Journal of Coatings Technology and Research

, Volume 11, Issue 1, pp 75–81 | Cite as

Liquid film coating of small molecule OLEDs

  • Katharina Peters
  • Lukas Wengeler
  • Philip Scharfer
  • Wilhelm Schabel


Organic small molecules typically deposited by vacuum deposition are a promising material for efficient, low-cost, area light-emitting diodes (OLEDs). In this article we discuss methods to apply these materials by solvent-based large area coating methods. As a basis for the technical description of the coating and wetting process, we present material properties, such as viscosity and surface tension of SMOLED solutions and polar and disperse part for the surface energy of typical substrates or semiconducting organic layers. Whereas SM content has little effect on the ink properties, impurities were identified as an important factor for the wetting behavior. Based on the material properties and coating experiments with SMOLED solutions, the coating methods of blade and slot die coating are discussed with respect to film thickness and stability. We found that the film thickness of knife-coated films does depend on velocity, temperature, provided fluid volume, and composition. Calibration curves for commercial materials (NMP and Spiro-MeOTAD) are given. The stability of slot die coating was lower than expected from literature. However, homogeneous SMOLED layers could be produced by slot die coating at gap-to-film-thickness ratios of up to 50.


OLED Small molecule Roll to roll Coating Blade coating Slot die coating Dewetting Viscosity Surface tension 



The authors acknowledge financial support via the project PrintOLED of the Leading-Edge Cluster Forum Organic Electronics managed by InnovationLab GmbH within the High-Tech Strategy for Germany of the Federal Ministry of Education and Research and Philips Technologie GmbH. Special thanks goes to our cooperating partners BASF, Merck, and TSE Troller AG for the support. We would like to thank all involved mechanics, assistants, and our students for contributing to this work.


  1. 1.
    So, F, et al., “Organic Light-Emitting Devices for Solid-State Lighting.” MRS Bull., 33 663–669 (2008)CrossRefGoogle Scholar
  2. 2.
  3. 3.
    Duan, L, et al., “Solution Processable Small Molecules for Organic Light-Emitting Diodes.” J. Mater. Chem., 20 6392–6407 (2010)CrossRefGoogle Scholar
  4. 4.
    Chen, C-Y, et al., “Continuous Blade Coating for Multi-layer Large-Area Organic Light-Emitting Diode and Solar Cell.” J. Appl. Phys., 110 094501 (2011)CrossRefGoogle Scholar
  5. 5.
    Yeh, H-C, et al., “All-Small-Molecule Efficient White Organic Light-Emitting Diodes by Multi-layer Blade Coating.” Org. Electron., 13 914–918 (2012)CrossRefGoogle Scholar
  6. 6.
    Chang, Y-F, et al., “Unmodified Small-Molecule Organic Light-Emitting Diodes by Blade Coating.” Org. Electron., 13 (10) 2149–2155 (2012)CrossRefGoogle Scholar
  7. 7.
    Chao, Y-C, et al., “Highly Efficient Solution-Processed Red Organic Light-Emitting Diodes with Long-Side-Chained Triplet Emitter.” Synth. Met., 161 148–152 (2011)CrossRefGoogle Scholar
  8. 8.
    You, J-D, et al., “All-Solution-Processed Blue Small Molecular Organic Light-Emitting Diodes with Multilayer Device Structure.” Org. Electron., 10 1610–1614 (2009)CrossRefGoogle Scholar
  9. 9.
    Tseng, S-R, et al., “Multilayer Polymer Light-Emitting Diodes by Blade Coating Method.” Appl. Phys. Lett., 93 153308 (2008)CrossRefGoogle Scholar
  10. 10.
    Faircloth, TJ, et al., “Slot Die Coating for OLED Displays.” SID Symp. Dig. Tech. Papers, 39 645–647 (2008)CrossRefGoogle Scholar
  11. 11.
    Chesterfield, R, et al., “Solution-Coating Technology for AMOLED Displays.” Inf. Disp., 27 (1) 24–30 (2011)Google Scholar
  12. 12.
    van den Hoonaard, KR, “Towards All R2R Printed SMOLED for Lighting, Signage and Display.” The XVII International Display Workshop, IDW 2009, vol. 200, pp. 1619–1622Google Scholar
  13. 13.
    Benkreira, H, et al., “Classification and Analyses of Coating Flows.” J. Nonnewton. Fluid Mech., 54 437–447 (1994)CrossRefGoogle Scholar
  14. 14.
    Greener, Y, Middleman, S, “Blade-Coating of a Viscoelastic Fluid.” Polym. Eng. Sci., 14 (11) 791–796 (1974)CrossRefGoogle Scholar
  15. 15.
    Kistler, SF, Schweizer, PM, Liquid Film Coating. Chapman and Hall, London (1997)CrossRefGoogle Scholar
  16. 16.
    Krenn, J, et al., “Visualization of Surface Deformations During Thin Film Drying Using a Digital-Image-Correlation Method.” Chem. Eng. Process., 50 (5–6) 569–573 (2011)CrossRefGoogle Scholar
  17. 17.
    Harris, DJ, Lewis, JA, “Marangoni Effects on Evaporative Lithographic Patterning of Colloidal Films.” Langmuir, 24 (8) 3681–3685 (2008)CrossRefGoogle Scholar
  18. 18.
    Owens, DK, Wendt, RC, “Estimation of the Surface Free Energy of Polymers.” J. Appl. Polym. Sci., 13 (8) 1741–1747 (1969)CrossRefGoogle Scholar
  19. 19.
    Kwok, DY, Neumann, AW, “Contact Angle Measurement and Contact Angle Interpretation.” Adv. Colloid Interface Sci., 81 167–249 (1999)CrossRefGoogle Scholar
  20. 20.
    Voigt, MM, et al., “Gravure Printing Inverted Organic Solar Cells: The Influence of Ink Properties on Film Quality and Device Performance.” Sol. Energy Mater. Sol. Cells, 105 77–85 (2012)CrossRefGoogle Scholar
  21. 21.
    Zhou, Y-F, et al., “Improved Stability of OLEDs with Mild Oxygen Plasma Treated PEDOT:PSS.” J. Lumin., 122–123 602–604 (2007)CrossRefGoogle Scholar
  22. 22.
    Redecker, M, Nolte, K, Löcherinjektionsschicht einer organischen Leuchtdiode und Verfahren zu deren Herstellung. Samsung SDI Co., Ltd., Suwon, Kyonggi, KR, Patent DE 101 23 115 B4, 24 May 2006Google Scholar
  23. 23.
    Carvalho, MS, Kheshgi, HS, “Low-Flow Limit in Slot Coating: Theory and Experiments.” AIChE J., 46 (10) 1907–1917 (2000)CrossRefGoogle Scholar
  24. 24.
    Wengeler, L, et al., “Comparison of Large Scale Coating Techniques for Organic and Hybrid Films in Polymer Based Solar Cells.” Chem. Eng. Process. Process Intensif. (2012)Google Scholar

Copyright information

© American Coatings Association & Oil and Colour Chemists' Association 2013

Authors and Affiliations

  • Katharina Peters
    • 1
  • Lukas Wengeler
    • 1
  • Philip Scharfer
    • 1
  • Wilhelm Schabel
    • 1
  1. 1.Thin Film Technology (TFT), Institute of Thermal Process EngineeringKarlsruhe Institute of Technology (KIT)KarlsruheGermany

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