Impact of buffer layer on kesterite solar cells

Recently, several groups have demonstrated high efficiency (Eff) kesterite solar cells which are Cu₂ZnSnSe₄ (CZTSe), Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSn(SSe)₄ (CZTSSe) solar cells. The highest efficiency has been achieved via the solution-based CZTSSe single cell by IBM. Comprehensive researches in relation to buffer layer technologies, for instance, Cd-free buffer layers (Zn-based or In₂S₃), and hybrid buffer layer (CdS/In₂S₃) were conducted by Solar Frontier. Especially, the hybrid buffer layer showed 12.7% on CZTSSe single cell. Solar Frontier also succeeded in fabricating kesterite submodules and demonstrated high performance on them in NEDO project. Eff of 9.2% on CZTS submodule with hybrid buffer layer and 11.4% on CZTSSe submodule with just CdS buffer layer so far. In this work, we applied the hybrid buffer layer to the CZTSSe submodules and achieved the Eff of 11.8%.