Polymer-templated Molecular Ordering of Hole Transport Layers Enables High Efficiency and Stable Organic Photovoltaics
Carbazole phosphonic acid-based self-assembled molecules (SAMs) serve as effective hole-selective contacts in organic solar cells (OSCs), yet their molecular packing and aggregation behavior during solution processing remain difficult to control, limiting hole transport and device durability. This study introduces a polymer-templated self-assembly strategy to regulate molecular organization by one-step spin-coating a blend of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and PEDOT:PSS. The polycationic PEDOT+ framework acts as a template, providing supplementary anchoring interactions that promote ordered molecular arrangement and suppress unfavorable agglomeration. Pronounced face-on orientation and enhanced structural coherence of 2PACz within the polymer matrix are evidenced. The templated ordering improves vertical charge transport, interfacial homogeneity, and film morphology. In binary OSCs based on PM6:BTP-eC9, the hybrid hole transport layers (HTLs) yield a champion power conversion efficiency (PCE) of 20.26%, with an open-circuit voltage (VOC) of 0.874 V, a short-circuit current (JSC) of 28.97 mA cm-2, and a fill factor (FF) of 80.02%. Devices incorporating hybrid HTLs exhibit exceptional operational stability, retaining over 90% of initial PCE (T90) after 405 h of continuous operation at the maximum power point (MPP). This work establishes polymer-directed SAM assembly as a scalable route to simultaneously optimize nanoscale molecular packing, interfacial energetics, and long-term device stability for high-performance OSCs.