Annealing Effect on Morphology Optical and Crystallographic Properties of Solution-Based Cu₂ZnSnS₄ Thin Films

Abstract

CZTS chalcopyrite semiconductor has received attention as a promising alternative as an absorber in thin-film solar cells because of the high absorption coefficient, direct bandgap (1.5 eV), nontoxic elements and sustained high electrical and optical properties. In the present work, CZTS thin film has been developed by the sol–gel spin coating method by thermal decomposition of metal ions and thiourea complexes under ambient environment. Annealing study of the above prepared CZTS thin films has been performed. The prepared CZTS samples were annealed at different temperatures 250 °C, 275 °C, 300 °C, and 325 °C respectively. Crystallographic structure, surface morphology, and optical properties were studied. XRD pattern shows the kesterite structure of the films with characteristics peaks for planes (112), (200), (220), and (312). Crystallite size, strain and dislocation densities were calculated. Sample annealed at 300 °C shows the most intense XRD peak and hence larger grain size. Grain size tends to increase as the annealing temperature increases up to 300 °C. At 325 °C SEM images show that cracks are formed in the film. At lower temperatures uniform, homogenous, smooth and densely packed films are formed. Raman spectroscopy is used to determine phase purity because many of binary and ternary chalcogenides show XRD peaks at similar positions to that of CZTS. A single peak at 336 cm–1 shows the pure kestrite phase of CZTS for all films.