Schottky barrier is a fundamental problem when contacting n-type indium tin oxide with p-type hydrogenated amorphous silicon due to their mismatched work functions in silicon heterojunction solar cell. Here, we developed a facile and effective method to modify the electrical properties of ITO/a-Si:H(p) contact by thermal evaporation an ultrathin MoOx buffer layer. The transient photo-conductance decay measurements showed that both effective carrier lifetime and implied open-circuit voltage increased abruptly after inserting an ultrathin MoOx buffer layer, from 1.43 ms to 2.28 ms and 735 mV to 744 mV, respectively, which is mainly attributed to modification of MoOx. buffer layer on the Schottky barrier at the interface of ITO/a-Si:H(p) contact. By modulating the thickness of MoOx buffer layer, the MoOx based SHJ solar cell illustrated a champion efficiency up to 21.8%, companying with an absolute V-oc gain over 8 mV, and fill factor gain over 1.5%, respectively.