Research

Organic Semiconductor Surface Reactivity (2009-current)

Organic semiconductors are a remarkable class of materials that have revolutionized display technology (OLEDs) and are poised to make similar contributions to information display via OFETs. Over the last 15 years, we have been examining prototypical semiconductors (tetracene, rubrene, pentacene, TPBi) and trying to improve how these materials interact with top contact materials to improve device performance. We developed a means for chemically reacting acene surfaces via the classic Diels-Alder reaction (via a vapor/surface reaction) and use a variety of surface analysis techniques (XPS, PM-IRRAS, MALDI, SEM/EDX) to study the reacted surface. Studies were later extended to common electron transport materials in OLEDs (predominantly TPBi).

From a chemistry and fundamental scientific standpoint, the reactions of these materials are fascinating. Solution based precedence has little predictive power when reacting a solid organic substrate. Likewise, many of the properties unique to molecular solids (weak intermolecular forces, molecular anisotropy, etc.) mean the reaction of these surfaces bear little resemblance to their inorganic counterparts. Effectively the factors determining reactivity must be reevaluated with these surfaces.

Organic Semiconductor Device Improvement (2019-current)

Our fundamental studies have been utilized within OFETs and OLEDs to improve device performance. For example, the top contact configurations is optimal for OFETs within displays, but the process of evaporating metal contacts onto the organic semiconductor is damaging and the contacts are prone to delamination. By reacting metal binding groups onto the surface of the organic semiconductor we are able to reduce penetration, increase adhesion, and improve properties like sheet resistance in deposited metal contacts.

Photochromophore-Induced Electronic Effects (2008-2017)

Applying a self-assembled monolayer (SAM) to a gold surface is an effective means for altering the Fermi level of that species (as measured by the work function). Judiciously done, this can result in alignment of the metal's energy levels with those of the organic semiconductor active element. Such alignment can decrease contact resistance and results in dramatically decreased threshold voltages and up to six orders of magnitude increases in efficiencies in devices such as organic solar cells, organic light-emitting diodes, and organic field effect transistors.

We examined this phenomena in the context of a stimuli-induced response. By including a photochromic (light responsive) molecule in the monolayer, we controllably and reversibly altered the Fermi level of the surface. Spectroscopic studies of the molecular structure were correlated to the changes in the metal's Fermi level.

After years of synthesis and extensive studies on surface spectroscopy and device behavior, this project was ended to focus the group on the rich field of surface chemistry on organic semiconductors.

Surface Based Metal Organic Frameworks (MOFs) (2009-2012)

This project studied how the surface energy and terminal groups within a monolayer impact the adhesion of MOFs to surfaces. This project was discontinued in 2012.

Molecule Based Patterning (2009-2011)

The project examined how tethered catalysts could pattern the surfaces. This brief foray was discontinued in 2011.