ZnSe as a surface passivation layer in quantum dot-sensitized solar cells plays an important role in preventing charge recombination and thus improves the power conversion efficiency (PCE).However,as a wide bandgap semiconductor,ZnSe cannot efficiently absorb and convert long-wavelength light.Doping transition metal ions into ZnSe semiconductors is an effective way to adjust the band gap,such as manganese ions.In this paper,it is found by the method of density functional theory calculation that the valence band of ZnSe moves upward with manganese ions doping,which leads to acceleration of charge separation,wider light absorption range,and enhancing light harvesting.Finally,by using ZnSe doped with manganese ions as the passivation layer,the TiO2/CdS/CdSe co-sensitized solar cell has a PCE of 6.12％,and the PCE of the solar cell increases by 9％ compared with the undoped one (5.62％).