Phosphosulfides—New, Stable Thin-film PV Absorbers with Long Carrier Lifetimes

Phosphosulfides are an intriguing family of semiconductors with hardly any thin-film history. They are obtained by combining phosphorus with sulfur and one or more metals. Unlike the well-known III-V semiconductors, phosphosulfides incorporate phosphorus in the +5 (rather than -3) oxidation state [1].
We have been studying these exotic semiconductors with an integrated experimental/computational work strategy inspired by the FAIR data principles. Density functional theory calculations indicate that many more phosphosulfide compounds should be thermodynamically stable than previously thought, including materials with previously unreported stoichiometric coefficients and structures. Additionally, most phosphosulfides have band gaps in a useful range for photovoltaics, and these band gaps are often direct.
Backed by a unique suite of combinatorial thin-film deposition setups with access to S and P sources, we have explored the Cu-P-S, Sb-P-S, and Ba-P-S phase diagrams by high-throughput experiments and we can now report the first thin-film synthesis of various compounds. Most of these films are single-phase, stable in air, and semiconducting. In spite of unpassivated surfaces and lack of process optimization, some of these semiconductors already exhibit photoluminescence decay times above 100 ns and photoluminescence quantum yields above 0.001%.
To objectively assess the quality of these early-stage PV materials at their current development stage, I will discuss a recently proposed figure of merit for solar absorbers [2,3].

[1] L. A. Mittmann, A. Crovetto, J. Phys. Mater. 2024, 7, 021002.
[2] A. Crovetto, J. Phys. Energy 2024, 6, 025009.
[3] A. Crovetto, 2024, Arxiv preprint, 10.48550/arXiv.2404.14732.