Photovoltaic Properties of TiO2/Cu2O Heterostructure

TiO$_{2}$ is an $n$-type semiconductor with a wide band gap energy of 3.2 eV. It has been known for its photo catalytic effect and widely used in commercial products. Particularly in the growing photovoltaic industry, dye-sensitized solar cells (DSC) made by TiO$_{2}$ nanotube electrode have demonstrated to have conversion efficiency up to 6.9 {\%}. However, the TiO$_{2}$ nanotube based DSC is humbled by the nature of its electrolyte environment. Hence, an all solid-state core shell $p-n$ junction utilizing the TiO$_{2}$ nanostructure solar cell is of great potential to provide another solution for the rising photovoltaic industry. In order to fabricate heterostructures, cuprous oxide (Cu$_{2}$O), a $p$-type semiconductor with a direct band gap of 2.0 eV, is a promising candidate to form $p-n$ heterojunction with TiO$_{2}$. Here we present a method to achieve Cu$_{2}$O/TiO$_{2}$ $p-n$ junction through electrochemical approaches. A self-doping method is addressed on crystallized TiO$_{2}$ nanotubes to further improve the contact and device performance. The photovoltaic property of Cu$_{2}$O/TiO$_{2}$ hetero-structure is measured, giving an open circuit voltage $\sim $0.25 V, a short circuit current $\sim $0.33mA/cm$^{2}$, and filling factor $\sim $27{\%}. Although the efficiency is still low, it demonstrates promising potential to achieve low cost flexible photovoltaic device.