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

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 (τ₁ = 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.