Defect Tolerance in Halide Perovskites: Investigating the Absolute Volume Deformation Potential

Halide perovskite (HaP) semiconductors, commonly synthesized from room temperature solutions, possess exceptional optoelectronic properties that rival those achieved by more complex fabrication methods used for conventional semiconductors. The absence of detrimental defects in HaPs is a topic of debate, often attributed to their defect tolerance or self-healing ability.<br/><br/>To contribute to this discussion, we conducted an experimental investigation focused on determining the absolute volume deformation potential (AVDP) of CsPbBr3. The AVDP is a crucial physical parameter that characterizes the energy level shift of a semiconductor in response to volume changes. It therefore allows for quantifying of the amount of energy necessary to for example rearrange a crystal lattice locally to efficiently screen the electrical energy barrier of defects. Furthermore, it provides insights into the inherent molecular orbital bonding nature of semiconductor material.<br/>In our study, synchrotron radiation-based X-ray photoelectron spectroscopy was employed to measure the VBM (valence band maximum) energy of CsPbBr3 across a temperature range from room temperature to 125 K. Our experimental findings demonstrate that the AVDP of CsPbBr3 is negative and relatively small compared to conventional semiconductors. This observation suggests that electronic defects can be easily screened through lattice rearrangement. Moreover, the negative sign indicates that the VBM primarily consists of anti-bonding type molecular orbitals. The disruption of these bonds typically generates defect energy levels near or within the bands. Both the magnitude and sign of the AVDP support the notion of defect tolerance in Halide perovskites.<br/><br/>Additionally, we conducted measurements of transient photoluminescence and employed a comprehensive interpretation based on a kinetic rate equation encompassing various recombination processes of different orders. This allowed us to quantify the defect density in CsPbBr3 at similar temperatures, providing a deeper understanding of the evolution of defect properties under volumetric changes.<br/><br/>Our results offer valuable insights into the origins of defect tolerance in Halide perovskites, shedding light on their unique optoelectronic characteristics.