In the past decade, perovskite semiconductors have rapidly emerged as a promising photovoltaic materials with high power conversion efficiency (PCE). State-of-the-art the of the perovskite solar cells (PSCs) achieved the certified power conversion efficiency (PCE) exceeding 22% with the mesoporous device architecture, which demonstrates the potential of the PSCs among the solar cell technologies. However, the planar heterojunction architecture which possesses distinct advantages such as thinner device, short & low temperature device fabrication, and low processing cost, still exhibited inferior device performance as compared to the mesoporous devices. In order to further improve the planar heterojunction PSCs, improved and optimized interface is critical. To optimize the interface, we developed Zn-doped NiOx films as the hole-transporting layer in PSCs. As is well known, NiOx is a promising hole-transporting material for optoelectronics because of its high hole mobility, good chemical stability, and high optical transparency. However, pristine NiOx has unsatisfactory electrical properties, which could deteriorate the device performance. By considering that Zn has a similar atomic size with Ni, we adopted Zn as a dopant of NiOx to employ the Zn-doped NiOx in the planar heterojunction PSCs. As a result, 5% Zn-doped devices exhibited overal PCE up to 12.39% with improvements of a Voc by 4.0%, a Fill factor (FF) by 8.8% and a PCE by 9.7%, as compared to that of pristine NiOx. In the presentation, details of morphology investigations, optoelectronic properties of the Zn-NiOx and its devices will be discussed.