Figure 4(c) shows the normalized spectral response
of the external quantum efficiency (EQE) of a nanotube
CdS-CdTe solar cell on intrinsic SnO2/ITO/soda-lime
glass, which was measured by an independent group
at PV Measurements Inc. [29]. The EQE value increases
steadily from 80% at 385 nm to 90% at 445 nm; it peaks
at 565 nm, and then remains strong until 825 nm which
approximately corresponds to the energy band gap
of the CdTe absorber layer.