Fabrication of Two-Terminal Metal-Interconnected Multijunction III-V Solar Cells

Abstract — A novel approach has been developed to enable the creation of a fully lattice-matched two-terminal four-junction III-V solar cell is which an upper 1.85 eV GaInP / 1.42 eV GaAs two-junction (2J) tandem cell is bonded to a lower Eg3 eV GaInAsP / 0.74 GaInAs eV 2J tandem cell. In this configuration, the upper tandem is grown inverted and lattice-matched to a GaAs substrate, and the lower tandem is grown upright and lattice-matched to an InP substrate. Prove of concept devices have been fabricated using Au-Au bonding with either SiO2 or GaInP2 as a filler material. The bonding process is discussed in this paper as well as the result of an inverted GaAs cell bonded on a conducting GaAs wafer. The most complex device fabricated to date is a GaInP/GaAs 2J tandem cell bonded to a GaInAs cell using a GaInP2 optical coupling layer, with a post-bonding Voc of 2.7 eV. Index Terms — III-V multijunction solar cell, device bonding I