With its ease of manufacture, perovskite has the potential to replace silicon for inexpensive solar cells. But boosting its efficiency to 25 percent – that of the best, but expensive, silicon cells – has not been easy. UC Berkeley physicists have now mated two types of perovskite, separated by a single-layer of hexagonal boron nitride, to produce a solar cell that absorbs across the full solar spectrum and achieves a high efficiency of 21.7 percent.
Solar cells made from an inexpensive and increasingly popular material called perovskite can more efficiently turn sunlight into electricity using a new technique to sandwich two types of perovskite into a single photovoltaic cell.
Perovskite solar cells are made of a mix of organic molecules and inorganic elements that together capture light and convert it into electricity, just like today's more common silicon-based solar cells. Perovskite photovoltaic devices, however, can be made more easily and cheaply than silicon and on a flexible rather than rigid substrate. The first perovskite solar cells could go on the market next year, and some have been reported to capture 20 percent of the sun's energy.
In a paper appearing online today in advance of publication in the journal Nature Materials, University of California, Berkeley, and Lawrence Berkeley National Laboratory scientists report a new design that already achieves an average steady-state efficiency of 18.4 percent, with a high of 21.7 percent and a peak efficiency of 26 percent.
"We have set the record now for different parameters of perovskite solar cells, including the efficiency," said senior author Alex Zettl, a UC Berkeley professor of physics, senior faculty member at Berkeley Lab and member of the Kavli Energy Nanosciences Institute. "The efficiency is higher than any other perovskite cell - 21.7 percent - which is a phenomenal number, considering we are at the beginning of optimizing this."
"This has a great potential to be the cheapest photovoltaic on the market, plugging into any home solar system," said Onur Ergen, the lead author of the paper and a UC Berkeley physics graduate student.
The efficiency is also better than the 10-20 percent efficiency of polycrystalline silicon solar cells used to power most electronic devices and homes. Even the purest silicon solar cells, which are extremely expensive to produce, topped out at about 25 percent efficiency more than a decade ago.
The achievement comes thanks to a new way to combine two perovskite solar cell materials - each tuned to absorb a different wavelength or color of sunlight - into one "graded bandgap" solar cell that absorbs nearly the entire spectrum of visible light. Previous attempts to merge two perovskite materials have failed because the materials degrade one another's electronic performance.
"This is realizing a graded bandgap solar cell in a relatively easy-to-control and easy-to-manipulate system," Zettl said. "The nice thing about this is that it combines two very valuable features - the graded bandgap, a known approach, with perovskite, a relatively new but known material with surprisingly high efficiencies - to get the best of both worlds."