Accelerated lifetime testing of thin‐film solar cells at high irradiances and controlled temperatures

Within this study, we investigate the intrinsic photostability of thin-film solar cells,here organic photovoltaic cells. Since degradation under natural sun light proceedswithin the timeframe of months and years, the process needs to be speeded up forfast material analysis and screening, using high-concentration accelerated lifetimetesting (high-C ALT). For this purpose, we established setups allowing irradiances ofup to 730 sun equivalents (SE). One key finding of our study is that accelerating thetesting procedure by such large intensities is possible but a precise measurement andcontrol of the solar cell temperature is absolutely essential. Accordingly, we devel-oped an innovative method of determining the temperature of the active layer whichoffers significant advantages over commonly used measurement methods. Further-more, it was found that the degradation process under high illumination densities canbe well described by a stretched exponential law. We demonstrate that the tempera-ture kinetics of P3HT:PCBM was found to be Arrhenius governed with an activationenergy of 27.2 kJ/mol under continuous illumination of 300 SE. Finally, it was shownthat the velocity of light-induced degradation of short-circuit current depends line-arly on the used irradiance dose at a given temperature starting from normal illumina-tion conditions up to at least 300 SE. This makes high-C ALT a very valuable tool forswift screening of the lifetime of novel thin-film solar cells and materials