5 research outputs found
Microstructure of Polycrystalline PBTTT Films: Domain Mapping and Structure Formation
We utilize near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning transmission X-ray microscopy (STXM) to study the microstructure and domain structure of polycrystalline films of the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-<i>b</i>]thiophene) (PBTTT). Total electron yield NEXAFS spectroscopy is used to examine the surface structure of the first 1–2 molecular layers, while bulk-sensitive STXM is used to produce maps of domain orientation and order sampled through the entire film thickness. We study different phases of PBTTT including as-cast, terraced and nanoribbon morphologies produced <i>via</i> spin-coating as well as aligned films of as-cast and nanoribbon morphologies produced by zone-casting. For the terraced morphology, domains are observed that are larger than the size of the terraced surface features, and the calculated degree of order is reduced compared to the nanoribbon morphology. For zone-cast films, we find that, although little optical anisotropy is observed in the bulk of as-cast films, a high degree of surface structural anisotropy is observed with NEXAFS spectroscopy, similar to what is observed in annealed nanoribbon films. This observation indicates that the aligned surface structure in unannealed zone-cast films templates the bulk ordering of the aligned nanoribbon phase. STXM domain mapping of aligned nanoribbon films reveals elongated, micrometer-wide domains with each domain misoriented with respect to its neighbor by up to 45°, but with broad domain boundaries. Within each nanoribbon domain, a high degree of X-ray dichroism is observed, indicating correlated ordering throughout the bulk of the film
Oligomeric Compatibilizers for Control of phase Separation in Conjugated Polymer Blend Films
Control over phase separation and morphology is critical
to optimal function in polymer optoelectronic devices. Here, two fully
conjugated oligomeric compatibilizers are introduced, and their effect
on the phase separation of blends of poly(9,9′-dioctylfluorene-<i>co</i>-benzo-thiadiazole) (F8BT) with poly(9,9′-dioctylfluorene-<i>co</i>-bis-<i>N</i>,<i>N</i>′-(4,butylphenyl)bis-<i>N</i>,<i>N</i>′-phenyl-1,4-phenylenediamine)
(PFB) are reported. AFM and STXM analysis demonstrate that the addition
of compatibilizer altered the size and relative composition of phase-separated
domains formed during spin-casting. Small structural differences between
the two compatibilizers brought about significantly different morphological
changes to the blends, suggesting that further development of compatibilizer
structure could enable enhanced control toward desired blend film
morphologies
Identifying Photoreaction Products in Cinnamate-Based Photoalignment Materials
A novel joint computational and experimental
strategy is developed
and applied for the detection and the identification of photoreaction
products in cinnamate-based photoalignment materials. Based on NEXAFS,
IR, and NMR spectroscopies and supported by computer simulation tools,
this structural analysis method allows distinguishing the typical
signatures of products resulting from UV-induced photoreactions between
isomers of cinnamate-based model compounds. Besides deepening the
understanding of typical photoalignment reaction products, the proposed
strategy acquires technological relevance in supporting the realization
of next generation materials for the LCD panel industry
Asymmetry Matters: Structure Elucidation and Application Potential of Solution-Processed Monoalkylated BTBT Thin Films
Two-dimensionally (2D) extended thin films of p-type
organic semiconductor
C13-BTBT (BTBT = [1]benzothieno[3,2-b]-[1]benzothiophene)
were fabricated via self-controlled growth at the liquid–liquid
interface. Depicting a compound class originally developed for further
functionalization and subsequent realization of self-assembled monolayers
(SAMs), the potent BTBT core unit commonly excels in high-quality
structure formation as well as charge-transport characteristics. Utilizing
a manifold spectromicroscopic toolbox, we observe extraordinarily
crystalline C13-BTBT films with an upright standing configuration
of the backbone unit accounting for superior intermolecular orbital
overlap. The well-defined morphology and internal structure of the
film are being underpinned by charge-transport parameters that are
in the range of comparable organic electronic devices based on bisubstituted
BTBT films from the same processing technique. The inherently favorable
membrane-like bilayer molecular arrangement is confirmed by unambiguous
representation of the unit cell as derived from electron tomography
Asymmetry Matters: Structure Elucidation and Application Potential of Solution-Processed Monoalkylated BTBT Thin Films
Two-dimensionally (2D) extended thin films of p-type
organic semiconductor
C13-BTBT (BTBT = [1]benzothieno[3,2-b]-[1]benzothiophene)
were fabricated via self-controlled growth at the liquid–liquid
interface. Depicting a compound class originally developed for further
functionalization and subsequent realization of self-assembled monolayers
(SAMs), the potent BTBT core unit commonly excels in high-quality
structure formation as well as charge-transport characteristics. Utilizing
a manifold spectromicroscopic toolbox, we observe extraordinarily
crystalline C13-BTBT films with an upright standing configuration
of the backbone unit accounting for superior intermolecular orbital
overlap. The well-defined morphology and internal structure of the
film are being underpinned by charge-transport parameters that are
in the range of comparable organic electronic devices based on bisubstituted
BTBT films from the same processing technique. The inherently favorable
membrane-like bilayer molecular arrangement is confirmed by unambiguous
representation of the unit cell as derived from electron tomography