Optimization of MoSe2 formation for Cu(In,Ga)Se2-based solar cells by using thin superficial molybdenum oxide barrier layers

During the formation of Cu(In,Ga)Se2 thin films deposited on Mo substrate by the selenization of Cu-In-Ga precursor, the reaction of Mo with Se can lead to a high consumption of Mo back contact and the formation of a thick MoSe2 layer, thus deteriorating the electrical properties of the back contact. In this study, the effect of thermal oxidation pre-treatment on Mo has been investigated to control the growth of MoSe2. It has been demonstrated that a thin and covering MoO2 layer can block the selenization of Mo. Using this effect, a MoSe2 layer with controlled thickness can be formed by adding a thin and controlled Mo layer on top of an oxidized Mo substrate. In this configuration, only the Mo added on top of oxidized Mo forms MoSe2 and the whole Mo protected by MoO2 remains after selenization. Thanks to this Glass/Mo/MoO2/Mo substrate configuration and the metallic behavior of MoO2, the good electrical properties of the back contact are kept after selenization.