In a high efficiency CIGS solar cell, we observed a MoSe2, layer at the interface by SIMS, TEM and X-ray diffraction, MoSe2, had a layer structure and the layers were oriented perpendicular to the Mo layer. The MoSe2, contributes to the improvement of adhesion at the CIGS/Mo interface. The effects of the MoSe2, layer on the electrical and photovoltaic properties of CIGS solar cells were investigated. The CIGS/Mo heterocontact, including the MoSe2, layer, is not Schottky-type, but a favorable ohmic-type by the evaluation of dark I-V measurement at low temperature. A characteristic peak at 870 nm is observed in the differential quantum efficiency of a solar cell with a CIGS thickness of 500 nm. This peak relates to the absorption of the MoSe2 layer. The band gap of MoSe2, is calculated to be 1.41 eV from the absorption peak.