Hidden photoexcitations probed by multi-pulse photoluminescence

TL;DR

This paper introduces a multi-pulse photoluminescence technique that enables detection of hidden, slow photoexcitations in luminescent materials, demonstrated on perovskites to analyze carrier trapping and trap dynamics.

Contribution

The authors develop a novel multi-pulse excitation scheme that reveals hidden photoexcitations with slow dynamics, surpassing traditional time-resolved photoluminescence limitations.

Findings

Visualized carrier trapping in perovskites

Quantified trapped charge concentration

Determined trap depopulation rate constant

Abstract

Time-resolved photoluminescence is a validated method for tracking the photoexcited carrier dynamics in luminescent materials. This technique probes the photoluminescence decays upon a periodic excitation by short laser pulses. Herein, we demonstrate that this approach cannot directly detect hidden photoexcitations with much slower dynamics than the photoluminescence decay. We demonstrate a new method based on a multi-pulse excitation scheme that enables an unambiguous detection and an easily interpreted tracking of these hidden species. The multi-pulse excitation consists of a single pulse (Read) followed by a burst of many closely separated pulses (Write) and finally another single pulse (Read). To illustrate the efficacy of the Read-Write-Read excitation scheme, we apply it to metal halide perovskites to directly visualize carrier trapping, extract the concentration of trapped charges and determine the rate constant of trap depopulation. The developed approach allows studying performance-limiting processes in energy devices using a versatile, highly applicable all-optical method.