Towards a monolithic, substrate-reusable and an all-epitaxial design for III–V-on-Si solar cells

Integration of III-V multijunction solar cells on Si substrate can address the future levelized cost of energy by unifying the high-efficiency merits of III-V materials with the low-cost and abundance of Si. A Si-compatible monolithically integrated 3J InGaP/GaAs/Ge-Si cell design with a hybrid Ge-Si bottom cell is investigated. Utilizing a combination of comprehensive modeling and experimental material characterization techniques, we present our results for ultrathin epitaxial Ge directly grown on Si substrate using molecular beam epitaxy. Virtual “Ge-on-Si” substrates could provide a large-area, low-cost alternative to expensive GaAs wafers, a promising step towards realizing monolithic, high-efficiency and low-cost III-V-on-Si photovoltaics.