Defect-mediated electron-phonon coupling in halide double perovskite

TL;DR

This study investigates how defects in halide double perovskites influence electron-phonon interactions, revealing defect-induced mid-gap states and their thermal evolution through Raman and photoluminescence spectroscopy.

Contribution

It provides the first detailed analysis of defect-mediated electron-phonon coupling in halide double perovskites using temperature-dependent Raman and PL measurements.

Findings

Electron-phonon coupling manifests as a Fano anomaly in Raman spectra.

Defect presence induces a broad PL band absent in defect-free samples.

The electron-phonon interaction is tunable via crystal growth conditions.

Abstract

Optically active defects often play a crucial role in governing the light emission as well as the electronic properties of materials. Moreover, defect-mediated states in the mid-gap region can trap electrons, thus opening a path for the recombination of electrons and holes in lower energy states that may require phonons in the process. Considering this, we have probed electron-phonon interaction in halide perovskite systems with the introduction of defects and investigated the thermal effect on this interaction. Here, we report Raman spectroscopy study of the thermal evolution of electron-phonon coupling, which is tunable with the crystal growth conditions, in the halide perovskite systems Cs2AgInCl6 and Cs2NaInCl6. The signature of electron-phonon coupling is observed as a Fano anomaly in the lowest frequency phonon mode (51 cm-1) which evolves with temperature. In addition, we observe a broad band in the photoluminescence (PL) measurements for the defect-mediated systems, which is otherwise absent in defect-free halide perovskite. The simultaneous observation of the Fano anomaly in the Raman spectrum and the emergence of the PL band suggests the defect-mediated mid-gap states and the consequent existence of electron-phonon coupling in the double perovskite.