Radiant heat management for organic vapor-jet printing on plastic substrates

Abstract

Flexible organic light-emitting diodes (FOLEDs) are considered to be the next big step for the OLED display and lighting industry, but their commercialization is contingent upon development of effective fabrication techniques fit for large area plastic substrates. Organic vapor-jet printing (OVJP) is a direct printing method for organic thin-films in which organic material is vaporized by heat, and jetted through a heated nozzle with the help of a heated carrier gas stream. Due to its mask-free and on-demand character, the OVJP is expected to be cost-effective and scalable for large-area substrates.1 The heated components, especially the nozzle, however, makes it challenging for the OVJP to be used on flexible substrates, which usually have low glass transition temperature (Tg). In this study, a simple and stable low emissivity (low-ε) coating on the OVJP nozzle is proposed that enables the use of plastic substrates, without undermining the performance of the OVJP. With the proposed low-ε coating, the thermal radiation from the nozzle – the major source of heating – is greatly reduced and thus lowers the temperature of the substrate. (Fig. 1a) In this way, a flexible OLED was successfully printed on a PET substrate without substrate deformation, which occurred with the non-coated nozzle. FOLEDs realized with the proposed method shows comparable performance to an identical device fabricated by vacuum thermal evaporation, as shown in Fig. 1b.