Phenothiazine-Based Self-Assembled Monolayers for Highly Efficient and Stable Full Air-Fabricated Inverted Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved remarkable advances in photovoltaic performance; however, their severe performance degradation during air-based fabrication and poor long-term service durability have become major bottlenecks hindering their commercialization. NiO_x/SAM layers are plagued by disordered molecular packing and inadequate surface coverage, while perovskite films fabricated in air are highly susceptible to oxidative degradation. These issues collectively aggravate interfacial non-radiative recombination and accelerate device degradation. To address these challenges, a phenothiazine (PTZ)-based self-assembled monolayer (SAM) molecule was designed and synthesized to enhance the air-processing efficiency and stability of PSCs. The phosphoric acid functional groups interactions with the NiO_x substrate and regulates the valence state of nickel, while the sulfur-containing functional groups on the butterfly-shaped PTZ skeleton effectively passivate uncoordinated lead and improve the crystallization quality of perovskite films. Notably, the Me-4PACz/PTZ1 co-assembly system optimizes the energy band alignment between the SAM and the perovskite layer, and the PTZ moiety simultaneously suppresses the oxidation of iodide ions and formamidinium cations. Consequently, the optimized fully air-processed PSCs deliver a power conversion efficiency (PCE) of 26.1% and demonstrate excellent long-term stability under continuous illumination. This interface engineering strategy enables the fabrication of high-performance, stable PSCs that are compatible with environmentally benign large-scale manufacturing.