  Both axial and radial junction nanowire solar cells have their challenges and
advantages. However, so far, there is no review that explicitly provides a
detailed comparative analysis of both axial and radial junction solar cells.
This article reviews some of the recent results on axial and radial junction
nanowire solar cells with an attempt to perform a comparative study between the
optical and device behavior of these cells. In particular, we start by
reviewing different results on how the absorption can be tuned in axial and
radial junction solar cells. We also discuss results on some of the critical
device concepts that are required to achieve high efficiency in axial and
radial junction solar cells. We include a section on new device concepts that
can be realized in nanowire structures. Finally, we conclude this review by
discussing a few of the standing challenges of nanowire solar cells.
