Nitrogen-doped cuprous oxide as a p-type hole-transporting layer in thin-film solar cells
We demonstrate the potential of a nitrogen-doped cuprous oxide (Cu2O:N) film as a p-type hole-transporting layer for photovoltaic devices. To reduce back-contact resistance and create an electron-reflecting back surface field, high carrier density and appropriate work function are desired for the layer. Its electrical and optical properties can be appropriately tuned via nitrogen-doping to create a semi-transparent tunnel junction to a back-contact. We fabricate Cu2O-based heterojunction thin-film solar cells and insert a 20 nm-thick Cu2O:N hole-transporting layer between a silver back-contact and a Cu2O light-absorbing layer. The insertion of a 20 nm-thick Cu2O:N layer results in sizeable enhancements of fill-factor and power conversion efficiency of the solar cells. Cu2O:N thin-films may also be useful in other photovoltaic material systems, improving their back-contact properties as well as widening the range of possible back-contact materials.