GaAs/Si Tandem Solar Cells with an Optically Transparent InAlAs/GaAs Strained Layer Superlattices Dislocation Filter Layer

Abstract

Epitaxial growth of III–V materials on Si is a promising approach for large-scale, relatively low-cost, and high-efficiency Si-based multi-junction solar cells. Several micron-thick III–V compositionally graded buffers are typically grown to reduce the high threading dislocation density that arises due to the lattice mismatch between III–V and Si. Here, we show that optically transparent n-In0.1Al0.9As/n-GaAs strained layer superlattice dislocation filter layers can be used to reduce the threading dislocation density in the GaAs buffer on Si while maintaining the GaAs buffer thickness below 2 μm. Electron channeling contrast imaging measurements on the 2 μm n-GaAs/Si template revealed a threading dislocation density of 6 × 107 cm−2 owing to the effective n-In0.1Al0.9As/n-GaAs superlattice filter layers. Our GaAs/Si tandem cell showed an open-circuit voltage of 1.28 V, Si bottom cell limited short-circuit current of 7.2 mA/cm2, and an efficiency of 7.5%. This result paves the way toward monolithically integrated triple-junction solar cells on Si substrates.

Keywords

• solar cell
• Si tandem cell
• monolithic integration
• molecular beam epitaxy