Polymer solar cells with enhanced open-circuit voltage and efficiency

Abstract

Following the development of the bulk heterojunction1 structure, recent years have seen a dramatic improvement in the efficiency of polymer solar cells. Maximizing the open-circuit voltage in a low-bandgap polymer is one of the critical factors towards enabling high-efficiency solar cells. Study of the relation between open-circuit voltage and the energy levels of the donor/acceptor2 in bulk heterojunction polymer solar cells has stimulated interest in modifying the open-circuit voltage by tuning the energy levels of polymers3. Here, we show that the open-circuit voltage of polymer solar cells constructed based on the structure of a low-bandgap polymer, PBDTTT4, can be tuned, step by step, using different functional groups, to achieve values as high as 0.76 V. This increased open-circuit voltage combined with a high short-circuit current density results in a polymer solar cell with a power conversion efficiency as high as 6.77%, as certified by the National Renewable Energy Laboratory.

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Figure 1: Comparison of three different polymers.
Figure 2: Characterization of devices based on PBDTTT–E, PBDTTT–C and PBDTTT–CF.
Figure 3: Photoconversion efficiency study.
Figure 4: Tapping-mode atomic force microscopy images of the three films used in making the devices (under optimized device conditions).

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Acknowledgements

The National Renewable Energy Laboratory (NREL) is thanked for conducting the certification of devices. The authors in particular thank D.C. Olson at NREL for his help in verifying and certifying the performances of our devices.

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Contributions

H.Y.C. conceived and performed PSC fabrication, measurements and data analysis. Y.L. and L.Y. contributed to the design of the polymer's main chain structure. J.H. designed the polymer structures and synthesis routes. S.Z. synthesized the polymers. G.Y. performed the AFM image scans. J.H. and Y.W. conceptualized and directed the research project. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Jianhui Hou or Yue Wu.

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Chen, HY., Hou, J., Zhang, S. et al. Polymer solar cells with enhanced open-circuit voltage and efficiency. Nature Photon 3, 649–653 (2009). https://doi.org/10.1038/nphoton.2009.192

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