Buckingham MA, Norton K, McNaughter PD, Whitehead G, Vitorica-Yrezabal I, Alam F, Laws K, Lewis DJ. Investigating the Effect of Steric Hindrance within CdS Single-Source Precursors on the Material Properties of AACVD and Spin-Coat-Deposited CdS Thin Films.
Inorg Chem 2022;
61:8206-8216. [PMID:
35583220 PMCID:
PMC9157504 DOI:
10.1021/acs.inorgchem.2c00616]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Cadmium sulfide (CdS)
is an important semiconductor for electronic
and photovoltaic applications, particularly when utilized as a thin
film 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 the precursor to affect the decomposition properties
is commonly employed to tune desirable temperatures of decomposition.
However, altering the precursor structure and the effect this has
on the nature of the deposited material is an area far less commonly
investigated. Here, we seek to investigate this by altering the ligands
around the Cd metal center to increase the steric hindrance of the
precursor and investigate the effect this has on the decomposition
properties and the properties of deposited thin-film CdS from these
precursors. For this, we report the synthesis of four CdS precursors
with xanthate and pyridyl ligands ([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
fully characterized by elemental analysis, NMR spectroscopy, single-crystal
X-ray diffraction (XRD), and thermogravimetric analysis. It was found
that even with subtle alterations in the xanthate (n-ethyl to isopropyl) and pyridine (3-methyl and 3,5-dimethyl) ligands,
a range of hexa-coordinate precursors were formed (two with cis configuration, 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) and spin-coating
experiments to deposit eight thin films of CdS, which were characterized
by Raman spectroscopy, powder X-ray diffraction, and scanning electron
microscopy. Comparative quantitative information concerning film thickness
and surface roughness was also determined by atomic force microscopy.
Finally, the optical properties of all thin films were characterized
by ultraviolet–visible (UV–Vis) absorption spectroscopy,
from which the band gap of each deposited film was determined to be
commensurate with that of bulk CdS (ca. 2.4 eV).
Four single-source CdS precursors were
synthesized based
on a combination of xanthate- and pyridyl-derived ligands to investigate
increasing the steric hindrance of the precursor. Two cis, one trans, and one 1D polymer complexes were developed.
These precursors were then deposited as thin films through both spin
coating and aerosol-assisted chemical vapor deposition techniques,
and the morphology, film thickness, film surface roughness, particle
size distribution, and band gap energy were assessed.
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