Low temperature green synthesis of red emitting Pb-free CsMnBr3 perovskite films

Abstract

Lead halide perovskites (APbX₃) have demonstrated exceptional opto-electronic properties, but their inherent toxicity and environmental hazards hindered their practical deployment in display technologies such as liquid crystal display (LCD) backlights. Herein, we report for the first time a facile, water-mediated synthesis of red-emitting CsMnBr₃ thin films from an aqueous solution of CsBr and MnBr₂ precursors at a low temperature of ∼50 °C. Unlike traditional synthesis routes reported for synthesis of CsMnBr₃ powders or nanocrystals, relying heavily on toxic solvents, high temperatures, or inert atmospheres, the green approach utilizes water as a benign medium to facilitate the [MnBr₆] octahedral coordination assembly, yielding continuous red films with strong photoluminescence (λ: ∼644 nm, FWHM: ∼75 nm). The as-synthesized CsMnBr₃ films exhibit remarkable optical quality with an ultra-wide color gamut coverage (∼132% of NTSC 1953 and ∼186% of sRGB color standards), making them a promising alternative for traditional red phosphors in LCD backlight applications. The characterization of electrical and photo-responses reveals a negative photoconductivity under UV irradiation, attributed to the powdered microstructure and hygroscopic nature of MnBr₂ under ambient air conditions. The photo-response of the red-emissive CsMnBr₃ films exhibits a power-law dependence on high-energy irradiation under ambient conditions at ∼18 °C and a relative humidity of ∼65%, along with faster self-recovery behavior, highlighting the complex role of defect-mediated charge transport. This green, low-cost, and scalable synthesis route offers a promising pathway toward sustainable and lead-free phosphor materials for next-generation wide-color-gamut display technologies.