A-site cation modification of Cs-based perovskite thin film for green light-emitting diodes

Light-emitting diodes based on metal halide perovskites have gained significant research interest due to their exceptional properties, including tunable emission wavelengths and high photoluminescence quantum yield (PLQY), and offer the potential for solution-based fabrication. However, the antisolvent approach in forming perovskite thin films and the delicate modification of A-site cations in metal halide perovskite materials remain ongoing topics of discussion. In this study, we investigate the morphology, crystal structure, photoluminescence, and optical and photoelectronic spectroscopy characteristics of perovskite materials containing cesium (Cs⁺) and a mixture of formamidinium (FA⁺) and Cs⁺. We begin by exploring the formation of CsPbBr₃ perovskite films using three different antisolvents, including chlorobenzene (CB) and eco-friendly solvents toluene and anisole. Our findings indicate that toluene significantly improves the surface morphology and crystallinity of the film compared to anisole and CB, and a small portion of FA⁺ in Cs-based perovskite potentially influences charge transport in device applications. Based on these results, we use toluene for FA_xCs_1−xPbBr₃ (0 < x < 0.15) perovskite thin films for the rest of the study. The results show that incorporating a small portion of FA⁺ in Cs-based perovskite, annealed at different temperatures, leads to enhanced crystallinity, larger grain sizes, a negligible change in the band gap, effective charge transport, and improved device luminance. These findings broaden the A-site cation options for efficient mixed-cation perovskite light-emitting diodes.