Molecular Organic Materials Properties and Controlled Film Growth via Organic Vapor Jet Printing.

Abstract

This dissertation describes advances in printing small molecular organic compounds having important applications, including two with major societal impact: the additive patterning of organic semiconductors and the continuous production of pharmaceutics. Rapid progress in research and development of organic electronics has resulted in many exciting discoveries and applications, including OLEDs and OPVs. Small molecular organic optoelectronic devices are usually multilayer films and patterns comprised of sharp interfaces and highly pure materials. Solvent-based deposition and patterning methods compromise the purity and interface sharpness, calling for solvent-free methods. Vacuum thermal evaporation is a common technique used currently, with inherent limits for scale-up. Instead, organic vapor jet printing (OVJP) is proposed, enabling solvent-free patterning of molecular semiconductors. In OVJP, a carrier gas is used to drive collimated flow, resulting in additive patterning, while preserving advantages of vacuum thermal evaporation. For process and equipment design and scale-up, knowing the evaporation properties of organic semiconductors, and having the ability to predict film morphology formation for a range of process conditions used in devices is crucial. To address these needs, we studied the thermophysical properties of small molecular organic compounds and demonstrated a new predictive relationship between material density and sublimation enthalpy. We then applied this knowledge to enhance patterning resolution and materials utilization, using flow simulations to design new evaporation systems that achieve micrometer-scale patterning resolution. The gas-to-solid phase transition in OVJP was studied, identifying process conditions for unique surface morphologies, with potentially useful properties. A phase diagram was developed that predicts surface morphology as a function of molecular properties and deposition conditions. These discoveries were then used to produce films of organic compounds with enhanced dissolution kinetics, which are found to be beneficial for many medical applications. OVJP technique was shown to break fundamental barriers for the deployment of some drug candidates by enhancing their dissolution kinetics by orders of magnitude, while enabling novel drug delivery systems, such as medicines deposited onto microneedles, patches, biodegradable polymers. Direct in vitro treatment of breast and ovarian cancer cell cultures in aqueous media, by tamoxifen films shows significantly improved bioavailability as compared to powders.