Researchers from Colorado University in Boulder with the US Department of Energy’s National Renewable Energy Laboratory (NREL) are pushing the efficiency of a tandem perovskite and silicon solar cell over 27 per cent using a low cost material.
Researchers around the world are looking at new peroskite materials paired with silicon cells for the next generation of solar cells, reaching 26 percent, compared to 21 per cent for silicon-only large panels. Oxford PV for example is currently building a production line in Germany for such tandem cells.
The average efficiency of solar panels is lower than the maximum efficiency as small cells lose about three percentage points when applied over a large panel. "We took a product that is responsible for a $30 billion a year industry and made it 30 per cent better," said Michael McGehee, a professor in the Department of Chemical and Biological Engineering. "That's a big deal."
The stacked cell with a perovskite layer made from a triple-halide alloy of chlorine, bromine, and iodine over a silicon cell. The bromine raises the bandgap, but when used with iodine and exposed to light, these elements don't always stay in place. Previous studies have tried to use chlorine and iodine together, but due to the differing particle sizes of these elements, not enough chlorine could fit into the perovskite crystal structure. But by using different amounts of chlorine, bromine, and iodine, the researchers found a way to shrink the crystal structure, allowing more chlorine to fit in, thereby stabilizing and improving the cell's efficiency.
The new material was tested for 1000 hours, or 42 days, of intensive light and heat testing and the tandem cells showed degradation of less than 4 percent at 60 ºC. At 85 degrees and after operating for 500 hours, the solar cell lost only about 3 per cent of its initial efficiency. "We believe it can take us over 30% efficiency and that it can be stable," said McGehee.