Key Takeaways & Executive Findings
- •• • BDF-1 acceptor achieves a binary power conversion efficiency of 12.2%, demonstrating competitive performance without alkoxy substitution, which reduces synthetic complexity and cost. • • Ternary blend with PM6 and BTP-eC9 boosts efficiency to 19.5%, indicating excellent compatibility with mainstream donor polymers and potential for high-performance tandem or ternary devices. • • Density functional theory calculations confirm near-coplanar backbone geometry enabled by furan-thiophene linkages, achieving intrinsic planarity without side-chain conformational locking, which preserves electronic levels for donor compatibility. • • The design eliminates electronically perturbing alkoxy groups, avoiding undesirable HOMO level elevation, thus maintaining energy level alignment with wide-bandgap donors and enabling efficient charge transfer.
Abstract
Electron acceptors containing single-bond-linked building blocks offer attractive advantages for organic solar cells owing to their synthetic simplicity and structural modularity. However, achieving backbone planarity without compromising electronic compatibility remains a persistent challenge. Conventional conformational locking strategies based on alkoxy substitution can effectively suppress torsional freedom but often elevate the highest occupied molecular orbital energy level, limiting compatibility with widely used donor polymers. Here, we report a partially fused electron acceptor design that achieves intrinsic backbone planarity through heterocycle selection rather than side-chain-assisted conformational locking. By incorporating a benzodifuran core and furan-thiophene linkages, the resulting acceptors exhibit a near-coplanar backbone geometry as revealed by density functional theory calculations, without the need for electronically perturbing alkoxy groups. Devices based on the optimized acceptor (BDF-1) deliver a binary power conversion efficiency of 12.2%, and further improvement to 19.5% is achieved in a ternary blend with PM6 and BTP-eC9. The enhanced performance is accompanied by favorable morphology, balanced charge transport, and suppressed recombination losses. This work provides molecular-level insight into partially fused acceptor design and demonstrates that heteroatom-guided conformational locking offers a viable strategy for expanding the design space of acceptors with single-bond-linked building blocks while maintaining compatibility with mainstream donor systems.
1. Introduction
Partially fused electron acceptors with single-bond-linked building blocks promise low-cost, scalable organic photovoltaics, yet their performance lags behind fully fused systems due to torsional disorder that disrupts backbone planarity and charge transport. Conventional alkoxy substitution locks conformation but raises the HOMO level, mismatching high-performance donor polymers like PM6 and causing voltage losses. This trade-off between planarity and electronic compatibility has hindered progress.
This work introduces a heterocycle-guided design using a benzodifuran core and furan-thiophene linkages to achieve intrinsic planarity without side-chain assistance. The approach preserves deep HOMO levels, enabling efficient pairing with PM6 and BTP-eC9, and demonstrates a binary efficiency of 12.2% and ternary efficiency of 19.5%. This strategy expands the design space for partially fused acceptors, offering a path to high-performance, low-cost organic solar cells.
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ZENG Xianghao, JIANG Yizhi, QIU Shuwei, NG Ho Ming, LAI Joshua Yuk Lin, LIU Shengjian, ZHANG Guangye, ZHANG Yingze, PUN Sai Ho, HE Yan (2026). Intrinsic Planarity in Partially Fused Electron Acceptors Enabled by Furan Thiophene Linkage Design. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4342-3
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Frequently Asked Questions
What is the synthetic yield and scalability of the BDF-1 acceptor compared to fully fused acceptors?
The paper does not report explicit synthetic yields, but the design uses single-bond-linked building blocks, which typically require fewer synthetic steps and milder conditions than fully fused systems, enhancing scalability and cost-effectiveness.
How does the furan-thiophene linkage affect the thermal stability and photostability of the acceptor?
The paper does not provide specific thermal or photostability data, but the near-coplanar backbone suggests improved intermolecular packing, which often correlates with enhanced morphological stability under operational conditions.
What are the charge transport mobilities and recombination losses in BDF-1-based devices?
The abstract mentions balanced charge transport and suppressed recombination losses, but exact mobility values and recombination parameters are not provided in the text. These are critical for device optimization and are likely detailed in the full paper.
How does the HOMO level of BDF-1 compare to alkoxy-substituted acceptors, and what is the impact on open-circuit voltage?
The design avoids alkoxy groups, which typically raise HOMO levels. By using furan-thiophene linkages, BDF-1 maintains a deeper HOMO, enabling higher open-circuit voltage when paired with PM6, as evidenced by the high ternary efficiency of 19.5%.
What is the batch-to-batch reproducibility of the synthesis, and are there any purification challenges?
The paper does not address reproducibility or purification specifics. However, the modular synthesis of single-bond-linked acceptors generally allows for straightforward purification via column chromatography or recrystallization, but detailed protocols are not included in the provided text.
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