Many studies have proven the significant roles of side chains far beyond being the solubilizing groups as well as the interesting merits of fluorination on π-backbones in the intrinsic properties and device performances of organic semiconductors. Considering the integration of the two features, we herein introduce a 4,4,4-trifluorobutyl (CF3-terminated) side chain into a 2H-1,2,3-benzotriazole-core-based acceptor–donor–acceptor–donor–acceptor-type nonfullerene acceptor (NFA) named YCF3 and demonstrate its effectiveness in optoelectronic, morphological, and photovoltaic properties. Comparative experimental and theoretical studies confirmed the unique features of YCF3 (e.g., red-shifted film absorption, better absorptivity, finely adjusted energies, and higher mobility) associated with its enhanced crystalline nature, compared with its analogous NFA with an n-butyl side chain named YCH3. The best power conversion efficiency (PCE) of 18.21% is achieved in a YCF3-based binary organic solar cell (OSC) together with good heat and light stability. Moreover, a YCF3-based OSC presents a remarkable PCE of 16.11% in an inverted-structure large-area device.

The side-chain engineering of A-DA'D-A-type nonfullerene acceptors (NFAs), well-known as Y6 series, is an efficient approach for retaining the physical properties of Y6-series but allowing manipulation of the solubility, crystallization,...

Alongside high power conversion efficiencies (PCEs), device stability, especially thermal issues, is another key factor for the successful commercialization of nonfullerene acceptor (NFA)-based organic solar cells (OSCs). Considering the significant effects of the side-chain engineering of NFAs on molecular packing and/or locking strongly associated with the thermal stability of OSCs, herein, we present two new isomeric NFAs with 4-fluoro-and 2-fluoro-substituted hexylphenyl twodimensional (2D) outer side chains (4FY and 2FY, respectively). In contrast with the 2FY having a horizontal stretching conformation, 4FY exhibits a diagonal stretching conformation of the 2D outer side chains and a higher dipole moment, resulting in a huge difference in their crystalline/aggregation characteristics, i.e., 4FY possesses a higher crystallinity with a denser molecular packing than the 2FY neat film, as evidenced by thermal and morphological characterizations. Encouragingly, relative to the one based on 2FY, the OSC based on 4FY delivers a PCE as high as 16.4%, together with excellent thermal stability (88.4% PCE retention under 85 °C for 360 h), which is attributed to a more optimal and robust blend morphology induced by its better compatibility into the used donor component and stronger crystallinity. This work demonstrates that in addition to the improved photovoltaic property, the appropriate F-positioning on the 2D outer side chains can play a key role in controlling their conformations, which can promote the increase of the thermal stability of OSCs.