Development of MoOx thin films as back contact buffer for CdTe solar cells in substrate configuration

Molybdenum oxide compounds exhibit unique electrical and optical properties depending on oxygen vacancy concentration and composition and therefore, have recently attracted a lot of attention as a hole transport layer in various devices.In this work CdTe solar cells in substrate configuration were grown with evaporated MoOx back contact buffer layers and efficiencies of up to 10% could be achieved without using Cu in the back contact processing. The buffer layer – at the CdTe/back contact interface – in the finished cell was found to consist of MoO2 phase instead of the expected MoO3 phase as observed in as-deposited or annealed MoOx layers without CdTe deposition.In order to obtain MoOx buffer layers with desired stoichiometry, MoOx thin films were deposited by radio-frequency sputtering under different growth conditions. The chemical phase, composition, microstructure and optical properties of such layers were studied for their possible use in CdTe solar cells.

► MoOx is used as a back contact buffer in CdTe solar cells in substrate configuration. ► Efficiency of 10.0% was achieved without the addition of Cu. ► The back contact buffer in the finished device consists only of MoO2. ► Phases and microstructure of MoOx can be controlled by sputtering conditions.