The Role of the Atmosphere on the Photophysics of Ligand‐Free Lead‐Halide Perovskite Nanocrystals

Lead halide perovskite (LHP) nanocrystals (NCs) have gained attention over the past decade due to their outstanding optoelectronic properties, making them a suitable material for efficient photovoltaic and light emitting devices. Due to its soft nature, these nanostructures undergo strong structural changes upon irradiation, where these light‐induced processes are strongly influenced by the environment. Since most processing routes for LHP NCs are based on colloidal approaches, the role of factors such as stabilizing ligands or solvents is usually hard to disentangle from the interaction of external radiation with the perovskite material. Employing a recently proposed synthetic approach, where ligand‐free NCs can be grown within metal‐oxide‐based insulating nanoporous matrices, it has been feasible to perform a clean study of the effect of the surrounding atmosphere on the photophysical properties of perovskite NCs, avoiding the interference of protective capping layers or solvents. Simultaneous light‐induced photo‐activation and darkening processes are monitored and disentangled, and their relation with bulk and surface processes, respectively, demonstrated. The photophysical properties of ligand‐free MAPbBr3 nanocrystals grown within metal‐oxide matrices are studied under different atmospheres. Simultaneous light‐induced photo‐activation and darkening processes are monitored and disentangled, and their relation with bulk and surface processes, respectively, are demonstrated. The reversibility of both processes is studied and the possible structural changes behind them are discussed.