Development of molecular precursors for deposition of indium sulphide thin film electrodes for photoelectrochemical applications

Symmetrical and unsymmetrical dithiocarbamato pyridine solvated and non-solvated complexes of indium(iii) with the general formula [In(S ₂CNRR′)₃]·n(py) [where py = pyridine; R,R′ = Cy, n = 2 (1); R,R′ = ⁱPr, n = 1.5 (2); NRR′ = Pip, n = 0.5 (3) and R = Bz, R′ = Me, n = 0 (4)] have been synthesized. The compositions, structures and properties of these complexes have been studied by means of microanalysis, IR and ¹H-NMR spectroscopy, X-ray single crystal and thermogravimetric (TG/DTG) analyses. The applicability of these complexes as single source precursors (SSPs) for the deposition of β-In₂S₃ thin films on fluorine-doped SnO₂ (FTO) coated conducting glass substrates by aerosol-assisted chemical vapour deposition (AACVD) at temperatures of 300, 350 and 400 °C is studied. All films have been characterized by powder X-ray diffraction (PXRD) and energy dispersive X-ray analysis (EDX) for the detection of phase and stoichiometry of the deposit. Scanning electron microscopy (SEM) studies reveal that precursors (1)-(4), irrespective of different metal ligand design, generate comparable morphologies of β-In₂S₃ thin films at different temperatures. Direct band gap energies of 2.2 eV have been estimated from the UV-vis spectroscopy for the β-In₂S₃ films fabricated from precursors (1) and (4). The photoelectrochemical (PEC) properties of β-In₂S₃ were confirmed by recording the current-voltage plots under light and dark conditions. The plots showed anodic photocurrent densities of 1.25 and 0.65 mA cm^-2 at 0.23 V vs. Ag/AgCl for the β-In₂S₃ films made at 400 and 350 °C from the precursors (1) and (4), respectively. The photoelectrochemical performance indicates that the newly synthesised precursors are highly useful in fabricating β-In₂S₃ electrodes for solar energy harvesting and optoelectronic application.