Enhancement of Photocarrier Lifetimes in Infrared-Laser-Deposited CsPbBr₃ Films Using a CsBr Underlayer

This study used photocarrier lifetime measurements to demonstrate that the insertion of a CsBr underlayer enhances the quality of CsPbBr 3 films grown via infrared (IR) laser deposition. Thermal desorption spectrometry indicated that the CsPbBr 3 crystal tended to be Cs-deficient under vacuum. In fact, direct growth of a CsPbBr 3 film on an α-Al 2 O 3 (0001) substrate resulted in contamination by an impurity phase of CsPb 2 Br 5, thereby degrading the optical characteristics of the CsPbBr 3 films. To mitigate CsPb 2 Br 5 contamination, a two-step film preparation process was employed to obtain the growth window for the IR-laser deposition of the CsPbBr 3 thin films. First, a CsBr underlayer was deposited at room temperature. CsPbBr 3 thin films were subsequently deposited onto the underlayer at 150 °C. Consequently, the CsBr underlayer was found to suppress the precipitation of the impurity phase and improve the functional properties of the CsPbBr 3 films. Furthermore, photocarrier lifetime measurements were performed to assess the quality of the CsPbBr 3 thin films. Notably, time-resolved microwave conductivity measurements revealed that the CsBr underlayer not only doubled the photocarrier lifetime but also tripled the photoconductivity. Thus, the use of a thin underlayer is expected to be an essential synthesis parameter for fine-tuning the growth window and improving the physical properties of halide perovskite films.