Cost-efficient thermophotovoltaic cells based on germanium substrates

This paper describes the realisation of cost-efficient thermophotovoltaic (TPV) cells based on germanium substrates. Because the majority of the photons incident on the TPV cell in a typical TPV system will have along wavelength it is important to apply optical confinement in the TPV cell. In this paper this has been done by using a highly reflective rear contact. Electrical contact at the rear has been created with a laser (laser fired contact, LFC) such that the metal is locally heated and contact is formed. The optimal TPV cell is based on a low doped (1 x 10(15) cm(-3)) p-type germanium substrate having a 500 nm thick n-type emitter (1 x 10(19) cm(-3)), where front and rear are both passivated with hydrogen rich PECVD amorphous silicon. An AM 1.5G record efficiency has been measured for a germanium TPV cell with an LFC rear contact. The application of optical confinement leads to a clear improvement of the spectral response in the wavelength region which is dominant in TPV systems and results in a potential 20 % increase of current density compared to the use of a classical germanium photovoltaic cell. (C) 2009 Elsevier B.V. All rights reserved.