Halogenated additive-driven morphology optimization enables universal performance enhancement in multiple electron acceptor-based organic solar cells

Abstract

Halogen-based solid additives (SAs) that utilize noncovalent interactions have demonstrated remarkable success in precisely modulating the morphology of active layers to enhance organic solar cell (OSC) performance. Nevertheless, systematic investigations into how these halogen-based SAs regulate OSC morphology through molecular-level interactions remain significantly limited. Herein, we present two hetero-halogenated SAs, 1,5-dibromo-2,4-difluorobenzene (DBDF) and 1,5-dibromo-2,4-diiodobenzene (DBDI), specifically designed to selectively modulate PM6/L8-BO blend crystallinity and π–π stacking via intermolecular interactions. By strategically combining halogen atoms with distinct electronegativities and polarizabilities at nucleophilic regions of PM6/L8-BO, we achieved precise control over both halogen bonding strength hierarchy, enabling programmable molecular alignment. The synergistic halogen-bonding networks established by DBDF and DBDI within the active layer significantly enhance molecular packing order while optimizing the phase-separated interpenetrating network morphology. Consequently, DBDI-treated devices achieve a champion power conversion efficiency (PCE) of 19.42%, representing a notable improvement over control devices (17.37%). The universality of this halogenated additive-driven morphology control is further demonstrated by enhanced performance across multiple A–DA′D–A acceptor systems (BZ4F, Y6, QM1, and PY-IT), highlighting DBDI's broad applicability in OSCs.