Revealing the Stress-Stability Relationship in Perovskite Thin Films—An In Situ Perspective

Metal halide perovskites have the potential to become the leading thin film photovoltaic (PV) technology as a high efficiency, low-cost alternative for PV. Initial power conversion efficiencies are superb, but improvements to the operational stability of perovskites are needed to enable extensive deployment. Mechanical stress is an important, but often misunderstood factor impacting chemical degradation and reliability during thermal cycling of perovskites. In this talk we will discuss three main topics, namely (1) origins of residual stress formation associated with film formation via solution processing, (2) stress and strain relaxation mechanisms and their relationship to halide diffusion and ion migration, and (3) stability and degradation of perovskites exhibiting different initial stress states in different environments and external stressors. These mechanisms were disclosed thanks to the recent introduction of in situ stress monitoring methodologies including during film formation, thermal annealing, thermal cycling, and relaxation in different environmental conditions. In situ stress measurements reveal the dynamic nature of stress and are especially powerful when combined with complementary in situ optical spectroscopies and/or in situ grazing incidence x-ray diffraction (GIXRD), making them capable of providing mechanistic insights into stress formation and relaxation mechanisms.