A Relationship Between Semiconducting Thin Film's Electronic Structure Heterogeneity and Defect Tolerance

Analyzing the defect states presence in semiconductors and understanding their impact on charge transport is essential to the solar cells' functionality. In recent years, there has been a focus on the concept of "defect tolerance" observed in perovskite solar cells. The energy-resolved electrochemical impedance spectroscopy (ER-EIS) is crucial for measuring the density distribution of defect states in the energy scale from valence to conductance band (or from HOMO to LUMO) and their spatial localization on a thin film. In this study, the aim is to better understand the concept of "defect-tolerant materials" by comparing the surface and bulk densities of defect states obtained from ER-EIS with the loss tangent at the frequency where the redox reactions determine the real part of the impedance. This comparison shows that the heterogeneity of the electronic structure across the thin film manifested as a higher surface density of states significantly impacts the failure of "defect tolerance" properties. The proposed procedure, being fast and efficient, has potential in the search for new materials and effective technological procedures for the conversion of solar energy into electricity.