Nanocrystalline ITO-Sn₂S₃ transparent thin films for photoconductive sensor applications

Nanocrystalline indium tin oxide (ITO) film containing 5 wt% Sn was prepared on glass substrate by the spray pyrolysis technique at a substrate temperature of 500 °C. In order to enhance the photosensitivity of ITO, thiourea (CS(NH₂)₂ was added to the precursor to obtain the [S]/[In] proportion of 0.1, 0.2, 0.4 and 0.6. The X-ray diffraction patterns showed that beside the bixbyite structure of ITO, the characteristic peaks corresponding to Sn₂S₃ appeared in XRD profiles recorded for the films with [S]/[In] = 0.1 and 0.2. In addition, sulfur additive caused a considerable decline in crystallinity quality. The optical properties of the films were studied using transmittance measurements in the wavelength range 300–1,000 nm. As a result, ITO and ITO-Sn₂S₃ thin films were prepared with resistivity of 3.06–3.7 × 10⁻⁴ Ω cm and a transmittance of 88–91 % at the wavelength of 550 nm. Moreover, the electrical resistances of ITO and ITO-Sn₂S₃ films as a function of time were measured in darkness and under illumination of light in the visible range. The photoresistance results revealed that the ITO-Sn₂S₃ film with [S]/[In] = 0.2 was efficiently sensitive to visible light for photoconductive sensor applications, besides being high conductive and transparent.