Long Carrier Diffusion Length and Slow Hot Carrier Cooling in Thin Film Mixed Halide Perovskite

The long diffusion length is the key to achieve remarkable power conversion efficiency and delayed hot carriers (HCs) relaxation helps to overcome the theoretical Shockley-Queisser limit in perovskite photovoltaic. Here, we investigate the incident photon density dependent bandedge bleaching and HCs dynamics in thin film methyl-ammonium lead iodide-chloride (mixed halide) perovskite using transient absorption spectroscopy. The bandedge bleaching dynamics shows the radiative recombination rate constant of the order of ~10
^-11
cm
^-3
s
^-1
results in the maximum carrier diffusion length of the order of ~10 μm. The HCs dynamics indicates cooling occurs by longitudinal-optical (LO) phonon emission in early ~800 fs via Fröhlich electron-phonon interaction at low-carrier concentration (~1.7 × 10
¹⁸
cm
^-3
) and an efficient phonon bottleneck due to the delayed LO-phonon decay by two order of magnitude about ~11 ± 1.3 ps at high carrier density (~10
¹⁹
cm
^-3
). Our finding shows the potential of thin film mixed halide perovskite in HCs photovoltaic and light emission application.