Polycrystalline $Cd_{1-x}Zn_xS$ films were prepared by coating (1-x) CdS + x ZnS slurries which contained various amounts of $CdCl_2$ on amorphous glass substrate followed by sintering in nitrogen. All-polycrystalline $Cd_{1-x}Zn_xS/CdTe$ heterojunction solar cells have been fabricated by coating the $Cd_{1-x}Zn_xS$ layer with a CdTe slurry, which contained 4.5wt% of $CdCl_2$, and sintering at $625\circ{C}$ for 1h in nitrogen.
Photovolatic properties of sintered CdS/CdTe and $Cd_{0.94}Zn_{0.06}S/CdTe$ solar cells have been investigated by varying cell width to maximize solar cell module efficiency. Short-circuit current density, fill factor and efficiency of the solar cells degrade with increasing cell width. Series resistance of the solar cells increases with the cell width resulting in the degradation of solar cell efficiency. Since the ratio of the active area of the solar cell to the module area increases with the cell width, module efficiency shows a maximum value at the cell width of 4mm. A sintered CdS/CdTe solar cell with an active area of 10mm × 4mm shows a solar efficiency of 10.0% and a $Cd_{0.94}Zn_{0.06}S$/CdTe solar cell with the same dimension shows an efficiency of 11.0% under solar illumination with an intensity of 85mW/㎠. The estimated values of the module efficiency were 6.7% and 7.3%, respectively.
Degradation of photovoltaic properties of sintered $Cd_{1-x}Zn_xS/CdTe$ solar cells are observed. This phenomenon is related to the increase in series resistance which is caused by the poor stability of carbon electrode. By packaging the solar cells and optimizing carbon electrode, it is possible to produce sintered $Cd_{1-x}Zn_xS/CdTe$ solar cells with good stability. Improved cells show solar efficiencies of ~10% under 50mW/㎠ tungsten lamp and no degradation in efficiency over periods of 180 days.