The properties and optimization of ZnTe:Cu back contacts on CdTe/CdS thin film solar cells

Vacuum-evaporated Cu-doped ZnTe films have been studied as the intermediate layer between CdTe and metal contacts in CdTe/CdS thin-film solar cells for the formation of low resistance back contacts. Different metals (Au, Ni, Co) were used as the contact material to the ZnTe layer. The effects of Cu concentration, ZnTe:Cu layer thickness, and ZnTe post-deposition annealing temperature on the cell performances have been investigated. We found that different metal contacts on the ZnTe layer lead to different doping densities in the CdTe layer and different open-circuit photovoltages of the solar cells. The series resistance of the CdTe/CdS cells was reduced significantly by the introduction of the ZnTe layer. Fill factors greater than 0.76 and an energy conversion efficiency of 12.9% have been achieved using ZnTe back contacts on electrodeposited CdTe. Preliminary studies showed good stability of Au/ZnTe-contacted cells under illumination and different bias conditions.