US researchers mull zinc oxide as solar cell manufacturing alternative to titanium dioxide

A group of scientists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory has conducted research, published in the scientific magazine Nature, into the replacement of titanium dioxide in the manufacture of solar cells.

Argonne’s researchers said their study provides more insight on how holes get trapped in nanoparticles made of zinc oxide, a material which is considered vey promising for potential solar PV applications.

Understanding how this trapping process takes place may be key in the use of zinc oxide for solar applications. They explained that if the two particles that generate energy in a PV device – the negatively charged electron and the positively charged “hole” – are not fully separate before they are trapped in the solar material, the material itself has less capacity to convert the light into power.

The experiment has allowed the researchers to observe the trapping of holes in specific regions of the nanoparticle, while in previous experiments only the observation of the trapping of the electrons had been possible.

They used two different X-ray techniques to observe the process: X-ray absorption spectroscopy and resonant X-ray emission spectroscopy. As a result, they figured out that the holes became trapped in “oxygen vacancies”, which they define as places within the crystal lattice where an oxygen atom is missing.

“Zinc oxide,” said project lead Christopher Miln, “has a crystalline structure that allows it to have many of these vacancies. The trapping happens because the vacancies have a lower energy level than the surrounding environment, creating an energetic crevasse for passing holes.”

The research team believes that these findings may be further improved by an extremely quick snapshot of the trapping behavior. “Essentially, we want to see the same process but have the ability to take images a thousand times faster,” the research team concluded.

Author: Emiliano Bellini