Experimental analysis of drainage and water storage of litter layers

International audienceMany hydrological studies of forested ecosystems focus on the study of the forest canopy and have partitioned gross precipitation into throughfall and stemflow. However, the presence of forest litter can alter the quantities of water available for soil infiltration and runoff. Little information exists regarding the value of storage and drainage parameters for litter layers. Vegetation parameters of this kind are required in physically-based and lumped conceptual models to quatify the availabilty and distribution of water. Using a rainfall simulator and laboratory conditions two main objectives were investigated using layers of recently seneced poplar leaves, fresh grass or woodchips: 1) Effect of rain intensity on storage. With this respect we found that: maximum storage (Cmax), defined as the detention of water immediately before rainfall cessation, increased with rainfall intensity. The magnitude of the increment was up to 0.5 mm kg?1 m?2 between the lowest (9.8 mm h?1) and highest (70.9 mm h?1) rainfall intensities for poplar leaves. Minimum storage (Cmin), defined as the detention of water after drainage ceased, was not influenced by rainfall intensity. Repeated wetting-draining cycles or layer thickness have no effect on Cmax or Cmin. 2) The evaluation of drainage coefficient for the Rutter model. This model was found accurate to predict storage and drainage in the case of poplar leaves, was less accurate for fresh grass and resulted in overestimations for woodchips. Additionally, the effect of an underlaying soil matrix on lateral movement of water and storage of poplar leaves was studied. Results indicated that the soil matrix have no effect on Cmax or Cmin of the litter layer. Lateral movement of water in the poplar layer was observed at intermediate rainfall intensities (30.2 and 40.4 mm h?1), but not a the lowest or highest rates

A digitally printed optoelectronic nose for the selective trace detection of nitroaromatic explosive vapours using fluorescence quenching

We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapours. The sensor arrays, fabricated by aerosol-jet printing, consist of six different commercially available polymers as transducers. We assess the within-batch reproducibility of the printing process and we report that the sensor polymers show efficient fluorescence quenching capabilities with detection limits of a few parts-per-billion in air. We further demonstrate the nose\u27s ability to discriminate between several nitroaromatics including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene at three different concentrations using linear discriminant analysis. Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapours using a potentially low-cost digital printing technique suitable for high-volume fabrication

Polarization-Sensitive Photodetectors Based on Directionally Oriented Organic Bulk-Heterojunctions

Polarized spectroscopic photodetection enables numerous applications in diverse areas such as sensing, industrial quality control, and visible light communications. Although organic photodetectors (OPDs) can offer a cost-effective alternative to silicon-based technology—particularly when flexibility and large-area arrays are desired—polarized OPDs are only beginning to receive due research interest. Instead of resorting to external polarization optics, this report presents polarized OPDs based on directionally oriented blends of poly(3-hexylthiophene) (P3HT) and benchmark polymer or nonfullerene acceptors fabricated using a versatile solution-based method. Furthermore, a novel postprocessing scheme based on backfilling and plasma etching is advanced to ameliorate high dark-currents that are otherwise inherent to fibrillar active layers. The resulting polarized P3HT:N2200 OPDs exhibit a broad enhancement across all principal figures of merit compared to reference isotropic devices, including peak responsivities of 70 mA W$^{-1}$ and up to a threefold increase in 3 dB bandwidth to 0.75 MHz under parallel-polarized illumination. Polarization ratios of up to 3.5 are obtained across a spectral range that is determined by the specific donor–acceptor combinations. Finally, as a proof-of-concept demonstration, polarized OPDs are used for photoelasticity analysis of rubber films under tensile deformation, highlighting their potential for existing and emerging applications in advanced optical sensing

Polarization-Sensitive Photodetectors Based on Directionally Oriented Organic Bulk-Heterojunctions

Polarized spectroscopic photodetection enables numerous applications in diverse areas such as sensing, industrial quality control, and visible light communications. Although organic photodetectors (OPDs) can offer a cost-effective alternative to silicon-based technology—particularly when flexibility and large-area arrays are desired—polarized OPDs are only beginning to receive due research interest. Instead of resorting to external polarization optics, this report presents polarized OPDs based on directionally oriented blends of poly(3-hexylthiophene) (P3HT) and benchmark polymer or nonfullerene acceptors fabricated using a versatile solution-based method. Furthermore, a novel postprocessing scheme based on backfilling and plasma etching is advanced to ameliorate high dark-currents that are otherwise inherent to fibrillar active layers. The resulting polarized P3HT:N2200 OPDs exhibit a broad enhancement across all principal figures of merit compared to reference isotropic devices, including peak responsivities of 70 mA W$^{-1}$ and up to a threefold increase in 3 dB bandwidth to 0.75 MHz under parallel-polarized illumination. Polarization ratios of up to 3.5 are obtained across a spectral range that is determined by the specific donor–acceptor combinations. Finally, as a proof-of-concept demonstration, polarized OPDs are used for photoelasticity analysis of rubber films under tensile deformation, highlighting their potential for existing and emerging applications in advanced optical sensing

Ink Formulation for Printed Organic Electronics: Investigating Effects of Aggregation on Structure and Rheology of Functional Inks Based on Conjugated Polymers in Mixed Solvents

The utilization of solution‐processable organic semiconducting (OSC) polymers and the development of industrial‐relevant printing techniques enable cost‐efficient fabrication of optoelectronic devices for the mass market. Yet, the adaptation of viscoelastic properties of a functional ink to the respective printing technology is challenging. One crucial parameter is the formulation of the ink, which can be adjusted by selecting the combination of solvents that are mixed with the OSC. The current study considers model functional inks composed of a poly‐phenylene‐vinylene‐based OSC and two solvents, empirically known to be good. Their quality is quantified using the Hansen solubility parameters. The influence of the composition of the solvent mixture on structural, dynamical, and rheological behavior of the ink is investigated with light scattering, viscometry, and rheometry. Although both solvents are considered good, polymer aggregation is found at all compositions. Aggregation depends on composition in a nontrivial way. For dilute and semi‐dilute inks, the effects of aggregates on the ink viscosity are hidden by the difference in viscosities of the neat solvents. For elevated concentrations, the aggregates produce a hysteresis in the shear‐dependent viscosity, which should be considered when developing a functional ink for a particular printing technique

Analytical Study of Solution-Processed Tin Oxide as Electron Transport Layer in Printed Perovskite Solar Cells

Solution‐processed tin oxide (SnO$_{x}$ ) electron transport layers demonstrate excellent performance in various optoelectronic devices and offer the ease of facile and low cost deposition by various printing techniques. The most common precursor solution for the preparation of SnO$_{x}$ thin films is SnCl$_{2}$ dissolved in ethanol. In order to elucidate the mechanism of the precursor conversion at different annealing temperatures and the optoelectronic performance of the SnO$_{x}$ electron transport layer, phonon and vibrational infrared and photoelectron spectroscopies as well as atomic force microscopy are used to probe the chemical, physical, and morphological properties of the SnO$_{x}$ thin films. The influence of two different solvents on the layer morphology of SnO$_{x}$ thin films is investigated. In both cases, an increasing annealing temperature not only improves the structural and chemical properties of solution‐processed SnO$_{x}$, but also reduces the concentration of tin hydroxide species in the bulk and on the surface of these thin films. As a prototypical example for the high potential of printed SnO$_{x}$ layers for solar cells, high performance perovskite solar cells with a stabilized power conversion efficiency of over 15% are presented