Ambient operando self-healing in tin perovskite solar cells

Tin-based perovskite photovoltaics offer promising optoelectronic properties and a less toxic alternative to lead-based counterparts but suffer from rapid degradation under ambient conditions, primarily due to Sn²⁺ oxidation. We leverage the chemically dynamic nature of halide perovskites to demonstrate a functional operando self-healing effect in unencapsulated Sn-based perovskite solar cells (Sn-PSCs). This is enabled by incorporating thiophene-2-ethylammonium (TEA) halide as an additive in FASnI₃ devices. Remarkably, under continuous ambient operation (30 °C, 60% RH) and one sun simulated illumination, these devices can spontaneously overcome initial performance losses, progressively enhancing their power conversion efficiency (PCE) beyond their initial values. In particular, following self healing, devices with TEAI retain 80% of their initial PCE for over 25 hours, whereas control devices degrade in less than one hour. This self-healing behavior is significantly influenced by external parameters such as illumination intensity or additional applied bias, key factors triggering or hindering the recovery process. The underlying mechanism is discussed in the context of the potential TEAI additive reducing capability. These unprecedented findings provide new insights into the dynamic stability and recovery behaviors of Sn-PSCs, a step toward stable and efficient lead-free perovskite solar cells. A deeper understanding of this phenomenon can be key to designing strategies for more sustainable photovoltaic technologies.