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Fluorinated Copolymer PCPDTBT with enhanced open-circuit voltage and reduced recombination for highly efficient polymer solar cells

  • A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC70BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced.A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC70BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC70BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells.show moreshow less

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Metadaten
Author:Steve AlbrechtGND, Silvia JanietzORCiDGND, Wolfram Schindler, Johannes Frisch, Jona Kurpiers, Juliane Kniepert, Sahika Inal, Patrick Pingel, Konstantinos Fostiropoulos, Norbert Koch, Dieter NeherORCiDGND
DOI:https://doi.org/10.1021/ja305039j
ISSN:0002-7863 (print)
Parent Title (English):Journal of the American Chemical Society
Publisher:American Chemical Society
Place of publication:Washington
Document Type:Article
Language:English
Year of first Publication:2012
Year of Completion:2012
Release Date:2017/03/26
Volume:134
Issue:36
Pagenumber:13
First Page:14932
Last Page:14944
Funder:BMBF project PVCOMB [FKZ 03IS2151D]; SOHyb [FKZ 03X3525]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
Peer Review:Referiert