[High efficiency Cu2ZnSnSe4 solar cells with a TiN diffusion barrier on the molybdenum bottom contact

We report on the structural properties and device results of Cu₂ZnSnSe₄ (CZTSe) solar cells deposited using a vacuum deposition process on glass substrates coated with a molybdenum bottom electrode. Compared to similarly-prepared pure sulfide Cu₂ZnSnS₄ (CZTS) devices, CZTSe devices exhibit a much thicker interfacial MoSe₂ reaction layer. This poses a serious problem in achieving high efficiency CZTSe solar cells-an overall reverse correlation between device performance and MoSe₂ thickness is observed. We show that the interfacial MoSe₂ formation can be controlled by the use of thin TiN diffusion barriers. Using this process we demonstrate a CZTSe device with 8.9% efficiency.