In this work, p-type NiO thin film was applied as a buffer layer in the back contact for CdTe thin film solar cell fabrication. The NiO layers were prepared by electron beam evaporation. By optimizing NiO layer thickness in the back contact a CdTe solar cell with an efficiency of 12.17% and an open-circuit voltage V-oc of 790 mV has been fabricated. X-ray photoelectron spectroscopy study showed that NiO has a staggered band alignment with CdTe. Such an electronic band structure alignment allows smooth hole transport from CdTe to NiO and at the same time NiO acts as a surface field layer to reduce electron recombination at the back contact interface, thus leading to improved Voc. This study also demonstrates that by employing NiO as a buffer layer, much less Cu was needed for the CdTe solar cell fabrication and the cell device stability had been significantly enhanced compared to the CdTe solar cell with a conventional Cu/Au bimetal layer as the back contact.