Faceting and disorder in nanowire solar cell arrays

Arrays of semiconductor nanowires have been discussed as a method of fabricating lower-cost, higher-efficiency solar cells. This is accomplished by shortening the minority carrier path to the contacts and by nanoscale light trapping effects. Numerical simulations have played a large role in the development of these cells. However, the approximation of the nanowire array as a group of uniformly spaced cylinders has limitations, as disorder is often present in fabricated devices. Here, we show that introducing disorder into simulated arrays of semiconductor nanowires enhances the calculated absorption. Additionally, facets and other surface features serve to reduce reflection and enhance light trapping over the model of the nanowire as a cylinder. An optimal disorder between 10-20% from uniform is predicted for both cylindrical and hexagonally arranged wires. This effect holds for various semiconductor materials. Preliminary electrical simulations are also presented for Si, GaAs, and Ge nanowires.