Optimizations of GaAs Nanowire Solar Cells

The efficiency of GaAs nanowire (NW) solar cells can be significantly improved with no new processing steps or material requirements. We report coupled optoelectronic simulations of a GaAs NW solar cell with a vertical p-i-n junction and a high-bandgap AlInP passivating shell. Our frequency-dependent model facilitates calculation of quantum efficiency for the first time in NW solar cells. For passivated NWs, we find that short-wavelength photons can be most effectively harnessed by using a thin emitter, while long-wavelength photons are best utilized by extending the intrinsic region to the NW/substrate interface and using the substrate as a base. These two easily implemented changes, coupled with the increase of NW height to 3.5 μm with realistic surface recombination in the presence of a passivation shell, result in an NW solar cell with greater than 19% efficiency.