In lead halide perovskite solar cells (PSCs), the valence band maximum of NiOx matches well with that of MAPbI(3) or FAPbI(3), while its conduction band minimum is much higher than that of the perovskite materials. Consequently, it can serve the function of hole transport layers (HTL), as well as light-in window of p-i-n inverted planar PSCs owing to its large band gap of 3.7 eV. In this work, MAPbI(3) and mixed cation FA(0.85)MA(0.15)Pb(Br0.15I0.85)(3) devices with room temperature solution processed NiOx as HTL were fabricated in a typical device structure of "ITO\NiOx\Perovskites\PC61BM\Zirconium (IV) Acetylacetonate\Ag". Both kinds of devices exhibit excellent performance with a champion cells conversion efficiency of 19.45% and 17.77% for the FAMA and the pure MA, respectively. The hole extraction ability of NiOx as HTLs was extensively characterized by different techniques, and it was confirmed that room temperature solution processed NiOx serves as an excellent HTL in the inverted planar PSCs. (C) 2018 Elsevier B.V. All rights reserved.