Growth, structure, optical and optoelectrical characterizations of the Cu₂NiSnS₄ thin films synthesized by spray pyrolysis technique

Earth-abundant Kesterite materials are very important to fabricate low-cost solar cells. Here, good quality Cu₂NiSnS₄ (CNSS) thin films were successively manufactured on a glass substrate at 350 °C using a simple spray pyrolysis system. The structural characterization of the sprayed Cu₂NiSnS₄ thin films was examined by the FE-SEM and XRD techniques. X-ray diffraction patterns indicate that the sprayed Cu₂NiSnS₄ films are single phase and having polycrystalline structure. The elemental composition analysis of the sprayed Cu₂NiSnS₄ thin films confirmed that the Cu₂NiSnS₄ film is near stoichiometric in compound. Our optical observations indicate that the refractive index (n) of the sprayed Cu₂NiSnS₄ films was increased by increasing the film thickness. Moreover, the sprayed Cu₂NiSnS₄ films exhibit a direct optical transition and the magnitudes of the energy gap have been decreased from 1.28 to 1.14 eV with the increase of thickness. The optoelectrical parameters of the Cu₂NiSnS₄ films, like optical conductivity, optical mobility, optical resistivity, optical carrier concentration and relaxation time were estimated with different thickness. Additionally, the nonlinear optical parameters of the Cu₂NiSnS₄ films were estimated. The fabricated CNSS/n-Si heterojunction achieved a conversion efficiency of 11.34%.