Kesterite Cu₂ZnSnS₄ (CZTS) thin film formation using sequential annealing process under N₂ and H₂S atmosphere

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).