Nickel oxide (NiOx) is a promising hole transport layer (HTL) for perovskite solar cells (PSCs), as it combines good chemical stability, high broadband optical transparency, and a high work function. Excellent power conversion efficiencies (PCEs) have already been reported using solution-processed NiOx. However, solution-based techniques usually require high-temperature postannealing to achieve the required HTL properties of NiOx, which jeopardizes its use for many applications, such as monolithic tandem solar cells. To resolve this issue, we developed room-temperature-sputtered NiOx and demonstrated p–i–n PSCs with 17.6% PCE (with negligible hysteresis), which are comparable to the best PSCs using sputtered and annealed NiOx without heteroatom doping. Through detailed characterization and density functional theory (DFT) analysis, we explored the electrical and optical properties of the obtained NiOx films and find that they are strongly linked with the specific defect chemistry of this material. Finally, in view of its use in perovskite/silicon tandem solar cells, we find that direct sputtering on random-pyramid textured silicon wafers results in highly conformal NiOx films.