Monolithic integration of GaAsPN dilute-nitride compounds on silicon substrates: toward the III-V/Si tandem solar cell
Résumé
GaAsPN semiconductors are promising material for the elaboration of high efficiencies tandem solar cells on silicon substrates. GaAsPN diluted nitride alloy is studied as the top junction material due to its perfect lattice matching with the Si substrate and its ideal bandgap energy allowing a perfect current matching with the Si bottom cell. We review our recent progress in materials development of the GaAsPN alloy and our recent studies of all the different building blocks toward the elaboration of a PIN solar cell. A lattice matched (with a GaP(001) substrate) 100 nm-thick GaAsPN alloy has been grown by MBE. After a post-growth annealing step, this alloy displays a strong absorption around 1.8-1.9 eV eV, and efficient photoluminescence at room temperature suitable for the elaboration of the targeted solar cell top junction. An early stage GaAsPN PIN solar cell prototype have been grown on a GaP (001) substrate. The quantum efficiency and the I-V curve show that carriers have been extracted from the GaAsPN alloy absorber, with an open-circuit voltage around 1 eV, while however displaying a low short circuit current meaning that the GaAsPN structural properties needs an optimization. Considering all the pathways for improvement, the >2% efficiency obtained under AM1.5G is however promising, therefore validating our approach for obtaining a lattice-matched dual junction solar cell on silicon substrate. This work was supported by the French ANR, project MENHIRS (grant N°ANR-2011-PRGE-007-0).