High‐Rate Thermal Evaporation of CsPb(Br _{1− <i>x</i>} Cl _<i>x</i> ) ₃ Thin Films and their Optoelectronic Properties for Photovoltaic Power Converters in Optical Wireless Power Transmission

Herein, high‐rate thermal evaporation of cesium lead bromide chloride (CsPb(Br 1− x Cl x ) 3 ), a wide‐bandgap perovskite material, using a single powder evaporation source is investigated. The Cl/(Cl + Br) ratio ( x ) in the deposited films is controlled by adjusting the source composition, enabling precise bandgap tuning from 2.38 to 2.76 eV. The optimal composition for absorbing 455 nm blue light is achieved at x = 0.58. An average deposition rate of ≈100 nm min −1 is achieved for CsPb(Br 0.42 Cl 0.58 ) 3 films. The electrical conductivity and carrier diffusion length of the films are evaluated and a strong dependence on post‐deposition annealing and moisture‐absorption treatment is found. A relatively long carrier diffusion length of ≈3.91 μm is achieved under blue‐light illumination (400 nm, 600 μW cm −2 ). A prototype photovoltaic power converter employing CsPb(Br 1− x Cl x ) 3 as the light‐absorbing layer exhibited a power conversion efficiency of 1.38% under AM 1.5 G illumination, corresponding to an estimated efficiency of 11.7% under monochromatic 455 nm blue light. These results highlight the potential of CsPb(Br 1− x Cl x ) 3 as a light‐absorbing layer for photovoltaic power converters in optical wireless power transmission systems and suggest that further improvements in device performance will require careful interface engineering between the absorber and both the electron and hole transport layers.