Zinc oxide (ZnO) is a wide bandgap semiconductor with optoelectronic and photocatalytic properties, which depend on its optical, structural, and morphological characteristics. In this study, we synthesized ZnO thin films by chemical bath deposition (CBD) and then thermally annealed them at 400 °C and 600 °C to evaluate the effect of thermal treatments. We characterized their structural, optical, morphological, and chemical properties using X-ray diffraction (XRD), UV–Vis spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The optical bandgap values were 3.20 eV for the as-grown thin films, and 3.23 eV and 3.21 eV after annealing at 400 °C and 600 °C, respectively. SEM micrographs revealed a change from elongated agglomerates in the as-grown thin films to uniform flower-like structures after annealing at 600 °C. XPS analysis confirmed ZnO formation in all samples, and we detected residual precursor species only in the as-grown thin films, which were completely removed by annealing at 600 °C. These results demonstrate that the CBD synthesis of ZnO can tune its optical and morphological properties through thermal annealing, making it suitable for optoelectronic, sensing, and photocatalytic applications.

It is well established that solar cells convert solar energy into electrical energy, thereby contributing to environmental sustainability by reducing dependence on fossil fuels. In the present study, thin films composed of different materials were employed with the aim of mitigating efficiency losses in polycrystalline solar cells, which operate at a specific output voltage of 0.5 V. To evaluate the performance of these films, solar irradiation tests were conducted in Ciudad Obregón, Sonora, Mexico, during periods that accounted for both seasonal and diurnal variations in solar irradiance. The experiments were carried out during peak solar hours, a time frame that represents the conditions of highest thermal stress and irradiance intensity and is therefore relevant for analyzing heat-related efficiency losses. The thin films investigated included silver nanoparticles, copper sulfide, potassium permanganate, zinc sulfide, and lead sulfide. An improvement of 0.5% in open circuit voltage gain was achieved, corresponding to a temperature difference of 13.5 °C between the hottest and coolest cells. Notably, the cells that exhibited efficiency enhancement were those incorporating silver nanoparticles and potassium permanganate, with varying deposition times in the chemical bath. Among these, the latter demonstrated superior performance (KMnO₄ performed best). So, the objective of this experimental work was to assess the effect of various thin film coatings on the performance of polycrystalline silicon solar cells under natural sunlight.