Structure, composition and optical properties of Cu_2ZnSnS _4 thin films deposited by Pulsed Laser Deposition method

摘要

Polycrystalline Cu_2ZnSnS_4 (CZTS) thin films have been directly deposited on heating Mo-coated glass substrates by Pulsed Laser Deposition (PLD) method. The results of energy dispersive X-ray spectroscopy (EDX) indicate that these CZTS thin films are Cu-rich and S-poor. The combination of X-ray diffraction (XRD) results and Raman spectroscopy reveals that these thin films exhibit strong preferential orientation of grains along [1 1 2] direction and small Cu_(2-x)S phase easily exists in CZTS thin films. The lattice parameters and grain sizes have been examined based on XRD patterns and Atom Force Microscopy (AFM). The band gap (E_g) of CZTS thin films, which are determined by reflection spectroscopy varies from 1.53 to 1.98 eV, depending on substrate temperature (T_(sub)). The optical absorption coefficient of CZTS thin film (T_(sub)=450 °C) measured by spectroscopic ellipsometry (SE) is above 10~4 cm~(-1).