Impact of oxygen concentration during the deposition of window layers on lowering the metastability effects in Cu(In,Ga)Se₂/CBD Zn(S,O) based solar cell

The purpose of the present paper is to focus on the impact of oxygen gas partial pressure during the sputtering of i-ZnO and ZnMgO on the transient behavior of Cu(In,Ga)Se₂ (CIGSe) based solar cells parameters when a CBD-Zn(S,O) buffer layer is used. Based on electrical characterization of cells, it is observed that the effect of light soaking is different on J-V characteristics depending on whether oxygen is or is not present during the first deposition time of the i-ZnO or ZnMgO layers. In fact, when cells are prepared with standard i-ZnO, the efficiencies are very low and a pronounced transient behavior is observed. However, when the first 10 nm of i-ZnO or ZnMgO is formed by sputtered layer without adding oxygen during the process, depending on the thickness of the buffer layer, the transient effects strongly decreases. It is then possible to get stable cells reaching efficiencies quite similar to the CdS reference cells, especially with ZnMgO, without any post-treatments.