Electron Beam‐Processed Nickel Oxide Coupled with a <i>p</i> ‐Type Small Molecule for Efficient and Stable Inverted Perovskite Solar Cells

Abstract Nickel oxide (NiO x ) is a promising hole transport layer (HTL) for commercial‐scale perovskite solar cells (PSCs) due to its low cost and robust chemical stability. However, the direct contact between perovskite and NiO x leads to interfacial stress and redox reactions, as well as trap‐assisted charge recombination issues, which significantly limit the performance of PSCs. Here, a bilayer HTL coupling strategy is proposed by introducing a low‐cost p ‐type small molecule material N,N“‐diphenyl‐N,N”‐di(3‐methylphenyl)‐1,1′‐biphenyl‐4,4′‐diamine (TPD) as an interfacial layer to collaboratively construct a hole transport system with electron beam‐processed NiO x , which optimizes energy level alignment and facilitates hole extraction capability. Meanwhile, the introduction of TPD regulates the perovskite crystallization process and alleviates residual stress. Furthermore, TPD protects the perovskite layer by preventing adverse reactions between the perovskite and NiO x . With these advantages, the E‐beam NiO x /TPD‐based inverted PSCs achieve a record efficiency of 25.80%, retaining 92% of their initial efficiency for 197 h. The flexible device achieves an efficiency of 23.69%, maintaining 91% of the initial efficiency after 8000 bending cycles with a radius of 4 mm.