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Conductive polymers are a very promising alternative for the fabrication of transparent conductive materials. They have many advantages compared to existing materials, like a low-cost and a high flexibility. However, electrical conductivity still needs to be improved. We report a straightforward solution-based approach for the fabrication of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films with conductivity as high as 6046 ± 510 S cm−1, based on accurate water content control during the polymerization step. The crystallinity improvement is evidenced by GIWAXS characterization, and low temperature electrical conductivity measurements give new insights on the transport mechanisms at stake. This very high conductivity is, to our knowledge, the highest reported value for solution-based synthesis of PEDOT based materials. [ABSTRACT FROM AUTHOR]

Oxygen plasma is a widely used treatment to change the surface properties of organic layers. This treatment is particularly interesting to enable the deposition from solution of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) on top of the active layer of organic solar cells or photodetectors. However, oxygen is known to be detrimental to organic devices, as the active layer is very sensitive to oxygen and photo-oxidation. In this study, we aim to determine the impact of oxygen plasma surface treatment on the performance of organic photodetectors (OPD). We show a significant reduction of the sensitivity as well as a change in the shape of the external quantum efficiency (EQE) of the device. Using hole density and conductivity measurements, we demonstrate the p-doping of the active layer induced by oxygen plasma. Admittance spectroscopy shows the formation of trap states approximately 350 meV above the highest occupied molecular orbital of the active organic semiconductor layer. Numerical simulations are carried out to understand the impact of p-doping and traps on the electrical characteristics and performance of the OPDs. [ABSTRACT FROM AUTHOR]

The polymer Poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b’)dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno [3,4- b ]thiophene-)-2-6-diyl)] (PBDTTT-c) p-doped with the molecular dopant tris[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd-COCF 3 ) 3 ) exhibits a decline in transport properties at high doping concentrations, which limits the performance attainable through organic semiconductor doping. Scanning Electron Microscopy is used to correlate the evolution of hole conductivity and hopping transport activation energy with the formation of aggregates in the layer. Transmission Electron Microscopy with energy-dispersive X-ray analysis along with liquid-state Nuclear Magnetic Resonance experiments are carried out to determine the composition of the aggregates. This study offers an explanation to the limited efficiency of doping at high dopant concentrations and reinforces the need to increase doping efficiency in order to be able to reduce the dopant concentration and not negatively affect conductivity. [ABSTRACT FROM AUTHOR]

In this work, the authors study active layers of organic photodetector devices containing phenyl-C61- butyric acid methyl ester and Poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b')dithiophene)-2,6- diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene-)-2-6-diyl)] (PBDTTT-C). Thin films are examined by x-ray photoemission spectroscopy coupled with argon gas cluster ion sputtering. The use of massive cluster projectiles instead of monoatomic ions has the advantage of not destroying the chemical structure of organic materials under study. The authors show how simulated aging influences the chemistry of these blends and how these alterations extend from sample surface into the bulk of the film. The authors identify several possible processes resulting from aging, including C=O bond breakage and PBDTTT-C diffusion. [ABSTRACT FROM AUTHOR]

Optimization of light emitting devices when light is trapped within the dielectric structures opens the question of the management of light propagation and of control of the directionality of extracted light. These phenomena are closely connected to the so‐called extraction length of light propagating within the device, a parameter that is poorly discussed when considering the design and architecture of devices. In this work, a straightforward method for the measurement of the extraction length in the case of luminescent sol–gel films patterned with a 2D photonic bandgap structure is presented. Quantitative information usually obtained by spectro‐angular measurements can be retrieved from simpler standard spectrometry, allowing discussion of the influence of pattern depth, which determines the extraction by the photonic structure as compared to other uncontrolled pathways such as diffusion from defects in the film coating. These assessments provide a quick and safe method for the quantitative evaluation of light extraction strategies toward a rational design of light emitting devices with optimized properties. [ABSTRACT FROM AUTHOR]

Abstract: Our work is devoted to the development of YAG:Ce3+ phosphor nanoparticle-based converter layer for white LEDs. To avoid losses due to scattering effects, the strategy is to control separately the down-conversion and the extraction of light instead of using micron-sized luminescent particles acting simultaneously as both converter and scatterer. YAG:Ce nanoparticles were synthesized by a glycothermal method in autoclave at low temperature (300°C). Y3Al5O12 garnet phase with a crystallite size of 25nm was obtained, as verified by X-ray diffraction and electron microscopy. The quantum yield of nanoparticles is 55%. The colloidal nanoparticles are finally incorporated into a sol–gel matrix of TiO2. The small difference in refractive index between particles and matrix and the nanosize of the particles contribute to the transparency of the converter films. The surface of these layers can be periodically patterned by soft nano-imprint lithography. The diffraction due to the obtained photonic crystal at the surface may offer the opportunity to compensate the absence of scattering to extract the converted light. [Copyright &y& Elsevier]

In nanoimprint lithography (NIL) viscous flow in polymeric thin films is the primary mechanism for the generation and the relaxation of the structures. Here we quantify the impact of confinement on the flow rate. Pattern relaxation experiments were carried out above the glass transition temperature as a function of film thickness. The results are adequately fitted by a simple expression for the flow rate valid at all confinements. This expression, based on Newtonian viscosity, should be of use in NIL process design and for the measurement of the rheological properties of confined polymers. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a physically-based model was adapted to P-type organic thin-film transistors (P-OTFTs) by describing the accumulation charge with a Lambert W (LW) function in order to extract their figures of merit as threshold voltage, low-field mobility and subthreshold slope related to the interface traps density. This continuous and differentiable model, implemented for the first time on OTFTs, allows an accurate evaluation of the output and transfer characteristics, reproducing well the OTFT behaviour below and above the threshold region. Additionally, it was validated for different channel lengths (from 10 to 100 μm), taking into account short-channel effects. This model was also used to extract the parameters of P-OTFTs measured at low temperatures, showing a thermally activated transport in the polymer organic semiconductor (OSC) with an effective width of localized states around 90 meV and a relatively high band-like mobility. We also showed that the evolution of the threshold voltage versus temperature was related to the electrostatic effect of the interface trapped charge. The comparison between classical extraction methods and our LW-function based method validated the application of our model to P-OTFTs parameters extraction, opening a possibility for compact modelling. Graphical abstract Image 1 Highlights • Physically-based model adapted to P-type OTFTs for parameters extraction. • Validated below and above threshold region in linear and saturation regimes. • Taking into account short-channel effects. • Used to study P-type OTFTs behaviour during low-temperature measurements. • Potential for organic transistors compact modelling. [ABSTRACT FROM AUTHOR]

When placed in the vicinity of metal nanoparticles, fluorophore molecules can have their fluorescence intensity enhanced. In order to engineer highly fluorescent thin films, surface plasmon enhancement fluorescence was studied on macroscopic systems composed of gold nanoparticles deposited on a substrate and coated by a dye-containing polymer film. We developed a simple method based on surface silanization to get a good dispersion of up to 100 nm gold nanoparticles on a substrate. While controlling the nanoparticle size and the fluorophore concentration, we measured the fluorescence enhancement factors of systems doped with dyes possessing different quantum yields. We evidenced experimentally that a fluorescence enhancement factor of 4 could be reached for a low-quantum yield dye and that the fluorophore quantum yield affects significantly the enhancement factor. We then discussed how our experimental results agree with previously developed models.

Surfaces that are strongly nonwetting to oil and other low surface tension liquids can be realized by trapping microscopic pockets of air within the asperities of a re-entrant texture and generating a solid-liquid-vapor composite interface. For low surface tension liquids such as hexadecane (gamma(lv) = 27.5 mN/m), this composite interface is metastable as a result of the low value of the equilibrium contact angle. Consequently, pressure perturbations can result in an irreversible transition of the metastable composite interface to the fully wetted interface. In this work, we use a simple dip-coating and thermal annealing procedure to tune the liquid wettability of commercially available polyester fabrics. A mixture of 10% 1H,1H,2H,2H-heptadecafluorodecyl polyhedral oligomeric silsesquioxane (fluorodecyl POSS) and 90% polyethyl methacrylate (PEMA) is used to uniformly coat the fabric surface topography. Contact angle measurements show that a robust metastable composite interface with high apparent contact angles can be supported for hexadecane (gamma(lv) = 27.5 mN/m) and dodecane (gamma(lv) = 25.3 mN/m). To tune the solid surface energy of the coated surface, we also developed a reversible treatment using thermal annealing of the surface in contact with either dry air or water. The tunability of the solid surface energy along with the inherent re-entrant texture of the polyester fabric result in reversibly switchable oleophobicity between a highly nonwetting state and a fully wetted state for low surface tension liquids such as hexadecane and dodecane. This tunability can be explained within a design parameter framework, which provides a quantitative criterion for the transition between the two states, as well as accurate predictions of the measured values of the apparent contact angle (theta*) for the dip-coated polyester fabrics.