Extending the Defect Tolerance of Halide Perovskite Nanocrystals to Hot Carrier Cooling Dynamics

TL;DR

This study investigates how defects affect hot carrier relaxation in CsPbX3 nanocrystals, revealing that hot carriers are not universally defect tolerant and are directly captured by traps, influencing material design for advanced optoelectronic applications.

Contribution

It provides the first detailed analysis of hot carrier defect tolerance in lead-halide perovskite nanocrystals, linking trap depth to hot carrier cooling dynamics.

Findings

Hot carriers are not universally defect tolerant in CsPbX3.

Hot carriers are directly captured by traps, bypassing cold carriers.

Deeper traps accelerate hot carrier cooling, affecting device performance.

Abstract

Defect tolerance is a critical enabling factor for efficient lead-halide perovskite materials, but the current understanding is primarily on band-edge (cold) carriers, with significant debate over whether hot carriers (HCs) can also exhibit defect tolerance. Here, this important gap in the field is addressed by investigating how internationally-introduced traps affect HC relaxation in CsPbX3 nanocrystals (X = Br, I, or mixture). Using femtosecond interband and intraband spectroscopy, along with energy-dependent photoluminescence measurements and kinetic modelling, it is found that HCs are not universally defect tolerant in CsPbX3, but are strongly correlated to the defect tolerance of cold carriers, requiring shallow traps to be present (as in CsPbI3). It is found that HCs are directly captured by traps, instead of going through an intermediate cold carrier, and deeper traps cause faster HC cooling, reducing the effects of the hot phonon bottleneck and Auger reheating. This work provides important insights into how defects influence HCs, which will be important for designing materials for hot carrier solar cells, multiexciton generation, and optical gain media.