(Invited) Polaron Mediated Cooling Dynamics in Perovskite Materials: Effect of Temperature

摘要

During last decade huge number of research investigations are going on different kind of halide perovskite materials due to their exciting optoelectronic properties which includes ability to provide very efficient solar devices. Charge carrier cooling process is one of the key process for design and development of any higher efficient optoelectronic devices. Ultrafast hot carrier cooling is the key loss channel which limits achievable solar conversion efficiency. Delaying the carrier cooling high efficient hot-carrier solar cell can be realized. Thus, delayed hot carrier cooling in the cell absorber layer can make hot carrier extraction a relatively easier 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 has eventually triggered interest in the radical understanding of the native photophysics driving the device design. In our recent investigation, we have demonstrated dramatic dip in the cooling rate in CsPbBr_3 NC after growing Cs_4PbBr_6 shell over it, in contrast to the bare CsPbBr_3 core NCs. By employing ultrafast transient absorption spectroscopy, we have investigated the disparity in the hot carrier thermalization pathways in the CsPbBr_3 and CsPbBr_3@Cs_4PbBr_6 core-shell NCs under same laser fluence, which can be validated as a corollary of polaron formation in the later NCs. Role of phonon in the cooling process has also been investigated by carrying out the ultrafast transient studies in the temperature range of 5K-300K.