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

Lisa Merklein,Wilhelm Schabel,Marvin Mink,Dimitrios Kourkoulos,Dominik Daume,Stefan Schlisske,Hans Sauer,Philip Scharfer,Benjamin Ulber,Gerardo Hernandez-Sosa,Klaus Meerholz,Uli Lemmer,Edgar Dörsam,Manuela Di Biase,Tobias Rödlmeier,Felix Braig

doi:10.3390/colloids3010032

Abstract

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.

Highlights

Organic electronic devices such as thin-film-transistors (TFTs) as well as organic light-emitting diodes (OLEDs) for display and lighting applications are increasingly available for the end consumer
In the course of this work, the suitability of the three techniques, slot die coating, inkjet printing and gravure printing, as well as combinations thereof was investigated for the application of three functional materials used for multilayer OLEDs
In order to compare the application techniques regarding a large area layer homogeneity, the layer thicknesses were measured for each layer using Imaging Color Reflectometry (ICR)

Summary

Introduction

Organic electronic devices such as thin-film-transistors (TFTs) as well as organic light-emitting diodes (OLEDs) for display and lighting applications are increasingly available for the end consumer. They are still an expensive choice [1]. The purchase and operation costs of the used equipment are high Solution processing allows both the usability of small molecules as well as polymers and the manufacturing of large area devices using continuous roll-to-roll (R2R) processes [2,3]. To the best of our knowledge, there are no previous comparative works, where a qualitative and quantitative comparison of the application of different industrial solution processes and techniques for the fabrication of OLEDs, which includes device performance investigation, are reported

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