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Gupta S.,TU Dresden | Agrawal M.,Leibniz Institute of Polymer Research | Conrad M.,TU Dresden | Hutter N.A.,TU Munich | And 6 more authors.
Advanced Functional Materials | Year: 2010

A simple, fast, and versatile approach to the fabrication of outstanding surface enhanced Raman spectroscopy (SERS) substrates by exploiting the optical properties of the Ag nanoparticles and functional as well as organizational characteristics of the polymer brushes is reported. First, poly(2- (dimethylamino)ethyl methacrylate) brushes are synthesized directly on glassy carbon by self-initiated photografting and photopolymerization and thoroughly characterized in terms of their thickness, wettability, morphology, and chemical structure by means of ellipsometry, contact angle, AFM, and XPS, respectively. Second, Ag nanoparticles are homogeneously immobilized into the brush layer, resulting in a sensor platform for the detection of organic molecules by SERS. The surface enhancement factor (SEF) as determined by the detection of Rhodamine 6G is calculated as 6 × 10 6. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wunsche J.,Institute For Angewandte Photophysik | Wunsche J.,Ecole Polytechnique de Montreal | Reineke S.,Institute For Angewandte Photophysik | Lussem B.,Institute For Angewandte Photophysik | Leo K.,Institute For Angewandte Photophysik
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A detailed investigation of the diffusion of triplet excitons in a layer of N, N′ -di-1-naphthalenyl- N, N′ -diphenyl- [1, 1′: 4′, 1″: 4″, 1‴ -quaterphenyl]- 4, 4‴ -diamine (4P-NPD) incorporated in organic light-emitting diodes is presented. An appropriate method to measure the triplet diffusion length in fluorescent host materials is the spatial separation of the site of exciton generation from the site of radiative triplet decay by inserting a host spacer layer of varying thickness. However, cavity effects, the quenching and blocking of excitons at the boundaries of the spacer layer, and direct charge-carrier recombination in the sensing layer need to be taken into account. We use a specially designed layer stack, which excludes the influence of cavity effects on the measurements and a strongly quenching sensing layer, which ensures well-defined boundary conditions. The quenching of excitons by the sensing layer, the generation zone, and direct charge-carrier recombination are investigated experimentally and their influence on the extracted diffusion length are discussed. The significance of triplet-triplet annihilation in this analysis is estimated by a current-dependent evaluation. An analytic model for the dependence of the sensing layer emission on the spacer thickness is presented, which includes the important effects. By this means, we find a triplet diffusion length of 11±3 nm in 4P-NPD. © 2010 The American Physical Society.

Gohri V.,Institute For Angewandte Photophysik | Hofmann S.,Institute For Angewandte Photophysik | Reineke S.,Institute For Angewandte Photophysik | Rosenow T.,Institute For Angewandte Photophysik | And 6 more authors.
Organic Electronics: physics, materials, applications | Year: 2011

We investigate white top-emitting organic light-emitting diodes (OLEDs) based on a heterostructure of down-conversion (DC) layers. The white DCOLED comprises consecutive organic conversion layers of 4-dicyanomethylene-2-methyl- 6-p-dimethylaminostyryl-4H-pyran (DCM) doped in a matrix of tris(8-hydroxy- quinolinato)aluminum (Alq3), and N4,N41′-bis-(4-tert-butyl- phenyl)-N4,N4′-di-fluoranthen-3-yl-diphenylether-4,4′-diamine (OYSE). The DC layers also function as capping layers to enhance the light outcoupling and optical modification of the underlying blue OLED. White light emission with CIE color coordinates of (0.27, 0.26) and a color rendering index of 60 is achieved. Furthermore, the spectral angular dependence of the white device is examined. © 2011 Elsevier B.V. All rights reserved.

Chang H.-W.,Institute For Angewandte Photophysik | Chang H.-W.,National Taiwan University | Kim Y.H.,Institute For Angewandte Photophysik | Kim Y.H.,Pukyong National University | And 9 more authors.
Organic Electronics: physics, materials, applications | Year: 2014

In this work, we demonstrate color-stable, ITO-free white organic light-emitting diodes (WOLEDs) with enhanced efficiencies by combining the high-conductivity conducting polymer PEDOT:PSS as transparent electrode and a nanoparticle-based scattering layer (NPSL) as the effective optical out-coupling layer. In addition to efficiency enhancement, the NPSL is also beneficial to the stabilization of electroluminescent spectra/colors over viewing angles. Both the PEDOT:PSS and the NPSL can be fabricated by simple, low-temperature solution processing. The integration of both solution-processable transparent electrodes and light extraction structures into OLEDs is particularly attractive for applications since they simultaneously provide manufacturing, cost and efficiency advantages. © 2014 Elsevier B.V. All rights reserved.

Kim Y.H.,Institute For Angewandte Photophysik | Kim Y.H.,Pukyong National University | Muller-Meskamp L.,Institute For Angewandte Photophysik | Leo K.,Institute For Angewandte Photophysik
Advanced Energy Materials | Year: 2015

A hybrid ultratransparent poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/metal grid thin-film is demonstrated as a transparent electrode for organic solar cells. The transmittance of the PEDOT:PSS thin-films on glass reaches values as high as 91.5%, a nearly 100% transmittance ratio. The device with the hybrid electrode shows an efficiency of 2.8%, which is comparable to that of an indium tin oxide based reference device. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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