Morphology and Composition of Cu2S Ultra-Thin Films Deposited by E-ALD

Tuesday, 3 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
F. Russo, A. Giaccherini, E. Salvietti (Department of chemistry - University of Florence), E. Berretti (Department of Chemistry - University of Florence), M. Passaponti (Department of chemistry - University of Florence), A. Lavacchi (CNR-ICCOM), G. Montegrossi (CNR-IGG), E. Piciollo (LEM S.r.l.), F. Di Benedetto (Department of earth sciences - University of Florence), and M. Innocenti (CNR-ICCOM, Department of Chemistry - University of Florence)
CIGS are very promising semiconducting materials for solar energy conversion due to their high efficiency. However, when analyzing the full life cycle assessment the toxicity and shortage of the involved elements along with the EROEI (Energy Return Over Energy Investment) needed to assemble the devices are considered unfavorable for the large scale exploitation of the CIGS. To overcome this issues, scientific community is focusing attention on new compounds based on economic and low-environmental impact elements such as Cu, Sn, Fe and Zn. In particular, quaternary semiconducting materials based on the kesterite (Cu2ZnSnS4) mineral structure are the most promising candidates to overtake the current generation of light-absorbing materials for thin-film solar cells. Electrodeposition is known as a low-cost semiconductor technique for the growth of semiconducting materials in electronic devices. Surface limited electrodeposition of atomic layers, can be performed by means of Electrochemical Atomic Layer Deposition (E-ALD) technique to obtain ultra-thin films of copper sulphides on a Ag(111) single crystal. Although its band gap it is not optimal for solar energy conversion, this materials can have interesting electronic proprieties, for instance Cu2S is a superionic conductor. However, from the E-ALD scheme one would expect a CuS hexagonal structure (covellite) with no any important electronic proprieties. Still, recently reported operando SXRD on this material allowed to assign a crystallographic cell corresponding to a cell directly derived from chalcocite’s (Cu2S). These unexpected results are confirmed by the analysis of the growth mechanism performed by means of operando SXRD and XRR. In this communication we reports a morphological and compositional study, confirming the composition and morphology expected from the results of the SXRD operando measurements pointing to the growth of Cu2S by means of E-ALD.