Hydrogen Plasma\nTreatment Compensates for the Intrinsic\nDefects in Cs<sub>2</sub>AgBiBr<sub>6</sub> Thin Films

The prospects of lead-free halide double perovskites\nin optoelectronic\napplications are often limited by their indirect bandgap, polaronic\ncarrier transport, and intrinsic electronic defect levels. This work\ndemonstrates a nearly 10-fold enhancement in self-trapped exciton\nemission intensity for Cs<sub>2</sub>AgBiBr<sub>6</sub> thin films\nat room temperature following mild hydrogen plasma treatment. Analyzing\nthe emission line widths at varying temperatures indicates that carrier–phonon\ncoupling remains similarly prevalent. However, time-resolved photoluminescence\nand transient absorption measurements show that defect-mediated recombination\nis greatly suppressed in hydrogenated Cs<sub>2</sub>AgBiBr<sub>6</sub> films. Based on photoelectron spectroscopy results, we propose that\nhydrogens can effectively compensate for deep-level Ag-on-Bi antisite\ndefects, consequently shifting the Fermi level toward the conduction\nband edge. Below the cubic-to-tetragonal structural phase transition\ntemperature, however, hydrogens act instead as nonradiative recombination\ncenters. Taken together, this study highlights the potential of combining\nhydrogen plasma treatment with B-site disorder engineering to improve\nthe functional characteristics of lead-free halide double perovskites.