Deposition heating effect on CdS thin films prepared by thermal evaporation for CdTe solar cells

Cadmium sulfide (CdS) thin films were prepared by thermal evaporation at different substrate temperature in order to compare their influence on properties of the films for CdS/CdTe solar cells. The investigated substrate temperature during CdS deposition was ranged from 30°C(room temperature) to 200°C. An increase in the substrate temperature yielded to highly transparent CdS thin films. However, the resistivity increased significantly with decrease of carrier concentration and mobility as substrate temperature increased. Photovoltaic properties of devices using the CdS thin films were investigated by fabricating CdS/CdTe solar cells at different CdS deposition temperature. CdS preparation temperature influenced significantly on open-circuit voltage which decreased with increasing deposition temperature. It is found that the CdTe solar cell using the CdS thin film deposited at room temperature had higher efficiency because substrate heating at 330°C during CdTe deposition also improved the optical and electrical properties of the CdS thin films simultaneously.