| 1. |
- Shard, A. G., et al.
(författare)
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Measuring Compositions in Organic Depth Profiling: Results from a VAMAS Interlaboratory Study
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:33, s. 10784-10797
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of a VAMAS (Versailles Project on Advanced Materials and Standards) interlaboratory study on the measurement of composition in organic depth profiling. Layered samples with known binary compositions of Irganox 1010 and either Irganox 1098 or Fmoc-pentafluoro-L-phenylalanine in each layer were manufactured in a single batch and distributed to more than 20 participating laboratories. The samples were analyzed using argon cluster ion sputtering and either X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (ToF-SIMS) to generate depth profiles. Participants were asked to estimate the volume fractions in two of the layers and were provided with the compositions of all other layers. Participants using XPS provided volume fractions within 0.03 of the nominal values. Participants using ToF-SIMS either made no attempt, or used various methods that gave results ranging in error from 0.02 to over 0.10 in volume fraction, the latter representing a 50% relative error for a nominal volume fraction of 0.2. Error was predominantly caused by inadequacy in the ability to compensate for primary ion intensity variations and the matrix effect in SIMS. Matrix effects in these materials appear to be more pronounced as the number of atoms in both the primary analytical ion and the secondary ion increase. Using the participants' data we show that organic SIMS matrix effects can be measured and are remarkably consistent between instruments. We provide recommendations for identifying and compensating for matrix effects. Finally, we demonstrate, using a simple normalization method, that virtually all ToF-SIMS participants could have obtained estimates of volume fraction that were at least as accurate and consistent as XPS.
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| 2. |
- Anselmo, Ana Sofia, 1980-, et al.
(författare)
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Tuning the Vertical Phase Separation in Polyfluorene: Fullerene Blend Films by Polymer Functionalization
- 2011
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Ingår i: Chemistry of Materials. - Washington : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:9, s. 2295-2302
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Svanstrom, C. M. B., et al.
(författare)
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Device Performance of APFO-3/PCBM Solar Cells with Controlled Morphology
- 2009
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Ingår i: Advanced Materials. - Weinheim : Wiley. - 0935-9648 .- 1521-4095. ; 21:43, s. 4398-
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Tidskriftsartikel (refereegranskat)abstract
- Polymer/fullerene solar cells with three different device structures: A) diffuse bilayer, B) spontaneously formed multilayer and C) vertically homogeneous thin films, are fabricated. The photocurrent/voltage performance is compared and it is found that the self-stratified structure (B) yields the highest energy conversion efficiency.
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