Development of the Cu2ZnSnSe4 absorption layer with “passivated” large grains for a thin-film solar cell device

• Sputtered Cu–Zn–Sn films were selenized at 600 °C with a two-selenide approach.
• The progress in obtaining the two-selenide selenization method was presented.
• Dense Cu2ZnSnSe4 with “passivated” large grains of 1–6 μm was achieved at 600 °C.
• Conventionally, selenization at 600 °C with Se led to porous or small-grained CZTSe films.
• CZTSe solar cell devices with world record in efficiency have grains of 1–2 um.

Dense Cu2ZnSnSe4 (CZTSe) thin films with large grains of 1–6 μm were prepared by sputtering a metallic Cu–Zn–Sn target followed by a selenization process at 600 °C. Selenization of Cu–Zn–Sn metallic films with the aid of (SnSe2+Se) and CuSe2 was explained, which involved the nucleation and growth stages. The design of modified Cu(In,Ga)Se2 barrier layer prevented high-temperature reactions between the Mo electrode and as-deposited film and led to a pore-free interface. Using our simple approach, passivated and large grains were formed in an absorption layer, which is important for fabricating CZTSe solar cells.