Voc approaches a value of Eg/q = 1.45 volts
(the band gap of the CdTe absorber) as T approaches
zero, indicating an ideal p-n junction [33]. For our
device, Voc in Fig. 5(d) extrapolates to a value of 1.18
volts as T approaches 0 K. This is lower than the value
of 1.45 volts for CdTe and is an indication of the
presence of non-ideal current transport mechanisms
involving tunneling and interface recombination at
the CdS-CdTe interface [33]. We are in the process of
devising strategies for reducing the tunneling and
interface recombination currents at the junction
interfaces in these nanotube solar cells.