<p>In this work, Cu₂O/SnO₂, ZnO/Cu₂O, and NiO/ZnO heterojunctions were successfully fabricated by spray pyrolysis technique. The performance of the fabricated diodes was evaluated through structural, optical, and electrical characterizations. Scanning electron microscopy (SEM) results showed spherical, hexagonal, and uniform morphologies, depending on the layer being studied. The Tauc exponent (direct or indirect) was determined from the ultraviolet–visible (UV–Vis) spectrum and subsequently used as an input to calculate the bandgap of the individual layers. Hall effect measurements indicated that ZnO and SnO₂ showed an <i>n</i>-type conductivity, whereas NiO and Cu₂O exhibited <i>p</i>-type conductivity. Current–voltage (<i>I</i>–<i>V</i>) measurements showed the proper rectification curve and parameters such as rectification ratio (RR) and ideality factor (<i>n</i>). The RR showed values at 6 V of 314.39, 5.52, and 377.15, and an ideality factor of 9.77, 6.19, and 7.88 for Cu₂O/SnO₂, ZnO/Cu₂O, and NiO/ZnO, respectively. The Cu₂O/SnO₂, ZnO/Cu₂O, and NiO/ZnO diodes exhibit significant photo-response under halogen lamp illumination, with the NiO/ZnO heterojunction demonstrating the fastest transient response.</p> Graphical Abstract <p></p>