Four-Terminal Mechanically Stacked GaAs/Si Tandem Solar Cells

TL;DR

This paper presents a four-terminal mechanically stacked GaAs/Si tandem solar cell that independently collects carriers from each subcell, achieving over 27% efficiency without the constraints of lattice matching or tunnel junctions.

Contribution

It introduces a novel four-terminal mechanically stacked design allowing material flexibility and higher efficiency in tandem solar cells compared to traditional series-connected devices.

Findings

Achieved over 27% conversion efficiency.

Independent carrier collection improves efficiency.

No need for lattice matching or tunnel junctions.

Abstract

This study investigates a four-terminal mechanically stacked double junction photovoltaic device based on GaAs as a top subcell and Si as a bottom subcell. Unlike two terminal monolithically series connected double junction photovoltaics, four-terminal mechanically stacked devices benefit from the ability to choose a combination of materials that are not constrained to lattice matching condition. GaAs top subcell is the best sensitive to visible light and Si bottom subcell is chosen to be grown on Si substrate which has relatively low cost. Moreover, the carriers generated by each subcell is collected independently to the external circuit. This electrical isolation of the subcells ensures higher efficiency, where no current matching nor tunnel junctions and related losses exist. A conversion efficiency of the device with a thickness in the order of 10 microns surpassed 27%.