Inverted Lattice-Matched Triple Junction Solar Cells With 1.0 eV GaInNAsSb Subcell by MOCVD/MBE Hybrid Growth

In this paper, lattice-matched GaInP/GaAs/GaIn NAsSb 3-junction (3J) solar cells were fabricated using a hybrid growth technique consisting of metalorganic chemical vapor deposition (MOCVD) for the upper two subcells and molecular beam epitaxy (MBE) for the bottom cell. In the normal upright configuration, the MBE-grown GaInNAsSb solar cells often suffer from unintentional hydrogen incorporation due to the pyrolysis of MOCVD precursors during the growth of other subcells, which can lead to a degradation of the cell performance of GaInNAsSb subcell. In contrast, we studied the inverted growth sequence in order to avoid hydrogen incorporation. Then, we applied post-growth annealing to improve the carrier collection efficiency of GaInNAsSb bottom cell. The annealing effectively improved the carrier collection and increased the quantum efficiency of GaInNAsSb bottom cell in the present inverted 3J structure, whereas no significant disadvantages for the top and middle cells were observed. As a result, we achieved external quantum efficiency beyond 90% in 1.0 eV GaInNAsSb bottom cells with thicknesses of 1.5 and 2.0 μm, and successfully demonstrated high enough photocurrents, fulfilling the current matching condition in the 3J solar cells.