Phase-Controlled Strategy for High-Quality Single-Source Vapor-Deposited Cs₂AgBiBr₆ Thin Films

Environmentally friendly lead-free Cs2AgBiBr6 double perovskites have emerged as potential materials for photovoltaic applications owing to their nontoxicity and high stability. However, the low solubility of precursors in the solution method and the deviated composition in the reported sequential evaporation process are still the challenges to obtain highly pure Cs2AgBiBr6 phase films. In this work, we proposed a single-source vapor deposition process for high-quality Cs2AgBiBr6 films with an effective thermally induced phase-controlled strategy. The microstructure, composition, and photoelectric properties of Cs2AgBiBr6 films with different heat treatments were investigated, and the phase evolution of Cs2AgBiBr6 film formation was figured out. High-phase purity, uniformity, smoothness of the surface, well-defined grain structure, and desired composition stoichiometry of Cs2AgBiBr6 films led to an optimized power conversion of 1.38% for a planar device structure with excellent stability. Our results demonstrate the feasibility of employing a single-source vapor deposition technique to fabricate high-quality double perovskite thin films, which paves the way for further development of various optoelectronic devices based on these promising lead-free semiconductors.