Lattice-matched GaNPAs-on-silicon tandem solar cells

A two-junction device consisting of a 1.7-eV GaNPAs junction on a 1.1 -eV silicon junction has the theoretical potential to achieve nearly optimal efficiency for a two-junction tandem cell. We have demonstrated a monolithic III-V-on-silicon tandem solar cell in which most of the III-V layers are nearly lattice-matched to the silicon substrate. The cell includes a 1.8 eV GaNPAs top cell, a GaP-based tunnel junction (TJ), and a diffused silicon junction formed during the epitaxial growth of GaNP on the silicon substrate. This tandem on silicon has a V_OC of 1.53 V and an AM1.5G efficiency of 5.2% without any antireflection coating. Low currents in the top cell are the primary limitation to higher efficiency at this point.