Analysis of the electronic properties of all-electroplated ZnS, CdS and CdTe graded bandgap photovoltaic device configuration

All-electrodeposited ZnS, CdS and CdTe thin layers have been incorporated in a graded bandgap solar cell structure of glass/FTO/n-ZnS/n-CdS/n-CdTe/Au have been fabricated and an average conversion efficiency of 14.18% was achieved under AM1.5 illuminated condition. Based on former work in which 10% conversion efficiency was reported, optimisation has been made to the semiconductor layers, precursors, thicknesses and the post-growth treatment. These results demonstrate the advantages of multi-layer graded bandgap device configuration and the inclusion of gallium based post-growth treatment (CdCl2 + Ga-2(SO4)(3)) on the CdS/CdTe-based device structure. The fabricated devices were characterised using both current-voltage (I-V) and capacitance voltage (C-V) techniques. Under dark I-V condition, a rectification factor (R.F.) of 10(4.8), ideality factor (n) of 1.60 and a barrier height (phi(b)) > 0.82 eV were observed. Under AM1.5 illuminated I-V condition, short-circuit current density (J(sc)) of 34.08 mA cm(-2), open-circuit voltage (V-oc) of 730 mV, fill-factor (FF) of 0.57 and conversion efficiency of 14.18% were observed. Under dark C-V condition, doping density (N-D) of 7.79 x 10(14) cm(-3) and a depletion width (W) of 1092 nm were achieved. In addition, the work demonstrates the capability of two electrode system as a simplification to the conventional three-electrode system in the electrodeposition of semiconductors.