Researchers at Technion, the Israel Institute of Technology, are on the way to developing a unique photovoltaic solar cell that could convert up to 50 percent of the sun’s energy into electricity—which is 70 percent higher than the best single-layer PV cells today. The device would use a photoluminescence material to recapture some of the energy emitted by the sun that other PV devices can’t capture.
Even the best commercially-available solar cells are limited in their ability to convert sunlight into electricity. That limit, called the Shockley–Queisser efficiency limit, found that even under the best conditions with concentration, a single-layer solar cell can only reach 41 percent efficiency. That hasn’t happened yet.
Solar cells can only absorb a narrow spectrum of light and much of the rest of the energy from the sun is cast off as heat energy, which PV devices can’t harness. In fact, hotter conditions can reduce the efficiency of solar panels.
Most commercial solar panels are somewhere around 18 percent efficient at converting the sunlight into electricity and SunPower’s solar panels are the most efficient commercial line at over 22 percent efficient per panel. There is a way to surpass the limit with multi-junction solar cells. Cells with multiple layers that absorb different spectra of the sun’s light. As of November 2016, the best of those cells—developed by the Fraunhofer Institute and Soitec—has reached a 46 percent efficiency level under concentration.
This technology being developed at Technion’s Excitonics Lab would add a layer of photoluminescence material between the sun and the solar cell itself. “Solar radiation, on its way to the photovoltaic cells, hits a dedicated material that we developed for this purpose, the material is heated by the unused part of the spectrum,” explained project lead and graduate student Assaf Manor. “In addition, the solar radiation in the optimal spectrum is absorbed and re-emitted at a blue-shifted spectrum. This radiation is then harvested by the solar cell. This way both the heat and the light are converted to electricity.”
The team published its research “Thermally enhanced photoluminescence for heat harvesting in photovoltaics” in Nature Communications. The research describes how its device was inspired by the process of optical refrigeration, where absorbed light is re-emitted at higher energy and cools the emitter. The new technology re-emits sunlight which can be absorbed by the PV, enhancing its efficiency without adding layers of photovoltaic materials.
The team hopes to have a demonstration device working at record efficiency levels ready within five years.Tweet