Polymer:Nonfullerene Bulk Heterojunction Solar Cells with Exceptionally Low Recombination Rates
Matt, Gebhard J.
Brabec, Christoph J.
KAUST DepartmentKAUST Solar Center (KSC)
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AbstractOrganic semiconductors are in general known to have an inherently lower charge carrier mobility compared to their inorganic counterparts. Bimolecular recombination of holes and electrons is an important loss mechanism and can often be described by the Langevin recombination model. Here, the device physics of bulk heterojunction solar cells based on a nonfullerene acceptor (IDTBR) in combination with poly(3-hexylthiophene) (P3HT) are elucidated, showing an unprecedentedly low bimolecular recombination rate. The high fill factor observed (above 65%) is attributed to non-Langevin behavior with a Langevin prefactor (β/βL) of 1.9 × 10−4. The absence of parasitic recombination and high charge carrier lifetimes in P3HT:IDTBR solar cells inform an almost ideal bimolecular recombination behavior. This exceptional recombination behavior is explored to fabricate devices with layer thicknesses up to 450 nm without significant performance losses. The determination of the photoexcited carrier mobility by time-of-flight measurements reveals a long-lived and nonthermalized carrier transport as the origin for the exceptional transport physics. The crystalline microstructure arrangement of both components is suggested to be decisive for this slow recombination dynamics. Further, the thickness-independent power conversion efficiency is of utmost technological relevance for upscaling production and reiterates the importance of understanding material design in the context of low bimolecular recombination.
CitationGasparini N, Salvador M, Heumueller T, Richter M, Classen A, et al. (2017) Polymer:Nonfullerene Bulk Heterojunction Solar Cells with Exceptionally Low Recombination Rates. Advanced Energy Materials: 1701561. Available: http://dx.doi.org/10.1002/aenm.201701561.
SponsorsThis project received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 607585 project OSNIRO. M.S. acknowledges primary support from a fellowship by the Portuguese Fundação para a Ciência e a Tecnologia (SFRH/BPD/71816/2010). The authors gratefully acknowledge the support of the Cluster of Excellence “Engineering of Advanced Materials” at the University of Erlangen-Nuremberg, which was funded by the German Research Foundation (DFG) within the framework of its “Excellence Initiative,” Synthetic Carbon Allotropes (SFB953), Research Training Group (GRK 1896), and Solar Technologies go Hybrid (SolTech).
JournalAdvanced Energy Materials