Thin film cadmium telluride-cadmium sulfide alloys and devices [solar cells]

The CdTe-CdS alloy system has been characterized at typical solar cell processing temperatures in order to elucidate the role of interdiffusion in CdTe/CdS-based solar cells. Predominately single-phase CdTe/sub 1-x/S/sub x/ thin films with x/spl equiv/[S]/([S]+[Te]) ranging from 0 to 0.45, were grown by vacuum co-evaporation of CdS and CdTe. Phase segregation was promoted by heat treatment of the films at 415/spl deg/C in the presence of CdCl/sub 2/. The solubility limits of S in CdTe and Te in CdS at 415/spl deg/C were derived by measuring the compositions of the two phases in the films after the CdCl/sub 2/ treatment. The solubility limit of S in CdTe was determined to be 5.8%. Solar cells were fabricated with compositionally uniform absorber layers of CdTe/sub 1-x/S/sub x/ with x near the solubility limit before heat treatment. An efficiency of 10.8% was achieved by a CdTe/sub 1-x/S/sub x//CdS device. The V/sub oc/, J/sub sc/, fill factor and spectral response of this device were all very similar to vacuum evaporated conventional CdTe/CdS cells where the alloy is formed by diffusion of S during cell processing.