Synergistic Side-Chain and End-Group Engineering of C-Shaped A–D–A Acceptors for Enhanced Performance of Organic Photovoltaics

Abstract

In this work, two ortho-benzodipyrrole-based non-fullerene acceptors, CBBO-Cl and CBHD-Cl, were designed and synthesized by introducing branched side chains at the β-position of the thieno[3,2-b]thiophene units in the outer convex region and incorporating chlorinated Cl-IC as the terminal group. Variations in alkyl chains significantly influence the intermolecular interactions, crystal structure, and morphology of both neat and blend films. Single-crystal structure analysis revealed that both CBBO-Cl and CBHD-Cl adopt compact 3D networks with three distinct dimeric packing modes. However, CBBO-Cl exhibits smaller elliptical voids along the c-axis and shorter π–π stacking distances, attributed to the reduced steric hindrance of its shorter side chains. GIWAXS measurements further confirm enhanced crystallinity and multiple π–π stacking orientations in the thermally annealed neat CBBO-Cl and PM6:CBBO-Cl blend films, which facilitate efficient charge transport. Consequently, the PM6:CBBO-Cl device achieves higher and more balanced charge mobilities, suppressed charge recombination, and an enhanced Jsc of 25.64 mA cm⁻², resulting in a superior PCE of 17.14% compared with the PM6:CBHD-Cl-based device (16.20%).