Polaron-Mediated Slow Carrier Cooling in a Type-1 3D/0D CsPbBr₃@Cs₄PbBr₆ Core-Shell Perovskite System

Rapid hot carrier cooling is the key loss channel overriding all possible energy loss pathways that limit achievable solar conversion efficiency. Thus, delayed hot carrier cooling in the cell absorber layer can make hot carrier extraction a less cumbersome task, assisting in the realization of hot carrier solar cells. There have been plentitude of reports concerning the slow carrier cooling in perovskite materials, which eventually triggered interest in radical understanding of the native photophysics driving the device design. Here in this finding, a further dramatic dip in the cooling rate has been discerned upon a growing Cs₄PbBr₆ shell over CsPbBr₃ core nanocrystals (NCs), in contrast to the bare CsPbBr₃ core NCs. Using transient absorption spectroscopy, we investigated the disparity in the hot carrier thermalization pathways in the CsPbBr₃ and CsPbBr₃@Cs₄PbBr₆ core-shell NCs under the same laser fluence, which can be validated as a corollary of polaron formation in the later NCs.