Synergistic Strategy of Manipulating the Number of Selenophene Units and Asymmetric Central Core of Small Molecular Acceptors Enables Polymer Solar Cells with 17.5% Efficiency.

Recently, despite the great achievement made in non-fullerene small molecular acceptors (NF-SMAs)-based polymer solar cells (PSCs), the favourable trade-off among device parameters is still quite difficult to obtain for further development. Herein, a novel synergistic strategy of the asymmetric backbone and selenophene substitution on the central core was applied for the first time and a new family of symmetric or asymmetric A-DA'D-A type NF-SMAs ( S-YSS-Cl , A-WSSe-Cl , and S-WSeSe-Cl ) with different numbers of selenophene were successfully synthesized. From S-YSS-Cl to A-WSSe-Cl and to S-WSeSe-Cl , a gradually red-shifted absorption and a gradually larger electron mobility and crystallinity in neat thin film was observed. Moreover, single crystals results indicate that A-WSSe-Cl and S-WSeSe-Cl exhibit stronger and tighter intermolecular π-π stacking interactions, extra S∙∙∙N non-covalent intermolecular interactions from central benzothiadiazole, better ordered 3D interpenetrating charge-transfer networks in comparison with thiophene-based S-YSS-Cl . Furthermore, PM6 :A-WSSe-Cl blend film exhibits the most favourable morphology with the best face-on intermolecular packing, and the most efficient charge separation, transport and collection. The asymmetric A- WSSe-C l -based device presents an impressive PCE of 17.51%, which is obvious higher than that of symmetric S-WSeSe-Cl- based (16.01%) and is the highest value for selenophene-based NF-SMAs in binary PSCs. These results demonstrate that the combination of the subtle asymmetric core and precise replacement of selenophene on the central core is an effective approach to improve J sc and FF without over sacrificing of V oc for efficient NF-SMAs.