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The morphology of polyfluorene: fullerene blend films for photovoltaic applications
Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för maskin- och materialteknik.
2011 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Polymer photovoltaic systems whose photoactive layer is a blend of a semiconducting polymer with a fullerene derivative in a bulk heterojunction configuration are amongst the most successful organic photovoltaic devices nowadays. The three-dimensional organization in these layers (the morphology) plays a crucial role in the performance of the devices. Detailed characterization of this organization at the nanoscale would provide valuable information for improving future material and architectural design and for device optimization.

In this thesis, the results of morphology studies of blends of several polyfluorene copolymers (APFOs) blended with a fullerene derivative are presented. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy was combined with dynamic Secondary Ion Mass Spectrometry (dSIMS) for surface and in-depth characterization of the blend films. NEXAFS was performed using two different electron detection methods, partial (PEY) and total (TEY) electron yield, which provide information from different depth regimes. Quantitative compositional information was obtained by fitting the spectra of the blend films with a linear combination of the spectra of films of the pure components. In blends of APFO3 with PCBM in two different blend ratios (1:1 and 1:4 of polymer:fullerene) NEXAFS data show the existence of compositional gradients in the vertical direction for both blend ratios, with clear polymer enrichment of the free surface. A series of APFOs with systematic changes in the side-chains was studied and it was shown that those small modifications can affect polymer:fullerene interaction and induce vertical phase separation. Polymer-enrichment of the free surface was clearly identified, in accordance with surface energy minimization mechanisms, and a compositional gradient was revealed already in the first few nanometers of the surface of the blend films. dSIMS showed that this vertical phase separation propagates throughout the film. It was possible to determine that as the polar character of the polymer increases, and thus the polymer:fullerene miscibility is improved, the tendency for vertical phase separation becomes stronger.

sted, utgiver, år, opplag, sider
Karlstad: Karlstad University , 2011. , s. 47
Serie
Karlstad University Studies, ISSN 1403-8099 ; 2011:36
Emneord [en]
Materials Science, Organic Photovoltaics, Polymer Solar Cells
HSV kategori
Forskningsprogram
Materialteknik
Identifikatorer
URN: urn:nbn:se:kau:diva-7950ISBN: 978-91-7063-370-6 (tryckt)OAI: oai:DiVA.org:kau-7950DiVA, id: diva2:430532
Presentation
2011-09-02, 21D 302, Karlstads universitet, Karlstad, 10:15 (svensk)
Opponent
Merknad

Paper II was not published at the time of the licentiate defence and had the title: NEXAFS spectroscopy study of the surface composition in APFO3:PCBM blend films

Tilgjengelig fra: 2011-08-10 Laget: 2011-07-11 Sist oppdatert: 2016-08-16bibliografisk kontrollert
Delarbeid
1. Tuning the Vertical Phase Separation in Polyfluorene:Fullerene Blend Films by Polymer Functionalization
Åpne denne publikasjonen i ny fane eller vindu >>Tuning the Vertical Phase Separation in Polyfluorene:Fullerene Blend Films by Polymer Functionalization
Vise andre…
2011 (engelsk)Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 23, nr 9, s. 2295-2302Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Achieving control over the nanomorphology of blend films of the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester, PCBM, with light-absorbing conjugated polymers is an important challenge in the development of efficient solution-processed photovoltaics. Here, three new polyfluorene copolymers are presented, tailored for enhanced miscibility with the fullerene through the introduction of polymer segments with modified side chains, which enhance the polymer’s polar character. The composition of the spincoated polymer:PCBM films is analyzed with dynamic secondary ion mass spectrometry (dSIMS). The dSIMS depth profiles demonstrate compositional variations perpendicular to the surface plane, as a result of vertical phase separation, directed by the substrate. These variations propagate to a higher degree through the film for the polymers with a larger fraction of modified side chains. The surface composition of the films is studied by Near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Quantitative analysis of the NEXAFS spectra through a linear combination fit with the spectra of the pure components yields the surface composition. The resulting blend ratios reveal polymer-enrichment of the film surface for all three blends, which also becomes stronger as the polar character of the polymer increases. Comparison of the NEXAFS spectra collected with two different sampling depths shows that the vertical composition gradient builds up already in the first nanometers underneath the surface of the films. The results obtained with this new series of polymers shed light on the onset of formation of lamellar structures in thin polymer:PCBM films prepared from highly volatile solvents

sted, utgiver, år, opplag, sider
Washington: ACS Publications, 2011
Emneord
morphology; polymer−fullerene interaction; solar cell
HSV kategori
Forskningsprogram
Fysik
Identifikatorer
urn:nbn:se:kau:diva-7817 (URN)10.1021/cm1021596 (DOI)000290063600004 ()
Forskningsfinansiär
Swedish Research Council
Tilgjengelig fra: 2011-06-27 Laget: 2011-06-27 Sist oppdatert: 2017-12-11bibliografisk kontrollert
2. Molecular orientation and composition at the surface of APFO3:PCBM blend films
Åpne denne publikasjonen i ny fane eller vindu >>Molecular orientation and composition at the surface of APFO3:PCBM blend films
Vise andre…
2012 (engelsk)Inngår i: Hybrid and Organics Photovoltaics Conference: Uppsala, Sweden, 2012 / [ed] Anders Hagfeldt, SEFIN, Castelló (Spain), 2012, s. 278-Konferansepaper, Poster (with or without abstract) (Fagfellevurdert)
sted, utgiver, år, opplag, sider
SEFIN, Castelló (Spain): , 2012
Serie
Nanoenergy Series ; Vol. 9
Emneord
polymer, solar cell, photovoltaics
HSV kategori
Forskningsprogram
Materialvetenskap; Fysik; Kemi
Identifikatorer
urn:nbn:se:kau:diva-29032 (URN)978-84-940189-0-9 (ISBN)
Konferanse
4th international Conference on Hybrid and Organic Photovoltaics, HOPV12, Uppsala, 6-9 May 2012
Forskningsfinansiär
Swedish Research Council, 2010-4155
Tilgjengelig fra: 2013-09-13 Laget: 2013-09-13 Sist oppdatert: 2019-05-20bibliografisk kontrollert

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