In this paper, the autor discusses the arguments in favor of development of thin film solar cells, and the areas which pose problems to their development. Of the many materials combinations investigated, only CdS/Cu2S, CdS/CuInSe2 and CdS/CdTe polycrystalline thin film polycrystalline cells have demostrated efficiencie greater than 10%. Of these the first has effectively been abandoned, at least in the USA and discussion will be limited to these latter two.
Thekey factors governing the success of all solar cells are their cost, theirefficiencyand their stability. Thecost of cells is governed by several factors, probably themost important of which is the capital equipment involver in their production. Examples are given of equipment in use at present and the potential for scale-up is discussed. The efficiency of cells can be described by fairly simple theory involving basic material and devide parameters. Although than above material largely meet the criteria, the devices themselves depend on other factors and it is pointed out that major improvement in the CdS/CuInSe2 cells depend on reduction of the reverse saturation current. In the Case of the CdS/CdTe cells,prospective improvement depend on improved contacting to the CdTe. The long term electrical stability of cells is governed by the physical and chemical stabilityof the various components involved in the device construction. There is limited experience in this area;laboratory cells appear not to have a stability problem, whereas field tested have shown degradation of A.R. coatings and electrical contacts.
Finally, the problem areas relating to these cells, and promising future research directions are indicated. Thelatter include the problem of low open circuit coltage in CdS/CuInSe2,contacts to p-type CdTe, the development of p-type windowlayers, and research on cascaded thin filme devices.
