Exploring Carrier Dynamics in Ternary Chalcohalides

Ternary chalcohalide compounds, such as (Bi,Sb)(S,Se)(Br,I), have emerged as a promising class of inorganic materials for optoelectronic and energy conversion applications. These materials have the potential to combine the stability of chalcogenides with the superior optical and electronic properties of halides, making them suitable for rapid industrial applications. Carrier properties, such as carrier concentration, lifetimes and mobility play a crucial role in the development of these materials, and thus require a thorough investigation.
Here, we explore the tunable carrier properties and dynamics of (Bi,Sb)(S,Se)(Br,I) photoluminescence (PL), time-resolved PL (TRPL), and terahertz time-domain spectroscopy (THz-TDS). THz-TDS results have revealed carrier concentrations of about ~10¹⁸ cm^-3, in all compounds, while mobilities were ranging from 5 to 50 cm²/Vs, with SbSe(Br,I) and BiS(Br,I) having lower motilities than SbS(Br,I) and BiSe(Br,I), respectively. Carrier lifetimes were extracted from TRPL measuremnts, with decay rates ranging from 300 ps to 5 ns. Bi-based compounds have shown longer carrier lifetimes when compared to Sb-based chachohalides. We discuss this trend in terms of the changes in the structural and defect properties of Bi and Sb based compounds, with the Bi-based materials having more robust structure due to stronger bonds, and spin-orbital coupling. We further investigate optoelectronic properties of these materials, by utilizing power and temperature dependent PL spectroscopy, allowing identification of the dominating recombination pathways. Finally, using the recently suggested Figure of Merit^[1], we showcase the potential of photovoltaic application of these materials, with champion efficiency of >20 %, for the measured carrier properties.

[1] A. Crovetto, A figure-of-merit-based framework to evaluate photovoltaic materials, arXiv:2404.14732 (2024)