Hot carrier redistribution, electron-phonon interaction, and their role in carrier relaxation in thin film halide perovskites
Temperature dependent (4K-300K) photoluminescence and transmission spectra are analyzed to study the effect of changing the different components of a perovskite compound, be it A, B, or X. Four different films are compared: FAMAPbSnI3, FAPbI3, FAMAPbI3, and FAPbBr3. The low temperature results highlight the changes that occur especially, underlying ones that are easily masked at room temperature. The overall Stokes shift is of similar magnitude at room temperature for the 3 Pb only based samples. This is governed by the interaction strength GammaLO, phonon energy ELO, and the exciton binding energy Eex. One exception to this behavior is the Sn-based FAMAPbSnI3 film which shows a lack of Stokes shift between the absorption and photoluminescence. However,the strong absorption (more than 100 meV) below the band gap is indicative of an excitonic feature that has a large density of states. Transient absorption measurements confirm the trends observed in continuous wave (CW) measurements, the 3 Pb only films all show the convolution of an excitonic feature within 20 meV of the band gap as a contributing factor to the photobleach along with a region of high energy PIA. However, the behavior for the Sn-based film is notably different (just as in the CW measurements) with an unusual low energy PIA and a lack of high energy PIA. The large low energy PIA is attributed to the large sub band gap absorption observed in the CW transmission/absorption measurements. Notably regardless of interchanging components, the slow cooling of carriers in metal-halide perovsites shows little effect of GammaLO, ELO, and Eex. As such, here it is proposed: while the initial cooling of carriers is attributed to LO phonons, the overall cooling of carriers is dominated by the intrinsic low thermal conductivity of all metal-halide perovskites which limits the dissipation of acoustic phonons in these systems.
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