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Stability of electron acceptor materials for organic solar cells: a work function study of C60/C70 derivatives and N2200
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Stabilitet av elektron acceptor material för organiska solceller : en studie av utträdesarbetet i C60/C70 derivator samt N2200 (Swedish)
Abstract [en]

Thin films of the fullerenes PC60BM and PC70BM and the non-fullerene N2200, three popular electron acceptor materials in organic photovoltaics, have been studied, using both the Kelvin probe method as well as ultraviolet photoelectron spectroscopy. With these methods the work function was measured, as well as the highest occupied molecular orbital (HOMO) onset. Additionally band bending effects were studied by illuminating the samples while measuring the work function with the Kelvin probe so called surface photovoltage. Sample of each material was exposed to either air and simulated sunlight or N2 and simulated sunlight, for different length of time, to observe how the materials work function evolves after exposure to the different conditions. It was observed that, as expected from previous studies, that PC60BM was less photo-stable than PC70BM. Additionally, the work function of PC60BM changed significantly by storage in N2. Each material after exposure for 24h to air and light, was annealed and measured with the Kelvin probe. A restoring effect was observed,  for the non-fullerene material N2200. All three materials developed an increasing surface photovoltage, which suggest increased band bending, when exposed to air and light, indicating that due phot-oxidization, charges are redistributed at the surface of the film. The fullerenes showed a larger surface photovoltage effect than the non-fullerene materials. A difference between the work function values obtained from the Kelvin probe method and the ultraviolet photoelectron spectroscopy could be seen, however the exact reason for this couldn't be isolated within this thesis, but was discussed.

Place, publisher, year, edition, pages
2019. , p. 54
National Category
Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:kau:diva-72727OAI: oai:DiVA.org:kau-72727DiVA, id: diva2:1327030
Subject / course
Physics
Educational program
Master of Science in Engineering, Degree Programme in Engineering Physics (120 ECTS credits)
Presentation
2019-06-03, 21A 244, Universitetsgatan 2, Karlstad, 11:15 (English)
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Available from: 2019-06-19 Created: 2019-06-18 Last updated: 2019-06-19Bibliographically approved

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