NEW LEAD-FREE PEROVSKITE MATERIAL FOR SOLAR CELLS
Perovskites have emerged as a promising alternative to silicon for making inexpensive and efficient solar cells. A group of researchers at Brown University and University of Nebraska—Lincoln (UNL) has come up with a new titaniumbased material for making lead-free, inorganic perovskite solar cells. In a paper published in the journal Joule, the researchers show that the material can be a good candidate, especially for making tandem solar cells—arrangements in which a perovskite cells are placed on top of silicon or another established material to boost the overall efficiency.
“Titanium is an abundant, robust, and biocompatible element that, until now, has been largely overlooked in perovskite research,” said the senior author of the new paper, Nitin Padture, the Otis E Randall University Professor in Brown’s School of Engineering and director of Institute for Molecular and Nanoscale Innovation. “We showed that it’s possible to use titanium-based material to make thin-film perovskites and that the material has favourable properties for solar applications which can be tuned.”
Interest in perovskites, a class of materials with a particular crystalline structure, for clean energy emerged in 2009, when they were shown to be able to convert sunlight into electricity. The first perovskite solar cells had a conversion efficiency of only about 4%, but that has quickly skyrocketed to near 23%, which rivals traditional silicon cells. And perovskites offer some intriguing advantages. They’re potentially cheaper to make than silicon cells, and they can be partially transparent, enabling new technologies like windows that generate electricity.
“One of the big thrusts in perovskite research is to get away from lead-based materials and find new materials that are non-toxic and more stable,” Padture said. “Using computer simulations, our theoretician collaborators at UNL predicted that a class of perovskites with cesium, titanium and a halogen component (bromine or/and iodine) was a good candidate. The next step was to actually make a solar cell using that material and test its properties, and that is what we’ve done here.” The team made semi-transparent perovskite films that had bandgap—a measure of the energy level of photons the material can absorb— of 1.8 electron volts, which is considered to be ideal for tandem solar applications. The material had a conversion efficiency of 3.3%, which is well below that of leadbased cells, but a good start for an all-new material, the researchers say.