Tracking deep-level defects in degrading perovskite solar cells with a multifactorial approach

In this work, we provide a mechanistic understanding of the degradation of perovskite solar cells in operation by focusing on methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) and tracking the evolution of electronic defects via photo-induced current transient spectroscopy (PICTS). Moreover, we also record the degradation of its photovaltaic characteristics over time under various electric load and temperature conditions. Using PICTS, we found that bands of trap states, initially highly localized deep within the band gap of the perovskite, widened over the exposure period. This effect was exacerbated with increasing temperature. Further, using the design of experiment methodology for this multifactorial study, we found that two interaction factors (temperaturex load & temperaturex time) were significant in the degradation of the perovskite cells, validating the importance of our holistic approach. Through these observations, we establish a mechanistic link between deep-level traps and photovoltaic characteristics.