Effect of CdTe nucleation layer on the performance of CdS/CdTe thin film solar cells

In this study, an electrodeposited CdTe nucleation layer (ED-CdTe*) was introduced on a chemical bath deposited (CBD) CdS layer prior to close-spaced sublimation (CSS) of the CdTe absorber layer to improve the efficiency of the CdS/CdTe solar cell by reducing the recombination mechanism in the depletion region. The ED-CdTe* nucleation layer grown in 40 s produced the highest efficiency of 9.12% with an open-circuit voltage (VOC) of 640 mV, while the CBD-CdS/CSS-CdTe solar cell delivered 8.07% efficiency, with a VOC of 596 mV. The ideality factor and the reverse saturate current density of the CBD-CdS/ED-CdTe*/CSS-CdTe solar cell were 2.28 and 6.65 × 10–5 mA/cm2, respectively. After being treated with CdCl2, the efficiency of the device with the nucleation layer (40 s) was elevated to 15.6% with a VOC of 761 mV, and that of the device with no nucleation layer was raised up to 14.6% with a VOC of 737 mV. Further, the solar cell with optimal ED-CdTe* nucleation layer showed the highest spectral response within the 400–900 nm wavelength range. The SEM and AFM analysis verified the formation of an ultrathin ED-CdTe* nucleation layer that can catalyse the film formation of CdTe by the CSS method while reducing the interface incongruity between CdS and CdTe layers.