  Hot-carrier cooling (HCC) in metal halide perovskites in the high-density
regime is significantly slower compared to conventional semiconductors. This
effect is commonly attributed to a hot-phonon bottleneck but the influence of
the lattice properties on the HCC behaviour is poorly understood. Using
pressure-dependent transient absorption spectroscopy (fs-TAS) we find that at
an excitation density below Mott transition, pressure does not affect the HCC.
On the contrary, above Mott transition, HCC in methylammonium lead iodide
(MAPbI3) is around two times as fast at 0.3 GPa compared to ambient pressure.
Our electron-phonon coupling calculations reveal about two times stronger
electron-phonon coupling for the inorganic cage mode at 0.3 GPa. However, our
experiments reveal that pressure promotes faster HCC only above Mott
transition. Altogether, these findings suggest a change in the nature of
excited carriers in the high-density regime, providing insights on the
electronic behavior of devices operating at such high charge-carrier density.
