Ionic conductivity of vanadium-doped tin disulfide for photovoltaic applications

Tin disulfide (SnS₂) is an environmentally friendly and widely available material with a band gap ranging from approximately 2.20 to 2.45 eV, making it a strong candidate for use as a buffer layer in photovoltaic technologies. In this study, SnS₂ was synthesized using the hydrothermal method. To enhance its interaction with visible light, vanadium (V) atoms-also earth-abundant and characterized by a low band gap-were incorporated into the SnS₂ matrix. The atomic percentage of vanadium was varied from 0% to 10% in increments of 2%. A previous study conducted on similar mixed Sn_1-xV_xS₂ samples, though with different vanadium concentrations, suggested that V-doped SnS₂ thin films could be suitable as buffer layers for solar cell fabrication. However, the electrical conductivity of these samples had not been quantified, and therefore, such a conclusion cannot be definitively confirmed. In this work, electrochemical impedance spectroscopy was used to determine the conductivity and diffusivity of vanadium-doped samples as a function of temperature. Our results revealed a percolation threshold at approximately 6% vanadium content, with notable changes in conductivity observed around 120 °C. The sample doped with 6% vanadium exhibited a significantly enhanced photocurrent response (3.0 × 10^-6 A cm^-2) compared to the undoped SnS₂ thin films (4.0 × 10^-7 A cm^-2). These findings indicate that vanadium incorporation significantly alters the crystallinity of SnS₂, leading to changes in the melting temperature of the mixed Sn_1-xV_xS₂ samples. Such changes may induce structural relaxation, lattice dilation, or enhanced atomic interactions. Together with previous studies, these results highlight that V-doped SnS₂ is a promising candidate for optoelectronic applications, including photoelectrochemical catalysis, photodetectors, and photovoltaic devices.