Design and characterization of a chloride-free organic copper solution: Electrochemical synthesis of Zn/Cu/Sn precursor stack for CZTS-based photoconversion devices

In the present study, an ethylene glycol-based electrolyte is used to electrodeposit copper onto zinc for the synthesis of the Zn/Cu/Sn stack, precursor of Cu2ZnSnS4. The employed solution contains diethanolamine (DEA) which supports the formation of amine-complexes, whose features are studied by UV-vis absorption, ESI-MS, and FTIR measurements, providing insight on the optimal concentration of DEA for copper complexation. Cyclic voltammetries (CVs) are carried out at increasing [DEA]/[Cu2+] ratios, highlighting the amine effect on the reduction potential of the copper species. The displacement reaction between copper and zinc is investigated by immersion potential measurements, showing a direct correlation to the voltammetric data. The optimized copper solution resulted in a negligible displacement contribution, allowing the electrochemical synthesis of Mo-(sub)/Zn/Cu/Sn stack on a relatively large area (4 cm(2)). The metallic precursor is analyzed by SEM/EDS, AFM, XRD, and GDOES techniques. Finally, the kesterite CZTS phase is obtained through reactive annealing with elemental sulfur and it is characterized by SEM/EDS, XRD, and Raman spectroscopy. Photoelectrochemical water splitting on CZTS/CdS/Pt heterostructure is carried out in an aqueous solution at pH 6.85, showing a photocurrent of -5.05 mA/cm(2) at 0 V vs RHE. A maximum applied bias photon-to-current efficiency (ABPE) value of 2.15% was found at 0.84 V bias. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In this study, an ethylene glycol-based electrolyte was used to electrodeposit copper onto zinc for the synthesis of the precursor of Cu2ZnSnS4. The optimal concentration of DEA for copper complexation, the effect of amine on the reduction potential of copper species, and the displacement reaction between copper and zinc were investigated. The optimized copper solution allowed for the electrochemical synthesis of Mo-(sub)/Zn/Cu/Sn stack on a relatively large area, leading to the formation of Kesterite CZTS phase. Photoelectrochemical water splitting on CZTS/CdS/Pt heterostructure exhibited a promising photocurrent and photon-to-current efficiency.