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.