Retarded Charge Recombination to Enhance Photocatalytic Performance for Water-Free CO 2 Reduction 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 PbBr 3 (CF, x = 0.45) and CsPbBr 3 (CS), which served as efficient photocatalysts for splitting of CO 2 into CO and O 2 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.