Dual-functional Cu⁺/Cu²⁺-doped SnS thin films via spray coating: Optoelectronic tuning and superior humidity sensor performance

This study investigates the influence of copper doping on the structural, morphological, optical, electrical, and humidity sensing properties of tin sulfide (SnS) thin films synthesized via spray coating. Copper (I) chloride (CuCl) and copper (II) chloride (CuCl₂) were employed as precursors to assess their impact on film characteristics. This is the first time such a comparison has been systematically analyzed in this context.X-ray diffraction (XRD) confirmed successful Cu incorporation, leading to a reduction in crystallite size to 18.7 nm and 13.8 nm for Cu⁺- and Cu²⁺-doped films, respectively, along with increased strain and dislocation density. Raman spectroscopy validated the retention of the orthorhombic SnS phase.X-ray photoelectron spectroscopy (XPS) confirmed Cu incorporation and its electronic interactions within the SnS matrix. Optical studies indicated bandgap modulation due to Cu doping, impacting the material’s optoelectronic properties. Electrical and dielectric measurements demonstrated doping-induced variations in charge carrier dynamics and conductivity. Notably, humidity sensing evaluations revealed that Cu²⁺- doped SnS exhibited enhanced sensitivity, achieving a capacitive sensitivity coefficient of 50% at 25% relative humidity ( RH ), significantly outperforming both undoped and Cu⁺-doped films.These findings highlight the tunability of Cu-doped SnS thin films through precursor selection, positioning them as promising candidates for next-generation optoelectronic devices and high-performance humidity sensors. • Simultaneous optoelectronic enhancement and humidity sensing. • Cu⁺ vs. Cu²⁺ ions tailored distinctively influence SnS properties. • Smooth, dense morphology achieved without high-temperature annealing. • Cu doping reduced crystallite size and increased microstrain. • First report on Cu²⁺-doped SnS films as capacitive humidity sensors.