Synthesis, optical and optoelectrical analysis of the Cu_2CoSnS_4 thin films as absorber layer for thin-film solar cells

摘要

In this work, the optical and optoelectrical characterizations of the quaternary kesterite Cu_2CoSnS_4 (CCTS_4) thin films were studied. The polycrystalline CCTS_4 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 CCTS_4 films have a polycrystalline nature with tetragonal single phase. The linear optical parameters of the CCTS_4 films were computed by finding the transmission and reflection data. The magnitudes of the absorption coefficient for the CCTS_4 films were high in the order of 10~5 cm~(-1) while the energy gap of the CCTS_4 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 CCTS_4 films were computed from the absorption coefficient data. In addition, the nonlinear optical parameters represented in the nonlinear refractive index n_2 and the third-order nonlinear optical susceptibility x~((3)) of the CCTS_4 films were boosted with rising up the film thickness.