High efficiency chalcopyrite solar cells with ILGAR-ZnO WEL-device characteristics subject to the WEL composition

The composition of the ZnO/Zn(OH)₂ material system deposited by ILGAR (ion layer gas reaction) has been investigated by means of FTIR spectroscopy. Thereby, the O/OH-ratio was of special interest. It has been shown, that from almost impurity-free ZnO to hydroxide-rich Zn(O,OH) any desired mixture can be prepared by ILGAR just by varying the process temperature. In order to attain general information about the requirements on a buffer material in chalcopyrite solar cells, such Zn(O,OH) mixtures were introduced as intermediate layer implemented by the WEL concept (window extension layer). Superior solar cell performances compared to chemical bath deposited CdS buffered references were already reported earlier for ILGAR-ZnO WEL devices based on Cu(In,Ga)(S,Se)₂ ("CIGSSe"). The influence of varying material properties of the Zn(O,OH) WELs on the characteristics of corresponding CIGSSe devices has been investigated. It has been found that below a critical process temperature the WEL constitution has no major influence on the power conversion efficiency of these cells, but a significant impact on their device stability.