| 1. |
- Anselmo, Ana Sofia, 1980-, et al.
(author)
-
Characterisation of vertical phase separation in polymer : fullerene blend films for photovoltaics by dSIMS and NEXAFS
- 2011
-
In: E-MRS 2011 Spring Meeting. - Malden, MA : John Wiley & Sons. ; , s. 62-63
-
Conference paper (peer-reviewed)abstract
- Morphological control and characterization of blend films is key in the development of viable polymer solar cells. Spontaneous formation of vertical compositional gradients during solution processing has been shown for polyfluorene:PCBM blends and rationalized with thermodynamic and kinetic models of nucleation and spinodal decomposition.[1, 2] The extent of vertical stratification is affected by polymer side-chain modification aimed at controlling polymer:fullerene miscibility.[3] Here we present high-resolution film morphology results for several polymer:fullerene systems as obtained from near-edge X-ray fine structure spectroscopy (NEXAFS) in partial and in total electron yield modes. Blend films were found to be polymer- enriched at the surface. Dynamic secondary ion mass spectrometry (dSIMS) and NEXAFS give compositional information at different depths, resulting in a more complete picture of the film morphology.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Anselmo, Ana Sofia, 1980-, et al.
(author)
-
Molecular Orientation and Composition at the Surface of Spin-Coated Polyfluorene:Fullerene Blend Films
- 2013
-
In: Journal of Polymer Science Part B. - Hoboken, New Jersey : John Wiley & Sons. - 0887-6266 .- 1099-0488. ; 51:3, s. 176-182
-
Journal article (peer-reviewed)abstract
- The surface composition in spin-coated films of polyfluorene:fullerene blends was determined quantitatively by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. By comparing partial and total electron yield spectra, we found vertical compositional differences in the surface region. Furthermore, the orientation of the polymer chains was investigated by variable-angle NEXAFS. Blend films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] with [6,6]-phenyl-C61-butyric acid methyl ester in two different blend ratios were studied. Results showed polymer enrichment of the surfaces for films with a polymer:fullerene weight ratio of 20:80 and of 50:50, spin-coated from both chlorobenzene and chloroform solutions. The angular dependence of the NEXAFS spectra of the pure polymer films showed a preferential plane-on orientation, which was slightly stronger in the subsurface region than at the surface. In blend films, this orientational preference was less pronounced and the difference between surface and subsurface vanished
|
|
| 5. |
- Anselmo, Ana Sofia, 1980-, et al.
(author)
-
Photodegradation of the electronic structure of PCBM and C60 films in air
- 2016
-
In: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 652, s. 220-224
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 6. |
|
|
| 7. |
- Brumboiu, Iulia E., et al.
(author)
-
Near-edge X-ray Absorption Fine Structure Study of the C60-derivative PCBM
- 2013
-
In: Chemical Physics Letters. - Amsterdam : Elsevier BV. - 0009-2614 .- 1873-4448. ; 568-569, s. 130-134
-
Journal article (peer-reviewed)abstract
- The fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first π∗-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C60-cage.
|
|
| 8. |
- Buga, Sergei G., et al.
(author)
-
Electrical properties of 3D-polymeric crystalline and disordered C60 and C70 fullerites.
- 2005
-
In: Diamond and Related Materials vol. 14, special Issue (3-7). - : Elsevier B.V.. ; , s. 896-901
-
Conference paper (peer-reviewed)abstract
- Crystalline and disordered 3D-polymeric C60 and C70 with different lattice parameters and with densities in the range of 2.2÷3.25 g cm−1 were obtained by high-pressure-high-temperature treatment at P=11.5÷15 GPa, T=670÷1800 K. Their d.c. electrical conductivity was investigated at temperatures 30÷350 K. The variable range hopping mechanism dominates in all samples up to room temperature. A temperature activated conductivity via delocalized states was observed at T>160÷260 K in crystalline C60 samples and in some samples with disordered structure. The evaluated band gap value is Eg=0.28÷0.54 eV for different crystalline structures and 0.06÷0.25 eV for disordered ones
|
|
| 9. |
- Dmitriev, Vladimir, et al.
(author)
-
Pressure-temperature phase diagram of LiBH4: Synchrotron x-ray diffraction experiments and theoretical analysis
- 2008
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 77:17
-
Journal article (peer-reviewed)abstract
- An in situ combined high-temperature high-pressure synchrotron radiation diffraction study has been carried out on LiBH4. The phase diagram of LiBH4 is mapped to 10 GPa and 500 K, and four phases are identified. The corresponding structural distortions are analyzed in terms of symmetry-breaking atomic position shifts and anion ordering. Group-theoretical and crystal-chemical considerations reveal a nontrivial layered structure of LiBH4. The layers and their deformations define the structural stability of the observed phases.
|
|
| 10. |
|
|
