Structural, Optical, and Photoelectrochemical Evaluation of TiO₂/SnO₂/Zn₀₃Cd₀₇S Multilayer Heterostructures for Enhanced Solar-driven Applications

This study presents the fabrication and characterization of a multilayer TiO₂/SnO₂/Zn₀₃Cd₀₇S thin film heterostructure for optoelectronic applications. This heterostructure system was prepared by thermochemical decomposition method. Structural analysis via X-ray diffraction (XRD) confirmed the polycrystalline nature of the films with distinguishable peaks for each constituent layer. The incorporation of Zn₀₃Cd₀₇S into the TiO₂/SnO₂ system led to a reduction in crystallite size and an increase in microstrain, suggesting enhanced lattice distortion and interfacial stress conducive to charge separation. Surface morphology assessed through SEM and AFM revealed uniform grain distribution and improved film compactness in the heterostructure. Optical characterizations conducted by UV-Vis absorption spectroscopy and Tauc analysis revealed that the band gap energy in the pristine SnO₂ and TiO₂ material was 3.20 eV and 3.10 eV, respectively, and reduced to 2.25 eV in the resulting composite, which improves the visible light absorption. The refractive index and extinction coefficient were improved in the heterostructured film, and light interaction with matter also improved. Mott–Schottky analysis revealed that all samples are n-type with TiO₂/SnO₂/Zn₀₃Cd₀₇S having a higher flat-band potential (+0.22 V) and lower donor concentration. Such shifts indicate a better band bending and carrier separation. Under illumination, the I–V characteristics showed an increase in photocurrent and a reduction in the dark current in the heterostructure, emphasizing its enhanced photoelectrochemical performance. The overall multilayer TiO₂/SnO₂/Zn₀₃Cd₀₇S system has desirable structural, optical, and electronic characteristics, rendering it a feasible next-generation photovoltaic and photoelectrochemical application.