Molecular Design of Fully Nonfused Acceptors for Efficient Organic Photovoltaic Cells

Abstract

The nonfused thiophene−benzene−thiophene (TBT) unit offers advantages in obtaining low-cost organic photovoltaic (OPV) materials due to its simple structure. However, OPV cells, including TBT-based acceptors, exhibit significantly lower energy conversion efficiencies. Here, we introduce a novel approach involving the design and synthesis of three TBT-based acceptors by substituting different positionbranched side chains on the TBT unit. In comparison to TBT-10 and TBT-11, TBT-13, which exclusively incorporates α-position branched side chains with a large steric hindrance, demonstrates a more planar and stable conformation. When blended with the donor PBQx-TF, TBT-13-based blend film achieves favorable π−π stacking and aggregation characteristics, resulting in excellent charge transfer performance in the corresponding device. Due to the simultaneous enhancements in short-circuit current density and fill factor, the TBT-13-based OPV cell obtains an outstanding efficiency of 16.1%, marking the highest value for the cells based on fully nonfused acceptors. Our work provides a practical molecular design strategy for high-performance and low-cost OPV materials.

Cyclization Engineering of Electron-Deficient Maleimide Unit for Nonfused Ring Electron Acceptors Enables Efficient Organic Solar Cells

“…Organic solar cells (OSCs) have attracted widespread attention owing to their advantages, such as flexibility, semitransparency, and environmental friendliness. − The active layer of OSCs is made up of materials that function as both donors and acceptors. With the development and design of nonfullerene fused ring acceptor materials, especially A-DA’D-A type acceptor of Y6, OSC device efficiency has exceeded 19%. − However, the complex synthesis step, high cost, and low yield of these acceptor materials are not conducive to further commercial application. , Nonfused ring electron acceptors (NFREAs) have the advantages of a simple structure and synthesis with a high yield, making them an effective alternative to solve the above problem. − …”

Enhanced crystal network and charge transfer of non-fused ring electron acceptors via interchain interaction for efficient and stable organic solar cells

“…19 In the early stage for NFREAs, intramolecular non-covalent interactions, 20–23 such as F⋯H in DF-PCIC, 20 O⋯S in DOC2C6-2F, 24 and S⋯N in X-PCIC, 25 were adopted to construct a planar molecular geometry for efficient intramolecular charge transfer and intermolecular π–π stacking; in this phase, PCEs were improved to over 13%. 26–29 In the later phase, bulky side chains introduced on the center molecular backbones of NFREAs, 30–33 typically like triisopropylbenzene in A4T-16, 31 diphenylamine in 2BTh-2F, 34 and α-position branched alkoxyl in TBT-13, 35 were also believed to restrict the rotation of the C–C single bond in the molecular mainchain. For a delicate balance between suitable crystallinity and appropriate phase separation morphology, PCEs were enhanced to over 17%.…”