Pentacene thin film on CH3NH3PbI3 was studied by in-situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy to determine their interfacial energy level alignment. A 0.2 eV downward band bending together with a 0.1 eV interfacial dipole was found at the pentacene side, whereas there was no band bending found at the CH(3)NH(3)Pbl(3) side. The offset between CH3NH3PbI3 Valance Band Maximum (VBM) and pentacene Highest Occupied Molecular Orbital (HOMO) and that between CH3NH3PbI3 Conduction Band Minimum (CBM) and pentacene Lowest Unoccupied Molecular Orbital (LUMO) was determined to be 0.7 and 1.35 eV, respectively. The band alignment at this interface is favor of efficient hole transfer, which suggests pentacene as a viable HTL candidate to be explored in perovskite solar cells. (C) 2016 Elsevier B.V. All rights reserved.