Time resolved photoemission spectroscopy of electronic cooling and localization in CH$_3$NH$_3$PbI$_3$ crystals

TL;DR

This study uses two-photon photoemission spectroscopy to investigate hot carrier dynamics, surface recombination, and electron localization in CH$_3$NH$_3$PbI$_3$ crystals, revealing key processes affecting solar cell efficiency.

Contribution

It provides new insights into hot carrier dissipation, surface recombination limits, and trap effects in CH$_3$NH$_3$PbI$_3$, informing strategies to improve solar cell performance.

Findings

Hot carriers dissipate in 0.25 ps

Surface recombination velocity is below 4000 cm/s

Shallow traps cause electron localization and efficiency reduction

Abstract

We measure the surface of CH$_3$NH$_3$PbI$_3$ single crystals by making use of two photon photoemission spectroscopy. Our method monitors the electronic distribution of photoexcited electrons, explicitly discriminating the initial thermalization from slower dynamical processes. The reported results disclose the fast dissipation channels of hot carriers (0.25 ps), set a upper bound to the surface induced recombination velocity ($<4000$ cm/s) and reveal the dramatic effect of shallow traps on the electrons dynamics. The picosecond localization of excited electrons in degraded CH$_3$NH$_3$PbI$_3$ samples is consistent with the progressive reduction of photoconversion efficiency in operating devices. Minimizing the density of shallow traps and solving the aging problem may boost the macroscopic efficiency of solar cells to the theoretical limit.