Photovoltaic energy conversion with n-CdS—p-CdTe heterojunctions and other II-VI junctions

n-CdS-p-CdTe heterojunctions have been prepared by close-spaced vapor transport of p-CdTe films onto single crystal n-CdS, by vacuum evaporation of n-CdS films onto single crystal p-CdTe, and by solution spraying of n-CdS films onto single crystal p-CdTe. In addition, a number of other II-VI p-n heterojunctions have been prepared by the close-spaced vapor transport technique. The highest solar efficiency to date has been obtained with a cell prepared by vacuum evaporation of n-CdS film onto p-CdTe crystal, in which the CdS is covered with an indium-tin-oxide coating and then with an antireflection coating; the photovoltaic parameters of this cell are an open-circuit voltage of 0.63 V, a quantum efficiency of 0.82, a fill factor of 0.66, and a solar efficiency of 7.9 percent. II-VI heterojunction cells with efficiency greater than 10 percent are expected in the near future.