Halide perovskites show unusual thermalization kinetics for above-bandgap photoexcitation. We explain this as a consequence of excess energy being deposited into discrete large polaron states. The crossover between low-fluence and high-fluence "phonon bottleneck" cooling is due to a Mott transition where the polarons overlap (n ≥ 1018 cm-3) and the phonon subpopulations are shared. We calculate the initial rate of cooling (thermalization) from the scattering time in the Fröhlich polaron model to be 78 meV ps-1 for CH3NH3PbI3. This rapid initial thermalization 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 ultralow thermal conductivity of the perovskite lattice.
Bibliographical noteFunding Information:
We thank Jonathan M. Skelton for discussions concerning the thermal conductivity calculations. Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk). This work was funded by the EPSRC (Grant Numbers EP/ L01551X/1, EP/L000202, and EP/K016288/1), the Royal Society, and the ERC (Grant No. 277757).
© 2017 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Chemistry (miscellaneous)
- Renewable Energy, Sustainability and the Environment
- Fuel Technology
- Energy Engineering and Power Technology
- Materials Chemistry