Hydrogen Plasma Treatment Compensates for the Intrinsic Defects in Cs2AgBiBr6 Thin Films

The prospects of lead-free halide double perovskites in optoelectronic applications are often limited by their indirect bandgap, polaronic carrier transport, and intrinsic electronic defect levels. This work demonstrates a nearly 10-fold enhancement in self-trapped exciton emission intensity for Cs2AgBiBr6 thin films at room temperature following mild hydrogen plasma treatment. Analyzing the emission line widths at varying temperatures indicates that carrier-phonon coupling remains similarly prevalent. However, time-resolved photoluminescence and transient absorption measurements show that defect-mediated recombination is greatly suppressed in hydrogenated Cs2AgBiBr6 films. Based on photoelectron spectroscopy results, we propose that hydrogens can effectively compensate for deep-level Ag-on-Bi antisite defects, consequently shifting the Fermi level toward the conduction band edge. Below the cubic-to-tetragonal structural phase transition temperature, however, hydrogens act instead as nonradiative recombination centers. Taken together, this study highlights the potential of combining hydrogen plasma treatment with B-site disorder engineering to improve the functional characteristics of lead-free halide double perovskites.