Cu2ZnSnS4 Thin Films Annealed in H2S Atmosphere for Solar Cell Absorber Prepared by Pulsed Laser Deposition

Cu 2 ZnSnS 4 (CZTS) precursors were prepared by pulsed laser deposition while controlling the energy density to eliminate grains of Cu–Sn–S compounds. The precursor prepared with an energy density of 0.7 J/cm 2 was flat and of better quality than the precursor prepared with an energy density of 1.5 J/cm 2 . The precursors were annealed in N 2 +H 2 S (5%) atmosphere. As a result of annealing, the decrease of the compositional ratio of sulfur was suppressed and the films became nearly stoichiometric. Some peaks in the an X-ray diffraction pattern of thin films are attributed to (112), (220), (312), and (200) planes of CZTS. The direct band-gap energy of the film annealed at 500 °C was about 1.5 eV, which is very close to the optimum value for a solar-cell absorber, and hence was used for a solar cell. The CZTS thin film solar cell with an active area of 0.12 cm 2 showed an open-circuit voltage of 336 mV, a short-circuit current of 6.53 mA/cm 2 , a fill factor of 0.46, and a conversion efficiency of 0.64%.