Browsing by Author "Smith, ARG"

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    Investigating morphology and stability of Fac-tris (2-phenylpyridyl)iridium(III) films for OLEDs
    (Wiley-Blackwell Publishing, 2011-06-21) Smith, ARG; Ruggles, JL; Cavaye, H; Shaw, PE; Darwish, TA; James, M; Gentle, IR; Burn, PL
    Stable film morphology is critical for long-term high performance organic light-emitting diodes (OLEDs). Neutron reflectometry (NR) is used to study the out-of-plane structure of blended thin films and multilayer structures comprising evaporated small molecules. It is found that as-prepared blended films of fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)(3)] in 4,4'-bis(N-carbazolyl) biphenyl (CBP) are uniformly mixed, but the occurrence of phase separation upon thermal annealing is dependent on the blend ratio. Films comprised of the ratio of 6 wt% of Ir(ppy)(3) in CBP typically used in OLEDs are found to phase separate with moderate heating while a higher weight percent mixture (12 wt%) is found to be stable. Furthermore, it is found that thermal annealing of a multilayer film comprised of typical layers found in efficient devices ([tris(4-carbazoyl-9-ylphenyl)amine (TCTA)/Ir(ppy)(3):CBP/bathocuproine (BCP)]) causes the BCP layer to become mixed with the emissive blend layer, whereas the TCTA interface remains unchanged. This significant structural change causes no appreciable difference in the photo luminescence of the stack although such a change would have a dramatic effect on the charge transport through the device, leading to changes in performance. These results demonstrate the effect of thermal stress on the delicate interplay between the chemical composition and morphology of OLED films. © 2011, Wiley-Blackwell.
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    Morphology of all-solution-processed “bilayer” organic solar cells
    (Wiley-VCH Verlag Berlin, 2011-02-08) Lee, KH; Schwenn, PE; Smith, ARG; Cavaye, H; Shaw, PE; James, M; Krueger, KB; Gentle, IR; Meredith, P; Burn, PL
    We investigate the evolution of the vertical morphology in a solution-processed P3HT/PCBM “bilayer” organic solar cell using a combination of techniques, including neutron reflectometry. By correlating the device performance with the active layer morphology, we establish that the solution processed bilayer concept is a misnomer and sequential solution processing is an elegant way to make bulk heterojunction organic solar cells with high efficiency. © 2011, Wiley-VCH Verlag Berlin
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    Solid state dendrimer sensors: effect of dendrimer dimensionality on detection and sequestration of 2,4-dinitrotoluene
    (American Chemical Society, 2011-09-22) Cavaye, H; Shaw, PE; Smith, ARG; Burn, PL; Gentle, IR; James, M; Lo, SC; Meredith, P
    We compare two dendrimers, which contain the same luminescent chromophores but differ in dimensionality, for the detection of an explosive analyte via PL quenching. Each dendrimer has first generation biphenyl dendrons with 2-ethylhexyloxy surface groups but differ in the core units. One dendrimer has a bifluorene core and hence has a “planar†structure, whereas the second has four bifluorene units tetrahedrally arranged around an adamantyl center and hence has a “three-dimensional†structure. Solution Stern–Volmer measurements have previously been reported to show that the three-dimensional dendrimer has a higher binding constant than that of the more planar compound. Films of the dendrimers rapidly detect 2,4-dinitrotoluene (DNT) with thinner films (∼25 nm) being more responsive than thicker films (∼85 nm). Neutron reflectometry measurements show that the analyte can diffuse completely through the films with the three-dimensional dendrimer absorbing more of the analyte. The rate of recovery of the PL was faster for the planar dendrimer than the three-dimensional material showing that large binding constants are not necessary for reversible detection of analytes.© 2011, American Chemical Society
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    Solid-state dendrimer sensors: probing the diffusion of an explosive analogue using neutron reflectometry
    (American Chemical Society, 2009-11-03) Cavaye, H; Smith, ARG; James, M; Nelson, A; Burn, PL; Gentle, IR; Lo, SC; Meredith, P
    Determining how analytes are sequestered into thin films is important for solid-state sensors that detect the presence of the analyte by oxidative luminescence quenching. We show that thin (230 ± 30 Å) and thick (750 ± 50 Å) films of a first-generation dendrimer comprised of 2-ethylhexyloxy surface groups, biphenyl-based dendrons, and a 9,9,9′,9′-tetra-n-propyl-2,2′-bifluorene core, can rapidly and reversibly detect p-nitrotoluene by oxidative luminescence quenching. For both the thin and thick films the photoluminescence (PL) is quenched by p-nitrotoluene by 90% in 4 s, which is much faster than that reported for luminescent polymer films. Combined PL and neutron reflectometry measurements on pristine and analyte-saturated films gave important insight into the analyte adsorption process. It was found that during the adsorption process the films swelled, being on average 4% thicker for both the thin and thick dendrimer films. At the same time the PL was completely quenched. On removal of the analyte the films returned to their original thickness and scattering length density, and the PL was restored, showing that the sensing process was fully reversible. © 2009, American Chemical Society