Review of the development of copper oxides with titanium dioxide thin-film solar cells

Copper oxide-titanium dioxide (TiO2) p–n junctions are promising materials for photovoltaic devices and may reduce production costs due to their low cost and inexpensive production methods compared with silicon solar cells. The present review compares solar cells made with copper oxides combined with TiO2–TiO2/Cu2O and TiO2/CuO heterojunctions, and “cascade heterojunction systems.” First, we describe the main properties of titanium (iv) dioxide (TiO2), cuprous oxide (Cu2O), and cupric oxide (CuO), and their potential applications. Next, we explain the concept of copper oxide and TiO2 heterojunctions. We summarize and present the photovoltaic characteristics (efficiency, fill factor, circuit current density, and open circuit voltage), thickness, preparation method, and electrode type for solar cells comprising copper oxide and TiO2. The efficiency of the solar cells ranged from 0.0005% to 1.62%. The thickness of the TiO2 and cupric oxide layers ranged from 0.06 to 16 µm, and from 0.18 to 1.5 µm, respectively, depending on the fabrication method. Additionally, we review and discuss the available combinations of copper oxide with other materials (Cu2O with ZnO, CuO with ZnO, and CuO with Si), as well as the effect of the thickness of the copper (i) oxide and copper (ii) oxide on the solar cell performance. Finally, we present aspects to improve the conversion efficiency of heterojunction solar cells with copper oxides combined with TiO2. This review will be useful for the construction and further development of thin-film solar cells.