Galli Group engineers inexpensive new silicon-based semiconductor for solar energy conversion

Work by Pritzker School of Molecular Engineering (PME) faculty member Giulia Galli and colleagues is featured on the cover of the August 2014 issue of Energy & Environmental Science.

Galli and postdoctoral scholar Yuping He have predicted a new, silicon-based clathrate for solar energy conversion, which has been synthesized by the group of Prof. Susan Kauzlarich at the University of California, Davis. This type of material has usually attracted attention for thermoelectric applications (conversion of temperature gradients into electricity) instead of for photovoltaic applications.

The new material, K8Al8Si38, is a single-crystal clathrate with a cage-like structure. It absorbs light in the visible range, having a band gap of about 1 eV. The material is synthesized in a straightforward process and is composed only of elements abundant in nature, making it a good candidate for future commercial production. Thermal testing showed the material to be stable up to 1270 K (996° C).

The team performed detailed first-principles modeling of charge carrier mobility, which influences overall efficiency. The results show that these properties of K8Al8Si38 compare well with those of crystalline silicon. Among alternatives to crystalline silicon, the new material is much better than amorphous silicon and organic photovoltaics, in terms of mobilities, and competitive with tin sulfide (SnS) and cuprous oxide (Cu2O) as well.

Models were used to predict the stable atomic configurations of potassium and aluminum and the energies of the solid as a function of composition. The results were in good agreement with the values measured for the synthesized crystals. In addition, the team modeled the effect of defects in the crystal structure and the spatial distribution of charge carriers, and both are favorable for solar energy conversion.

Galli is Liew Family Professor in Molecular Engineering in the University of Chicago’s Pritzker Molecular Engineering and a Senior Scientist at Argonne National Laboratory. First author Yuping He is a postdoctoral associate in Prof. Galli’s group and currently based at the University of California, Davis; co-authors Fan Sui and Susan M. Kauzlarich are members of the Department of Chemistry at the University of California, Davis. The work of Galli and He is funded by the U.S. Department of Energy’s Office of Basic Energy Sciences.