Halide perovskites show unusual thermalisation kinetics for above bandgap photo-excitation. We explain this as a consequence of excess energy being deposited into discrete large polaron states. The cross-over between low-fluence and high-fluence 'phonon bottleneck' cooling is due to a Mott transition where the polarons overlap (n ≥ 1018cm-3) and the phonon sub-populations are shared. We calculate the initial rate of cooling (thermalisation) from the scattering time in the Fröhlich polaron model to be 78 meVps-1for CH3NH3PbI3. This rapid initial thermalisation involves heat transfer into optical phonon modes coupled by a polar dielectric interaction. Further cooling to equilibrium over hundreds of picoseconds is limited by the ultra-low thermal conductivity of the perovskite lattice.
|Publication status||Published - 2017 Aug 14|
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