Spectroscopic ellipsometry and photovoltaic characteristics for n-CdS/p-Cu2ZnSnS4 heterojunction by annealing for solar cells

Abstract

Owing to its direct bandgap in the range to be used as an absorbent material and due to its high absorption rate, kesterite Cu2ZnSnS4 (CZTS) is a p-type prospective absorber material (with thickness 500 nm) for solar cell applications. Kesterite Cu2ZnSnS4 (CZTS) thin films were prepared using the thermal evaporation technique. The (CZTS) thin films were annealed at different annealing temperatures chosen according to TGA analysis in the range of (400o C, 450o C, 475o C, and 500o C). The influence of annealing temperatures on the structural, morphology and optical properties of the CZTS films was investigated. The XRD patterns and Raman spectra have revealed the formation of CZTS thin with a high-quality crystal structure. The optical constants refractive index n, and extinction coefficient, k consequently band gap are estimated from SE via construction an optical model. The refractive index n of the CZTS /glass films received from SE model increases with the annealing temperature that is credited to the rise of the size of the crystal. It was also found that when the annealing temperature of the CZTS layer increases, the general behavior of the extinction coefficient k of the CZTS /glass film increases. In addition, it is found that the direct optical transition with energy band gap is compact from 1.75 eV at RT to 1.49 eV at maximum crystallization 500 o C. The Ni/n-CdSe/p-CdTe/Pt heterojunction has been successfully assembled. The dark and illumination (currentvoltage) behavior of fabricated heterojunctions had been suggested at distinctive different annealing of CZTS layer, as well as for voltages ranging from -2 to 2 volts.