Impacts of Dislocations and Residual Thermal Tension on Monolithically Integrated InGaP/GaAs/Si Triple-Junction Solar Cells

Abstract

Direct epitaxy of III−V materials on Si is a promising approach for highly stable, scalable, and efficient Si-based multijunction solar cells. However, challenges lie in overcoming epitaxial dislocations and residual thermal strain generated by lattice constant and thermal-expansion-coefficient mismatches, respectively. Herein, a 15.2% efficient InGaP/GaAs/Si triple-junction solar cell with an open-circuit voltage of 2.36 V by using In_0.10Al_0.16Ga_0.74As digital-alloy dislocation filter layers is first demonstrated. The filter layers are utilized in the n-GaAs buffer on Si to reduce threading dislocation density to 4 × 10⁷ cm⁻² while maintaining optical transparency to Si bottom cell. Then, the impacts of threading dislocations and residual tension on InGaP/GaAs/Si cells are systematically investigated by comparing them to the co-grown InGaP/GaAs tandem cells on a native GaAs substrate. Based on the comparative analysis, a strategy to suppress material deformation and defect formation toward 30% efficient InGaP/GaAs/Si triple-junction solar cells is proposed.