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Efficient organic solar cells processed from hydrocarbon solvents

Nature Energy volume 1, Article number: 15027 (2016) Cite this article

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Abstract

Organic solar cells have desirable properties, including low cost of materials, high-throughput roll-to-roll production, mechanical flexibility and light weight. However, all top-performance devices are at present processed using halogenated solvents, which are environmentally hazardous and would thus require expensive mitigation to contain the hazards. Attempts to process organic solar cells from non-halogenated solvents lead to inferior performance. Overcoming this hurdle, here we present a hydrocarbon-based processing system that is not only more environmentally friendly but also yields cells with power conversion efficiencies of up to 11.7%. Our processing system incorporates the synergistic effects of a hydrocarbon solvent, a novel additive, a suitable choice of polymer side chain, and strong temperature-dependent aggregation of the donor polymer. Our results not only demonstrate a method of producing active layers of organic solar cells in an environmentally friendly way, but also provide important scientific insights that will facilitate further improvement of the morphology and performance of organic solar cells.

Organic solar cell (OSC) technology is considered one of the most promising cost-effective and environmentally friendly solar cell technologies, as it can be produced using low-cost printing processes and the end product contains no toxic materials1,2,3,4,5,6,7,8,9. One of the major problems holding back the widespread use of OSCs is that all high-efficiency (>10%) devices are at present processed from hazardous halogenated solvents such as chlorobenzene (CB), 1,2-dichlorobenzene and additives such as 1,8-diiodooctane (DIO; refs 10,11,12,13,14). These solvents are harmful to people and the environment, and current state-of-the-art OSCs are thus not truly environmentally friendly in their production processes. In addition, halogenated solvents do not exist in nature, and their production requires relatively costly synthetic steps. Hydrocarbons are better choices of solvents for OSC production, as they are more environmentally friendly and readily available from petroleum. However, several reports have indicated that OSCs processed from non-chlorinated solvents generally result in significantly reduced power conversion efficiency (PCE) levels15,16,17,18,19,20,21,22, and that the best OSCs are still processed from halogenated solvents10,11,12,13,14. One reason for the much poorer performance is that state-of-the-art donor and/or acceptor materials for OSCs typically exhibit poor solubility in non-halogenated solvents, which results in a poor bulk-heterojunction (BHJ) morphology containing excessively large domains15. On the other hand, controlling and optimizing BHJ morphology is one of the most important challenges for OSCs (ref. 23). Some morphology parameters (for example, molecular orientation at or relative to the donor/acceptor (D/A) interface, polymer backbone orientation, and domain purity) are challenging to control. Therefore, new tools and insights are needed to improve the morphology and performance of OSCs.

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Figure 1: Chemical structures and characterizations.
Figure 2: Characterization of PffBT4T-C9C13:PC71BM processed from CB–DIO and TMB–PN.
Figure 3: The influence of alkyl chain lengths on polymer texture.

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Acknowledgements

The work was partially supported by the National Basic Research Program of China (973 Program; 2013CB834705), HK JEBN Limited (Hong Kong), the Hong Kong Research Grants Council (T23–407/13-N, N_HKUST623/13, and 606012), HKUST President’s Office through SSTSP scheme (project ref number: EP201) and the National Natural Science Foundation of China (NSFC, #21374090, 21504066, 21534003 and 51320105014). We thank Enli Technology Co., Ltd (Taiwan) for carrying out EQE measurements and Raynergy Tek Incorporation (Taiwan) for providing building blocks. H.A. is supported by ONR grants N000141410531 and N00141512322. X-ray data was acquired at beamlines 11.0.1.2 and 7.3.3 at the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.

Author information

Author notes

  1. Jingbo Zhao and Yunke Li: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Chemistry and Energy Institute, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

    Jingbo Zhao, Yunke Li, Guofang Yang, Kui Jiang, Haoran Lin & He Yan

  2. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China

    Guofang Yang & Wei Ma

  3. HKUST-Shenzhen Research Institute, No. 9 Yuexing 1st Road, Hi-tech Park, Nanshan, Shenzhen 518057, China

    Kui Jiang & He Yan

  4. Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA

    Harald Ade

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  1. Jingbo Zhao
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Contributions

J.Z. selected the solvent/additive and synthesized PffBT4T-C9C13; Y.L. fabricated and optimized the devices; Y.L. prepared the devices for certification and samples for X-ray characterization; W.M. collected the X-ray data; G.Y. analysed the X-ray data supervised by W.M.; K.J. fabricated and optimized the devices based on PTB7 and PffBT4T-C8C12; H.L. synthesized PffT2-FTAZ-C10C14; J.Z., H.Y., W.M. and H.A. integrated the interpretation and drafted the paper; H.Y. conceived and directed the project; all authors commented on the final paper.

Corresponding authors

Correspondence to Wei Ma or He Yan.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Tables 1-5, Supplementary Figures 1-42, Supplementary Note, Supplementary Methods, Supplementary References. (PDF 3280 kb)

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Zhao, J., Li, Y., Yang, G. et al. Efficient organic solar cells processed from hydrocarbon solvents. Nat Energy 1, 15027 (2016). https://doi.org/10.1038/nenergy.2015.27

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