Toward a Better Understanding of the Use of Additives in Zn(S,O) Deposition Bath for High-Efficiency Cu(In,Ga)Se₂-Based Solar Cells

The purpose of this paper is to focus on the impact of the use of peroxide during the chemical bath deposition (CBD) of Zn(S,O) buffer layer on its deposition rate and on the performance of Cu(In,Ga)Se₂ (CIGSe)/CBD Zn(S,O)-based solar cells. For that, the effect of two peroxides have been compared: H₂O₂ and (NH₄)₂S₂O₈. Based on in-situ quartz μ-balance analyses, it has been shown that while it is necessary to introduce an important concentration of H₂O₂ (at least 0.11 M) to accelerate the deposition rate of Zn(S,O) layers, only 10^-3 M of S ₂O₈^2- is enough to improve highly its deposition rate. Moreover, X-ray photoelectron spectroscopy analyses have shown that the introduction of H₂O₂ in Zn(S,O) deposition bath leads to an oxidation of the CIGSe surface, which is not the case when persuflate or peroxodisulfate is used in very low concentration. Based on electrical characterization of CIGSe/CBD Zn(S,O)-based solar cells, it appears that the use of persulfate allows not only a decrease in metastable behavior of solar cells, which is generally observed with hydrogen peroxide, but the outperfomance of CdS-buffered reference cells as well.