Lab-on-Chip, Surface-Enhanced Raman Analysis by Aerosol Jet Printing and Roll-to-Roll Hot Embossing.

Surface-enhanced Raman spectroscopy (SERS) combines the high specificity of Raman scattering with high sensitivity due to an enhancement of the electromagnetic field by metallic nanostructures. However, the tyical fabrication methods of SERS substrates suffer from low throughput and therefore high costs. Furthermore, point-of-care applications require the investigation of liquid solutions and thus the integration of the SERS substrate in a microfluidic chip.

Reliability of Aerosol Jet Printed Fluorescence Quenching Sensor Arrays for the Identification and Quantification of Explosive Vapors.

One of the primary challenges in explosive detection using fluorescence quenching is the identification and quantification of detected targets. In this work, we explore the reliability of aerosol jet printed sensor arrays for the discrimination of nitroaromatic traces using linear discriminant analysis (LDA). We varied the amount of the deposited material by controlling the printer's shutter to investigate the impact on the detection reliability.

OLED Luminaires: Device Arrays with 99.6% Geometric Fill Factor Structured by Femtosecond Laser Ablation.

The plethora of design opportunities renders organic light emitting diodes (OLEDs) ideal luminaires for general lighting applications. Progressing from lab-scale device concepts to large-area applications calls for smart device designs that are scalable and, at the same time, unsusceptible to resistive losses within the electrodes. By employing direct pulsed femtosecond laser structuring, we fabricate OLED luminaires comprising monolithically interconnected OLED arrays.

Excitonically Coupled States in Crystalline Coordination Networks.

When chromophores are brought into close proximity, noncovalent interactions (π-π/CH-π) can lead to the formation of excitonically coupled states, which bestow new photophysical properties upon the aggregates. Because the properties of the new states not only depend on the strength of intermolecular interactions, but also on the relative orientation, supramolecular assemblies, where these parameters can be varied in a deliberate fashion, provide novel possibilities for the control of photophysical properties. This work reports that core-substituted naphthalene diimides (cNDIs) can be incorporated into surface-mounted metal- organic structures/frameworks (SURMOFs) to yield optical properties strikingly different from conventional aggregates of such molecules, for example, formed in solution or by crystallization.

Transport-related triplet states and hyperfine couplings in organic tandem solar cells probed by pulsed electrically detected magnetic resonance spectroscopy.

Tandem solar cells constitute the most successful organic photovoltaic devices with power conversion efficiencies comparable to thin-film silicon solar cells. Especially their high open-circuit voltage - only achievable by a well-adjusted layer stacking - leads to their high efficiencies. Nevertheless, the microscopic processes causing the lossless recombination of charge carriers within the recombination zone are not well understood yet.

Electric-Field-Controlled Dopant Distribution in Organic Semiconductors.

Stable electrical doping of organic semiconductors is fundamental for the functionality of high performance devices. It is known that dopants can be subjected to strong diffusion in certain organic semiconductors. This work studies the impact of operating conditions on thin films of the polymer poly(3-hexylthiophene) (P3HT) and the small molecule Spiro-MeOTAD, doped with two differently sized p-type dopants.

Assessing the influence of structural disorder on the plant epidermal cells' optical properties: a numerical analysis.

Many plant surfaces, such as rose petals, display lens-like epidermal cells that are known to assist the collection and focusing of the sunlight. Those cells form an array with a high degree of structural irregularities including disorder in the height and orientation of the cells, and in their arrangement. In this study, we numerically analyze the influence of structural disorder on the optical properties of a 3D modeled epidermal cell array using ray tracing simulations.

Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces.

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%.

Beyond Donor-Acceptor (D-A) Approach: Structure-Optoelectronic Properties-Organic Photovoltaic Performance Correlation in New D-A -D-A Low-Bandgap Conjugated Polymers.

Low-bandgap near-infrared polymers are usually synthesized using the common donor-acceptor (D-A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though.

Room-Temperature High-Efficiency Solid-State Triplet-Triplet Annihilation Up-Conversion in Amorphous Poly(olefin sulfone)s.

Triplet-triplet annihilation up-conversion (TTA-UC) is a developing technology that can enable spectral conversion under sunlight. Previously, it was found that efficient TTA-UC can be realized in polymer hosts for temperatures above the polymer's glass transition (T > T). In contrast, TTA-UC with high quantum yield for temperatures below T is rarely reported.

Surface Lattice Resonances for Enhanced and Directional Electroluminescence at High Current Densities.

Hybrid photonic-plasmonic modes in periodic arrays of metallic nanostructures offer a promising trade-off between high-quality cavities and subdiffraction mode confinement. However, their application in electrically driven light-emitting devices is hindered by their sensitivity to the surrounding environment and to charge injecting metallic electrodes in particular. Here, we demonstrate that the planar structure of light-emitting field-effect transistor (LEFET) ensures undisturbed operation of the characteristic modes.

Degradation Mechanisms in Organic Light-Emitting Diodes with Polyethylenimine as a Solution-Processed Electron Injection Layer.

In this work, we investigate the performance and operational stability of solution-processed organic light-emitting diodes (OLEDs), which comprise polyethylenimine (PEI) as an electron injection layer (EIL). We show that the primary degradation mechanism in these OLEDs depends on the cathode metal that is used in contact with the EIL. In the case of Al, the deterioration in OLED performance during electrical driving is mainly caused by excitons which reach and subsequently degrade the emitter/PEI interface.

Biodegradable Polycaprolactone as Ion Solvating Polymer for Solution-Processed Light-Emitting Electrochemical Cells.

In this work, we demonstrate the use of the biodegradable polymer polycaprolactone (PCL) as the ion solvating polymer in solution-processed light-emitting electrochemical cells (LEC). We show that the inclusion of PCL in the active layer yields higher ionic conductivities and thus contributes to a rapid formation of the dynamic p-i-n junction and reduction of operating voltages. PCL shows no phase separation with the emitter polymer and reduces film roughness.

Bioinspired Superhydrophobic Highly Transmissive Films for Optical Applications.

Inspired by the transparent hair layer on water plants Salvinia and Pistia, superhydrophobic flexible thin films, applicable as transparent coatings for optoelectronic devices, are introduced. Thin polymeric nanofur films are fabricated using a highly scalable hot pulling technique, in which heated sandblasted steel plates are used to create a dense layer of nano- and microhairs surrounding microcavities on a polymer surface. The superhydrophobic nanofur surface exhibits water contact angles of 166 ± 6°, sliding angles below 6°, and is self-cleaning against various contaminants.

Digitally Printed Dewetting Patterns for Self-Organized Microelectronics.

Self-organization of functional materials induced by low surface-energetic direct printed structures is presented. This study investigates fundamental fluid and substrate interactions and fabricates all-printed small area organic photodetectors with On-Off ratios of ≈10(5) and dark current densities of ≈10(-4) mA cm(-2) , as well as ring oscillators based on n-type organic field-effect transistors showing working frequencies up to 400 Hz.

High-Performance Electron Injection Layers with a Wide Processing Window from an Amidoamine-Functionalized Polyfluorene.

In this work, we present organic light-emitting diodes (OLEDs) utilizing a novel amidoamine-functionalized polyfluorene (PFCON-C) as an electron injection layer (EIL). PFCON-C consists of a polyfluorene backbone to which multiple tertiary amine side chains are connected via an amide group. The influence of molecular characteristics on electronic performance and morphological properties was tested and compared to that of the widely used, literature known amino-functionalized polyfluorene (PFN) and polyethylenimine (PEI).

Organic solar cells with graded absorber layers processed from nanoparticle dispersions.

The fabrication of organic solar cells with advanced multi-layer architectures from solution is often limited by the choice of solvents since most organic semiconductors dissolve in the same aromatic agents. In this work, we investigate multi-pass deposition of organic semiconductors from eco-friendly ethanol dispersion. Once applied, the nanoparticles are insoluble in the deposition agent, allowing for the application of further nanoparticulate layers and hence for building poly(3-hexylthiophene-2,5-diyl):indene-C60 bisadduct absorber layers with vertically graded polymer and conversely graded fullerene concentration.

Emissive Polyelectrolytes As Interlayer for Color Tuning and Electron Injection in Solution-Processed Light-Emitting Devices.

Herein we present a solution-processed hybrid device architecture combining organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) in a bilayer architecture. The LEC interlayer promotes the charge injection from an air-stable Ag cathode as well as permits the color tuning of the device emission. To this end, we used an alcohol-soluble anionic polyfluorene derivative, the properties of which were investigated by absorption and photoluminescence spectroscopy as well as by cyclic voltammetry.

Tuning the Microcavity of Organic Light Emitting Diodes by Solution Processable Polymer-Nanoparticle Composite Layers.

In this study, we present a simple method to tune and take advantage of microcavity effects for an increased fraction of outcoupled light in solution-processed organic light emitting diodes. This is achieved by incorporating nonscattering polymer-nanoparticle composite layers. These tunable layers allow the optimization of the device architecture even for high film thicknesses on a single substrate by gradually altering the film thickness using a horizontal dipping technique.

All-solution processed transparent organic light emitting diodes.

In this work, we report on indium tin oxide-free, all-solution processed transparent organic light emitting diodes (OLEDs) with inverted device architecture. Conductive polymer layers are employed as both transparent cathodes and transparent anodes, with the top anodes having enhanced conductivities from a supporting stochastic silver nanowire mesh. Both electrodes exhibit transmittances of 80-90% in the visible spectral regime.

Dipolar SAMs Reduce Charge Carrier Injection Barriers in n-Channel Organic Field Effect Transistors.

In this work we examine small conjugated molecules bearing a thiol headgroup as self assembled monolayers (SAM). Functional groups in the SAM-active molecule shift the work function of gold to n-channel semiconductor regimes and improve the wettability of the surface. We examine the effect of the presence of methylene linkers on the orientation of the molecule within the SAM.

Light emission, light detection and strain sensing with nanocrystalline graphene.

Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically, the light-matter interaction in graphene is of a broadband type. However, by integrating graphene into optical micro-cavities narrow-band light emitters and detectors have also been demonstrated.

The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly.

The glasswing butterfly (Greta oto) has, as its name suggests, transparent wings with remarkable low haze and reflectance over the whole visible spectral range even for large view angles of 80°. This omnidirectional anti-reflection behaviour is caused by small nanopillars covering the transparent regions of its wings. In difference to other anti-reflection coatings found in nature, these pillars are irregularly arranged and feature a random height and width distribution.

Charge generation layers for solution processed tandem organic light emitting diodes with regular device architecture.

Tandem organic light emitting diodes (OLEDs) utilizing fluorescent polymers in both sub-OLEDs and a regular device architecture were fabricated from solution, and their structure and performance characterized. The charge carrier generation layer comprised a zinc oxide layer, modified by a polyethylenimine interface dipole, for electron injection and either MoO3, WO3, or VOx for hole injection into the adjacent sub-OLEDs. ToF-SIMS investigations and STEM-EDX mapping verified the distinct functional layers throughout the layer stack.

Photophysical properties and synthesis of new dye-cyclooctyne conjugates for multicolor and advanced microscopy.

Cyclooctyne conjugates with fluorophores are often used for bioorthogonal labeling in cells and tissues. However, no comprehensive library of one cyclooctyne core structure with different fluorescent dyes spanning the whole visible spectrum up to the NIR had been described so far. Hence, we synthesized and evaluated one cyclooctyne core structure which is easily accessible for the attachment of different dyes for multicolor imaging, FRET analysis, and study of metabolism in vivo.