Temperature-Dependent Interplay of Polaron Formation and Hot Carrier Cooling Dynamics in CsPbBr3 Nanocrystals: Role of Carrier-Phonon Coupling Strength

Photovoltaic devices with CsPbBr3 nanocrystals as the working layer are generally subjected to wide variance of extreme temperatures during operation. Thus, the underlying photophysics, which is undeniably a temperature-dependent entity, demands intricate understanding. In this finding, with the assistance of temperature-dependent transient absorption spectroscopy, an endeavor has been made to disentangle the detrimental conflict between polaron formation and hot carrier relaxation for CsPbBr3 nanocrystal systems. Carrier relaxation pathways are seen to diverge drastically upon varying the lattice temperature from 300 to 5 K. Acquired results indicate the involvement of polarons for retarded carrier cooling dynamics observed at 300 K, whereas its absence at lower temperatures (<200 K) provides the basis for relatively quicker cooling. Additionally, despite the expected participation from the polaron due to the onset of strong carrier-longitudinal optical phonon coupling at 200 K, the reason for its absence in the cooling dynamics at 200 K has been revealed.