G. Kedarnath

Copper(I) 2-pyridyl selenolates and tellurolates: Synthesis, structures and their utility as molecular precursors for the preparation of copper chalcogenide nanocrystals and thin films

The complexes, [Cu{EC(5)H(3)(R-3)N}](4) (E/R = Se/Me or Te/R; R = H or Me) were isolated by the reaction between CuCl and NaEC(5)H(3)(R-3)N and were characterized by elemental analyses, uv-vis and NMR ((1)H, (13)C) spectroscopy. The crystal structures of [Cu{SeC(5)H(3)(Me-3)N}](4) and [Cu(TeC(5)H(4)N)](4) revealed that the molecules are tetrameric in which each copper atom lies at the vertex of the tetrahedron and each face of the tetrahedron is capped by the bridging pyridylchalcogenolate ligand. Thermal behavior of these complexes was studied by thermogravimetric analysis. Depending on reaction conditions, thermolysis gave both stoichiometric and non-stoichiometric copper chalcogenides, which were characterized by XRD, EDX, SEM, TEM and SAED techniques. These precursors were used for the preparation of nanocrystals and for deposition of thin films of copper chalcogenides by AACVD (Aerosol Assisted Chemical Vapor Deposition).

Bis(3-methyl-2-pyridyl)ditelluride and pyridyl tellurolate complexes of zinc, cadmium, mercury: Synthesis, characterization and their conversion to metal telluride nanoparticles

Treatment of an acetonitrile solution of metal chloride with bis(3-methyl-2-pyridyl)ditelluride, [Te(2)(pyMe)(2)], in the same solvent yielded complexes of composition [MCl(2){Te(2)(pyMe)(2)}] (M = Zn or Cd) whereas reactions of [MCl(2)(tmeda)] with NaTepyR (R = H or Me) gave tellurolate complexes of the general formula [M(TepyR)(2)] (M = Cd or Hg). When the cadmium complex [Cd(Tepy)(2)] was crystallized in the presence of excess tmeda, [Cd(Tepy)(2)(tmeda)] was formed exclusively. These complexes were characterized by elemental analyses, uv-vis, (1)H NMR data. The crystal structures of [ZnCl(2){Te(2)(pyMe)(2)}] and [Cd(Tepy)(2)(tmeda)] were established by single crystal X-ray diffraction. In the former zinc is coordinated to nitrogen atoms of the pyridyl group, while in the latter the coordination environment around tetrahedral cadmium is defined by the two neutral nitrogen atoms of tmeda, and two pyridyl tellurolate ligands. Thermal behavior of some of these complexes was studied by thermogravimetric analysis. Pyrolysis of [M(Tepy)(2)] in a furnace or in coordinating solvents such as hexadecylamine/tri-n-octylphosphine oxide (HDA/TOPO) at 350 and 160 degrees C, respectively gave MTe nanoparticles, which were characterized by uv-vis, photoluminiscence, XRD, EDAX and TEM.

Synthesis of Undoped and Manganese-Doped HgTe Nanoparticles Using [Hg(TeCH 2 CH 2 NMe 2 ) 2 ] as a Single Source Precursor

The Reaction of [HgCl2(tmeda)] with NaTeCH2CH2NMe2 gave a mercury tellurolate, [Hg(TeCH2CH2. NMe2)2] (1) as a yellow crystalline solid, which was characterized by elemental analysis, UV-vis, mass and NMR (1H, 13C, 125Te, 199Hg) spectroscopy. Thermolysis of 1 in hexadecylamine (HDA) at 90 degrees C in the absence and presence of Mn(OAc)2.4H2O gave undoped and Mn-doped HgTe nanoparticles which were characterized by XRD, EDAX, TEM, EPR and magnetic measurements. These particles could be synthesized with mean particle size of 6-7 nm (from TEM). Manganese substitution at Hg site in HgTe lead to a linear decrease in lattice parameter with increasing concentration of Mn. Magnetization measurements showed ferromagnetic ordering at room temperature with very small coercive field (Hc, 50 Oe) for Hg0.973 Mn0.027 Te sample. This sample also exhibited distinct ferromagnetic resonance (FMR) in the EPR spectrum.

Group 12 metal monoselenocarboxylates: synthesis, characterization, structure and their transformation to metal selenide (MSe; M = Zn, Cd, Hg) nanoparticles

Reactions of [MCl2(tmeda)] with potassium salts of monoselenocarboxylic acids gave complexes of the general formula [M(SeCOR)2(tmeda)] (M = Zn, Cd; R = Ph, Tol; Tol = C6H4-p-CH3; tmeda = Me2NCH2CH2NMe2). The analogous mercury complexes were unstable at room temperature and afforded HgSe nanoparticles during the course of reaction. All the complexes were characterized by elemental analysis, IR, UV-vis, NMR (1H, 13C, 77Se, 113Cd) data. The X-ray structural analysis of [Cd(SeCOPh)2(tmeda)] revealed that the complex is a discrete monomer having an approximate tetrahedral coordination environment around the central metal atom with monodentate (Se-bonded) selenocarboxylates. Thermal behavior of these complexes was studied by TG analysis. Pyrolysis in a furnace or in HDA (hexadecylamine) gave MSe nanoparticles, which were characterized by XRD, EDAX, SEM and absorption spectroscopy.

Diorganotin(IV) 4,6-dimethyl-2-pyrimidyl selenolates: synthesis, structures and their utility as molecular precursors for the preparation of SnSe2 nano-sheets and thin films

The complexes of composition [R2Sn{SeC4H(Me-4,6)2N2}2] (R = Me, Et, nBu or tBu) have been isolated by the reaction of R2SnCl2 with NaSeC4H(Me-4,6)2N2. The treatment of [R2Sn{SeC4H(Me-4,6)2N2}2] with R2SnCl2 afforded chloro complexes [R2SnCl{SeC4H(Me-4,6)2N2}] (R = Me, nBu or tBu). These complexes were characterized by elemental analyses and NMR (1H, 13C, 77Se, 119Sn) spectroscopy. The molecular structures of [tBu2Sn{SeC4H(Me-4,6)2N2}2] and [tBu2SnCl{SeC4H(Me-4,6)2N2}] were established by single crystal X-ray diffraction analyses. Thermolysis of [R2Sn{SeC4H(Me-4,6)2N2}2] (R = Et, nBu or tBu) in oleylamine (OLA) afforded the nanocrystalline hexagonal phase of SnSe2. Thin films of SnSe2 were deposited on silicon wafers by AACVD of [tBu2Sn{SeC4H(Me-4,6)2N2}2]. The nanostructures and thin films were characterized by solid state diffuse reflectance spectroscopy, XRD, EDX, SEM and TEM techniques. The solid state diffuse reflectance measurements of the nanosheets showed direct and indirect band gaps in the ranges of 1.76–2.30 eV and 1.38–1.49 eV, respectively, which are blue shifted relative to bulk tin selenide.

Diorganotin(IV) 2-pyridyl and 2-pyrimidyl thiolates: synthesis, structures and their utility as molecular precursors for the preparation of tin sulfide nanosheets

The complexes of composition, [R2Sn(2-SC5H4N)2] (R = Me (1) or Et (2)), [Et2SnCl(2-SC5H4N)] (3) and [R2SnCl{SC4H(Me-4,6)2N2}] (R = Me (4), Et (5)) were prepared and characterized by elemental analyses and NMR (1H, 13C, 119Sn) spectroscopy. The molecular structures of [Et2Sn(2-SC5H4N)2] (2), [Me2SnCl{SC4H(Me-4,6)2N2}] (4) and [Et2SnCl{SC4H(Me-4,6)2N2}] (5) were established unambiguously by single crystal X-ray diffraction analyses. The central tin atom acquires a skew trapezoidal bipyramidal configuration in the former (2) while distorted trigonal bipyramidal geometry in the latter two complexes (4 and 5), respectively. Thermolysis of diethyltin complexes [Et2Sn(2-SC5H4N)2] (2) and [Et2SnCl{SC4H(Me-4,6)2N2}] (5) in oleylamine (OLA) afforded orthorhombic phase SnS nano-sheets of thickness 30–80 nm which were characterized by solid state diffuse reflectance spectroscopy, XRD, EDX, SEM and TEM techniques. The solid state diffuse reflectance measurements of the nanosheets showed direct and indirect band gaps in the ranges of 1.61–1.90 eV and 1.46 eV, respectively which are blue shifted relative to bulk tin sulfide [Eg (direct) = 1.3 eV and Eg (indirect) = 1.1 eV].

CHAPTER 13:Quantum Dots for Type III Photovoltaics

Quantum dots are tiny particles of semiconducting materials in the nano-regime and have exciting physicochemical properties. They are important constituents of third-generation photovoltaic devices, such as dye-sensitized solar cells, organic photovoltaic devices, hybrid solar cells and quantum dot solar cells. Quantum dots improve the efficiency and help in the design of novel solar cell architectures based on new concepts such as hot carrier capture and multiple exciton generation. This chapter gives a brief background to photovoltaic devices and their classification, followed by a short discussion on quantum dots and their properties. The subsequent discussion includes the synthesis and characterization of quantum dots and their relevance to third-generation photovoltaic devices and quantum dot solar cells.