Non-fused-ring asymmetrical electron acceptors assembled by multi-functional alkoxy indenothiophene unit to construct efficient organic solar cells

Due to the complicated synthesis routes of ladder-typed fused ring small molecule acceptors (SMAs), simple non-fused-ring SMAs have been received attention. However, their photovoltaic properties have not made great progress due to the subtle crystallinity and intramolecular interaction. In this work, in order to advance photovoltaic properties, a type of non-fused-ring asymmetrical SMAs with an A-D-D'-A framework, named as IOMe-4Cl and IOEH-4Cl, was primarily designed and synthesized with a multifunctional alkoxy indenothiophene (INT) unit assembled with a classic dithienocyclopentadiene (DTC) unit as an electron-donating D-D' central build. The influence of asymmetric structure, non-covalent bond and alkoxy chain from the alkoxy INT unit on optical, electrochemical and photovoltaic properties was systemic studied. It was found that both SMAs exhibited strong near infrared absorption at about 900 nm. In comparison to the IOMe-4Cl with methoxy, the IOEH-4Cl with 2-ethyl-hexyloxy exhibited better regular film morphology and more suitable frontier orbital energy level with polymer PM6. As a result, IOEH-4Cl exhibited better photovoltaic properties than IOMe-4Cl in the solution-processing binary OSCs using polymer PM6 as donor material. A compelling PCE of 13.67% with high Jsc of 23.00 mA cm−2, Voc of 0.85 V and FF of 70.19% was obtained for the PM6:IOEH-4Cl based binary cells. This work clearly states that the multifunctional alkoxy INT is an appealing unit to construct high-performance non-fused-ring asymmetric SMAs by asymmetric unit, non-covalent bond and alkoxy chain effect.