Nonfullerene Small-Molecule Acceptors with Extended Optical Absorption Based on the “Spliced” Strategy for Organic Solar Cells

Abstract

Abstract How to broaden the optical absorption of photovoltaic materials is one of the key issues in the design of high-performance organic solar cells. Nowadays, the sunlight of 400–550 nm wavelength range is not effectively utilized for most small-molecule nonfullerene acceptors. In this work, we proposed the “spliced” strategy of combining the acceptor–donor–acceptor type narrow band-gap small molecules and wide-band-gap perylene diimide (PDI) moieties via a flexible alkyl chain linkage, which could give the superposition effect of the absorption spectra, and three small-molecule acceptors (S1, S2, and S3) were designed based on various end-capping groups with different electron withdrawing abilities. Encouragingly, the as-constructed molecules can well make use of 400–550 nm sunlight with two independent absorption regions. Meanwhile, the aggregation of S1 with a highly planar end-capping group was dominated by both the PDI unit and main skeleton, while S2 and S3 exhibited PDI-controlled aggregation. When fabricated into organic solar cells, S1-based devices achieved a superior efficiency of 3.41% in comparison with those of the other two. The poor photovoltaic performance could be attributed to severe PDI aggregation, which can hinder the charge transfer through the main skeletons. This work could provide a new perspective to modulate optical absorption through the spliced strategy.

Keywords

• organic solar cells
• nonfullerene acceptor
• spliced strategy
• optical absorption
• aggregation