The strategic position: How molecules sit on surfaces drives energy and electron transfer

Florida State University researchers seeking to make newer, more energy efficient materials have made a breakthrough in understanding how structure dictates electron transfer across surfaces.

It all has to do with how the molecules are positioned.

Ken Hanson, associate professor in the Department of Chemistry, and his colleagues found that the way molecules assemble on an inorganic material plays a key role in how energy and electrical current move across these interfaces, thus driving the functionality.

His research is published in the Journal of Physical Chemistry C.

“Natural systems like photosynthesis and millions of years of evolution have been able to control the orientation of molecules to make energy and electron transfer very efficient,” Hanson said. “We would love to attain the same level of structural control with human made assemblies.”

Molecule-inorganic interfaces are commonly used in applications like biosensors, solar cells and organic light-emitting devices. The ability to move energy and electrical current across those interfaces dictates device performance.

Metal ion-linked multilayers have recently emerged as a strategy to control the interface by tuning the properties of each layer. These multilayers have been used for solar cells, solar fuels generation and molecular rectifiers. In addition to the properties of individual layers, the way surface molecules are positioned plays a critical role in how these layers communicate.

But until now, the positioning or orientation was unknown.

“Atoms in complex chemical systems are aimlessly jiggling and wiggling,” said FSU Professor of Chemistry and Biochemistry Wei Yang, a co-author of the study. “Understanding how complex chemical systems dynamically arrange so as to dictate essential properties, such as molecular photon upconversion, is not only practically meaningful to optimal design of materials, such as solar cells, but also intellectually truly satisfying."

Hanson said now that they have a better understanding of the structure and orientation, they want to control it to make more efficient solar cells or other technologies.

This research was supported by the Army Research Office, which has been interested in how foundational energy and materials research can be applied.

“The foundational results obtained in this study are of great importance to develop future advanced Army applications in sensing and energy storage,” said Pani Varanasi, branch chief, Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory.

Other authors of the paper are FSU graduate students Ashley Arcidiacono, Suliman Ayad, Jeffrey Ellison, Erica Knoff and Autumn Peters; FSU research assistant professor Lianqing Zheng; and Scott Saavedra and Wendi Zhang from University of Arizona.