInP/GaAs/InGaAs solar cells to assess the long-term stability. The solar cells were subjected to 85 °C/85% damp heat test for more than 1000 h and 420 cycles of thermal cycling test between -60 °C and 75 °C, respectively. The performance attenuations of flexible solar cells were less than 2% in both cases, which were due to the slow decline of the open-circuit voltage with aging time. The slight decrease in open voltage was attributed to the increase in reverse saturation current due to the enhanced recombination, which was in good agreement with the calculation based on the two-diode model. The good performance of the unencapsulated flexible GaInP/GaAs/InGaAs solar cells in severe environment indicated the stable and reliable device fabrication art in the experiment.