Investigating the Effect of Steric Hindrance within CdS Single-Source Precursors on the Material Properties of AACVD and Spin-Coat-Deposited CdS Thin Films br

Cadmium sulfide (CdS) is an important semi-conductor for electronic and photovoltaic applications, particularlywhen utilized as a thinfilm for window layers in CdTe solar cells.Deposition of thin-film CdS through the decomposition of single-source precursors is an attractive approach due to the facile, low-temperature, and rapid nature of this approach. Tailoring theprecursor to affect the decomposition properties is commonlyemployed to tune desirable temperatures of decomposition. However,altering the precursor structure and the effect this has on the nature ofthe deposited material is an area far less commonly investigated. Here,we seek to investigate this by altering the ligands around the Cd metalcenter to increase the steric hindrance of the precursor and investigatethe effect this has on the decomposition properties and the propertiesof deposited thin-film CdS from these precursors. For this, we report the synthesis of four CdS precursors with xanthate and pyridylligands ([Cd(n-ethyl xanthate)2(3-methyl pyridine)2][1], [Cd(n-ethyl xanthate)2(3,5-lutidine)2][2], [(Cd2(isopropyl xanthate)4(3-methyl pyridine)2)n][3], and [Cd(isopropyl xanthate)2(3,5-lutidine)2][4]). These single-source precursors for CdS were fullycharacterized by elemental analysis, NMR spectroscopy, single-crystal X-ray diffraction (XRD), and thermogravimetric analysis. Itwas found that even with subtle alterations in the xanthate (n-ethyl to isopropyl) and pyridine (3-methyl and 3,5-dimethyl) ligands, arange of hexa-coordinate precursors were formed (two withcisconfiguration, one with trans configuration, and one as a one-dimensional (1D) polymer). These four precursors were then used in aerosol-assisted chemical vapor deposition (AACVD) andspin-coating experiments to deposit eight thinfilms of CdS, which were characterized by Raman spectroscopy, powder X-raydiffraction, and scanning electron microscopy. Comparative quantitative information concerningfilm thickness and surfaceroughness was also determined by atomic force microscopy. Finally, the optical properties of all thinfilms were characterized byultraviolet-visible (UV-Vis) absorption spectroscopy, from which the band gap of each depositedfilm was determined to becommensurate with that of bulk CdS (ca.2.4 eV).