Photovoltaic cell

Abstract

There is disclosed a photovoltaic cell, such as a solar cell, incorporating one or more epitaxially grown layers of SiGe or another germanium material, substantially lattice matched to GaAs. A GaAs substrate used for growing the layers may be removed by a method which includes using a boundary between said GaAs and the germanium material as an etch stop.

Description

technical field [0001] The present invention relates to photovoltaic cells, in particular (but not exclusively) to multi-junction solar cells in which the lower photovoltaic junction for absorbing the long wave portion of the solar spectrum is germanium based. Background technique [0002] Photovoltaic cells convert light energy, such as sunlight, into useful electrical energy. Typically, electron-hole pairs are formed by the absorption of photons in semiconductor materials adjacent to p-n junctions that act to separate charge carriers, which are then transported into electrical circuits through metal contacts on the battery device. This absorption process occurs only when the photon energy is higher than the bandgap of the local semiconductor material, so low-bandgap materials tend to absorb more photons. The excess energy of a photon above the bandgap energy is lost as heat within the semiconductor lattice. If the p-n junction is made of a material with a high band gap, ...

AI Technical Summary

Problems solved by technology

However, it is still difficult to precisely control the thickness of the n-type doped layer using the described technique, the boundary between the n-type doped region and the p-type doped region is diffuse in nature, and the concentration of n-type doping must be high to offset Bulk p-type doping of the substrate

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