Conformation-Tuning Effect of Asymmetric Small Molecule Acceptors on Molecular Packing, Interaction, and Photovoltaic Performance

Understanding the conformation effect on molecular packing, miscibility, and photovoltaic performance is important to open a new avenue for small-molecule acceptor (SMA) design. Herein, two novel acceptor-(donor-acceptor1-donor)-acceptor (A-DA1D-A)-type asymmetric SMAs are developed, namely C-shapedBDTP-4Fand S-shapedBTDTP-4F. TheBDTP-4F-based polymer solar cells (PSCs) with PM6 as donor, yields a power conversion efficiency (PCE) of 15.24%, significantly higher than that of theBTDTP-4F-based device (13.12%). The better PCE forBDTP-4F-based device is mainly attributed to more balanced charge transport, weaker bimolecular recombination, and more favorable morphology. Additionally, two traditional A-D-A-type SMAs (IDTP-4FandIDTTP-4F) are also synthesized to investigate the conformation effect on morphology and device performance. Different from the device result above, here,IDTP-4Fwith S-shape conformation outperforms thanIDTTP-4Fwith C-shape conformation. Importantly, it is found that for these two different types of SMA, the better performing binary blend has similar morphological characteristics. Specifically, bothPM6:BDTP-4FandPM6:IDTP-4Fblend exhibit perfect nanofibril network structure with proper domain size, obvious face-on orientation and enhance donor-acceptor interactions, thereby better device performance. This work indicates tuning molecular conformation plays pivotal role in morphology and device effciciency, shining a light on the molecular design of the SMAs.