A novel one-step electrodeposition to prepare single-phase CuInS2 thin films for solar cells

Copper indium disulfide (CuInS2) thin films have been successfully prepared on Ni substrates using a novel one-step potentiostatic electrodeposition combined with a potassium hydrogen phthalate (C8H5KO4) complexing agent, accompanied by annealing at 350 °C. Electrodeposition in the solution of Cu and In salts and sodium thiosulfate (Na2S2O3) containing an adequate concentration of C8H5KO4 (e.g., [C8H5KO4]=23 mM) provides thin films comprised of a CuInS2 single phase as the bulk composition, without forming CuxS secondary phases. In addition to the effect on bulk-phase compositions, the adjustment of [C8H5KO4] 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 [C8H5KO4] (15 mM) to the In-rich smooth surface at high [C8H5KO4] (23 mM). The higher [C8H5KO4] induces the grains constructing the film to interconnect and form a densely packed CuInS2 film without voids and pinholes. The single-phase and void-free CuInS2 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 2.9×1021 cm−3 and a carrier mobility of 22.2 cm2 V−1 s−1.