Synthesis, X-ray Single-Crystal Structural Characterization, and Thermal Analysis of Bis(O-alkylxanthato)Cd(II) and Bis(O-alkylxanthato)Zn(II) Complexes Used as Precursors for Cadmium and Zinc Sulfide Thin Films.

This work investigates tuning of the molecular structure of a series of O-alkylxanthato zinc and cadmium precursor complexes to enhance production of ZnS and CdS materials. The structures of several bis(O-alkylxanthato) cadmium(II) complexes (8-13) and bis(O-alkyl xanthato)zinc(II) complexes (18 and 19) are reported based on single crystal X-ray diffraction data. CdS and ZnS films were produced by the spin-coating of these metal complexes followed by their thermal decomposition to the corresponding metal sulfides. Thin films of CdS were deposited by spin-coating the bis(O-alkylxanthato) cadmium(II) precursors (7-13) on glass substrates, followed by annealing at 300 °C for 60 min. Thin films of ZnS were deposited by spin-coating bis(O-alkylxanthato) zinc(II) (14-20), followed by annealing at 200 °C for 60 min. The molecular complexes and solid state materials are characterized using a range of techniques including single-crystal X-ray diffraction, pXRD, EDS and XPS, DSC and TGA, UV-vis and PL spectroscopies, and electron microscopy. These techniques provided information on the influence of alkyl chain length on the thermal conditions required to fabricate metal sulfide films as well as film properties such as film quality, and morphology. For example, the obtained crystallite size of metal sulfide films formed is correlated to the hydrocarbon chain length of xanthate ligands in the precursor. The behavior of the complexes under thermal stress was therefore studied in detail. DTA and TGA profiles explain the relationship between hydrocarbon chain length, decomposition temperatures, and the energies required for decomposition. A higher decomposition temperature for complexes with longer hydrocarbon chains is observed compared to complexes with shorter hydrocarbon chains. Band-gap energies calculated from the optical absorption spectra alongside steady state and time-resolved photoluminescence studies are reported for CdS films.

The deposition of thin films of cadmium zinc sulfide Cd1-x Zn x S at 250 °C from spin-coated xanthato complexes: a potential route to window layers for photovoltaic cells.

Thin films of Cd1-x Zn x S (CZS) were prepared by a novel spin coating/melt method from cadmium ethylxanthato [Cd(C2H5OCS2)2] and zinc ethylxanthato [Zn(C2H5OCS2)2] in x ratios of 0-0.15 and of 1. A solution of the precursor(s) in THF was spin coated onto a glass substrate and then heated at 250 °C for 1 h under N2. The thickness of the film formed can be controlled by varying the solution composition and/or the spin rate of the coating. A total metal precursor solution concentration of 50 mM was used in all cases. The films were characterized by p-XRD, SEM, EDX, ICP-AES, XPS, UV-Vis absorption spectroscopy, Raman spectroscopy and resistivity measurements. The band gaps of the films were between 2.35-2.58 and 3.75 eV (0 ≤ x ≤ 0.15 and at x = 1). The resistivity of Cd1-x Zn x S films was found to vary linearly with zinc contents, and the properties of the films suggest potential application to photovoltaics as window layers. This work is the first study to demonstrate Cd1-x Zn x S thin films by a spin coating/melt method from xanthato precursors.