A novel one-step electrodeposition to prepare single-phase CuInS 2 thin films for solar cells

Abstract

Copper indium disulfide (CuInS 2) thin films have been successfully prepared on Ni substrates using a novel one-step potentiostatic electrodeposition combined with a potassium hydrogen phthalate (C 8H 5KO 4) complexing agent, accompanied by annealing at 350 °C. Electrodeposition in the solution of Cu and In salts and sodium thiosulfate (Na 2S 2O 3) containing an adequate concentration of C 8H 5KO 4 (e.g., [C 8H 5KO 4]=23 mM) provides thin films comprised of a CuInS 2 single phase as the bulk composition, without forming Cu x S secondary phases. In addition to the effect on bulk-phase compositions, the adjustment of [C 8H 5KO 4] causes variation in morphology and atomic composition of the film surface. The surface states of the films change from the Cu-rich rough surface at low [C 8H 5KO 4] (15 mM) to the In-rich smooth surface at high [C 8H 5KO 4] (23 mM). The higher [C 8H 5KO 4] induces the grains constructing the film to interconnect and form a densely packed CuInS 2 film without voids and pinholes. The single-phase and void-free CuInS 2 film shows a band gap of 1.54 eV, satisfying the requirement of the absorber layers in solar cells. The electrical properties tests denote its n-type conductivity with a resistivity of 9.6×10 −5 Ω cm, a carrier concentration of 2.9×10 21 cm −3 and a carrier mobility of 22.2 cm 2 V −1 s −1.