In recent years the concept of ternary blend bulk heterojunction (BHJ) solar cells based on organic semiconductors has been widely used to achieve a better match to the solar irradiance spectrum, and power conversion efficiencies beyond 10% have been reported. However, the fill factor of organic solar cells is still limited by the competition between recombination and extraction of free charges. Here, we design advanced material composites leading to a high fill factor of 77% in ternary blends, thus demonstrating how the recombination thresholds can be overcome. Extending beyond the typical sensitization concept, we add a highly ordered polymer that, in addition to enhanced absorption, overcomes limits predicted by classical recombination models. An effective charge transfer from the disordered host system onto the highly ordered sensitizer effectively avoids traps of the host matrix and features an almost ideal recombination behaviour.
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This project has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreement no 607585 project OSNIRO. The authors gratefully acknowledge the support of the Cluster of Excellence ‘Engineering of Advanced Materials’ at the University of Erlangen-Nuremberg, which is funded by the German Research Foundation (DFG) within the framework of its ‘Excellence Initiative’, Synthetic Carbon Allotropes (SFB953) and Solar Technologies go Hybrid (SolTech). The authors also acknowledge the Solar Factory of the Future as part of the Energy Campus Nuremberg (EnCN), which is supported by the Bavarian State Government (FKZ 20-3043.5). X-ray and SIMS analysis by NCSU was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Science and Engineering under Contract DE-FG02-98ER45737. X-ray data were acquired at beamlines 220.127.116.11, 7.3.3 and 18.104.22.168 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. A. L. D. Kilcoyne, E. Schaible, C. Zhu, A. Hexemer, C. Wang and A. Young of the ALS (DOE) assisted with the measurements and provided instrument maintenance. X.J. acknowledges the use of the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation. S. Mukherjee and M. Ghasemi from NCSU are acknowledged for providing comments about the manuscript.
The authors declare no competing financial interests.
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Gasparini, N., Jiao, X., Heumueller, T. et al. Designing ternary blend bulk heterojunction solar cells with reduced carrier recombination and a fill factor of 77%. Nat Energy 1, 16118 (2016). https://doi.org/10.1038/nenergy.2016.118
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