High Efficiency Zno-Cds-Cuinse₂ Solar Cells Recent Results of Eurocis Collaboration

Abstract

This paper reports a systematic study on the influence of CBD-CdS and ZnO on cell performances carried out in the frame of the EUROCIS collaboration. The bath chemistry of the CBD-CdS, in particular the use of different Cd salts like CdCl₂, Cdl₂ and CdSO₄, plays an important role on the resulting cell performances. XPS and UPS analysis have been carried out in order to investigate contaminations, coverage of the CuInSe₂ surface and growth kinetics of the CdS layers grown in different baths. In the case of the CdCl₂ based chemical bath, Cl^- anion contamination can be observed. Optimial CdS thicknesses have been experimentally determined. Spectral response measurements indicate increased absorption below 600 nm in the CdS layer by increasing the thickness. Optimization of the ZnO window between conductivity of the ZnO:Al and infrared free carrier absorption has been carried out in connection with different n⁺n doping gradients. In these experiments, multilayer-windows lead to improved cell performances in comparison to the standard devices. Highest efficiency has been obtained by using Cdl₂ based chemical baths (η = 11.7%, V_oc= 450mV, FF = 68%), whereas CdSO₄ has also given good results (η = 11.5%, V_oc= 424mV FF = 70%).