Flexible device fabrication using organic vapor-jet printing with reduced heat trans

Abstract

The possibility of flexible electronic devices and their low-cost fabrication is among the most outstanding potentials of organic devices. With advantages such as mask-less direct on-demand patterning, high material utilization efficiency, and the elimination of solvent use, organic vapor-jet printing (OVJP), in which organic vapor is entrained in a heated carrier gas flow and ejected through a nozzle [1-2], is a promising technique for low-cost fabrication of organic electronic devices. However, the use of OVJP has been restricted to rigid substrates, failing to unlock its full potential. This is because all of the equipment within the path of the organic vapor should be heated in order to prevent organic vapor from condensing on its passage and thus blocking its flow. Such a thermal requirement applies also to the nozzle, which should be in proximity to the substrate for patterning resolution [1]. Due to a high local thermal load from the heated nozzle, the use of plastic substrates and organic materials with low glass transition temperature is challenging to realize in OVJP applications. [See Fig. 1(b)]. In this study, we aim to reduce the heat transfer from the OVJP nozzle to the substrate and enable the use of flexible plastic substrates in OVJP without the expense of patterning resolution, organic vapor throughput, or device performance. A simple low-emissivity (low-) coating is adopted on the nozzle to drop the surface emissivity (Fig.1 (a)), which is directly proportional to the radiative heat flux. Under real printing conditions, a substrate temperature drop of over 60 ℃ was realized when a nozzle with the low- coating coating coating was used. [See Fig. 1(d)] This enabled us to use plastic substrates such as PET virtually without any deformation as shown in Fig.1 (c). In addition, thermal analysis and heat transfer simulation are done to eventually control the temperature of the substrates while maintaining all other printing conditions. This study shows that OVJP could be extended to fabrication of flexible organic devices with little compromise in printing resolution and device performance.