15.8% Efficiency All-Small-Molecule Solar Cells Enabled by a Combination of Side-Chain Engineering and Polymer Additive

All-small-molecule OSCs (ASM-OSCs) are more suitable for commercial-scale manufacturing owing to the merits of small molecules, such as well-defined chemical molecular structures, easy synthesis, as well as less batch-to-batch variation. With the repaid development of non-fullerene acceptors, the design of small molecules donor and the optimization of bulk heterojunction (BHJ) morphologies will take greater responsibility to improve the power conversion efficiencies (PCE) of ASM-OSCs. Herein, a novel small molecular donor, BTR-SCl, with alkylthio and chlorine substitutions on the side-chains was designed and synthesized. BTR-SCl exhibits strong absorption in the wavelength range of 400–700 nm with a wide optical bandgap of 1.77 eV, a low-lying highest occupied molecular orbital (HOMO) energy level of –5.51 eV, and a strong crystallization property. Consequently, a PCE of 14.6% was obtained from BTR-SCl:Y6 solar cells with a V oc of 0.88 V, a J sc of 23.4 mA cm -2 , and an FF of 70.8%. Notably, with the incorporation of polymer PM7 as a morphology modulator, BTR-SCl:Y6 matrix achieved well-formed bicontinuous interpenetrating networks and ordered molecular packing. As a result, PM7-optimized devices achieved a significantly enhanced PCE of 15.8% with higher J sc of 24.5 mA cm -2 and FF of 73.1%