Temperature- and charge carrier density-dependent electronic response in methylammonium lead iodide

TL;DR

This study investigates how temperature and charge density affect carrier dynamics in methylammonium lead iodide perovskite, revealing different recombination regimes and enabling an electronic phase diagram to optimize optoelectronic devices.

Contribution

It provides a comprehensive mapping of carrier response regimes across densities and temperatures, introducing an electronic phase diagram for methylammonium lead iodide perovskite.

Findings

Fast trapping at low densities within a few picoseconds.

Saturation of trapping and stabilized response at intermediate densities.

Ultrafast Auger recombination above 10^18 cm-3 due to Mott transition.

Abstract

Understanding carrier dynamics in photoexcited metal-halide perovskites is key for optoelectronic devices such as solar cells (low carrier densities) and lasers (high carrier densities). Trapping processes at low carrier densities and many-body recombination at high densities can significantly alter the dynamics of photoexcited carriers. Combining optical-pump/THz probe and transient absorption spectroscopy we examine carrier responses over a wide density range (10^14-10^19 cm-3) and temperatures (78-315K) in the prototypical methylammonium lead iodide perovskite. At densities below ~10^15 cm-3 (room temperature, sunlight conditions), fast carrier trapping at shallow trap states occurs within a few picoseconds. As excited carrier densities increase, trapping saturates, and the carrier response stabilizes, lasting up to hundreds of picoseconds at densities around ~10^17 cm-3. Above 10^18 cm-3 a Mott transition sets in: overlapping polaron wavefunctions lead to ultrafast annihilation through an Auger recombination process occurring over a few picoseconds. We map out trap-dominated, direct recombination-dominated, and Mott-dominated density regimes from 78-315 K, ultimately enabling the construction of an electronic phase diagram. These findings clarify carrier behavior across operational conditions, aiding material optimization for optoelectronics operating in the low (e.g. photovoltaics) and high (e.g. laser) carrier density regimes.