<p>Cuprous oxide thin films were synthesized using the hydrothermal method at various copper precursor concentrations (0.025, 0.05, 0.1, 0.125, and 0.15 mg), followed by deionized water treatment at 100&#xa0;°C for 48 h. X-ray diffraction (XRD) results confirmed the polycrystalline nature of the copper oxide nanoparticles, with prominent diffraction peaks observed at the (220) plane. The crystal size increased from 25.2 to 33.8 nm as the copper concentration increased from 0.025 to 0.125 mg, before decreasing to 30.4 nm at 0.15 mg. Fourier transform infrared (FTIR) spectroscopy revealed characteristic functional groups associated with cuprous oxide synthesis, with a notable absorption at 630 cm⁻¹. Raman spectroscopy showed distinct peaks for Cu₂O at 220 and 665 cm⁻¹, with peak intensities increasing as the precursor concentration rose; however, the intensity decreased at 0.15 mg. Ultraviolet–visible (UV–Vis) spectroscopy revealed a red shift in the absorption peak as the precursor concentration increased. The energy bandgap decreased from 2.39 to 2.2 eV and marginally increased to 2.3 eV at higher concentrations, consistent with photoluminescence measurements. Atomic force microscopy (AFM) indicated changes in surface roughness, ranging from 4.5 to 53.3 nm, root mean square roughness, from 6 to 61.3 nm, and grain size, from 21 to 215 nm. Scanning electron microscopy (SEM) revealed truncated cubes and octahedral morphologies at lower concentrations, with irregular structures emerging at precursor concentrations above 0.125 mg. Conductivity increased with precursor concentration, leading to a decrease in resistivity. The optimal transparent oxide film, as indicated by the maximum figure of merit, was found at the 0.125 mg concentration. Additionally, the activation energy, determined from DC measurements, varied across concentrations: 0.035, 0.57, 0.06, 0.088, and 0.037 eV, respectively. The novelty of this work lies in the systematic tuning of Cu₂O thin film properties through controlled variation of copper precursor concentrations, using a simple, layer-by-layer, low-temperature hydrothermal process conducted without surfactants or additives. This approach enables precise control over the structural, optical, and electrical characteristics of the films. As a result, the synthesized Cu₂O thin films present themselves as promising candidates for use in low-cost optoelectronic devices, transparent conductive films, and photodetectors.</p>