Solution-based synthesis of nanocrystalline KBiS2 films at low temperatures and study of photoinduced charge generation

Abstract

Ternary metal sulfides have been widely investigated in recent years as solar absorber materials in photocatalysis and photovoltaics, where they have the potential to replace expensive or harmful materials like noble metals or lead-based compounds. Potassium bismuth sulfide has two polymorphs showing promise for solar applications. However, the preparation of KBiS₂ is hardly investigated beyond the originally proposed highly energy demanding solid state or salt melt syntheses. In order to facilitate the applicability of KBiS₂ films, we investigated the formation of cubic and rhombohedral KBiS₂ from metal xanthate precursors. The use of xanthates offers the advantages of low conversion temperatures and good solubility of the precursors in non-halogenated and non-aromatic solvents. We successfully prepared KBiS₂ films with rhombohedral and cubic crystal structures, which we could confirm with XRD and HR-STEM experiments, and found that the cubic phase forms at a relatively low temperature of 200 °C. Our findings provide a facile low temperature method to prepare KBiS₂ thin films and demonstrate well-suited optoelectronic properties of this material. In particular, the long charge recombination lifetime of 41.1 microseconds in TiO₂/KBiS₂/spiro-OMeTAD films highlights the suitability of KBiS₂ for potential applications in solar energy conversion devices.