Cu2ZnSnS4 thin films annealed in H2S atmosphere for solar cell absorber prepared by pulsed laser deposition

Cu2ZnSnS4 (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 + H2S (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 degrees 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%.