Seminar 31.12.14

Physical Electronics Dept.

***** Seminar *****

Gideon Segev

(PhD. student under the supervision of Prof. Yossi Rosenwaks and Prof. Abraham Kribus)

School of Electrical Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel

Photon Enhanced Thermionic Emission for Solar Energy Conversion

To date, the vast majority of solar energy conversion research focused on two parallel paths: photovoltaics and solar thermal energy conversion. Attempts were made to combine photovoltaic and thermal conversion such as cogeneration and thermo-photonics. However, these attempts did not yield very high efficiencies, and these concepts were not widely implemented. As a result, researchers are still looking for a conversion path that exploits both the photonic nature of sunlight and the high temperatures that can be achieved by focusing it.

Photon Enhanced Thermionic Emission (PETE) was recently proposed as a novel concept in solar energy conversion. Similar to traditional thermionic emission devices, a PETE device consists of a high-temperature cathode emitting energetic electrons and a lower temperature anode absorbing the electrons. By using a semiconductor cathode, optically generated electrons increase the cathode’s conduction band charge population allowing high electron emission at temperatures lower than the common range for thermionic emitters. In this seminar, we will discuss the efficiency limits of PETE devices. The theoretical efficiency limits of PETE converters can theoretically rise above 40% at concentration of 1000 suns, exceeding the Shockley Queisser limit for an ideal single junction PV cell. When coupled to secondary thermal cycle the limits were shown to be exceptionally high reaching close to 70% for a flux concentration 1000. Furthermore, unlike traditional thermionic converters, PETE conversion is possible even under isothermal conditions. Next, the loss mechanisms of more realistic PETE devices will be surveyed through elaborated models. Negative space charge between the two electrodes and surface recombination at the cathode contact are shown to heavily restrict the conversion efficiency. Implementation of back surface field layers in the form of homo-junction or hetero-junction cathodes can reduce surface recombination and bring the efficiency closer to the ideal limits.

Wednesday, December 31, 2014, at 16:00

Room 206, Wolfson Mechanical Engineering Building