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Universal modification of poor cathodes into good ones by a polymer interlayer for high performance reversed organic solar cells
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-3899-4891
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

In organic bulk-heterojunction solar cells, energy losses at the active layer/electrode interface are often observed. Modification of these interfaces with organic interlayers optimizes charge carrier injection and extraction and thus improves device performance. In this work, the effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer; further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep HOMO of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor. We demonstrate a possibility of improving photovoltaic performance of reversed solar cells via a simple and universal interface modification and provide the basic guidelines for development and characterization of interface materials for organic solar cells in general.

Place, publisher, year, edition, pages
2014.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-103928OAI: oai:DiVA.org:liu-103928DiVA: diva2:693133
Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2017-01-11Bibliographically approved
In thesis
1. Chargeand Light Management in Organic Solar Cells
Open this publication in new window or tab >>Chargeand Light Management in Organic Solar Cells
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solar cells based on organic materials are extensively investigated both in academia and industry, owing to their potential of being inexpensive, lightweight, flexible and suitable for roll-to-roll production. Performance of organic solar cells has been rapidly improving, and the state of the art organic solar cells have an efficiency over 10%.

This thesis aims to provide a comprehensive study of device engineering and device physics of organic solar cells. The ambition has been to investigate and optimize the conditions for light in-coupling and charge extraction in organic solar cells with alternative geometries. The ultimate goal is to propose methods that could potentially get the power conversion efficiency of organic solar cells with industrially compatible geometries over the current limit of 10%.

To achieve such a goal, we employed a conjugated polymer as an interface modifier to improve the surface and electrical properties of substrate electrodes for solar cells with active layers based on blends containing conjugated polymers and fullerenes. A possibility of improving photovoltaic performance of easily fabricated reverse geometry solar cells (bottom metal cathode/active layer/top  transparent anode) has been demonstrated via this simple interface modification. Systematic investigations revealed that the enhanced device performance was not only related to the modified active layer/electrode interface but also changes in the bulk of the active layer. Consequently, the device performance of a reversed solar cell was found to be as good as that of a standard solar cell. The understanding of the effects of the interlayer modification on the performance of reversed solar cells, and the methodology provided in this thesis is a guideline for further studying and developing interface materials for highly efficient organic solar cells.

An ITO electrode was further converted into a cathode by the polymer interlayer to construct semi-transparent solar cells with great potentials for building integrated photovoltaic applications. By stacking semi-transparent solar cells on top of each other, we showed that light can be more efficiently harvested compared to a conventional architecture solar cell. It has also been demonstrated that semitransparent solar cells combined with macroscopic light trapping elements can also be highly efficient.

However, this thesis is not only about papers that I have published as a graduate student. The first five chapters have been included to provide background in the field of organic photovoltaics.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 79 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1567
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-103930 (URN)978-91-7519-419-6 (ISBN)
Public defence
2014-03-07, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2014-02-03Bibliographically approved

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Tang, ZhengTress, WolfgangBao, QinyeJafari, Mohammad JavadBergqvist, JonasEderth, ThomasInganäs, Olle

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Biomolecular and Organic ElectronicsThe Institute of TechnologySurface Physics and ChemistryMolecular PhysicsFaculty of Science & Engineering
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