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Photodegradation of the electronic structure of PCBM and C60 films in air
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science. (Materialfysik)
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialvetenskap)
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialfysik)ORCID iD: 0000-0003-1711-5595
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialvetenskap)
2016 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 652, 220-224 p.Article in journal (Other academic) Published
Abstract [en]

Fullerenes are common electron acceptors in organic solar cells. Here the photostability in air of the electronic structures of spin-coated PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and evaporated C60 films are studied using ultraviolet photoelectron spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. After exposing these materials in air to simulated sunlight, the filled and empty molecular orbitals are strongly altered, indicating that the conjugated π-system of the C60-cage has degraded. Even a few minutes in normal lab light induces changes. These results stress the importance of protecting fullerene-based films from light and air during processing, operation, and storage.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 652, 220-224 p.
Keyword [en]
Degradation; Fullerene; Photostability; Photovoltaics; NEXAFS
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:kau:diva-16111DOI: 10.1016/j.cplett.2016.04.003OAI: oai:DiVA.org:kau-16111DiVA: diva2:574995
Note

The article was still in manuscript form in anna Anselmos thesis. It had then the title: Light-induced modification of the electronic structure of PCBM and C60 films

Available from: 2012-12-07 Created: 2012-12-07 Last updated: 2017-08-14Bibliographically approved
In thesis
1. Materials aspects in spin-coated films for polymer photovoltaics
Open this publication in new window or tab >>Materials aspects in spin-coated films for polymer photovoltaics
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polymer-based photovoltaics have the potential to contribute to boosting photovoltaic energy conversion overall. Besides allowing large-area inexpensive processing, polymeric materials have the added benefit of opening new market applications for photovoltaics due to their low-weight and interesting mechanical properties. The energy conversion efficiency values of polymer photovoltaics have reached new record values over the past years. It is however crucial that stability issues are addressed together with efficiency optimization. Understanding fundamental materials aspects is key in both areas.

In the work presented in this thesis, the morphology of polymer:fullerene films and its influence on device performance was studied, as well as the effect of light exposure on the surface of fullerene films. Several polyfluorene copolymers were used for the morphology studies, where the effects of changing spin-coating solvent and of side chain engineering were investigated with dynamic secondary ion mass spectrometry (dSIMS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Polymer-enriched surfaces were found in all blend films, even in the cases with homogeneous distributions in the bulk. Side chain engineering of the polymer led to gradual changes in the compositional variations perpendicular to the surface, and to slight variations in the photocurrent. The electronic structure of the fullerene derivative PCBM was studied in detail and the spectroscopic fingerprint of the materials was analysed by comparison with theoretically simulated spectra. Photo-stability studies done in air showed that the surface of fullerene films underwent severe damages at the molecular level, which is evident from changes in the valence band and X-ray absorption spectra. These changes were explained by transitions from sp2-type to sp3 hybridization of the carbon atoms in the cage that resulted in the destruction of the fullerene cage.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2013. 88 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2013:3
Keyword
materials science, photovoltaics, conjugated polymer, polymer solar cell, bulk heterojunction, coating, morphology, fullerene, photostability, degradation, X-ray absorption spectroscopy, synchroton-based techniques
National Category
Physical Sciences
Research subject
Materialvetenskap
Identifiers
urn:nbn:se:kau:diva-16107 (URN)978-91-7063-475-8 (ISBN)
Public defence
2013-01-25, 21A342, Karlstad University, SE-651 88, Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2013-01-07 Created: 2012-12-07 Last updated: 2013-01-07Bibliographically approved

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