Pulsed electrodeposition of CuInSe2 films for photovoltaic applications

Copper indium diselenide thin films have been prepared onto ITO (In2O3:Sn) substrates by a newly developed pulsed electrodeposition method. The proposed scheme consists of a cyclically repeated pulsed potential sequence at the corresponding deposition potentials of elemental Cu, Se and In. When the potential is stepped back to the initial Cu electrodeposition potential after a full cycle to start the subsequent three steps the excess of metallic In is dissolved and the formation of the desired CIS phase is enhanced. Two electrolyte concentrations and three different pulse durations were considered. The resulting films were compared to those grown with a program of potential sweep and step application. As grown films are nanocrystalline (112) oriented and p-type semiconducting with a bandgap around 1.1 eV. A second optical transition around 2.7-3.1 eV attributed to secondary Cu-Se phases was observed. Raman and photocurrent spectroscopies show a strong effect of the electrolyte concentration and pulse duration in the content of Se and Cu-Se unwanted phases, especially in the samples prepared at low concentration where Cu-Se is absent. The developed method represents a noticeable improvement in the phase purity and drops a hint towards the suppression of post-deposition treatments.