Self‐Assembled Bi‐Monolayer for Inverted Perovskite Solar Cells

Abstract Inverted perovskite solar cells have emerged as leading candidates in next‐generation photovoltaics due to their compatibility with tandem integration, high efficiency, and better stability. A crucial factor in boosting their power conversion efficiency (PCE) lies in optimizing buried interfaces via self‐assembled monolayers (SAMs), with (4‐(3,6‐Dimethyl‐9H‐carbazol‐9‐yl)butyl)phosphonic acid (Me‐4PACz) being the state‐of‐the‐art SAM. Nevertheless, its poor substrate coverage and limited surface wettability, due to weak phosphonic acid chemisorption and surface polarity reduction, impair device reproducibility. To address this, a bilayer SAM (bi‐SAM) approach is proposed by sequentially assembling Me‐4PACz and 3‐mercaptopropyltriethoxysilane (MPTS) on NiO _X . The multidentate binding of MPTS effectively launches a successful assembly on NiO _X , while its thiol terminal enhances surface polarity and coordinates with undercoordinated Pb ² ⁺, enabling enhanced surface wettability and improved perovskite film formation. This synergistic bi‐SAM interface promotes uniform crystal growth, reduces interfacial defects, and minimizes energy band offsets. Devices fabricated with a bi‐SAM configuration exhibit a PCE of 25.19 %, along with enhanced open‐circuit voltage and fill factor. Furthermore, the bi‐SAM‐based devices demonstrate excellent operational stability under high temperature, high humidity, and continuous light soaking, confirming the robustness of the bi‐SAM strategy.