Optical, Electronic Properties of Metal Oxides Tuned

Tuning the optical and electronic properties of metal oxides at the atomic level by creating a superlattice “sandwich” now makes it possible to harness the sunlight’s energy. The discovery could lead to applications in fuel cells, touchscreen technology, computer switches and battery storage.

Semiconductors are an important class of materials defined by the size of the bandgap. For transparent conductors, a large bandgap is required, whereas for artificial photosynthesis, a bandgap that corresponds to green light is needed. Metal oxides provide a means of tailoring the bandgap.

Although metal oxides are good electron conductors, they are very poor “hole” conductors. Holes refer to absence of electrons and can conduct positive charge. To maximize their potential for artificial photosynthesis and invisible electronics, hole conducting metal oxides are required.

To achieve such metal oxides, Louis Piper, an assistant professor of physics at Binghamton University, has begun studying layered metal oxide systems, which can be combined to selectively dope (replace a small number of one type of atom in the material) or tune (control the bandgap size). His work revealed that a superlattice of two hole-conducting copper oxides could cover the solar spectrum. His goal is to use environmentally benign, cheap metal alternatives to improve the performance.

Louis Piper, assistant professor of physics at Binghamton University, is harnessing the energy of sunlight by tuning the optical and electronic properties of metal oxides. (Image: Jonathan Cohen/Binghamton University)

Metal oxides are cheap, abundant and “green,” Piper said. “And as the study proved, quite versatile. With the right touch, metal oxides can be tailored to meet all sorts of needs, which is good news for technological applications, specifically in energy generation and flat screen displays.”

Indium oxide is one of the most commonly used oxides for coating flat screen displays and solar cells. Although it can conduct electrons very well and is transparent, it is rare and very expensive.

Piper’s current research aims at using cheaper tin oxide layers to achieve electron and hole conduction with optical transparency. His research shows that one glove will not fit all purposes, Piper said.

“It’s going to be a case of some serious detective work,” he said. “We’re working in a world where physics and chemistry overlap. And we’ve reached the theoretical limit of our calculations and fundamental processes. Now we need to audit those calculations and see where we’re missing things. I believe we will find those missing pieces by playing around with metal oxides.”

Piper is convinced that if he can reinforce metal oxides’ “good bits” and downplay its rough spots, a new and exciting type of metal oxide that can be tailored for specific applications will be well within reach.

“We’re talking battery storage, fuel cells, touchscreen technology and all types of computer switches,” he said. “We’re in the middle of a very important gold rush, and it’s very exciting to be part of that race to strike it rich.

“But first we have to figure out what we don’t know before we can figure out what we do. One thing’s for sure: Metal oxides hold the key.”

The research appeared in Physical Review B.

For more information, visit: www.binghamton.edu