Effect of potassium hydrogen phthalate (C_8H_5KO_4) on the one-step electrodeposition of single-phase CuInS_2 thin films from acidic solution

摘要

The effect of potassium hydrogen phthalate (C_8H_5KO_4) as a special additive on the one-step electrode-position of single-phase CuInS_2 thin films from acidic solution (pH 2.5) was investigated in detail. The XRD, SEM and UV-vis-NIR characterization confirms that the addition of an adequate concentration of C_8H_5KO_4 (23 mM) to the electrolytic bath containing 12.5 mM Cu~(2+), 10 mM In~(3+), 40 mM S_2(O_3)~(2-) and 100 mM LiCl can contribute greatly to the controllable growth of pure chalcopyrite CuInS_2 films with uniform surfaces and an ideal band gap of approximately 1.54 eV. Complexation studies of C_8H_5KO_4 with Cu~(2+) and In~(3+) in electrolytic solutions indicated that C_8H_5KO_4 can complex Cu~(2+) more strongly than In~(3+) and move the electrode potentials of Cu~(2+) and In~(3+) near each other as determined by polarization analysis. Furthermore, the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis performed in a series of solution systems revealed a three-step reaction mechanism for CuInS_2 deposition and considerable adsorption of C_8H_5(O_4)~- and Cu(C_8H_5O_4)~+ to the cathode surface. This deposition shows that the synergetic effects of complexation and adsorption originated from the additive on the Cu~(2+) electro-reduction, thus promoting the co-deposition of copper, indium and sulfur in the form of single-phase CuInS_2.