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 used in solar cells. Single crystals of bis(O-alkylxanthato) cadmium(II) complexes (8–13) and bis(O-alkyl xanthato)zinc(II) complexes (18 and 19) are reported. CdS and ZnS films were produced by the spin coating of these molecular precursors followed by thermal decomposition.Thin films of CdS were deposited by spin coating the bis(O-alkylxanthato) cadmium(II), precursors (7–13) on glass substrates, followed by annealing up to 300 °C for 60 min. The films of ZnS were deposited by spin coating bis(O-alkylxanthato) zinc(II), complexes (14–20), followed by annealing up to 200 °C for 60 min. The molecular complexes and solid state materials are characterised 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 relative numbers of defect sites, films quality and morphology, for example, the obtained crystallite size of metal sulfide films formed is correlated to the hydrocarbon chain length of the precursor. The behaviour of the complexes under thermal stress was studied. 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.