Two novel dithieno[3,2-b:2,3-d]pyrrol fused electron acceptors (FREAs) with branched alkyl side-chains have been developed. With 2-ethylhexyl and 2-butyloctyl introduced on the N-position of the pyrrol unit, the sidechain engineered acceptors (INPIC-EH and INPIC-BO) were evaluated for organic solar cells (OSCs) by comparison with our reference INPIC-4F bearing a linear octyl chain. The optoelectronic properties of the FREAs and their bulk-heterojunction (BHJ) with a PBDB-T donor for OSCs are systematically studied. All FREAs exhibit similar absorption spectra and energy levels. Notably, the charge dissociation process, charge mobility, and morphology of the BHJ films make a distinct difference. Consequently, the OSCs constructed with INPIC-EH and INPIC-BO delivered a power conversion efficiency (PCE) of 11.9% and 11.2%, lower than that of INPIC-4F devices (13.1%). The lower short-circuit current density (JSC) and fill factor (FF) of INPIC-EH and INPIC-OB based devices are attributed to unfavorable morphology of the active layers and more bimolecular recombination and unbalanced charge transport. Our investigation demonstrates that side-chain engineering on FREAs has a great impact on the morphology of blends and thus the photovoltaic properties of their OSCs.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was financially supported by the National Natural Science Foundation of China (Grant No. 51573077, 21875111), Jiangsu Province Natural Science Foundation (BK20180496), the 333 Project to Cultivate High Level Talents in Jiangsu Province, Six Talent Peaks Project in Jiangsu Province, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.