Growth of CdS and CdTe thin films for the fabrication of n-CdS/p-CdTe solar cell

Thin n-CdS and p-CdTe films were prepared by chemical spray pyrolysis and electrochemical deposition respectively. Excessive sulphur in the spray solution has promoted grain growth in CdS film. Microstructural features of CdS film with stoichiometric Cd:S concentration in the spray solution were more heterogeneous with grains, whereas film sprayed with excessive S show more uniformity, reduced grain boundary losses of current and improved shunt resistance through inhibition of leakage of current at narrow grain boundary or void site is expected and is indeed observed. Electrodeposition of CdTe films, beside the effect of the inherent process parameters, is also affected by crystalline and microstructural features of the underlying CdS. Nucleation of CdTe film is remarkably affected by CdS film spray deposited over glass substrate. Cell performance considerably depends upon the window layer CdS and the properties of sprayed CdS film depends considerably on the Cd:S ratio in the spray solution. A higher S content in the CdS film affects it optical transmission without changing the optical energy gap. This improves cell efficiency through reduction in CdS film resistivity. A typical increase in cell efficiency was found to increase from 8% to 10.5% using CdS film with Cd:S ratio as 1:1.1 and 1:1.3 respectively.