Versatile Self‐Assembled Hole Transport Monolayer Enables Facile Processing Organic Solar Cells over 18% Efficiency with Good Generality

Abstract Simplifying solution‐processing of bulk‐heterojunction (BHJ) organic solar cells (OSCs) via efficient interfacial layers with good generality is in great demand for pushing their large‐scale applications. In this study, such a novel and cost‐effective self‐assembled monolayer (SAM) is reported herein as efficient hole transport layer (HTL) for high efficiency OSCs. The SAM‐structured 4‐(5,9‐dibromo‐7H‐dibenzo[c,g]carbazol‐7‐yl)butyl)phosphonic acid (DCB‐BPA) enables not only enhanced photon harvesting in the active layer but also minimized nonradiative recombination losses to improve interface charge extraction/transport. As a consequence, high short‐circuit current (≈28.07 mA cm⁻²) is achieved for PM6:BTP‐eC9 based OSCs to deliver a champion power conversion efficiency of 18.16%, among the highest values for OSCs using small organic HTLs to date. Importantly, good generality of this SAMs is demonstrated for representative high‐efficiency BHJ OSCs systems like PM6:Y6 and PM6:PC₆₁BM, outperforming conventional poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate)‐based counterparts. Excitingly, the SAM is applicable for large‐area HTL processing via immersion method, affording 16.59% efficiency for PM6:BTP‐BO‐4Cl based OSCs. This study highlights the great potential of engineered SAMs for facile large‐scale fabrication of high performance OSCs.