Self-healing and -repair of nanomechanical damages in lead halide perovskites

Recovery from damage in materials helps extend their useful lifetime and of devices that contain them. Given that the photodamages in HaP materials and based devices are shown to recover, the question arises if this also applies to mechanical damages, especially those that can occur at the nanometer scale, relevant also in view of efforts to develop flexible HaP-based devices. Here, this question is addressed by poking HaP single crystal surfaces with an atomic force microscope (AFM) tip under both ultra-high vacuum (UHV) and variably controlled ambient water vapor pressure conditions. Sequential in situ AFM scanning allowed real-time imaging of the morphological changes at the damaged sites. Using methylammonium (MA) and cesium (Cs) variants for A-site cations in lead bromide perovskites, the experiments show that nanomechanical damages on methylammonium lead bromide (MAPbBr${}_3$) crystals heal an order of magnitude faster than Cs-based ones in UHV. However, surprisingly, under ≥40% RH conditions, cesium lead bromide (CsPbBr${}_3$) shows MAPbBr${}_3$-like fast healing kinetics. Direct evidence for ion solvation on CsPbBr${}_3$ is presented, leading to the formation of a surface hydration layer. The results imply that moisture improves the ionic mobility of degradation components and leads to water-assisted improved healing, i.e., repair of nanomechanical damages in the HaPs. (© 2023 The Authors. Advanced Functional Materials published by Wiley‐VCH GmbH)