Polar Indirect Valley as a Limiting Factor for Radiative Efficiency in Gold-Based Mixed-Valence Double Perovskites

TL;DR

This study investigates how polar indirect valleys in gold-based mixed-valence double perovskites limit their radiative efficiency by inducing forbidden recombination pathways, affecting their optoelectronic performance.

Contribution

It reveals the impact of strong polar electron-phonon coupling and temperature-dependent absorption tails on the radiative efficiency of gold-based double perovskites.

Findings

Polar electron-phonon coupling is strong in these materials.

Temperature influences the absorption spectrum significantly.

Forbidden band-edge recombination explains low photoluminescence detection.

Abstract

Double perovskites have emerged as promising alternatives to lead halide perovskites, aiming to mitigate challenges related to toxicity and chemical instability. Among them, mixed-valence gold halides such as Cs2Au+Au3+Cl6, which contain only a single type of metal cation in two oxidation states, stand out due to their unique structural and electronic properties. These materials exhibit strong absorption in the near-infrared range, making them attractive candidates for optoelectronic applications such as photovoltaics. In this work, we employ temperature-dependent optical spectroscopy techniques to demonstrate that these compounds exhibit particularly strong polar electron-phonon coupling, which has a profound impact on their optoelectronic properties. In particular, this coupling gives rise to a temperature-dependent absorption tail that reshapes the global spectral spectrum. We show that this tail leads to a forbidden band-egde recombination, which explains the reported difficulties in detecting a photoluminescence signal from this class of double perovskites.