Unveiling Key Limitations of ZnO/Cu₂O All-Oxide Solar Cells through Numerical Simulations

ZnO/Cu2O solar cells emerge as one of the most promising technologies with significant potential when considering the Schockley–Queisser limit (SQL) and taking into consideration other important factors such as materials abundance, low-cost fabrication, suitable band alignment, and the possibility of having semitransparent devices. However, the actual efficiency values obtained are still far from the expected theoretical values. The reasons behind this are mainly attributed to the low control over the properties of the oxides and the lack of knowledge on how the final device performance is affected by both materials properties and cell architecture. To close this gap, we explore the working mechanism of ZnO/Cu2O junctions thanks to numerical simulations based on the SCAPS-1D software. In particular, the present study aims at investigating the limiting factors and key parameters that affect the behavior of the ZnO/Cu2O junctions. The impacts of altering the absorber and collector film thickness, the diffusion length, side illumination, and the concentration of defects at the junction interface are explored. The data indicate that the thickness of Cu2O is critical for the output results when correlated with the diffusion length, which in turn is strongly affected by the oxide deposition technique and conditions. Bifacial illumination demonstrates a significant enhancement of the power conversion efficiency, while defects at the interface inhibit the charge generation drastically and enhance recombination at the subcell level. This study provides an overarching view of cell behavior and different routes toward the improvement of ZnO/Cu2O devices.