Diffusion-emission theory of photon enhanced thermionic emission solar energy harvesters

Abstract

Numerical and semi-analytical models are presented for photon-enhanced-thermionic-emission (PETE) devices. The models take diffusion of electrons, inhomogeneous photogeneration, and bulk and surface recombination into account. The efficiencies of PETE devices with silicon cathodes are calculated. Our model predicts significantly different electron affinity and temperature dependence for the device than the earlier model based on a rate-equation description of the cathode. We show that surface recombination can reduce the efficiency below 10 % at the cathode temperature of 800 K and the concentration of 1000 suns, but operating the device at high injection levels can increase the efficiency to 15 %.

Konwersja Energii Słonecznej W Elektryczną Z Wykorzystaniem Fotonowo Wzmocnionej Termoemisji Elektronowej

“…• modelowanie i optymalizacja procesu PETE [7,8,9,10,11], • dobór materiałów elektrod konwertera [12,13.14,15], • poszukiwanie metod ograniczenia wpływu ładunku przestrzennego na pracę konwertera [16,17,18,19]. Tabela 1.…”

Solar energy conversion with photon-enhanced thermionic emission

“…It is not known what fraction of these reflected electrons actually enters the conduction band, versus the fraction that may undergo immediate recombination at the surface and have no effect on the state of the cathode. The significant impact of surface recombination at the emitting surface was shown both theoretically [14,15] and experimentally [16], so the interaction of electron recycling with surface recombination should be considered. However, these investigations referred to the recombination of electrons already present in the cathode's conduction band, and do not provide the much needed insight about the fate of the reflected electrons.…”

“…Another exception is an intrinsic rather than a p-doped absorber [19], where a version of the diffusion model was used with two separate equations for the transport of electrons and holes. The generation profile can be represented according to two-pass absorption of collimated radiation [14]:…”

“…Several levels of complexity are possible in formulating an elaborate model. A simple model used a one-dimensional diffusion equation to describe the transport of excess electrons in a p-type cathode [15,14]:…”

Investigation of contact grid geometry for photon-enhanced thermionic emission (PETE) silicon based solar converters

“…Additional onedimensional models for PETE converter were proposed, but they provided lower detail and neglected some important physical effects. One solved only the electron continuity equation and did not account for the distribution of the electric field and the hole concentration inside the cathode (Varpula and Prunnila, 2012), which may be important in …”