Electrodeposition of semiconductor thin films for photovoltaic devices

Cu2SnZnS4-type compounds have attracted interest as low cost and high conversion efficiency solar cell devices, because of their appropriate band gap energies and absorption coefficients values. In the last years our group has developed an ongoing research aimed at the electrodeposition from aqueous solution of thin films of technological semiconductors. In this presentation, we exploited alternated electrodeposition of Cu, Sn, Zn and S by E-ALD (Electrochemical Atomic Layer Deposition) to obtain sulfide thin films, controlling the growth of the structures at the nanometric level. The presentation included the analysis of the electrochemical behavior of the solution containing the single elements, to assess the most efficient deposition of controlled amounts of material. By alternating deposition of the elements, growth of thin films has been obtained. Band gaps of the deposited materials exhibit modulation with sample composition and thickness. Structural characterization of thin films is generally a rather complex task as it requires high brilliance x-ray sources given the small thickness of the film. Nevertheless synchrotron light sources can provide such an high photon flux to perform this kind of experiment. Surface X-ray diffraction was used to identify the crystallographic structure and to investigate the order on the surface. The results confirm that E-ALD is an effective method to grow crystalline films with high level of order.