Integrating the spectral
response of EQE and assuming a maximum response
of 100% and no transmittance loss in the substrate, the
photocurrent density is calculated to be 28.05 mA/cm2.
The photocurrent density calculated from the EQE
response is in agreement with the photon flux
simulation. A strong EQE response over a broad spectral
range indicates that the nanotube solar cell structure
configuration can benefit photo-carrier generation
and collection. It should be noted that the above device
is fabricated on an inexpensive and low-transparency
intrinsic SnO2/ITO/soda-lime glass substrate. Subsequently,
when the low-transparency substrate is
replaced by a higher-transmission substrate, the spectral
response of the nanotube solar cells will be further
improved.