Direct Synthesis of Single-Phase p‑Type SnS by Electrodeposition from a Dicyanamide Ionic Liquid at High Temperature for Thin Film Solar Cells

Thin film solar cells based on nontoxic and earth-abundant elements are necessary for future-generation photovoltaic devices. Tin monosulfide is a promising candidate that can be used as an absorber material in thin film photovoltaics. In this paper, we introduce the direct synthesis of stoichiometric and single-phase p-type SnS films via the electrodeposition from the ionic liquid 1-butyl-3-methylimidazolium dicyanamide ([C₄mim]­[DCA]) containing elemental sulfur and SnCl₂ at high temperature. The electrochemical behavior is studied, and a deposition mechanism of tin monosulfide from the elemental sulfur saturated ionic liquid is proposed. XRD, XPS, and Raman spectroscopy demonstrate the sole presence of α-SnS without any secondary sulfide phases (e.g., SnS₂, Sn₂S₃). XPS depth profiling confirmed the phase purity and disproved the presence of organic contamination in the as-deposited films. Photoelectrochemical measurements affirmed the p-type conductivity of the SnS films. The as-deposited layers have an indirect optical band gap at 1.17 eV and high optical absorption (α ≥ 10⁴ cm^–1) at photon energy above 1.4 eV. First solar cells with a standard thin film substrate cell configuration are presented.