Integrating the photon flux
shown in Fig. 4(c) and assuming that each photon
generates one electron-hole pair (EHP), the 3D nanotube
CdS-CdTe solar cells create total electron-hole pairs
with a density of 18.23 × 1016/cm2s and a photocurrent
density of 29.18 mA/cm2. These data suggest that the
CdS nanotube array geometry, through tailoring of
the optical properties at the nanoscale, enhances the
photon current density.