Nickel oxide (NiOx) is a promising hole transport material (HTM) for perovskite photovoltaics owing to its chemical stability and low cost. However, most NiOx based solar cells deliver relatively weak performance because of its insufficient electrical property and interfacial contact. In this work, a self-formed PbI2/NiOx interface was developed to stabilize the Ni3+ centers, which was beneficial for electrical transport and band alignment in perovskite solar cells. Combined with ultraviolet ozone treatment (UVO) and sequential deposition, the density of Ni3+ centers was greatly increased and could be stabilized by the PbI2 interface. These merits contributed coordinately to the fast hole extraction and low energy loss across the PbI2/NiOx interface, yielding power conversion efficiencies (PCEs) of over 19 %.