Abstract
In an ideal model, a p–n junction is formed by two stacked slabs of semiconductors. Although the construction of actual devices is generally more complex, we show that such a simple method can in fact be applied to the formation of organic heterojunctions. Two films of the organic semiconductors poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) can be connected by a simple film-transfer method without disturbing their flat surfaces. Each film can further be modified with a surface-segregated monolayer to tune the strength and direction of the surface dipole moment. Using this method, we fabricated bilayer organic photovoltaic devices with interfacial dipole moments that were selected to align the energy levels at the heterojunction. The open-circuit voltages of the P3HT/PCBM devices could be tuned over a wide range between 0.3 and 0.95 V, indicating that, even if the same combination of bulk materials is used, the interfacial properties drastically alter the performance of organic photovoltaic devices.
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Acknowledgements
Y.F.G. thanks the Chinese Scholarship Council for financial support.
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A.T. and Y.F.G. contributed equally to this work. A.T. fabricated and evaluated the OPV devices and carried out the external quantum efficiency, XPS, UPS and X-ray reflectivity measurements. Y.F.G. synthesized and characterized the P3DDFT and carried out the XPS depth profile measurements. Q.S.W. synthesized and characterized the FC8. K.H. and K.T. directed the research. A.T., K.H. and K.T. wrote the paper.
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Tada, A., Geng, Y., Wei, Q. et al. Tailoring organic heterojunction interfaces in bilayer polymer photovoltaic devices. Nature Mater 10, 450–455 (2011). https://doi.org/10.1038/nmat3026
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DOI: https://doi.org/10.1038/nmat3026
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