Synthesis, optical and optoelectrical analysis of the Cu2CoSnS4 thin films as absorber layer for thin-film solar cells

In this work, the optical and optoelectrical characterizations of the quaternary kesterite Cu2CoSnS4 (CCTS4) thin films were studied. The polycrystalline CCTS4 films have prepared by the spray pyrolysis method at four different thicknesses (160 nm, 230 nm, 297 nm and 345 nm). The X-ray diffraction charts demonstrated that the as-prepared CCTS4 films have a polycrystalline nature with tetragonal single phase. The linear optical parameters of the CCTS4 films were computed by finding the transmission and reflection data. The magnitudes of the absorption coefficient for the CCTS4 films were high in the order of 105 cm−1 while the energy gap of the CCTS4 films has been reduced from 1.41 to 1.12 eV by raising the film thickness. The optical conductivity and the Urbach energy of the CCTS4 films were computed from the absorption coefficient data. In addition, the nonlinear optical parameters represented in the nonlinear refractive index n2 and the third-order nonlinear optical susceptibility χ(3) of the CCTS4 films were boosted with rising up the film thickness.