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 degrees 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 x 10(-5) Omega cm, a carrier concentration of 2.9 x 10(21) cm(-3) and a carrier mobility of 22.2 cm(2) V-1 s(-1). (C) 2010 Elsevier B.V. All rights reserved.