Exceptional Thermoelectric Performance of Cu2(Zn,Fe,Cd)SnS4 Thin Films

Yu Liu; Paul D McNaughter; Xiaodong Liu; Andrey V Kretinin; Jonathan M Skelton; Feridoon Azough; David J Lewis; Robert Freer

doi:10.1021/acsami.3c17730

Exceptional Thermoelectric Performance of Cu₂(Zn,Fe,Cd)SnS₄ Thin Films

ACS Appl Mater Interfaces. 2024 Mar 6;16(9):11516-11527. doi: 10.1021/acsami.3c17730. Epub 2024 Feb 23.

Authors

Yu Liu¹, Paul D McNaughter², Xiaodong Liu¹, Andrey V Kretinin^{1

3}, Jonathan M Skelton², Feridoon Azough¹, David J Lewis¹, Robert Freer¹

Affiliations

¹ Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
² Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
³ National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.

Abstract

High-quality Cu₂(Zn,Fe,Cd)SnS₄ (CZFCTS) thin films based on the parent CZTS were prepared by aerosol-assisted chemical vapor deposition (AACVD). Substitution of Zn by Fe and Cd significantly improved the electrical transport properties, and monophasic CZFCTS thin films exhibited a maximum power factor (PF) of ∼0.22 μW cm^-1 K^-2 at 575 K. The quality and performance of the CZFCTS thin films were further improved by postdeposition annealing. CZFCTS thin films annealed for 24 h showed a significantly enhanced maximum PF of ∼2.4 μW cm^-1 K^-2 at 575 K. This is higher than all reported values for single-phase quaternary sulfide (Cu₂BSnS₄, B = Mn, Fe, Co, Ni) thin films and even exceeds the PF for most polycrystalline bulk materials of these sulfides. Density functional theory (DFT) calculations were performed to understand the impact of Cd and Fe substitution on the electronic properties of CZTS. It was predicted that CZFCTS would have a smaller band gap than CZTS and a higher density of states (DoS) near the Fermi level. The thermal conductivity and thermoelectric figure of merit (zT) of the CZFCTS thin films have been evaluated, yielding an estimated maximum zT range of 0.18-0.69 at 550 K. The simple processing route and improved thermoelectric performance make CZFCTS thin films extremely promising for thermoelectric energy generation.

Keywords: Cu2ZnSnS4 (CZTS); Fe and Cd doping; aerosol-assisted chemical vapor deposition (AACVD); density functional theory; thermoelectrics; thin films.