Trap-Free Hot Carrier Relaxation in Lead-Halide Perovskite Films

Photovoltaic devices that employ lead-halide perovskites as photoactive materials exhibit power conversion efficiencies of 22%. One of the potential routes to go beyond the current efficiencies is to extract charge carriers that carry excess energy, that is, nonrelaxed or "hot" carriers, before relaxation to the band minima is completed. Lead halide perovskites have been demonstrated to exhibit hot-carrier relaxation times exceeding 100 ps for both single- and polycrystalline samples. Here, we demonstrate, using a combined time-resolved photoluminescence and transient absorption study supported by basic modeling of the dynamics, that the decay of the high-energy part of the photoluminescence occurs on a time scale (similar to 100 ps) very similar to the repopulation of the band minima when excited with a photon energy larger than 2.6 eV. The similarity between the two time scales indicates that the depopulation of hot states occurs without transient trapping of electrons or holes.