UK researchers seek to improve conductivity of fluorine doped tin dioxide in coatings for solar cells

At the University of Liverpool, researchers have published a paper in the Advanced Functional Materials journal, outlining how the conductivity of fluorine doped tin dioxide can be improved. This kind of glass is commonly used for the production of touchscreens, solar cells and energy efficient windows.

Coatings are applied to the glass on these items to make them electrically conductive while, at the same time, letting light through. The research team at the University of Liverpool believe there is untapped potential for improved performance on such devices.

Physicists have identified the factors that has been limiting the conductivity of fluorine doped tin dioxide. These should normally allow high levels of electricity conduction because fluorine atoms substituted on oxygen lattice sites are each expected to give an additional free electron for conduction.

However, the scientists have reported that, while using a mixture of experimental and theoretical data, they found that for every two fluorine atoms that provide an additional free electron, another one occupies a normally unoccupied lattice position in the tin dioxide crystal structure.

Each so-called “interstitial” fluorine atom, the scientists explain, captures one of the free electrons and thereby becomes negatively charged. This reduces the electron density by half and also results in increased scattering of the remaining free electrons. This results in limited conductivity for fluorine doped tin dioxide.

Jack Swallow, PhD student at the University’s Department of Physics and the Stephenson Institute for Renewable Energy, said: “Identifying the factor that has been limiting the conductivity of fluorine doped tin dioxide is an important discovery and could lead to coatings with improved transparency and up to five times higher conductivity, reducing cost and enhancing performance in a myriad of applications from touchscreens, LEDs, photovoltaic cells and energy efficient windows.” The team leading the research now plans on finding alternative novel dopants that avoid these drawbacks.

The research involved physicists from the University, the Surrey Ion Beam Centre, as well as collaboration with computational chemists at University College London and global glass manufacturer, NSG Group. The studies were funded by an Engineering and Physical Sciences Research Council grant and the EPSRC’s Centre for Doctoral Training in New and Sustainable Photovoltaics.