Retarded Charge Recombination to Enhance Photocatalytic Performance for Water-Free CO₂Reduction Using Perovskite Nanocrystals as Photocatalysts

Femtosecond transient absorption spectral (TAS) investigations were performed to understand the carrier relaxation mechanism for perovskite nanocrystals Cs_1-x FA_x PbBr₃ (CF, x = 0.45) and CsPbBr₃ (CS), which served as efficient photocatalysts for splitting of CO₂ into CO and O₂ in the absence of water. Upon light irradiation for 12 h, formation of deep trap states was found for both CS and CF samples with spectral characteristics of the TAS photobleach (PB) band showing a long spectral tail extending to the long wavelength region. The charge recombination rates at the shallow surface states, bulk states, and deep-trapped surface state were found to be significantly retarded for the CF sample than for the CS sample, in agreement with the photocatalytic performances for CO product yields of the CF catalyst being greater by a factor of 3 compared to those of the CS catalyst.