Generation of electricity from solar power either uses the thermal energy to power a heat engine or the energy of each photon to initiate a redox reaction in a photovoltaic cell.

Photon enhanced thermionic emission (PETE), the solar converter developed by Nicholas Melosh and colleagues, Stanford University, USA, combines the two approaches to create a photovoltaic cell that can power a secondary thermal engine with its waste heat. Current photovoltaic cells only operate at temperatures too low to do this.

Measurements from gallium nitride show strong evidence for photon-enhanced thermionic emission. Coating a GaN semiconductor with a thin layer of cesium could allow the device to operate at temperatures exceeding 200 °C with theoretical conversion efficiencies above 50 %.

• Photon-enhanced thermionic emission for solar concentrator systems
  J. W. Schwede, I. Bargatin, D. C. Riley, B. E. Hardin, S. J. Rosenthal et al.,
  Nat. Mat. 2010, 9.
  DOI: 10.1038/nmat2814