Kesterite Cu2ZnSnS4 (CZTS) Thin Film Formation Using Sequential Annealing Process Under N-2 and H2S Atmosphere

Abstract

Cu2ZnSnS4 (CZTS) thin films have been prepared by a two-step sequential annealing process under N-2 and H2S atmospheres at 500 and 550 degrees 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 N-2 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 N-2 + H2S annealing. The films are confirmed to be p-type semiconductors and the electrical properties include carrier concentration (2x10(18) to 3.5x10(19) cm(-3)), hole mobility (40 to 1780 cm(2)/V.s) and resistivity (1.7x10(-2) to 1.6x10(-3) Omega.cm).