Sulfur‐Modulated Fully‐Conjugated Self‐Assembled Monolayers for Synergistic Dual‐Interface Optimization in Inverted Perovskite Solar Cells

ABSTRACT To achieve high efficiency and stability in inverted perovskite solar cells (PSCs), it is essential to ensure uniform self‐assembled monolayers (SAM) coverage on the substrate and to passivate defects effectively at the buried interface of perovskite. Herein, two sulfur‐modulated fully‐conjugated SAMs, 4‐(bis(4‐methylthiophenyl)amino)phenylphosphonic acid (SMe‐TPA‐PA) and 5‐(4‐bis(4‐methylthiophenyl)amino)phenyl) thiophenylphosphonic acid (SMe‐TPA‐ThPA) are developed for inverted PSCs by employing substituent regulation and linker adjustment. The incorporation of methylthio substituents in both SAMs enhances their defect‐passivation capability at the interface. Moreover, the thiophene linker in SMe‐TPA‐ThPA strengthens intermolecular interactions, improves energy level alignment with the perovskite, enables stable and uniform molecular coverage on ITO, and facilitates efficient hole extraction. As a result of synergistic dual‐interface modification of the ITO/perovskite system, inverted PSCs based on SMe‐TPA‐ThPA and SMe‐TPA‐PA achieve significantly improved power conversion efficiencies (PCEs) of 26.52% and 25.40%, respectively, surpassing the control device based on methoxyl‐substituted SAM (OMe‐TPA‐PA, 24.31%). Remarkably, devices incorporating SMe‐TPA‐ThPA also exhibit exceptional operational stability, retaining 91.8% of their initial PCE after 1700 h of continuous light soaking and 91.2% after 1700 h of continuous thermal aging at 65 °C.