RUI: Organic Molecular Crystal Growth in Complex Solvent Environments

Western Washington University, Bellingham WA

Investigators

Abstract

Non-technical abstract Most modern electronic devices are based on inorganic semiconductors like silicon. For some applications though, significant cost or performance advantages could in principle be gained by changing to molecular semiconductors, composed of polymers or small molecules. Examples of technologies that could benefit from molecular semiconductors include less expensive, higher performance solar cells, thinner, mechanically flexible displays, and lower cost, higher efficiency lighting. Prior research has shown that for applications such as these, the microscopic structure of the molecular semiconductor domains - including their size, position, and crystallinity - critically affects performance. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, researchers are using spectral imaging and highly controlled growth methods, combined with theory and modeling, to study molecular semiconductor crystallization in technologically important hosts. The outcome will be improved fundamental understanding of the factors affecting microscopic structure, and ultimately of ways to better control it. The research will be conducted primarily by undergraduate students. Because the research bridges physics and chemistry, students are benefitting from a rich experience working with faculty and other students with different academic and preparatory backgrounds, educating them to become collaborative problem-solvers with strong interdisciplinary skills. Technical abstract Increasingly sophisticated architectures and materials combinations required for applications such as doped polymer organic light-emitting diodes, fission-sensitized organic photovoltaics, all-organic single-crystal field-effect transistors, place stringent demands on the morphology, dimensions, crystallographic orientation, spatial positioning, and other growth characteristics of small-molecule crystalline guests, incorporated within complex hosts. Organic molecular crystal (OMC) formation takes place in multicomponent, multiphasic environments, influenced by both thermodynamic and kinetic factors, surpassing the ability of current theory to provide insight, let alone predictive design guidance. Likewise, conventional methods for preparing OMC-containing active layers in complex matrices (e.g. physical vapor deposition, spin casting, etc.) typically do not afford sufficient control over the variables driving crystallization to enable the kinds of controlled observations needed to advance fundamental understanding in such chemically and structurally diverse solution environments. This research is addressing these challenges by studying small-molecule organic crystal formation through controlled measurements involving model polymeric, small-molecule, and mixed fluid phase hosts, and combining these studies with a closely integrated program of theory and modeling to make broad generalizations about the design rules governing OMC formation. The objective is to better understand the underlying chemical, kinetic, and thermodynamic factors influencing nucleation and growth in technologically-relevant solution matrices.