Polarized Heterojunction in a Doubly Doped Layer‐by‐Layer Structure to Obtain an Organic Photovoltaic Device of 20.5% Efficiency

Abstract Achieving efficient double doping in organic photovoltaic (OPV) devices is hindered by parasitic interactions between p‐ and n‐type dopants, which lead to radical accumulation, deep‐level traps, and reduced device performance. Herein, we report a solvent‐mediated infiltration doping strategy to overcome these challenges based on D18/L8‐BO layer‐by‐layer (LBL) system. By incorporating F4TCNQ as the p‐type dopant in the donor layer and DMBI as the n‐type dopant in the acceptor layer, with controlled infiltration via a chlorobenzene:ethanol (CB:EtOH) binary solvent mixture, we constructed a polarized heterojunction that mitigates dopant crosstalk. This approach reduces trap depths (activation energy E a = 0.2 eV vs. 0.84 eV for direct doping) and narrows lowest unoccupied molecular orbital (LUMO) density of states while enhancing built‐in potential and hole transfer rate ( τ 1 = 0.40 ps). Consequently, the optimized devices achieved a power conversion efficiency (PCE) of 20.5%, with a fill factor (FF) of 82.3%, surpassing control (19.5%) and direct doping (19.1%) configurations. These findings highlight the efficacy of spatially controlled doping for advancing high‐efficiency, scalable OPVs toward sustainable energy applications.