Design of high performance CdS/CdTe solar cells by optimization of step doping and thickness of the CdTe absorption layer

We have studied the effect of stepped doping of the absorber layer on performance of a single junction cadmium sulfide/cadmium telluride (CdS/CdTe) solar cell. First, the electrical characteristics of an experimentally-fabricated single junction CdS/CdTe solar cell are studied. Next, a structure with optimized doping and thickness of the absorption layer is presented. It is found that step-doping concentration of the absorber layer can increase the conversion efficiency of the solar cell by about 1.77%. The effects of the fields due to the doping grading in the CdTe layer on important parameters of CdTe solar cells are also studied. It is shown that performance increases considerably with the increase in stepping gradient of the doping of CdTe layer. Under global AM 1.5 conditions, the optimized solar cell structure has an open-circuit voltage of 860 mV, a short-circuit current density of 25.68 mA/cm², and a fill factor of 81.8%, corresponding to a total area conversion efficiency of 18.07%.