Improving the power conversion efficiency of polymer-based bulk-heterojunction solar cells is a critical issue. Here, we show that high efficiencies of ∼10% can be obtained using the crystalline polymer PNTz4T in single-junction inverted cells with a thick active layer having a thickness of ∼300 nm. The improved performance is probably due to the large population of polymer crystallites with a face-on orientation and the ‘favourable’ distribution of edge-on and face-on crystallites along the film thickness (revealed by in-depth studies of the blend films using grazing-incidence wide-angle X-ray diffraction), which results in a reduction in charge recombination and efficient charge transport. These results underscore the great promise of polymer solar cells and raise the hope of achieving even higher efficiencies by means of materials development and control of molecular ordering.
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This research was supported by Grants-in-Aid for Scientific Research from The Ministry of Education, Culture, Sports, Science and Technology (MEXT) (nos. 24685030 and 23245041) and by Precursory Research for Embryonic Science and Technology from the Japan Science and Technology Agency. This work was partly supported by the Nanotechnology Platform Program of MEXT. Two-dimensional GIWAXD experiments were performed at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI, proposal no. 2014A1530). The authors thank K. Tajima of CEMS, RIKEN, for helpful discussions regarding the fabrication of inverted cells and for the contact angle measurement, and K. Higashimine of the Center for Nano Materials and Technology, JAIST, for the EDS measurements. The authors thank Y. Hishikawa of the National Institute of Advanced Industrial Science and Technology (AIST) and H. Tobita of Japan Electrical Safety & Environment Technology Laboratories (JET) for technical discussions about the J–V measurements. The authors also thank Y. Hishikawa and A. Sasaki for measurement of the cell active area.
The authors declare no competing financial interests.
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Vohra, V., Kawashima, K., Kakara, T. et al. Efficient inverted polymer solar cells employing favourable molecular orientation. Nature Photon 9, 403–408 (2015). https://doi.org/10.1038/nphoton.2015.84
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