Band engineering of Ni_1-xMg_xO alloys for photocathodes of high efficiency dye-sensitized solar cells

Density functional theory calculations were carried out for Ni _1-xMg_xO alloys using both GGA+U method and hybrid exchange-correlation functional HSE06. We find that the band gap of Ni_1-xMg_xO is a nonlinear function of MgO concentration with a strong bowing behavior at high Mg content. Band edge alignment is determined using heterojunction superlattice models. The valence-band-maximum of Ni_1-xMg_xO is shown to be tunable within a range of 0.90 eV. By comparing with the highest-occupied- molecular-orbital levels of some of the most widely used dye molecules, we propose that Ni_1-xMg_xO is a promising alternate to replace NiO photocathode in dye-sensitized solar cells with an enhanced open-circuit voltage and transparency of cathode films.