Effect of Annealing on the Optical Properties of Copper Zinc Tin Sulfide (CZTS) Thin Films Deposited Using a Modified Successive Ionic Layer Adsorption and Reaction (SILAR) Method

Copper zinc tin sulfide (CZTS) films deposited using a modified successive ionic layer adsorption and reaction (SILAR) method were annealed in air. Surface growth was examined using X-ray photoelectron spectroscopy and scanning electron microscopy. With a suitable orientation in plane (112) at 2θ = 27.88°, the films crystallized in a kesterite structure. The impacts of annealing temperature and time on film optical properties were investigated using absorption and transmission spectroscopy. Whereas SILAR-grown CZTS films usually exhibit a somewhat disorganized nanocrystalline structure and band gaps of 1.3–1.8 eV, annealing lowered the band gap to 1.4–1.5 eV and improved absorption while weakly affecting composition. The films annealed at 250 °C for 120 min had a band gap of 1.3 eV and at 250 °C for 90 min displayed advantageous optical properties, namely an optical band gap of 1.5 eV, refractive index of 2.9, high-frequency dielectric constant of 8.5, and static dielectric constant of 13.900. These results demonstrate the effectiveness of the modified SILAR deposition method.