Synergistic Chlorine Source Regulation and Defect‐Passivation Strategy for Stable Blue‐Emitting Perovskite Films Toward Non‐Invasive Jaundice Therapy

Abstract Lead halide perovskites are promising next‐generation optoelectronic materials due to their solution processability, tunable bandgap and excellent photoelectric properties. However, achieving deep‐blue emission in all‐inorganic CsPbX 3 nanocrystals remains challenging due to phase separation, halide volatilization and insufficient stability, limiting industrial application. Herein, a collaborative strategy of “chlorine source regulation—defect passivation—fiber integration” is proposed. By incorporating β‐cyclodextrin chloride (βCD‐Cl) into CsPbBr 3 , we synthesized large‐scale deep‐blue CsPbBr 3‐x Cl x @βCD‐Cl microcrystals via a mechanosynthesis route. Flexible blue‐light fiber films are fabricated via electrospinning, showing a photoluminescence quantum yield (PLQY) of 55.79% and excellent environmental stability, with only a 16 nm red shift observed after 171 days in water. Additionally, the fiber films enable near‐infrared (750 nm)‐to‐blue photon upconversion (450‐490 nm), achieving unprecedented bilirubin degradation efficiency (40% within 20 min). They can serve as core components for next‐generation phototherapeutic blankets, combining spectral selectivity (blocking harmful radiation < 420 nm) with therapeutic light transmission, eliminating neonatal retinal phototoxicity risks without requiring protective eyewear. The full solution‐processed white‐light fiber film is prepared, with CIE coordinates (x = 0.32, y = 0.34) near the ideal white light point. Overall, this study clarifies the molecular structure—performance relationships, overcomes stability bottlenecks, and supports photodynamic therapy and bio‐photonic devices.