Realization and optimization of organic electronic devices manufactured by innovative technique: inkjet printing

Abstract

Inkjet printing is a nascent technology that is evolving from text and graphic printing into a major topic of scientific research and R&D, where it can be used as a highly reproducible non-contact patterning technique to deposit liquid functional materials at high speed on either small or large areas of flexible and non-flexile substrates. It is a low cost technique because minimizes the waste products and reduces the process steps. Nevertheless, the inkjet printing technology has some intrinsic limits, mainly related to the drying process of the printed droplet. In detail, during the drying process the fast evaporation of the solvent at the contact line induces an outward convective flow of the solute to compensate the evaporation losses and, in turn, transports the suspending solute to the edge region. This effect is known as “coffee-stain effect”. Objective of this PhD thesis was to analyze the critical states of this deposition method and to identify the working parameters for optimizing the deposition conditions. The study on the ink formulation through the definition of its chemico-physical properties, on the wetting of the ink/substrate system through the employment of surface treatments, on the ink processing through the definition of the printing parameters supplies the fundamental elements for controlling the droplet drying and, hence, the quality of the printed material. The printing parameters act differently on different ink/substrate systems. Therefore, studying the optimization of the deposition for different applications allows to understand how the printing conditions differently affect the working of different devices. In particular, the research activity pertains the employment of the inkjet printing (IJP) technology for optical and electronic applications, specifically focusing on the realization of optical structures, like microstructuring and microlenses, and organic electronic devices, such as volatile organic compounds (VOCs) sensors, organic field effect transistors (OFETs) and organic solar cells (PSC).