Defects Activity in Wide Bandgap Metal Halide Perovskite Semiconductors

Metal halide perovskites (MHPs) have demonstrated huge potential to build a rich library of materials for a new disruptive optoelectronic technology. The main strength comes from the possibility of easily tune the semiconductor bandgap in order to integrate it in devices with different functionalities – in principle. In reality, this cannot be achieved yet. In fact, while defect tolerance is claimed for MHPs with a bandgap of about 1.6 eV, the model system object of intense investigations, MHPs with lower and higher bandgaps are far from this claim. They show various forms of instabilities which are mainly driven by a strong defect activity.<br/>Regarding wide band gap semiconductors, it is a common strategy to synthetize lead halide perovskites and partially substituting the iodine with bromine – the so called mix halide perovskites. However, it also notorious that in such samples, photoinduced ion-migration processes results in bandgap instabilities. The combinatory optimization of the chemical composition of perovskites with respect to the organic-inorganic cations, as well as the use of additives acting as passivating agents, which overall act on the reduction of the density of the native defects, have demonstrated to work towards the stabilization of the phenomenon. However, the identity of the defects responsible for these processes is unknown, as unknown is whether they are responsible or not of non-radiative carrier recombination as well. Without such information reliable tailored strategies to address the detrimental impact of the different defect types in hybrid perovskite solar cells is not possible. Here we identify the point defect and the relative localized electronic state which upon charge trapping triggers the material transformation with consequent modification of the semiconductor bandgap. We also distinguish it from those which are only responsible for photo-carrier loss. This knowledge allows us to design the chemical composition of the metal halide perovskite in order to deactivate such defects and stabilize the bandgap over the entire spectral range above 1.6 eV.