Determination of Binary Interaction Parameters for Ternary Polymer–Polymer–Solvent Systems Using Raman Spectroscopy

Multilayer coatings and drying of polymer films are widely used to produce different applications like organic electronics or barrier foils. If the product quality requires separated layers, partial or immiscible systems can be used to avoid interdiffusion between the layers. For the prediction of a possible phase separation of a ternary polymer–polymer–solvent system, it is required to measure or obtain from a data bank the three binary interaction parameters of the system to describe its thermodynamic behavior. This poses a challenge due to the scarce data and measurement techniques for polymer–solvent interaction parameters, but even more for polymer–polymer interaction parameters. In this work, a numerical routine is developed to predict the phase separation for given interaction parameters and is validated with literature results. Subsequently, different ternary polystyrene–poly(methyl methacrylate)–toluene mixtures are prepared and the resulting composition of the phase (or phases) is measured via Raman spectroscopy. The determined equilibrium data are used to fit the binary interaction parameters, which can be used afterward as input parameters for the numerical routine in order to predict the ternary phase diagram of the system

Multilayer OLEDs with four slot die-coated layers

For the first time, multilayer OLEDs with four solution-processed layers are fabricated step-bystep using slot die coating. A suitable choice of coating parameters and fluid formulation enables the application of different material classes as large-area homogeneous layers with thicknesses in the nanometer range. The AFM measurements of the slot die-coated layers consisting of small molecules showed Ra values of 0.21-0.28 nm, less than previously reported in the literature. Based on a two-layer reference OLED consisting of a HIL and EML, the stack architecture is first extended by a crosslinked HTL. These threelayer OLEDs with a crosslinked HTL achieve 70% higher efficiency, compared to that of the reference devices, thus assuming successfully separated layers. In a further step, an additional ETL is applied via the orthogonal solvent approach to obtain four solutionprocessed layers. The averaged power efficiency of the four-layer OLEDs is increased by a factor of 2.2 compared to the reference OLEDs up to a value of 3.5 lm/W. Based on these results, it can be assumed that both approaches, the use of orthogonal solvents as well as the application of crosslinkable materials, have been successfully combined to fabricate multilayer OLEDs with four separated slot die-coated layers

Comparative Study of Printed Multilayer OLED Fabrication through Slot Die Coating, Gravure and Inkjet Printing, and Their Combination

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N '-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N '-bis(4-methoxyphenyl)biphenyl-4,4 '-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A(-1) is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance

Comparative Study of Printed Multilayer OLED Fabrication through Slot Die Coating, Gravure and Inkjet Printing, and Their Combination

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N′-bis(4-methoxyphenyl)biphenyl-4,4′-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A⁻¹ is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance