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Polymer:Nonfullerene Bulk Heterojunction Solar Cells with Exceptionally Low Recombination Rates
Author(s) -
Gasparini Nicola,
Salvador Michael,
Heumueller Thomas,
Richter Moses,
Classen Andrej,
Shrestha Shreetu,
Matt Gebhard J.,
Holliday Sarah,
Strohm Sebastian,
Egelhaaf HansJoachim,
Wadsworth Andrew,
Baran Derya,
McCulloch Iain,
Brabec Christoph J.
Publication year - 2017
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201701561
Subject(s) - recombination , materials science , polymer solar cell , charge carrier , chemical physics , heterojunction , context (archaeology) , acceptor , optoelectronics , electron mobility , energy conversion efficiency , physics , condensed matter physics , chemistry , paleontology , biochemistry , biology , gene
Organic 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/β L ) 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.