A rapid molecular precursor solid-state route to crystalline Fe2GeS4 nanoparticles

[Display omitted] •The first reported molecular precursors synthesis of Fe2GeS4 via solid-state route.•Fe2GeS4 formation mechanism study shows that precursor choice impacts phase purity.•Fe2GeS4 thin films show high stability, retaining phase purity up to 500 °C. Iron germanium sulfide (Fe2GeS4) recently emerged as a potential thin film solar photovoltaic absorber. The introduction of the third element—germanium (Ge)—viewed as a solution for overcoming multiple barriers of a photovoltaic pyrite, confers stability to Fe2GeS4 at elevated temperatures, typically required for accomplishing grain growth in Gen 2 thin film PV. A facile synthesis of Fe2GeS4 nanoparticles from molecular precursors, comprising mechanical mixing of starting materials followed by a two-hour annealing in a sulfur-rich atmosphere is presented herein. Further processing of the resulting Fe2GeS4 nanopowders at elevated temperatures demonstrates high thermal stability of Fe2GeS4 (up to 500 °C), in comparison with pyrite, which shows onset of pyrrhotite upon heating above 160 °C. Based on the secondary crystalline phases formed, we propose a mechanism of decomposition of Fe2GeS4 at high temperatures. Films fabricated with Fe2GeS4 were further annealed and revealed that Fe2GeS4 withstands high temperatures in thin film.