Temperature-Dependent Photophysics of Lead-Free Germanium Halide Perovskites

Halide perovskites and their low-dimensional analogs feature excellent optoelectronic properties, resulting in efficient solar cells, detectors, and light-emitting applications. One hurdle toward widespread adoption and commercialization of halide perovskites remains their reliance on toxic lead. Substitution of Pb has been largely difficult, as geometric constraints can lead to the formation of non-perovskite structures, particularly when germanium is used. <br/><br/>Here, employing a recently reported organic scaffolding synthesis route¹ a series of high-purity 2D Ge perovskite single crystals with persistent octahedral structure were synthesized. We then investigated their temperature-dependent photophysical properties with that of their Pb-analogs.² In contrast to most existing studies to date focusing on room temperature response and limited by low luminescence yields, we find that the germanium-based material compares favorably to its Pb-analog at low temperatures, shedding light on the mechanism of temperature-dependent non-radiative decay channels for both Ge and Pb based 2D perovskites. Most notably, we report the lowest full-width-at-half-maximum photoluminescence peak reported for germanium halide perovskites to date. The insights into the photophysical mechanisms of these materials are a prerequisite to enable less toxic lead-free optoelectronic devices, where future design principles aimed at preventing non-radiative decay result in Ge-based perovskites with performance on par with or exceeding their Pb-based counterparts. <br/><br/>References: <br/>1. Morteza Najarian, A., Dinic, F., Chen, H. <i>et al.</i> Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites. <i>Nature</i> <b>620</b>, 328–335 (2023).<br/>2. Unpublished results (2024).