In-Situ Cu(In,Ga)Se2 composition control by Optical Emission Spectroscopy during hybrid co-sputtering/evaporation process

In this work, we have developed a hybrid one-step co-sputtering/evaporation Cu(In,Ga)Se₂ process, where Cu, In and Ga are sputtered simultaneously with the thermal evaporation of selenium, thus avoiding the use of H₂Se. An appropriate control of the selenium flux is very important to prevent the target poisoning and hence some material flux variations. Indeed, the control of the CIGS composition must be rigorous to ensure reproducible solar cell properties. In this regard, a study of the correlations between plasma species, thin film composition and morphology has been performed by varying Se evaporation temperature in the 170 to 230 °C range.