Impact of Bi³⁺ and Cu²⁺ doping on the optical and electronic properties of CsPbBr₃ for photocatalytic toluene oxidation

Doping of metal halide perovskites (MHPs) offers an opportunity to introduce trap states that are reported to be beneficial for the charge carrier dynamics. Herein, we investigated the electronic structure-photocatalytic relationship of CsPbBr₃ doped with Bi³⁺ and Cu²⁺ cations. Bi doping necessitates a reduction in the hot-injection temperature to avoid the formation of Bi nanoparticles, leading to the formation of two-dimensional CsPbBr₃ with a variable aspect ratio. Bi doping causes no significant changes in the band gap energy but leads to the gradual appearance of a band-tail in the absorbance spectrum and a broad-band emission peak covering a large wavelength range. A photoluminescent quenching is observed as the ratio of Bi³⁺ increases, indicating shallow trap generation. Cu²⁺ doping does not affect the morphology of the 3D crystalline CsPbBr₃ and shows a photoluminescent blueshift, which translates to a change in the bandgap energy. The CsPbBr₃ doping, with an adequate amount of Cu, provides the best photocatalytic activity, surpassing Bi-doped CsPbBr₃. Time-resolved photoluminescence analysis indicated that Bi³⁺ introduces a shallow trap that captures electrons while leaving the holes free, leading to an increase in the charge carrier lifetime, thus favoring charge carrier separation. Unlike bismuth, Cu²⁺ affects both the conduction and valence band positions, making the oxidation reaction more favorable.