Effects of deposition parameters on the composition of Cu(In,Ga)Se2 thin films deposited by magnetron pulsed DC sputtering
Résumé
Industrial Cu(In,Ga)Se2 (CIGS) thin films formation process generally require two steps : 1) Cu-In-Ga precursors deposition 2) crystallization under selenium atmosphere (H2Se). Unfortunately, hydrogen selenide is very hazardous, being the most toxic selenium compound. Nevertheless, recent works have shown that it is possible to obtain good quality CIGS absorbers by sputtering in an inert atmosphere without additional selenium supply. From an industrial point of view, it is interesting to simplify CIGS formation process and to avoid the use of H2Se. This work shows the effect of deposition parameters on the composition of CIGS thin films deposited by a simple method: magnetron pulsed DC sputtering from a single quaternary target in an inert atmosphere without additional selenium. This straightforward method doesn't allow a direct tuning of the films composition but a good control of the composition is important to achieve good quality absorbers. For example, good photovoltaic properties can be obtained only if the composition is slightly Cu-deficient and Se-rich. The evolution of CIGS thin film composition is studied when working pressure, gas flow, power, substrate temperature, type of substrate, pulse frequency and duration are modified and these evolutions are interpreted. Taking into account industrial application, the possibilities of adapting the CIGS target composition is discussed.