Mn ²⁺ ‐Doped CsPbCl ₃ Perovskite Quantum Dots@Ethyl Cellulose Composite Films With Down‐Conversion Luminescent Properties Through Ultrasonic Spray Coating Technology

Herein, highly crystalline, well‐dispersed Mn 2+ ‐doped CsPbCl 3 perovskite quantum dots (PQDs) were synthesized via the hot‐injection method, and their down‐conversion luminescent properties were optimized by adjusting the Mn 2+ doping concentration. Upon excitation with 365 nm UV light, CsPbCl 3 :Mn PQDs show bright orange luminescence at ≈600 nm, which is ascribed to the 4 T 1 → 6 A 1 transition of Mn 2+ ions. An ultrasonic spray coating technology is introduced to fabricate flexible, high‐performance down‐conversion film based on PQDs embedded in ethyl cellulose (EC) polymer matrix. The as‐prepared composite film exhibits a dense, uniform, crack‐free morphology and a smooth surface. EC polymer significantly improves the environmental stability of CsPbCl 3 :Mn PQDs. Mn 2+ emission intensity of CsPbCl 3 :Mn@EC film could retain 67.8% of its initial value after 20 mins of water immersion, and more than 90% of the initial value after continuous exposure to ambient air for 40 days. When these PEQs are applied as a down‐conversion layer of Sb 2 Se 3 solar cells, it significantly enhances the external quantum efficiency values in the ultraviolet region (250–360 nm). This work demonstrates that ultrasonic spray coating enables large‐scale production of high‐quality perovskite films, providing a novel type of high‐performance down‐conversion layer material in fields such as flexible optoelectronic devices.