Mechanism of slow hot-carrier cooling in lead-halide perovskites
In plain words
Light with extra energy creates hot charges that normally lose that excess to the lattice within a fraction of a trillionth of a second. In perovskites they stay hot much longer at high light intensity, and why is debated.
Precise statement
At excitation densities above about $1e18\,\mathrm{cm}^{-3}$, hot-carrier cooling in MAPbI3 and CsPbBr3 slows from about 0.3 ps to tens or hundreds of ps. Separate the contributions of the hot-phonon bottleneck (slow decay of longitudinal-optical phonons), Auger reheating, and large-polaron screening, and determine whether any slowdown persists below $1e17\,\mathrm{cm}^{-3}$, the density under sunlight. An answer is quantified cooling-time contributions versus density and temperature.
What would settle it
Density-resolved two-dimensional or transient spectroscopy with direct phonon-population probes, reproduced by a coupled carrier-phonon kinetic model.
Status in the literature
The hot-phonon bottleneck at high density is widely accepted; the low-density polaron-screening claim remains contested.