CdS1-xSex Window Layer for CdTe Prepared by the Exchange of S with Se in CdS Films

Recent studies show that using CdSe as a window material for CdTe solar cells can enhance the current density in both short and long wavelength regions. However, to preserve the high open circuit voltage in this structure, a thin CdS layer at the transparent conducting oxide layer interface is still required. As an alternative to the CdS/CdSe bilayer, we attempted to use a CdS_1-xSe_x window layer to fabricate CdTe devices. Preparation of the CdS_1-xSe_x film was done by heat treating pure CdS films with Se vapor, converting a fraction of the CdS to CdSe by an exchange reaction. The degree of conversion increased as the selenization time was increased. The resultant films showed a mixture of CdSe and CdS phases at short times, and the formation of CdS_1-xSe_x phases at longer times. To study the effect of the selenized window on device performance, sputtered CdTe films were prepared and devices were finished. Current-voltage characteristics and external quantum efficiency measurements showed that the selenized CdS did not perform as well as either sputtered CdS or sputtered CdSe windows. Better control of the intermixing with CdTe and the defect physics could lead to higher performance devices in the future.