The nature of defect tolerance in (some) halide perovskites

The quest for defect tolerant semiconductors is at once riveting and perplexing. A measure of success would be a major leap toward developing device-specific and multimodal materials. Yet, decades of experience with conventional semiconductors reveal that defects are ubiquitous and require constant attention. Nonetheless, halide perovskites, recognized for their record-setting performance in solar cells, rivaling that of Si-photovoltaics, have since proliferated into a wide range of applications. Mounting experimental data, albeit indirect, suggests a tangible link between their exceptional performance and insensitivity to harmful defects. This demands an in-depth look into the issue of defect tolerance and underlying causes. Could it be that an average crystalline order coexisting with highly anharmonic lattice dynamics is key to their superior properties? Perhaps their mixed ionic–covalent bonding and ion migration confer intrinsic self-healing capabilities? Over the past decade(s), researchers have identified a series of beneficial features that combine to lend halide perovskites, especially Pb-halide perovskites, their special characteristics. We explore these developments primarily from a computational (density functional theory) perspective and examine concepts that support defect tolerant behavior. They are discussed in terms of material features and mechanisms that could mitigate charge carrier trapping and recombination at defect centers, offering a framework for the possible discovery and design of a class of defect-resistant semiconductors.