Modification of Ultrathin NPB Interlayer on the Electronic Structures of the CH3NH3PbI3/NPB/MoO3 Interface

Modification of the ultrathin N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB) insertion layer on the electronic structures of the CH3NH3PbI3 (MAPbI(3))/MoO3 interfaces is investigated using ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It is found that when an ultrathin NPB insertion layer of 16 angstrom is inserted between MAPbI(3) and MoO3, the chemical reaction between the latter two can be effectively suppressed, and a favorable energy-level alignment is achieved. The valence band maximum (VBM) or highest occupied molecular orbital (HOMO) at the MAPbI(3)/NPB/MoO3 interface facilitates the hole transportation from the MAPbI(3) layer through the NPB layer toward the NPB/MoO3 interface. As a result, the holes can be efficiently extracted to the hole collection electrode due to the small energy offset between the conduction band minimum (CBM) of MoO3 and the HOMO of NPB. Therefore, the modification by the ultrathin NPB interlayer on the electronic structures of the MAPbI(3)/MoO3 interface can greatly improve the hole extraction and thus enhance the power efficiency of the corresponding solar cells.