Bicontinuous donor and acceptor fibril networks enable 19.2% efficiency pseudo‐bulk heterojunction organic solar cells

Realizing bicontinuous fibrillar charge transport networks in the photoactive layer has been considered a promising method to achieve high‐efficiency organic solar cells (OSCs); however, this has been rarely achieved due to the interference of molecular organization of donor and acceptor components during solution casting. In this contribution, the fibrillization of polymer donor PM6 and small molecular nonfullerene acceptor L8‐BO is realized with the assistance of conjugated polymer D18‐Cl. Atomic force microscopy and photo‐induced force microscopy reveal that PM6 and D18‐Cl co‐assemble into long and slender fibrils within wide blending ratios due to their high compatibility; in contrast, the fibrillization of L8‐BO can be encouraged with the incorporation of 1% D18‐Cl. By utilizing a pseudo‐bulk heterojunction (p‐BHJ) active layer fabricated by layer‐by‐layer deposition, the optimized PM6+20% D18‐Cl/L8‐BO+1% D18‐Cl OSCs obtain bicontinuous fibril networks, leading to enhanced exciton dissociation and charge transport processes and superior power conversion efficiency of 19.2% (certified 18.91%) compared to 18.8% of the PM6:D18‐Cl:L8‐BO ternary BHJ OSCs.