Eli Yablonovitch

Electrical Engineering and Computer Sciences Department

University of California, Berkeley, CA

& UCLA Electrical Engineering Department

Abstract:        A new scientific principle has produced record-breaking solar cells. The 28.8% single-junction solar efficiency record, by Alta Devices, was achieved by recognizing the importance of extracting luminescent emission. This is exemplified by the mantra: “A great solar cell also needs to be a great LED”. It was essential to remove the original semiconductor substrate, which absorbed luminescence, and to replace it with a high reflectivity mirror. The solar efficiency record crept up as the rear reflectivity behind the photovoltaic film was increased, 96% reflectivity–97% –98% luminescent reflectivity;– each produced a new world efficiency record.

In thermo-photovoltaics, high energy photons from a thermal source are converted to electricity. The question is what to do about the majority of low energy infrared photons? It was recognized that the semiconductor band-edge itself can provide excellent spectral filtering for thermo-photovoltaics, efficiently reflecting the unused infrared radiation back to the heat source. Exactly those low energy photons that fail to produce an electron-hole pair, are the photons that need to be recycled. Thus the effort to reflect band-edge luminescence in solar cells has serendipitously created the technology to reflect all infrared wavelengths, which can revolutionize thermo-photovoltaics. We have never before had such high rear reflectivity for sub-bandgap radiation, permitting step-function spectral control of the unused infrared photons for the first time. This enables conversion from heat to electricity with >50% efficiency. Such a lightweight “engine” can provide power to electric cars, aerial vehicles, spacecraft, homes, and stationary power plants.

Eli Yablonovitch is Professor of Electrical Engineering and Computer Science at UC Berkeley where he also serves as Director of the NSF Center for Energy Efficient Electronics Science. He is world renown for his ground-breaking research that spans several areas. Professor Yablonovitch introduced the idea that strained semiconductor lasers could have superior performance due to reduced valence band (hole) effective mass. With almost every human interaction with the internet, optical telecommunication occurs by strained semiconductor lasers. In his photovoltaic research, ProfessorYablonovitch introduced the 4(n squared) (“Yablonovitch Limit”) light-trapping factor that is in worldwide use, for almost all commercial solar panels. Based on his mantra that “a great solar cell also needs to be a great LED”, his startup company Alta Devices Inc. has, since 2011, held the world record for solar cell efficiency, now 28.8% at 1 sun. Professor Yablonovitch is regarded as a Father of the Photonic Band Gap concept, and coined the term “Photonic Crystal”. The geometrical structure of the first experimentally realized Photonic bandgap, is often called “Yablonovite”. His startup company Ethertronics Inc., has shipped over one billion cellphone antennas. Professor Yablonovitch has been elected to the NAE, the NAS, the AmAAS, and as Foreign Member to the UK Royal Society. Among his honors is the Buckley Prize of the American Physical Society, and the Isaac Newton Medal of the UK Institute of Physics.