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Enhance performance of organic solar cells based on an isoindigo-based copolymer by balancing absorption and miscibility of electron acceptor
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
Chalmers.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
Chalmers.
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2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 14, 143302- p.Article in journal (Refereed) Published
Abstract [en]

Superior absorption of PC(71)BM in visible region to that of PC(61)BM makes PC(71)BM a predominant acceptor for most high efficient polymer solar cells (PSCs). However, we will demonstrate that power conversion efficiencies (PCEs) of PSCs based on poly[N,N-bis(2-hexyldecyl)isoindigo-6, 6-diyl-alt-thiophene-2,5-diyl] (PTI-1) with PC(61)BM as acceptor are 50% higher than their PC71BM counterparts under illumination of AM1.5G. AFM images reveal different topographies of the blends between PTI-1:PC(61)BM and PTI-1:PC(71)BM, which suggests that acceptors miscibility plays a more important role than absorption. The photocurrent of 9.1 mA/cm(2) is among the highest value in PSCs with a driving force for exciton dissociation less than 0.2 eV.

Place, publisher, year, edition, pages
American Institute of Physics (AIP) , 2011. Vol. 99, no 14, 143302- p.
Keyword [en]
photoconductivity, polymer blends, solar cells, solubility
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-72028DOI: 10.1063/1.3645622ISI: 000295625100091OAI: oai:DiVA.org:liu-72028DiVA: diva2:455999
Note

Funding Agencies|Swedish Energy Agency||Swedish Research Council (VR)||VINNOVA||

Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08
In thesis
1. Studies of Morphology and Charge-Transfer in Bulk-Heterojunction Polymer Solar Cells
Open this publication in new window or tab >>Studies of Morphology and Charge-Transfer in Bulk-Heterojunction Polymer Solar Cells
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented in this thesis focuses on the two critical issues of bulk-heterojunction polymer solar cells: morphology of active layers and energy loss during charge transfer process at electron donor/acceptor interfaces. Both issues determine the performance of polymer solar cells through governing exciton dissociation, charge carrier recombination and free charge carrier transport.

The morphology of active layers (spatial percolation of the donor and acceptor) is crucial for the performance of polymer solar cells due to the limited diffusion length of excitons in organic semiconductors (5-20 nm). Meanwhile, the trade-off between charge generation and transport also needs to be considered. On the one hand, a finely mixed morphology with a large donor/acceptor interface area is preferred for charge generation because efficient exciton dissociation only occurs at the interface, but on the other hand, proper phase separation is needed to reduce charge carrier recombination and facilitate free charge carrier transport to the electrodes. In this thesis, morphologies of the active layers based on different polymeric donors and fullerene acceptors are correlated to the performance of solar cells with various microscopic and spectroscopic techniques including atomic force microscope, transmission electron microscope, grazing incidence x-ray diffraction, photoluminescence, electroluminescence and Fourier transform photocurrent spectroscopy. Furthermore, methods to manipulate the morphologies of solution processed active layers to achieve high performance solar cells are also presented. Processing solvents, chemical structures of the donor and the acceptor materials, and substrate surface properties are found critically important in determining the nanoscale phase separation and performance of polymer solar cells.

Optimizing morphology of active layers alone does not guarantee high performance devices. In addition to spatial percolation, energy arrangements of donors and acceptors are also essential due to contrary requests of the photocurrent and the photovoltage: Efficient exciton dissociation or charge transfer at donor/acceptor interfaces requires large enough energetic driving force, which is also known as energy loss for charge transfer. However, the energy loss due to charge transfer will unavoidably reduce the photovoltage. In this thesis the balance between the photocurrent and the photovoltage in polymer solar cells due to charge transfer at donor/acceptor interfaces is investigated for different active material systems. The driving force tuned by synthesizing series of polymers is determined by directly measuring the optical band gap via UV-Vis spectroscopy and probing the charge transfer recombination via electroluminescence measurements. Influences of driving force on the photocurrent and the photovoltage are characterized via field dependent photoluminescence and internal quantum efficiency measurements. The results correlated well with the performance of the solar cells.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 53 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1545
National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-99430 (URN)10.3384/diss.diva-99430 (DOI)978-91-7519-509-4 (ISBN)
Public defence
2013-11-14, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
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Supervisors
Available from: 2013-10-17 Created: 2013-10-17 Last updated: 2013-10-17Bibliographically approved

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Ma, ZaifeiVandewal, KoenZhang, Fengling

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