  We present a model for simulating performance of 3D nano -coaxial and
-hemispherical thin film solar cells. The material system considered in these
simulations is hydrogenated amorphous silicon (a-Si:H), with solar cells
fabricated in an n-i-p stacking architecture. Simulations for the performance
of the planar a-Si:H device are compared against simulations performed using
SCAPS-1D and found to be in close agreement. Electrical and optical properties
of devices are discussed for the respective geometries. Maximum power point
efficiencies are plotted as a function of i-layer thickness for insight into
optimizing spatial parameters. Simulation results show that while geometrical
changes in the energy band diagram impact charge carrier collection, a-Si:H
solar cell performance is most significantly impacted by light absorption
properties associated with nanoscopic arrays of non-planar structures. We
compare our simulations to results of fabricated nanocoaxial a-Si:H solar cells
and infer the mechanisms of enhanced absorption observed experimentally in such
solar cells.
