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

Nickel oxide (NiO x ) 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 NiO x 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 NiO x (N:NiO x ), 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 NiO x as well as the quality of CH 3 NH 3 PbI 3 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 NiO x film, which are beneficial to interfacial hole transport. In addition, the trap density of the CH 3 NH 3 PbI 3 perovskite film atop N:NiO x layer is reduced, prohibiting unfavorable charge recombination.