This study presents the influence of pH control agents and pH value on the physical properties of ZnO thin films obtained by chemical bath deposition. ZnO thin films were synthesized on glass substrates using precursor solutions of different pHs prepared from two bases: sodium hydroxide (NaOH) and ammonia (NH₃). The effect of pH values on the morphological, structural, and optical properties of ZnO thin films was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV–Visible spectroscopy. XRD results showed that all the synthesized ZnO thin films are polycrystalline and crystallize in a hexagonal wurtzite structure. The crystallite size, calculated using the Debye–Scherrer formula, varied from 10.50 nm to 11.69 nm for ZnO thin films obtained with NH₃ and from 20.79 nm to 27.76 nm for those obtained with NaOH. FTIR analysis confirmed the presence of functional groups. SEM images indicated that not only the base but also the pH affects the morphology of the films, giving rise to different granular shapes. Overall, the ZnO thin films obtained with NaOH looked more mesoporous compared to those obtained with NH₃. Optical characterization results showed that whatever the base used, the pH of the precursor solution affected the ZnO thin film transmittance. Films synthesized with NH₃ exhibited the best transmittance (80%) at pH 8.5, while the best transmittance (81%) of films synthesized with NaOH was obtained at pH 8 in the visible region. Based on optical and morphological properties, ZnO films obtained from NH₃ at pH 8.5 are found to be more suitable as photoanodes in dye-sensitized solar cells.

The collection and transport of charges at the electrodes are the main factors limiting the efficiency of organic solar cells. Zinc oxide (ZnO) in nanostructured form helps to overcome this problem by introducing a ZnO buffer layer between the photoanode and the donor material. To achieve this, the ZnO thin film must exhibit good crystallinity, along with good electrical conductivity and high optical transparency in the visible range. The aim of this work is to investigate the effect of precursor sources and precursor concentrations on the structural, morphological, and optical properties of ZnO thin films. Three different precursor sources have been used: zinc acetate, zinc chloride and zinc nitrate. In each deposition solution, the precursor concentration varied from 0.1 M to 0.3 M. The ZnO films were deposited on glass substrates and all the films were annealed at 400°C for 3 hours. The structural, morphological and optical properties of deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible spectroscopy respectively. XRD results showed that, regardless of the precursor source, all the ZnO films are polycrystalline with a hexagonal wurtzite structure. ZnO films obtained from acetate and nitrate sources crystallize preferentially along (002) and the peak intensity increases as the precursor concentration increases. SEM images showed that all the ZnO films are homogeneous, but films deposited from zinc acetate and zinc nitrate looked more compact and smoother than those obtained with zinc chloride which looked porous. UV-visible spectroscopy results revealed that the films transmittance depends both on precursor source and concentration. ZnO thin films deposited from zinc acetate at 0.3M concentration exhibit the best transmittance of 95% due to their smooth and uniform surfaces. The band gap of ZnO obtained from the zinc acetate precursor decreases with increasing solution concentration. It is found to be 3.29 eV, 3.26 eV, and 3.22 eV for concentrations of 0.1 M, 0.2 M, and 0.3 M, respectively. It therefore appears that ZnO films obtained from zinc acetate can be used as an electron transport layer for solar cells as they exhibit the best crystallinity and the highest transmittance.

Using electrochemical impedance spectroscopy (EIS), a technique that analyzes the electrical response of a system subjected to a sinusoidal disturbance in order to probe its physicochemical properties, this study determined an optimal molar ratio of 1:7 between ethylene glycol (EG) and potassium iodide (KI). This composition significantly improves the electrochemical performance of the KI, EG, and I₂ electrolyte for photovoltaic applications. Four formulations with KI:EG molar ratios of 1:5, 1:7, 1:9, and 1:11 were synthesized. The amount of diiodine (I₂) was fixed at 0.1 mol% relative to the amount of KI. These electrolytes were then characterized by EIS. The series resistance (Rs), charge transfer resistance (Rct), diffusion resistance (Rw), CPE (constant phase element) parameter, and exponent (n) were extracted and compared. The results show that the formulation with KI:EG = 1:7 has the lowest Rct (3.054 Ω) and Rw (7.296 Ω) values, indicating optimal redox kinetics and improved ion transport within the electrolyte. This molar ratio corresponds to a minimum Rs value (5.612 Ω), indicating reduced series resistance. The mechanisms of solvation, viscosity, and ion diffusion are examined. This work, based exclusively on screening by electrochemical impedance spectroscopy (EIS), highlights the decisive role of solvent composition in electrolyte performance. It identifies an optimal molar ratio window that strikes a balance between redox efficiency and ion mobility, with a view to improving DSSC performance.