Room-temperature direct current magnetron sputtering was employed to prepare pristine and Cu+ doped NiOx films for perovskite solar cells (PSCs). Optimal power conversion efficiency (PCE) of about 15% was obtained with a 20 nm thick film with copper content of 5.7%. The solar cells based on as sputtered films demonstrated high reproducibility and stability. The origin of dramatically boosted photovoltaic performance of PSCs based on Cu doped NiOx was analysed from energy loss considerations. The optical, carrier transport as well as recombination losses were discussed. According to our results, PSC with Cu doped NiOx have lower recombination and transport loss which ensured the hysteresis free high efficiency.