This factor limits
the efficiency and needs to be improved in the future.
To identify the processes which limit device performance
in these nanotube solar cells, we conducted
I–V characteristics at different temperatures in the
300 to 200 K range. Figure 5(d) shows Voc as a
function of the temperature. As expected, Voc increases
as the temperature falls due to a reduction in the
temperature-dependent losses associated with the
reverse saturation current of the CdS-CdTe heterojunction.