<p>Cuprous oxide (Cu₂O)-based photocathodes have been explored intensively for solar water splitting applications because of their favorable band gap and elemental abundance. Despite these favorable properties, the practical efficiencies of these photocathodes are substantially hindered by high rates of charge recombination, which ultimately affect their photo-conversion efficiency and the overall performance in photoelectrochemical (PEC) water splitting systems. To address this issue, a four-layer tandem heterostructure FeOOH/Cu₂O/HfO₂/MoO_x was synthesized by the fabrication process consisting of electrodeposition and radio frequency (RF) magnetron sputtering method. Various physical and microscopic characterization techniques were employed to observe the surface modifications and optical properties of Cu₂O film after the heterostructure. Under 100 mW/cm² AM 1.5 G illumination, the amperometry, voltammetry and impedance photoelectrochemical tests were employed on Cu₂O, FeOOH/Cu₂O, FeOOH/Cu₂O/HfO₂ and FeOOH/Cu₂O/HfO₂/MoO_x photocathodes in a sodium sulfate (Na₂SO₄) solution (pH 6.9). The optimized heterostructure exhibited a progressive improvement in photocurrent (− 2.53&#xa0;mA/cm² at 0&#xa0;V vs. RHE), alongside enhanced stability in the performance of the noble metal-free Cu₂O photocathodes. In the multijunction photocathode, the tuned nanolayers of FeOOH, HfO₂, and MoO_x act as a hole transport layer, charge separation layer and electron extraction layer, respectively. Moreover, we conducted a detailed investigation into the specific effects of these nanolayers on the performance metrics of the Cu₂O photocathode, presenting insight into the role that each layer plays in enhancing the overall efficiency of the device. This study provides a novel method and strategy to enhance the photoelectrochemical performance of noble metal and sulfide-free Cu₂O photocathodes. </p>