Publication date: 15th December 2025
The search for non-toxic and stable optoelectronic materials has led to increasing interest in lead-free halide double perovskites [1]. Among them, mixed-valence gold halide double perovskites Cs2Au2X6 (X = Cl, Br, I) have emerged as promising candidates for lead-free optoelectronics due to their exceptional ambient stability and near-infrared band gaps [2], making them ideal for applications such as photovoltaics and infrared detectors. However, their notoriously low photoluminescence quantum efficiency continues to hinder device integration, and the fundamental mechanisms responsible for this inefficiency remain poorly understood.
In this work, we elucidate the dominant role of electron–phonon coupling in governing the optical response of these materials through a comprehensive multi-modal spectroscopy approach combining temperature-dependent photoluminescence, absorption spectroscopy, and Raman scattering [3]. Our PL measurements reveal broad, red-shifted emission with a strong temperature dependence, indicative of carrier localization and phonon assisted relaxation processes. On the other hand, absorption spectra exhibit a pronounced urbach tail, which we attribute to lattice distortions generating polar states that act as non-radiative recombination centers. This feature plays a crucial role in non-radiative carrier trapping and contributes to the low quantum efficiency typically observed in this class of materials.
Overall, these results provide new insight into the interplay between lattice dynamics and electronic processes in gold-based double perovskites. Beyond fundamental understanding, this work highlights the potential of gold perovskite as a model system for optimizing lead-free double perovskites and design new architectures for sustainable optoelectronics devices.
We thank the French Agence Nationale de la Recherche (ANR) for funding under the grant number ANR-22-CE42-0027
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