Investigation of sodium distribution in CuZnSnS thin films and its effects on the performance of the solar cells

• Na rich at CZTS surface and CZTS/Mo interface.
• In CZTS surface and CZTS/Mo interface, poor in Cu, but rich in Zn.
• Relationship between sodium and the modifications of CZTS phases.
• Effect of sodium on the performance of CZTS thin film solar cells.

In this work, we have studied the influence of sodium in CuZnSnS (CZTS) solar cells. The CZTS films were prepared on soda lime glass substrates with and without sodium barrier layers (the glass substrate served as a sodium source). Alternatively, a 40 nm NaF layer was deposited on the metallic precursor using glass substrates with a sodium barrier layer. The SEM showed a bi-layer structure of CZTS films. The bottom layer with small grains became thicker with sodium doping. Using the UV-Raman spectroscopy, ZnS phase was observed both in the surface and interface for the sample prepared with NaF. XPS indicated that sodium was rich on the film surface and at the CZTS/Mo interface. Simultaneously the surface and interface identified to be low concentrations of Cu as well as high concentrations of Zn. The I–V curve under light indicated that the performance could be improved by controlling the amount sodium.

Figure optionsDownload as PowerPoint slide