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

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).

Preparation of solution processed photodetectors comprised of two-dimensional tin(ii) sulfide nanosheet thin films assembled via the Langmuir-Blodgett method.

We report the manufacture of fully solution processed photodetectors based on two-dimensional tin(ii) sulfide assembled via the Langmuir-Blodgett method. The method we propose can coat a variety of substrates including paper, Si/SiO2 and flexible polymer allowing for a potentially wide range of applications in future optoelectronic devices.

Synthetic 2-D lead tin sulfide nanosheets with tuneable optoelectronic properties from a potentially scalable reaction pathway.

Solventless thermolysis of molecular precursors followed by liquid phase exfoliation allows access to two-dimensional IV-VI semiconductor nanomaterials hitherto unreachable by a scalable processing pathway. Firstly, the use of metal dithiocarbamate precursors to produce bulk alloys in the series Pb1-x Sn x S (0 ≤ x ≤ 1) by thermolysis is demonstrated. The bulk powders are characterised by powder X-ray diffraction (pXRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. It was found that there is a transition from cubic structures for the Pb-rich alloys including the end compound, PbS (0 ≤ x ≤ 0.4) to layered orthorhombic structures for Sn-rich alloys and the end compound SnS (0.5 ≤ x ≤ 1.0). A smooth elemental progression from lead-rich to tin-rich monochalcogenides across the series of materials is observed. Liquid phase exfoliation was applied to produce two dimensional (2D) nanosheets for a mixed Pb1-x Sn x S alloy (where x = 0.8) in 1-methyl-2-pyrrolidone (NMP) using the synthetic bulk powder as starting material. The nanosheet products were characterized by SEM, atomic force microscopy (AFM) and high angle annular dark field scanning transmission electron microscopy (HAADF STEM). First principle calculations of Pb1-x Sn x S alloys show that the Sn content x modifies the size of the band gap by several 100 meV and that x changes the gap type from indirect in SnS to direct in Pb0.2Sn0.8S. These results are supported by UV-Vis spectroscopy of exfoliated Pb0.2Sn0.8S. The method employed demonstrates a new, scalable, processing pathway which can potentially be used to synthesize a range of synthetic layered structures that can be exfoliated to as-yet unaccessed 2D materials with tunable electronic properties.

Correction: Synthetic 2-D lead tin sulfide nanosheets with tuneable optoelectronic properties from a potentially scalable reaction pathway.

[This corrects the article DOI: 10.1039/C8SC04018D.].