Article Highlight | 31-Dec-2025

Achieving 20% toluene‑processed binary organic solar cells via secondary regulation of donor aggregation in sequential processing

Shanghai Jiao Tong University Journal Center

Achieving 20% Toluene‑Processed Binary Organic Solar Cells via Secondary Regulation of Donor Aggregation in Sequential Processing

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  • Isomeric molecules are introduced to fine-tune the secondary nucleation process of the donor underlayer.
  • Binary organic solar cell processed with non-halogen solvent shows a champion efficiency of 20.0% (certified 19.7%).
  • Mechanism of the film formation processes and the sequential processing community about solvent design rules are proposed.
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Credit: Yufei Wang, Chuanlin Gao, Wen Lei, Tao Yang, Zezhou Liang, Kangbo Sun, Chaoyue Zhao, Lu Chen, Liangxiang Zhu, Haoxuan Zeng, Xiaokang Sun, Bin He, Hanlin Hu, Zeguo Tang, Mingxia Qiu, Shunpu Li, Peigang Han, Guangye Zhang*.

While single-junction organic solar cells (OSCs) have touched 20 % power-conversion efficiency (PCE), most records still rely on toxic chloroform and delicate post-treatments that are incompatible with roll-to-roll printing. Now researchers at Shenzhen Technology University—Prof. Guangye Zhang, Dr. Yufei Wang and Dr. Chuanlin Gao—report a hydrocarbon-only route that delivers a certified 19.7 % PCE using nothing but toluene and two newly-designed isomeric additives that “steer” the sequential-processing (SqP) swelling event at the molecular level.

Why Toluene-Only SqP Matters
• Green & Scalable: Toluene (b.p. 111 °C) replaces chloroform, cutting solvent cost by 60 % and meeting EU REACH standards for large-area coating.
• Secondary Nucleation Control: Liquid additive ODBC (μ = 2.59 D) forms −21 kcal mol-1 non-covalent complexes with PM6, extending donor crystallization time from 2.5 s to >8 s and yielding 11.1 nm π–π coherence length—an 18 % jump.
• Certified Performance: PM6/BTP-eC9 binary devices reach 20.0 % PCE (Voc = 0.861 V, Jsc = 28.9 mA cm-2, FF = 80.4 %) on 2PACZ interlayers, the highest value ever reported for halogen-free-processed binary OSCs.

Innovative Design & Features
• Additive Engineering: ODBC (oil) and PDBC (wax) are positional isomers that volatilize completely during spin-coating (Tcomplete <190 °C), leaving zero residue and avoiding extra annealing steps.
• Morphology Tuning: In-situ absorption and GIWAXS show that ODBC delays acceptor solidification, allowing optimal vertical segregation—81 % PM6 near the anode and 49 % acceptor at the cathode—minimizing recombination losses (ΔE₃ = 0.203 eV).
• Universality: The same ODBC strategy boosts toluene-cast PM6/L8-BO to 18.2 % and PM6/PJ1-γ all-polymer cells to 17.4 %, proving broad compatibility.

Applications & Future Outlook
• Roll-to-Roll Ready: 0.6 cm2 large-area modules retain >13 % PCE under slot-die coating; team is scaling to 30 cm-wide PET web at 15 m min-1.
• Enhanced Stability: MPPT shows T80 lifetime extends from 156 h (control) to 500 h with ODBC; thermal aging at 80 °C retains 59 % of initial PCE versus 51 % for additive-free devices.
• Next Steps: Researchers are transferring the concept to ternary blends and flexible Ag-nanowire electrodes, targeting 22 % PCE and 1,000 h operational lifetime for indoor photovoltaics.

This work demonstrates that rational additive design can turn an everyday solvent into a precision morphology tool, offering an immediately adoptable pathway for eco-friendly, high-performance organic photovoltaics. Stay tuned for more SqP advances from Prof. Zhang’s group at Shenzhen Tech!

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