Polycrystalline CdS films have been prepared by coating a slurry, which consisted of CdS, 11 wt\% $CdCl_2$ and appropriate amount of propylene glycol, on glass substrate and glass substrate coated with indium tin oxide(ITO) followed by sintering in a nitrogen atmosphere. CdTe slurries consisting of Te powder, Cd powders of various particle sizes prepared by grinding, and an appropriate amount of propylene glycol were coated on the sintered CdS films and were sintered in nitrogen to prepare sintered CdS/CdTe solar cells. The efficiency of a sintered CdS/CdTe solar cell increases with increasing Cd particle size up to $3 \sim 4 \mu m$ and then decreases with a further increase in the Cd particle size. The microstructures of the sintered CdTe layer and of the cross-section of the CdS/CdTe solar cell show that the structures are the most compact in a solar cell which started with a Cd particle size of $3 \sim 4 \mu m$. A sintered CdS/CdTe solar cell that was fabricated by using Cd powder with an average particle size of $\sim 4 \mu m$ shows a solar efficiency of 12\% when measured under a solar intensity of $80mW/cm^2$. The (Cd + Te) slurry contained (Cd + Te) powders mixed in a ball mill for $12 \sim 220$ hrs instead of more expensive CdTe powders. The shape of cadmium particles changed from sphere to plate and the diameter of the plate-shaped partkcles became smaller as the ball-milling time increased. Also, a compound CdTe started to form in a long milling time. The sintered CdTe layers were more compact as the diameter of plate-shaped Cd particles decreased. However, cracks were developed in the sintered CdTe layer when the diameter was small($\sim 2 \mu m$). The efficiency of sintered CdS/CdTe solar cells increased with decreasing particle diameter and then decreased with further decrease in particle diameter. The highest efficiency 12.1\% have been achieved by using a mixture of (Cd+Te) powders which had plate-shaped Cd particles with a diameter of $\sim 5 \mu m$. The results suggest that high-efficiency sintered CdS/CdTe solar cells can be fabricated by using CdTe slurry from the mixture of (Cd+Te) powders with an inexpensive ball milling process. The effects of annealing in nitrogen on the electrical and optical properties of indium tin oxide films were studied. The electron concentration of ITO films decreased and electron mobility increased with increase in annealing temperature and the conductivity remained constant. The optical band gap decreased due to the reduction of carrier concentration with increase in annealing temperature, which is consistent with Burstein-Moss shift. By screen printing and sintering of (Cd+Te) slurry on the sintered glass/ITO/CdS layer, ITO/CdS/CdTe solar cell was fabricated and cell parameters were measured. Series resistance and shunt resistance decreased due to highly conductive ITO film. Short circuit current did not change significantly. The value of fill factor increased due to low series resistance and open circuit voltage decreased due to low shunt resistance. The efficiency of ITO/CdS/CdTe solar cell with 3.5 mm width was the same as that of CdS/CdTe solar cell.
