Rationally Tailoring Simple Non‐Fused Ring Electron Acceptors Toward Zwitterionic Interlayers for Organic Photovoltaics: The Effect of Synergetic Sidechains Engineering

Advancing organic solar cells (OSCs) require simultaneous progress in organic semiconductors for both active layers and interlayers. The disparate electronic and structural properties of electron acceptors and interlayers present a significant challenge to optimal interfacial compatibility. Herein, we report four zwitterionic non-fused-ring electron acceptors (zNFREAs) as interlayer materials, featuring a simple thiophene-benzene-thiophene core and 5,6-difluoro-1,1-dicyanomethylene-3-indanone terminals, affording low synthetic complexity and low-lying energy levels. Synergistic modulation of central polar and peripheral non-polar sidechains effectively tunes optoelectronic properties and molecular aggregation. TBT-TMZ, integrating central hexyl-pendant zwitterionic groups with peripheral 2,4,6-trimethylphenyl substituents, exhibits favorable solubility and work function tunability, a well-balanced crystallinity and film-forming ability, as well as desirable active layer compatibility. PM6:Y6-based devices incorporating TBT-TMZ achieve a power conversion efficiency (PCE) of 18.21%, retaining approximately 90% of their peak PCE even with TBT-TMZ layers at a thickness of 101 nm, demonstrating exceptional thickness insensitivity. Furthermore, TBT-TMZ displays broad compatibility with diverse active layers, delivering an outstanding PCE of 20.73% for the D18:BTP-eC9:L8-BO blend. This work not only introduces an innovative class of zwitterionic materials based on state-of-the-art NFREAs but also sheds light on the critical role of systematical polar and non-polar sidechains optimization toward high performance water/alcohol-soluble n-type organic semiconductors.