Role of Aluminium in STE Engineering in Cs₂AgInCl₆:Al³⁺ Double Perovskite Nanocrystals

Significant research efforts have been directed towards modification of STEs in lead-free halide double perovskite Cs₂AgInCl₆ to improve its suitability for white light applications. However, limited attention has been given to exploring the fundamental photophysical phenomenon of this material. Herein, we have demonstrated that the precise introduction of Al³⁺ can effectively adjust the material's bandgap, leading to red shifted excitation energy and enhanced STE emission. Additionally, cryogenic PL measurements discovered an inhomogeneous nature of STE emission due to the presence of defect states and is subject to thermal quenching. The increased Hyang Rhys factor show better electron phonon coupling and high density of STE states post Al³⁺ doping. Ultrafast transient absorption spectroscopy elucidated the trapping of charge carriers and provided insights into the effects of Al³⁺ doping on the formation self-trapped states. Overall, this study offers a comprehensive understanding of the origins of self-trapping in Cs₂AgInCl₆ and emphasizes the potential of compositional engineering to mitigate self-trapping in this material.