First-principles study on the doping effects of nitrogen on the electronic structure and optical properties of Cu2O

Recent experimental literature (Sol. Energ. Mat. Sol. Cells, 2012, 105, 192) has reported that nitrogen doped Cu2O is a possible material for novel intermediate band solar cells. The doping effects of nitrogen on the crystal structure, electronic structure, and optical properties of Cu2O have been studied by an ultrasoft pseudopotential plane wave method based on first-principles calculations. The results show that nitrogen doping slightly widens the band gap of Cu2O, and form an intermediate band in the gap located at about 0.9 eV from the VBM (or CBM). This intermediate band is predominantly formed by hybridization between the N-2p states and the Cu-3d states. N-doped Cu2O is very likely to absorb at a maximum across the solar light spectrum, from the near infrared region to the ultraviolet region. Based on these results, N-doped Cu2O is considered to be a perfect intermediate band material for a novel kind of solar cells.