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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]

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]

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 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]

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a transparent conductive polymer widely used in flexible photonic and optoelectronic devices because of its excellent electrical and optical properties. However, its current range of applications is limited by its poor stability under high humidity and solar radiations. Encapsulation is an attractive solution to this problem and the development of a low-temperature and scalable deposition method is highly desirable. In this study, we report the use of spatial atomic layer deposition (SALD) to deposit ultrathin layers of ZnO, TiO 2 , and Al 2 O 3. These nanolayers maintain the electrical performance of the conductive polymer and its high optical transmittance. The use of SALD ensures low-cost and flexible processing with pinhole-free high-quality coatings at atmospheric pressure and high-throughput. The present study is the first to investigate the effect of various multilayer metal oxide encapsulations on the long-term stability of PEDOT-based transparent conductive materials under solar radiations. We demonstrate finally that bilayer TiO 2 /Al 2 O 3 and TiO 2 /ZnO coatings preserve the optoelectronic properties of three different PEDOT-based films, namely PEDOT:OTf (OTf = triflate), PEDOT:Sulf (Sulf = sulfate)and PEDOT:PSS (PSS = PolyStyreneSulfonate) films. [Display omitted] • PEDOT materials are encapsulated using spatial atomic layer deposition. • Deposition of nanolayers is an efficient method to preserve the electrical performances of highly conductive PEDOT. • Bilayer structures TiO 2 /ZnO and TiO 2 /Al 2 O 3 lead to the most effective protection. [ABSTRACT FROM AUTHOR]