Solar cells turn sunlight into electricity, but because they’re only about 20% efficient, much of the leftover energy turns into heat – which actually harms the solar cell, according to researchers from Stanford University.
The researchers say they have now developed and tested a new material that can cool a solar cell by up to 13 degrees C. Because heat makes solar cells less efficient, the researchers predict their cooling layer could help solar cells turn approximately 1% more sunlight into electricity. These cooler temperatures also mean the solar cells will likely last longer due to greatly reduced efficiency degradation rates.
“What’s unique about our work is that we demonstrate radiative cooling while preserving the amount of solar absorption,” says Linxiao Zhu, a graduate student in the research group of electrical engineering professor Shanhui Fan. In other words, the new material keeps the solar cell cooler even as the solar cell absorbs the same amount of sunlight.
The researchers achieved the combination of cooling plus maintaining sunlight absorption with a wafer made of silica, a colorless mineral found naturally as quartz. The researchers etched tapered holes, about 6 micrometers across and 10 micrometers deep, in the wafer. The holes are designed to smooth the path the thermal radiation takes to escape.
The team tested the silica layer by placing it on top of a solar cell mimic, a polished silicon wafer with an anti-reflection surface and aluminum back that has similar absorption characteristics to standard solar cells but wasn’t actually wired to produce electricity.
The testing verified that because the silica layer is transparent, approximately the same amount of sunlight still reaches the solar cell mimic. In fact, there was a slight increase in absorption because of anti-reflection and light trapping effects of the etched silica.
The researchers also found that the etched silica layer lowered the temperature 13 degrees C compared with the bare solar cell mimic. The next step for Zhu and his colleagues is to test the etched silica layer with a real solar cell to demonstrate the predicted efficiency improvements.