A better understanding of the growth mechanism of Zn(S,O,OH) chemical bath deposited buffer layers for high efficiency Cu(In,Ga)(S,Se)2 solar cells

In the field of Cu(Ga,In)(S,Se) 2 photovoltaic technology, zinc sulphide based buffer layers prepared by Chemical Bath Deposition (CBD) have already demonstrated their potential to replace CdS. This paper aims on a better understanding of deposition mechanism of the Zn(S,O,OH) buffer layers. First, the influence of deposition parameters is studied from solution chemistry considerations by constructing solubility diagrams of ZnS, ZnO, and Zn(OH) 2 . Experimental studies are then carried out by the in situ quartz crystal microgravimetry (QCM) technique. A global equation for the growth rate is derived from these experiments. The morphology and composition of Zn(S,O,OH) films are then determined using scanning electron microscopy and X-ray photoelectron spectroscopy techniques. Electro-deposited-CIS/Zn(S,O,OH)/ZnO and co-evaporated-CIGS/Zn(S,O,OH)/ZnO cells were prepared with efficiencies similar to that of reference CBD CdS buffer layers.