Development and Characterization of a Glued GaAs/Si Tandem Solar Cell in Four-Terminal Configuration

This work demonstrates a cost-effective fabrication method for a four-terminal (4T) GaAs/Si tandem solar cell using a commercial epoxy for mechanical stacking. The process involves the fabrication of individual cells, removal of the original GaAs substrate, and subsequent bonding. We characterized the electrical and optical properties of both subcells before and after integration. After bonding, the silicon cell showed a significant performance drop, with an 81% loss in efficiency and an 88% reduction in short-circuit current density. The GaAs cell's performance was less affected, with a 17% decrease in efficiency. The final combined efficiency of the tandem device reached approximately 7%, which is lower than the initial 9.4% efficiency of the standalone Si cell. The performance degradation is primarily attributed to optical losses from Fabry-Perot interference and increased surface roughness after processing. This initial study validates the bonding approach and identifies clear pathways for improvement, such as implementing anti-reflective coatings and optimizing the GaAs cell structure, to advance III-V/Si integration.