Printing organic semiconductor inks by means of roll-to-roll compatible techniques will allow a continuous, high-volume fabrication of large-area fl exible optoelectronic devices. The gravure printing technique is set to become a widespread process for the high throughput fabrication of functional layers. The gravure printing process of a poly-phenylvinylene derivative light-emitting polymer dissolved in a two solvent mixture on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is studied. The surface tensions, contact angles, viscosities, and drying times of the formulations are investigated as a function of the solvent volume fraction and polymer concentration. The properties of the ink grant a homogeneous printed layer, suitable for device fabrication, when the calculated fi lm leveling time is shorter than a critical time, at which the fi lm has been frozen due to loss of solvent via evaporation. The knowledge obtained from the printing process is applied to fabricate organic light-emitting diodes (OLEDs) on fl exible substrates, yielding a luminance of ≈ 5000 cd m − 2 .
The authors present the feasibility of sheet fed direct gravure printing for ultrathin, organic semiconductor films on ITO coated glass. Printing with chrome plated gravure cylinders is often believed to require flexible substrates to promote fluid transfer to the substrate. However, the results demonstrate a stable process for the smallmolecule Spiro-MeOTAD dissolved in toluene on rigid substrates. The authors obtained layer thicknesses in the range of 5-100 nm. They identified certain boundaries for gravure cell size yielding printed films with thickness of 10-15 nm with good homogeneity suitable for organic light emitting diodes or organic photovoltaics. For gravure cells smaller or larger than the optimal range, the printed layer is afflicted with dot-or ribbinglike structures. The authors show that the latter may result from nip-induced Saffman-Taylor instabilities rather than spinodal dewetting or Marangoni effects. Finally, electrical characterization of a completed stack (PEDOT:PSS electrode) give evidence for integrity of the printed semiconductor layers. V C 2011 Society for Imaging Science and Technology.[DOI: xxxxxx] INTRODUCTIONIn this article, we present our recent direct gravure printing experiments of ultrathin, small-molecule based semiconductor layers with thicknesses in the range of 5-100 nm on indium tin oxide (ITO) coated glass substrates. Smallmolecule semiconductors are well adapted materials for vacuum deposition of layers for organic devices such as organic light emitting diodes (OLEDs) and organic photovoltaics. This manufacturing technique imposes limits to high throughput and cost efficiency. A rapid and reliable solution based coating or printing process can offer many advantages in this respect, as many small-molecule materials are known to be soluble in a variety of solvents. Studies on principal differences between vacuum and solution processed layers and their effect on device performance have been done by Lee et al. using spin-coating techniques. 1 However, spin-coating technique is not suitable for large scale production. It is our aim to close the still persistent gap between spin-coating and laboratory-scale processing methods on one side and to develop a gravure printing process suitable for large volume production of OLED lighting, display, and photovoltaic applications.
Enabling solution-based printing techniques for sub-100 nm thin semiconductors for the application in large-area organic electronics is a challenging task. In order to optimize the process parameters, the layers have to be characterized on a large lateral scale while determining the nanometer thickness at the same time. We present a lateral and vertical resolving measurement method for large-area, semi-transparent thin films based on optical interference effects. We analyzed the RGB color images of up to 150 mm square-sized thin film samples obtained by a modified commercial flatbed scanner. Utilizing and comparing theoretical and measured color contrast values, we determined most probable thickness values of the imaged sample area pixel by pixel. Within specific boundary conditions, we found very good agreement between the presented imaging color reflectometry and reference methods. Due to its simple setup, our method is suitable to be implemented as part of a color vision inspection system in in-line printing and coating processes.
The compensation of quadratic Zeeman effect and trap energy in high-spin fermions is shown to lead to resonances in the spin-changing collisions that are typically absent in spinor condensates and spin-1/2 fermions. We study these resonances in lattice fermions, showing that they permit the targeting of a particular spin-changing channel while suppressing the rest and the creation of magnetically insensitive superpositions of many-body states with entangled spin and trap degrees of freedom. Finally, the intersite tunneling may lead to a quantum phase transition described by a quantum Ising model.
One of the main difficulties occurring in printed organic electronics is the intermixing between adjacent layers. This has to be quantified to optimise printed devices. Methods like sputter X-ray photoelectron spectroscopy (XPS) are suitable for this, but also complex, expensive and destructive. We propose impedance spectroscopy as an alternative for quantifying the degree of intermixing non-destructively. Here, after measuring a device's impedance spectrum its concentration profile is determined with a fit function. For this proof of concept we produced single and double layer samples of NPD and Alq3 with different interface widths by thermal evaporation. The concentration profiles were monitored with micro balances. The material parameters were extracted from single layer spectra and then set in a fit function used to determine the degree of intermixing in double layer devices. Even slight intermixing could be evaluated with this method and complete intermixing was detected as such. Due to the imprecise production of devices and certain simplifications used for this first test, the fit yielded too small interface widths, the deviation reaching almost 50%. The variation for devices produced in the same run was only about 10%, indicating that intermixing can be reliably quantified with impedance spectroscopy if the material's properties are accurately known.
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