Conventional solar panels capture less than 30 percent of the energy that falls on them
Marc Venema / Alamy Stock photo
A new kind of solar cell has broken a theoretical limit on the efficiency of silicon-based cells, allowing us to extract more energy from sunlight.
Almost all commercial solar cells are made of silicon. These can only convert a narrow frequency band of sunlight into electricity. Light that falls too far outside this range passes straight through or is lost as heat, giving silicon cells a theoretical efficiency limit of about 29.4 percent.
In theory, this limit could be higher if another material is stacked on top of the silicon layer that generates electricity from light in a different frequency range. Perovskite, a crystal of titanium and calcium, is well suited for this because it better absorbs light closer to the infrared spectrum, but making it efficient has proven difficult. This is due to wayward electrons being reabsorbed back into the crystal before they can be converted into current.
Now two research groups have found ways to couple perovskite with silicon and achieve higher efficiency.
In order for the silicon and perovskite to work together, Xin Yu Chin at the Swiss Federal Institute of Technology, Lausanne and his colleagues used a two-step process. The silicon cell is first coated with a well-matched layer of precursor chemicals, before adding a second layer of chemicals to convert the precursors to perovskite. This process causes fewer defects in the silicon-perovskite interface, says Chin, thus increasing the number of electrons available for current. The team’s device has an efficiency of 31.2 percent.
In a separate study Silvia Mariotti at Helmholtz-Zentrum Berlin and her colleagues injected liquid piperazinium iodide into the perovskite layer, which also seemed to reduce the wayward electrons — with an efficiency of 32.5 percent.
“The efficiency is phenomenal,” says Kyle Frohna at the University of Cambridge. However, these numbers are currently limited to solar cell sizes much smaller than what would be needed for commercial use, he says.
Solar energy company Oxford PV demonstrated this in May perovskite-silicon tandem cells could be manufactured at a production-ready scale, although they had a slightly lower efficiency level of 28 percent.
“If we can make these at scale, which some companies seem to be able to do, that’s great,” says Frohna. “The only caveat is that we want to make sure they’re stable enough to last.”
Subjects:
- solar energy/
- Renewable energy