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 a long 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. timal TPV cell is based on a low doped ( 1 × 10 15 cm - 3 ) p -type germanium substrate having a 500 nm thick n-type emitter ( 1 × 10 19 cm - 3 ) , where front and rear are both passivated with hydrogen rich PECVD amorphous silicon. An AM1.5G 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.