Bandgap optimized III–V (GaAsP) nanowire on silicon tandem solar cell, device and data

One way to achieve the next generation “Beyond Silicon” solar cell involves combining III-V with silicon. Silicon provides a cheap substrate, while the III-V materials supply a wide range of direct bandgaps that has demonstrated high conversion efficiencies in multi-junction solar cells. Their significant material differences have, however, prohibited commercial realization. The use of nanowires as the top junction removes any issues related to strain at the III-V/Si interface, which is normally induced by the mismatch in lattice coefficient, thermal expansion coefficients and polar/non-polar interface. Here, we present preliminary results from the first tandem solar cell where the top cell consists of bandgap optimized, III-V nanowires (GaAs_0.8P_0.2) and the bottom cell is in the silicon substrate. The grown structure was contacted, using indium-tin-oxide and characterized under AM1.5G illumination. All key elements are present in the device, and only optimizations are now needed towards a commercially viable solar cell.