Kesterite Cu2ZnSnS4 (CZTS) Thin Film Formation Using Sequential Annealing Process Under N₂ and H₂S Atmosphere

Abstract

Cu₂ZnSnS₄ (CZTS) thin films have been prepared by a two-step sequential annealing process under N₂ and H₂S atmospheres at 500 and 550 °C on physical vapor deposited (PVD) precursors, where the orders of the precursor stack are Sn/ZnS/Cu and ZnS/Cu/Sn on a soda-lime glass (SLG) substrate. The Sn/ZnS/Cu precursor is converted into Cu₂SnS₃ and Cu6Sn5 with N₂ annealing, and the (112) preferred orientation of the kesterite CZTS phase is detected with subsequent H₂S annealing. However, no complete CZTS phase is attained from the ZnS/Cu/Sn precursor using sequential annealing where some secondary phases such as Cu₄SnS₄, Cu₆Sn₅, Cu₂S and CuZn are formed, suggesting that ZnS significantly affects the final CZTS structure. The CZTS thin films exhibit an optical band gap with a range of 1.50 to 1.71 eV with sequential N₂ +H₂S annealing. The films are confirmed to be p-type semiconductors and the electrical properties include carrier concentration (2×10¹⁸ to 3.5×1019 cm⁻³), hole mobility (40 to 1780 cm²/V · s) and resistivity (1.7×10⁻² to 1.6×10⁻³Ω·cm).