Leveling and Drying Dynamics of Printed Liquid Films of Organic Semiconductor Solutions in OLED/OPV Applications

Abstract

Printing process development for fabrication of organic electronic devices is described, with focus on semiconductor layers for organic light-emitting diodes and photovoltaic cells. This development is considerably more complex than for a graphical printing process. Key aspects are an adequate dosing and transfer of highly volatile inks, the reliable coalescence of the droplets deposited on the substrate to a closed liquid film, and the successful relaxation and leveling of the liquid–air interface in the solvent evaporation phase in the presence of Marangoni stresses and pattern formation instabilities. The conditions for successful implementation of a gravure or inkjet process, using steadily developing, new generations of polymer as well as small molecule semiconductors are, to a large extent, but not exclusively, originating from the molecular features of organic semiconductors and their printable solutions. In addition, recent developments in surface technology, and in the physics of thin-film dynamics and spontaneous pattern formation contribute to a proper understanding of liquid layer dynamics in printed electronics. The role of ink formulation, Marangoni stresses related to concentration and temperature gradients, the effect of the disjoining pressure, and solvent evaporation are discussed.