Multifunctional Phenothiazine-Based Self-Assembled Monolayer as a Hole-Selective Contact for Efficient Wide-Band-Gap Perovskite Solar Cells

Wide-band-gap (WBG) perovskite solar cells (PSCs) are key components of tandem devices, offering the potential to exceed the Shockley-Queisser limit. Despite their promise, WBG PSCs often suffer from significant open-circuit voltage (<i>V</i>_oc) deficits, primarily caused by nonradiative recombination and mismatched interfacial energy alignment. Here, we present a novel multifunctional molecule, [4-(2-cyano-10<i>H</i>-phenothiazin-10-yl)butyl]phosphonic acid (CN-4PAPT), specifically designed to address these challenges. CN-4PAPT functions as a superior hole-transport material with well-aligned energy levels and as a passivating agent to simultaneously reduce interface defects. Additionally, the inclusion of the cyano (-CN) functional group enhances the molecule's dipole and also the binding interactions with both perovskite and transparent conductive oxide substrates, thus contributing to improved device stability. The integration of CN-4PAPT into WBG PSCs (1.67 eV) yields a certified power conversion efficiency of 22.66%. The device retained over 95% of its initial efficiency after 500 h of maximum power point tracking under one-sun illumination.