SinBeRISE talk by Prof Eli Yablonovitch
Event Date: 03 Jul 2015 07:00 AM - 03 Jul 2015 08:00 AM
Event Venue: Tower Building, Level 2, CREATE Theatrette
Conversion of Black Body Radiation to Electricity: Solar and non-Solar
By Prof Eli Yablonovitch, Dept of Electrical Engineering and Computer Sciences, UC Berkeley
A new scientific principle[i] has produced record-breaking solar cells. The 28.8% single-junction solar efficiency record, by Alta Devices[ii], 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 thermophotovoltaics, 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[iii] to electricity with >50% efficiency. Such a lightweight “engine” can provide power to electric cars, aerial vehicles, spacecraft, homes, and stationary power plants.
[i] O. D. Miller, Eli Yablonovitch, and S. R. Kurtz, “Strong Internal and External Luminescence as Solar Cells Approach the Shockley–Queisser Limit”, IEEE J. Photovoltaics, vol. 2, pp. 303-311 (2012). DOI: 10.1109/JPHOTOV.2012.2198434
[ii] Kayes, B.M.; Hui Nie; Twist, R.; Spruytte, S.G.; Reinhardt, F.; Kizilyalli, I.C.; Higashi, G.S. “27.6% Conversion Efficiency, A New Record For Single-Junction Solar Cells Under 1 Sun Illumination” Proceedings of 37th IEEE Photovoltaic Specialists Conference (PVSC 2011)Pages: 4-8, DOI: 10.1109/PVSC.2011.6185831
[iii] The heat source can be combustion, radio-activity, or solar thermal.