Unusual Bimodal Photovoltaic Performance of Perovskite Solar Cells at Real-World Operating Temperatures

A deep understanding of environmental effects on perovskite solar cell (PSC) performance is highly desirable for further progress toward large-scale deployment of this technology. We investigate the operation of PSCs in the temperature range 15-50 degrees C and report an unusual bimodal behavior in photovoltaic (PV) performance, with positive and negative temperature coefficients (TCs) below and above room temperature (RT), respectively. Furthermore, the performance metrics exhibit hysteresis, as their values depend on whether the measurements are made during the heating or cooling stages of the experiment. Conventional semiconductor solar cells, in contrast, exhibit a monotonic and nonhysteretic performance decline in this temperature range. The variations in power conversion efficiency primarily follow changes in open-circuit voltage and fill factor. Photoluminescence data suggest that the performance variations below RT are accompanied by a reduction in defect-related traps in the perovskite absorber and a drop in interfacial built-in potential at the perovskite/transport layer interface. The behavior above RT follows the conventional trend and can hence be explained by charge-phonon interactions. Our findings offer significant insight into the salient PV properties and photophysics of perovskite materials that define their performance in the real-world operating temperature range.