The effect of the Gd/Sn composition ratio of Cu₂Sn_1-xGd_xS₃ is examined. The films are fabricated on glass substrates in a sulfur atmosphere via the spin coating. The influence of the Gd/Sn composition ratio on the structural, morphological, optical, and electrical properties of the films is investigated using X-ray diffraction, FESEM, UV-Vis, and Hall effect. XRD patterns for the films revealed that all films have a monoclinic polycrystalline. The morphological and optical properties of the films show the formation of spherical grains and polygonal structures with an energy band in the range of 2.10–1.50 eV. The electrical properties of the films are changed by increasing the Gd/Sn composition ratio in the film. Furthermore, the Cu₂Sn_1-xGd_xS₃/CdS heterojunction solar cell was modeled by SCAPS-1D. The optimized conditions yielded exceptional photovoltaic parameters, achieving an open-circuit voltage of 0.7885 V, short circuit current density of 41.09 mA/cm², fill factor of 85.30%, and an efficiency of 27.3%.

Thin films of Cu2Sn1−xGdxS3 were prepared on soda-lime glass substrates using spin coating in a sulfur-rich environment. We investigated how doping Cu2SnS3 with gadolinium (Gd) affected its structural, morphological, and optical properties using X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), and UV-Vis spectroscopy. XRD showed that all samples had a polycrystalline monoclinic structure, while FE-SEM revealed a mix of spherical and polygon-shaped grains. Optical analysis indicated an energy gap ranging from 2.10 to 1.50 eV, increasing with higher Gd content. The films exhibited increasing transmittance with longer wavelengths in the UV-Vis region. When tested for photocatalytic activity, the Cu2Sn1−xGdxS3 films effectively degraded methylene blue (MB) dye under visible light within 220 minutes. The Cu2Sn0.25Gd0.75S3 film showed the highest degradation efficiency (90.77%) with a rate constant (k) of 0.093 min−1. Adjusting the pH of the dye solution improved the performance, reaching 90.77% degradation efficiency at pH 10, compared to 41.25% and 61.94% at pH 4 and 7, respectively. Tests with scavengers EDTA-Na, IPA, and BQ resulted in degradation efficiencies of 61.78%, 78.24%, and 43.56%, respectively, highlighting that the highest efficiency (90.77%) occurred without scavengers. The results show promising potential for these films in treating pollutants in industrial and domestic wastewater systems.