Piezoresistive properties of PEDOT:PSS

Recent market studies mention the necessity to include sensors in the design of organic electronic devices in order to broaden the range of applications. It is therefore essential to identify potential organic mechanical sensor materials and to develop processes and methods to structure them and characterize their piezoresistive properties. Furthermore, it is also essential for organic electronic devices to know the change of resistance upon bending of flexible substrates. A material widely used in organic electronics is the complex of the intrinsically conductive polymer poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT/PSS). In this paper first the fabrication of a polyimide (PI) membrane with integrated PEDOT/PSS strain gauges is presented. Upon a pressure difference the membrane is deflected and the resulting changes in resistance of the sensor elements are recorded. By applying a membrane mechanics model the resistance changes can be linked to the strain in the membrane and then the plane strain gauge factor k_PS for PEDOT/PSS of 0.48±0.07 at 36.6±3% rH can be determined.     

The Role of Heteroatoms Leading to Hydrogen Bonds in View of Extended Chemical Stability of Organic Semiconductors

The major challenge in organic electronics concerns the stability of organic semiconductor materials which affects the operational lifetime of devices. Recent reports have shown that hydrogen‐bonded pigments of the indigoid family are air‐ and moisture resistant. The magenta pigment quinacridone, a hydrogen‐bonded molecule in the solid state with a pentacene like frame, is a perfect example for extraordinary chemical stability. Here, studies using in situ spectroscopic methods comparing quinacridone and pentacene are presented. A different spectral response of their radical cations is observed upon chemical doping. While in pentacene the barrier between doping and irreversible overoxidation is small, this stability toward overoxidation is increased by the heteroatomic structure, leading to hydrogen‐bonded quinacridone. This work provides insight into molecular design principles that may lead to next‐generation organic semiconductors with enhanced stability and performance.     

A Biomimetic,Copolymeric Membrane for Cell-Stretch Experiments with Pulmonary Epithelial Cells at the Air-Liquid Interface

Chronic respiratory diseases are among the leading causes of death worldwide, but only symptomatic therapies are available for terminal illness. This in part reflects a lack of biomimetic in vitro models that can imitate the complex environment and physiology of the lung. Here, a copolymeric membrane consisting of poly(ε-)caprolactone and gelatin with tunable properties, resembling the main characteristics of the alveolar basement membrane is introduced. The thin bioinspired membrane (≤5 μm) is stretchable (up to 25% linear strain) with appropriate surface wettability and porosity for culturing lung epithelial cells under air–liquid interface conditions. The unique biphasic concept of this membrane provides optimum characteristics for initial cell growth (phase I) and then switch to biomimetic properties for cyclic cell-stretch experiments (phase II). It is showed that physiologic cyclic mechanical stretch improves formation of F-actin cytoskeleton filaments and tight junctions while non-physiologic over-stretch induces cell apoptosis, activates inflammatory response (IL-8), and impairs epithelial barrier integrity. It is also demonstrated that cyclic physiologic stretch can enhance the cellular uptake of nanoparticles. Since this membrane offers considerable advantages over currently used membranes, it may lead the way to more biomimetic in vitro models of the lung for translation of in vitro response studies into clinical outcome.     

Electrochemical doping for lowering contact barriers in organic field effect transistors

By electrochemically p-doping pentacene in the vicinity of the source-drain electrodes in organic field effect transistors the injection barrier for holes is decreased. The focus of this work is put on the influence of the p-doping process on the transistor performance. Cyclic voltammetry performed on a pentacene based transistor exhibits a reversible p-doping response. This doped state is evoked at the transistor injection electrodes. An improvement is observed when comparing transistor characteristics before and after the doping process apparent by an improved transistor on-current. This effect is reflected in the analysis of the contact resistances of the devices.     

Measurement of optical nonlinearity in silicon rich nitride waveguide ring resonators

The optical nonlinearities of amorphous silicon rich nitride corresponding to /spl chi//sup (3)/ in a static electric field have been measured by tracking wavelength shifts in the resonances of optical waveguide ring resonators as a function of an applied electrical field. The magnitude of the nonlinearity measured agrees well with expected values.     

Monolithic Si nanocrystal/crystalline Si tandem cells involving Si nanocrystals in SiC

Monolithic tandem cells involving a top cell with Si nanocrystals embedded in SiC (Si NC/SiC) and a c‐Si bottom cell have been prepared. Scanning electron microscopy shows that the intended cell architecture is achieved and that it survives the 1100 °C anneal required to form Si NCs. The cells exhibit mean open‐circuit voltages V_oc of 900–950 mV, demonstrating tandem cell functionality, with ≤580 mV arising from the c‐Si bottom cell and ≥320 mV arising from the Si NC/SiC top cell. The cells are successfully connected using a SiC/Si tunnelling recombination junction that results in very little voltage loss. The short‐circuit current densities j_sc are, at 0.8–0.9 mAcm⁻², rather low and found to be limited by current collection in the top cell. However, equivalent circuit simulations demonstrate that in current‐mismatched tandem cells such as the ones studied here, higher j_sc, when accompanied by decreased V_oc, can arise from shunts or breakdown in the limiting cell rather than improved current collection from the limiting cell. This indicates that V_oc is a better optimisation parameter than j_sc for tandem cells where the limiting cell exhibits poor junction characteristics. The high‐temperature‐stable cell architecture developed in this work, coupled with simulations highlighting potential pitfalls in tandem cell analysis, provides a suitable route for optimisation of Si NC layers for photovoltaics on a tandem cell device level. Copyright © 2016 John Wiley & Sons, Ltd.     

Imaginary carrot or effective fertiliser? A rejoinder on funding and productivity

The question of whether and to what extent research funding enables researchers to be more productive is a crucial one. In their recent work, Mariethoz et al. (Scientometrics, 2021. https://doi.org/10.1007/s11192-020-03.855-1) claim that there is no significant relationship between project-based research funding and bibliometric productivity measures and conclude that this is the result of inappropriate allocation mechanisms. In this rejoinder, we argue that such claims are not supported by the data and analyses reported in the article.

     

RAFT/MADIX rate coefficients measured via time-resolved EPR spectroscopy after pulse laser initiation

Addition and fragmentation rate coefficients, k_ad and k_β, have been measured by individually tracing intermediate and propagating radical concentrations via highly time-resolved EPR spectroscopy after applying a laser single pulse. The method is illustrated for butyl acrylate polymerization at −40 °C with EDTCP (ethyl 2-[1-diethoxyphosphoryl-2,2,2-trifluoroethoxythio carbonylsulfanyl] propionate) being the MADIX agent. Analysis of the radical concentration vs. time profiles yields k_ad = (2.5 ± 0.1) × 10⁴ L mol⁻¹ s⁻¹ and k_β = (2.3 ± 0.3) × 10³ s⁻¹. The associated K_eq = k_ad/k_β value is in close agreement with K_eq deduced from an earlier EPR method which rests on measuring the ratio of intermediate and propagating radical concentrations during stationary polymerization.     

Measuring binding and speciation of hydrophobic organic chemicals at controlled freely dissolved concentrations and without phase separation

The binding and speciation of hydrophobic organic chemicals (HOCs) in aqueous solutions were determined by controlling chemical activity and measuring total concentrations. Passive dosing was applied to control chemical activities of HOCs in aqueous solutions by equilibrium partitioning from a poly(dimethylsiloxane) polymer preloaded with the chemicals. The HOC concentrations in the equilibrated solutions [C(solution(eq))] and water [C(water(eq))] were then measured. Free fractions of the HOCs were determined as C(water(eq))/C(solution(eq)), whereas enhanced capacities (E) of the solutions for HOCs were determined as C(solution(eq))/C(water(eq)). A mixture of polycyclic aromatic hydrocarbons served as model analytes, while humic acid, sodium dodecyl sulfate, hydroxypropyl-β-cyclodextrin, and NaCl served as model medium constituents. The enhanced capacities were plotted versus the concentrations of medium constituents, and simple linear regression provided precise partition ratios, salting out constants, and critical micelle concentrations. These parameters were generally in good agreement with published values obtained by solid phase microextraction and fluorescence quenching. The very good precision was indicated by the low relative standard errors for the partition ratios of 0.5-8%, equivalent to 0.002-0.03 log unit. This passive dosing approach allows binding and speciation of HOCs to be studied without any phase separation steps or mass balance assumptions.