A Self‐Assembling Composite Structural Design for the Conversion of Hydroxyl‐Anchored Bonds Obtains High Efficient and Stable Perovskite Solar Cells

Abstract Self‐assembled monolayers (SAMs) serve as the hole‐transporting layer (HTL) in perovskite solar cells, yet their instability on indium tin oxide (ITO) substrates poses a challenge in practical. The typical SAMs are susceptible to solvents during the perovskite layer deposition process which can result in being washed or dislodged, thereby impeding the formation of a dense SAM. Here, a novel guanidine‐modified polyurethane siloxane elastomers is synthesized to enhance the anchoring capability of SAMs on ITO, which exhibits strong interactions with [2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl] phosphonic acid (MeO‐2PACz) SAMs, to co‐construct a self‐assembled composite structure (SACS). By utilizing this anchor strategy, the weakly bonded MeO‐2PACz adhering to ITO can be converted into a strongly bonded form, thereby curtailing the migration of MeO‐2PACz on the ITO surface during the spin‐coating process, as well as inhibiting shedding that may occur due to solvent washing during the device preparation process. SACS SAMs heighten the charge collection ability of SAMs and suppress interfacial recombination, as well as enhance the growth of the upper perovskite layer. Finally, the SACS‐based SAMs device with a power conversion efficiency of 26.37%. The unencapsulated device based on SACS SAMs can be stored for at least 5000 h with little degradation in performance.