The researchers used X-ray crystallography and Raman scattering spectroscopy to ensure they had produced the crystal structure and symmetry they intended. They also investigated its switchable polarity and bandgap, showing that they could indeed produce a bulk photovoltaic effect with visible light, opening the possibility of breaking the Shockley-Queisser limit.
Moreover, the ability to tune the final product's bandgap via the percentage of barium nickel niobate adds another potential advantage over interfacial solar cells.
"The parent's bandgap is in the UV range," Spanier said, "but adding just 10 percent of the barium nickel niobate moves the bandgap into the visible range and close to the desired value for efficient solar energy conversion. So that's a viable material to begin with, and the bandgap also proceeds to vary through the visible range as we add more, which is another very useful trait."
Another way to get around the inefficiency imposed by the Shockley-Queisser limit in interfacial solar cells is to effectively stack several solar cells with different bandgaps on top of one another. These multi-junction solar cells have a top layer with a high bandgap, which catches the most valuable photons and lets the less valuable ones pass through. Successive layers have lower and lower bandgaps, getting the most energy out of each photon, but adding to the overall complexity and cost of the solar cell.
"The family of materials we've made with the bulk photovoltaic effect goes through the entire solar spectrum," Rappe said. "So we could grow one material but gently change the composition as we're growing, resulting in a single material that performs like a multi-junction solar cell."
"This family of materials." Spanier said, "is all the more remarkable because it is comprised of inexpen
|Contact: Evan Lerner|
University of Pennsylvania