title: Photon-enhanced thermionic emission for solar concentrator systems.
abstract: Solar-energy conversion usually takes one of two forms: the 'quantum' approach, which uses the large per-photon energy of solar radiation to excite electrons, as in photovoltaic cells, or the 'thermal' approach, which uses concentrated sunlight as a thermal-energy source to indirectly produce electricity using a heat engine. Here we present a new concept for solar electricity generation, photon-enhanced thermionic emission, which combines quantum and thermal mechanisms into a single physical process. The device is based on thermionic emission of photoexcited electrons from a semiconductor cathode at high temperature. Temperature-dependent photoemission-yield measurements from GaN show strong evidence for photon-enhanced thermionic emission, and calculated efficiencies for idealized devices can exceed the theoretical limits of single-junction photovoltaic cells. The proposed solar converter would operate at temperatures exceeding 200 degrees C, enabling its waste heat to be used to power a secondary thermal engine, boosting theoretical combined conversion efficiencies above 50%.
authors.affiliation: Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA.
authors.forename: Jared W
authors.initials: JW
authors.lastname: Schwede
authors.forename: Igor
authors.initials: I
authors.lastname: Bargatin
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Riley
authors.forename: Brian E
authors.initials: BE
authors.lastname: Hardin
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Rosenthal
authors.forename: Yun
authors.initials: Y
authors.lastname: Sun
authors.forename: Felix
authors.initials: F
authors.lastname: Schmitt
authors.forename: Piero
authors.initials: P
authors.lastname: Pianetta
authors.forename: Roger T
authors.initials: RT
authors.lastname: Howe
authors.forename: Zhi-Xun
authors.initials: ZX
authors.lastname: Shen
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Melosh