Theoretical analysis of ZnO and ZnO based alloys as front electrode in CdS/CdTe solar cells

Abstract

ITO has unique properties to be used as front electrode in CdS/CdTe solar cells, however ITO is expensive not abundant and consequently this type of solar cells is still relatively expensive. This work studies the using of ZnO and ZnO based alloys such as ZnO:Sn, ZnO:Al and ZnO:In as alternative materials of ITO in order to develop the efficiency of CdS/CdTe solar cells. Both optical and recombination losses have been taken into consideration. The calculation of optical losses is carried out based on the multiple reflections effect as well as absorption in TCO and CdS layers. Both the front and back surfaces recombination of the CdTe layer are used to describe the recombination losses. It was found that ZnO and its alloys are considered good alternative materials of ITO that used as a front contact in CdS/CdTe cells. The best results were obtained for ZnO:Al, where the calculated short-circuit current density is 22.64mA/cm2 at width of depletion layer of 0.11μm, the optical and recombination losses are about 27% and the CdS/CdTe efficiency is about 17.9%.