Mechanically stacked solar cells for concentrator photovoltaics

Abstract

Access to the full text of the published version may require a subscription. Item AbstractThe power output of dual-junction mechanically stacked solar cells comprising different sub-cell materials in a terrestrial concentrating photovoltaic module has been evaluated. The ideal bandgap combination of both cells in a stack was found using EtaOpt. A combination of 1.4 eV and 0.7 eV has been found to produce the highest photovoltaic conversion efficiency under the AM1.5 Direct Solar Spectrum with x500 concentration. As EtaOpt does not consider the absorption profile of solar cell materials; the practical power output per unit area of a dual junction mechanically stacked solar cell has been modelled considering the optical absorption co-efficients and thicknesses of the individual solar cells. The model considered a GaAs top cell and a Ge, GaSb, Ga 0.47 In 0.53 As or Si bottom cell. It was found that GaSb gives the highest power contribution as a bottom cell in a dual junction configuration followed by Ge and GaInAs. While the additional power provided by a Si bottom cell is less than these it remains a suitable candidate for a bottom cell owing to its lower cost.

Numerical Simulation of a Mechanically Stacked GaAs/Ge Solar Cell

“…This cell could obtain 38.5% under x20 radiation [6]. As mentioned in [7], the optimum structure for these cells (by two separated cells) consists of supernatant cell with energy gap 1.4 eV and a cell with energy gap 0.7 eV so the supernatant cell made of GaAs and the underlying cell made of Ge have been selected.…”