Halogenation Engineering of Solid Additives Enables 19.39% Efficiency and Stable Binary Organic Solar Cells via Manipulating Molecular Stacking and Aggregation of Both Donor and Acceptor Components

By selectively interacting with acceptor components, various typed solid additives achieve boosted power conversion efficiency (PCE) in organic solar cells (OSCs). However, due to the efficient active layer being composed of donor and acceptor materials, it is difficult to obtain the desired morphology by manipulating the acceptor component alone, limiting further improvement of PCEs. Herein, two solid additives with a same backbone of thiophene-benzene-thiophene (halogen-free D1-H) but different halogen substituents (fluorinated D1-F and chlorinated D1-Cl) are developed to probe the working mechanism of halogenated variation of solid additives in OSCs. Unlike D1-H with continuous charge distributions, D1-F and D1-Cl show isolated positive charge distribution in benzene-core and negative charge distribution in thiophene, offering stronger non-covalent interactions with both donor (PM6) and acceptor (L8-BO), especially D1-Cl. Consequently, D1-Cl-treated active layer obtains an optimized phase separation and improved molecular packing, boosting PCE to 18.59% and device stability of OSCs, with 17.62% for D1-H-treated counterparts. Moreover, using D18:L8-BO and D18:BTP-eC9 as active layers, D1-Cl-treated binary OSCs obtain impressive PCEs of 19.29% and 19.39%, respectively. This work indicates that halogenation engineering developed in solid additives can effectively regulate morphology for improving PCE and stability of OSCs, and elucidates the underlying mechanism.