  Solar cell designs based on disordered nanostructures tend to have higher
efficiencies than structures with uniform absorbers, though the reason is
poorly understood. To resolve this, we use a semi-analytic approach to
determine the physical mechanism leading to enhanced efficiency in arrays
containing nanowires with a variety of radii. We use our findings to
systematically design arrays that outperform randomly composed structures. An
ultimate efficiency of 23.75% is achieved with an array containing 30% silicon,
an increase of almost 10% over a homogeneous film of equal thickness.
