Nitrogen-Doped Nickel Oxide as Hole Transport Layer for High-Efficiency Inverted Planar Perovskite Solar Cells

Nickel oxide (NiOx) is commonly used as a hole transport layer (HTL) in inverted-structure (p-i-n) planar perovskite solar cells (PSCs), playing a critical role in the device performance. However, a solution-processed NiOx HTL usually suffers from low electrical conductivity, consequently resulting in an inefficient interfacial charge transport. Herein, a facile method is developed to prepare nitrogen-doped NiOx (N:NiOx), which is applied as a novel HTL in inverted PSCs for the first time, achieving a decent improvement in average power conversion efficiency (PCE) from 15.28% to 17.02%. The effects of nitrogen doping on the electrical conductivity and the energy band structure of NiOx as well as the quality of CH3NH3PbI3 perovskite layer atop are studied by a series of characterizations, revealing that nitrogen doping leads to increased electrical conductivity and lowered valence band energy of the NiOx film, which are beneficial to interfacial hole transport. In addition, the trap density of the CH3NH3PbI3 perovskite film atop N:NiOx layer is reduced, prohibiting unfavorable charge recombination.