Sn compensation via SnSex binary vapor supply during Cu2ZnSnSe4 formation

An elemental stacked Mo/Sn/Cu/Zn/Se precursor was prepared by sputtering pure elemental targets of Sn, Cu, and Zn sequentially onto Mo-coated glass substrates, followed by thermal evaporation of Se. To compensate for typical Sn loss observed during the thermal annealing of precursors in a tube-type rapid thermal annealing reactor, a custom-designed quartz/Se/Sn cover was added to the sample tray. It was found that Sn was supplied in the form of a binary compound, SnSex, and thus, the delamination of Cu2ZnSnSe4 (CZTSe) from the Mo layer was well suppressed. It was also found that an increase in the Se layer thickness (1, 3, and 5 μm) in the precursor structure could result in more severe delamination of CZTSe from the Mo layer and an increase in the Sn thickness (300-500 nm) in the quartz/Se/Sn cover could lead to the incorporation of more Sn and Se into the CZTSe structure.