Vol. 7, Issue 2, Part D (2025)

This study presents a comprehensive voltage-dependent electrical characterization of Sn (5%) doped nanocrystalline CdS (nc-CdS) thin film heterojunctions fabricated on FTO substrates, with a particular focus on the impact of illumination at 8.5 mW   for advanced optoelectronic applications. Structural and device-level analyses reveal that the series and parallel capacitance, obtained from precise impedance measurements, exhibit pronounced modulation under both dark and illuminated states, with capacitance values and depletion width showing significant sensitivity to applied bias and photoinduced charge carrier generation. Series resistance measurements Sdemonstrate a decrease under illumination, highlighting enhanced carrier conduction and improved device efficiency. Time constant investigations indicate accelerated carrier relaxation dynamics under light, verifying the device’s potential for fast photoresponse and photodetector utility. The voltage-dependent depletion width calculated via   shows dynamic variation and a consistent reduction under photoactive conditions. Mott-Schottky analyses further unravel the donor carrier density and flat-band potential, documenting an increase in donor density from     (dark) to     (illuminated), signifying efficient photogeneration and interfacial modulation. These results collectively affirm that Sn-doped nc-CdS/FTO heterojunctions possess tunable and robust optoelectronic properties, rendering them highly suitable for next-generation photodetectors and related applications.