Plasma-Driven Atomic-Scale Tuning of Metal Halide Perovskite Surfaces: Rationale and Photovoltaic Application

The effective defect passivation of metal halide perovskite (MHP) surfaces is a key strategy to simultaneously tackle MHP solar cell performances enhancement and their stability under operative conditions. Plasma-based dry processing is an established methodology for the modification of materials surfaces as it does not present the disadvantages often associated with wet treatments. This is becoming a fine tool to reach precise atomic-scale engineering of the MHP surfaces. Herein is reported a comprehensive picture of the interaction between different plasma chemistries and MHP thin films. The impact of Ar, H-2, N-2, and O-2 low-pressure plasmas on MHP optochemical properties and morphology is correlated with the performance of photovoltaic devices and rationalized by density functional theory calculations. Strong morphological modifications and selective removal of the uppermost methylammonium moieties are deemed responsible for nonradiative surface defects suppression and higher solar cell performances. Ellipsometry and X-ray photoelectron spectroscopies shine light on the subtle modifications induced by the different plasma environments, paving the way for the more effective engineering of plasma-based (deposition) processing. Notably, for O-2 plasma treatment, deep-state traps induced by the formation of IO4- species are demonstrated and rationalized, highlighting the challenges in optimizing O-2 plasma-based solutions for MHP-based devices.