Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk-heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2-b:2ʹ,3ʹ-d]pyrrol) core with meta- or para-alkoxyphenyl sidechains are designed and denoted as m-INPOIC or p-INPOIC, respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart (INPIC-4F) bearing para-alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m-INPOIC presents predominant face-on orientation to promote charge transport. The as-cast organic solar cells (OSCs) by blending m-INPOIC and PBDB-T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC71BM as the solid processing-aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as-cast single-junction OSCs reported in literature to date. More attractively, PBDB-T:m-INPOIC:PC71BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as-cast devices make m-INPOIC a promising candidate NFA for large-scale solution-processable OSCs.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: H.F., X.S., and Z.Z. contributed equally to this work. The authors thank the financial support from the National Natural Science Foundation of China (grant nos. 51573077, 21875111, and 51861145401), Jiangsu Province Natural Science Foundation (BK20180496), the 333 Project to Cultivate High Level Talents in Jiangsu Province, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.