  Non-planar solar-cell devices have been promoted as a means to enhance
current collection in absorber materials with charge-transport limitations.
This work presents an analytical framework for assessing the ultimate
performance of non-planar solar-cells based on materials and geometry. Herein,
the physics of the p-n junction is analyzed for low-injection conditions, when
the junction can be considered spatially separable into quasi-neutral and
space-charge regions. For the conventional planar solar cell architecture,
previously established one-dimensional expressions governing charge carrier
transport are recovered from the framework established herein. Space-charge
region recombination statistics are compared for planar and non-planar
geometries, showing variations in recombination current produced from the
space-charge region. In addition, planar and non-planar solar cell performance
are simulated, based on a semi-empirical expression for short-circuit current,
detailing variations in charge carrier transport and efficiency as a function
of geometry, thereby yielding insights into design criteria for solar cell
architectures. For the conditions considered here, the expressions for
generation rate and total current are shown to universally govern any solar
cell geometry, while recombination within the space-charge region is shown to
be directly dependent on the geometrical orientation of the p-n junction.

Materials Science;Mesoscale and Nanoscale Physics