Dean M. Giolando

Blocking thin-film nonuniformities: Photovoltaic self-healing

An approach is developed to block the effects of lateral nonuniformities in thin-film semiconductor structures. The nonuniformity modulates the surface photovoltage distribution. When exposed to light and immersed in a proper electrolyte, this distribution will generate laterally nonuniform electrochemical reactions. Such treatments result in a nonuniform interfacial layer that balances the original nonuniformity. This approach has been implemented for CdTe/CdS photovoltaic devices, in which it improved the device efficiency from 1%–3% to 11%–12%.

Synthesis, crystal structure and electrochemistry of bis(N,N-dimethylammonium) tris(1,2-benzenedithiolato)titanate(IV)

Abstract Synthesis, electrochemical and structural data for [NH2(CH3)2]2[Ti(S2C6H4)3] (1 are described. Treating Ti{N(CH3)2}4 with 1,2-(HS)2C6H4 in a 1 : 3 ratio affords 1 in 94% isolated yield. Dark red single crystals of 1, suitable for X-ray crystallography, were obtained from CH3CNEt2O mixtures. The molecular structure of the anion of 1, [Ti(S2C6H4)3]2−, provides a rare example of a homoleptic thiolate complex of titanium, but more importantly, the titanium centre contains the unusual TiS6 coordination of a skew-trapezoidal bipyramid (S-TzBP) with angular coordinates φA = 60°, φB = 140E = 75°. The S6 polyhedron in 1 can be alternatively described as a pentagonal bipyramid with an equatorial vertex missing. A spectropotentiostatic experiment for 1 verified that a reversible one-electron reduction occurs at −1.51 V (vs Ag/AgCl, DMF). The electrochemical product was characterized by UV-vis (347, 414 and 434 nm) and ESR (77 K, rhombic: g1 = 2.18 g2 = 2.04 and g3 = 2.00) spectroscopies.

Reach-through band bending in semiconductor thin films

We describe a phenomenon of reach-through band bending in thin film semiconductors. It occurs through generation of defects that change the semiconductor work function. This translates the effect of the metal presence through the semiconductor film and induces a Schottky barrier in another semiconductor tangent to the film on the opposite side (reach-through band bending). We have found experimental evidence of this effect in CdTe photovoltaics.

Synthesis and reactivity of mononuclear molybdenum phosphido complexes, [Mo(CO)2{P(Cl)R}(η-C5H5)][R = CH(SiMe3)2 or NCMe2CH2CH2CH2CMe2]. X-Ray crystal structures of [Mo(CO)2{P(X)(NCMe2CH2CH2CH2CMe2)}(η-C5H5)](X = Cl or NMe2) and [Mo2(CO)4{µ-P2[CH(SiMe3)2]2}(η-C5H5)2]

Reaction of K[Mo(CO)3(η-C5H5)] with PCl2R affords the mono-chlorophosphido species, [Mo(CO)2{P(Cl)R}(η-C5H5)][R = 2,2,6,6-tetramethyl-1-piperidyl (tmp), (1), or CH(SiMe3)2, (3)]. Both (1) and (3) contain a three-electron donor phosphido ligand featuring Mo–P multiple bonding and a trigonal-planar configuration at phosphorus. Compound (1) has been characterised by X-ray diffraction. The reaction of (1) with Li[NMe2] affords [Mo(CO)2{P(NMe2)(tmp)}(η-C5H5)](7), which has also been characterised by X-ray crystallography. The synthesis of (7) demonstrates the reactivity of the P–Cl functionality but (7) may also be prepared by direct reaction between K[Mo(CO)3(η-C5H5)] and PCl(NMe2)(tmp). Reduction of (3) with sodium dihydronaphthylide leads to a coupling reaction via P–P bond formation resulting in the cis-diphosphene complex [Mo2(CO)4{µ-P2[CH(SiMe3)2]2}(η-C5H5)2](8), which was characterised by X-ray diffraction. Spectroscopic evidence is also presented for a dimolybdenum diphosphinidene complex, isomeric with (8).

Alkyl hex-1-ynyl tellurides: Syntheses and multinuclear NMR (125Te-, 13C{1H}-, 1H-) studies

Abstract Alkyl hex-1-ynyl tellurides, n -C 4 H 9 CCTeR, where R=CH 3 , CH(CH 3 ) 2 , cyclo-C 6 H 11 , CH 2 CH(CH 3 ) 2 , CH 2 (CH 2 ) 6 CH 3 , CH 2 (CH 2 ) 10 CH 3 , CH 2 CH 2 CH(Br)CH 3 , CH 2 C 6 H 5 , 4-CH 2 C 6 H 4 NO 2 , CH 2 CH 2 C 6 H 5 and CH 2 CH 2 OC 6 H 5 , have been prepared in good yields by the anaerobic reaction of lithium hex-1-ynyl tellurolate with the appropriate alkyl halides in the absence of light. While most of these reactions have been performed at −5 to −10°C the reaction with cyclo-hexyl halide has been conducted at lower temperature (−30°C). Alkyl chloro, bromo and iodo derivatives have provided the same products in the same yields. The reaction has produced n -C 4 H 9 CCTe(CH 2 ) 5 TeCCC 4 H 9 - n when Br(CH 2 ) 5 Br has been used as alkylating agent, while BrCH 2 CH 2 CH(Br)CH 3 has produced only the monotelluride compound n -C 4 H 9 CCTeCH 2 CH 2 CH(Br)CH 3 even when employing excess lithium hex-1-ynyl tellurolate. In contrast ( n -C 4 H 9 CC) 2 Te has been the major tellurium-containing product when (C 6 H 5 ) 3 CCl, 4-BrC 6 H 4 C(O)CH 2 Br, CH 2 CHCH 2 Br, ClCH 2 C(O)CH 2 Cl and ClCH 2 CCCH 2 Cl have been employed. The 1 H-NMR spectra of alkyl hex-1-ynyl tellurides display deshielded resonances for the CH x ( x =1, 2, 3) group directly bound to tellurium. In many cases, specific couplings between tellurium and hydrogen are observed around these resonances. Characteristic features in the 13 C-NMR spectra include a shielding effect of the sp 3 and sp carbons directly bound to tellurium, and a deshielding effect to the other sp carbon. Closer analysis of the 13 C{ 1 H}-NMR spectra reveals satellites due to coupling with tellurium. Nuclear magnetic resonances measurements of the 125 Te nucleus show a correlation of 125 Te chemical shift to the alkyl group of n -C 4 H 9 CCTeR. In addition, the 125 Te-NMR spectra show a splitting of the 125 Te nuclear magnetic resonances due to coupling through up to three bonds with 1 H nuclei.

CVD of Alumina on Carbon and Silicon Carbide Microfiber Substrates for Microelectrode Development

Using a vacuum CVD technique, alumina films were deposited on 10 μm diameter carbon fibers, and 120 μm diameter silicon carbide fibers. This was accomplished by exposing resistively heated microfiber substrates to a sublimate of [Al(O- t Bu) 3 ] 2 , while the reaction chamber was maintained at 120 °C under a pressure of 0.15 torr. The coated substrates were then sealed into glass capillaries, using an epoxy sealant, to form microelectrode devices. The quality of the alumina films was found to be dependent on the substrate temperature, with optimum film quality being obtained at substrate temperatures between 750 °C and 800 °C. Film thickness was controlled by deposition time, and films from 1-100 μm were routinely produced. Films were characterized by microscopy and electrochemical techniques.

Sputtered HRT layers for CdTe solar cells

This work focuses on demonstrating the suitability of various high resistivity transparent (HRT) layers prepared by magnetron sputtering for sputtered CdS/CdTe cells. HRT buffer layers added between the transparent conducting oxide (TCO), and the CdS layer are important for reducing the effects of non-uniformities and shunts in large-area thin-film devices. CdS/CdTe cells were fabricated on Pilkington TEC 7 glass coated with a sputter deposited HRT layer of ZnO:Al or SnO2. In some cases O2 was added to the Ar sputter gas to increase the resistivity of the HRT buffer layers. Film properties were optimized for HRT performance by adjustments in the substrate deposition temperature, sputter gas pressure, and RF power. Best results have been obtained with reactively sputtered ZnO:Al with 2 % O2 in Ar.

Silicon carbide: a new electrode material for voltammetric measurements

Chemical vapour deposition of tetramethylsilicon at a resistively heated carbon fibre substrate produces a concentric silicon carbide conductor suitable for use as a solid electrode material for electrochemical measurements.

Homoleptic phenolate complexes of zirconium(IV): syntheses and structural characterization of the first six coordinate complexes

Homoleptic phenolate complexes of zirconium, [Na(THF)2]2[Zr(OC6H4-2-Cl)6] and [NH2(CH3)2]2[Zr(OC6H4-2-Cl)6]·2THF, were synthesized and fully characterized. To our knowledge, these complexes are the first examples for homoleptic six coordinated phenolate complexes of zirconium. Anaerobic reaction of zirconium tetrachloride with six equivalents of sodium 2-chlorophenolate afforded [Na(THF)2]2[Zr(OC6H4-2-Cl)6] in excellent isolated yields. The geometry of the ZrO6 core is octahedral with some distortion due to interactions of the sodium cations with oxygen atoms of the 2-chlorophenolate groups. The sodium cations are bound to five oxygen atoms: three to 2-chlorophenolate groups and two to THF. The coordination sphere is completed by interaction with chloride substituents of three 2-chlorophenolate ligands. A second example of a six coordinate complex of zirconium, [NH2(CH3)2]2[Zr(OC6H4-2-Cl)6]·2THF, was synthesized by the reaction of zirconium tetrakis(dimethylamino) with six or four equivalents of 2-chlorophenol. The ZrO6 core adopts a distorted octahedral geometry. Distortion is caused by hydrogen bonding between the dimethylammonium cation and the oxygen atom of one 2-chlorophenolate ligand. 1H- and 13C-NMR spectroscopy revealed that [NH2(CH3)2]2[Zr(OC6H4-2-Cl)6]·2THF decomposes in solution. These observations illustrate the profound influence that weaker secondary interactions to the donor atoms can have on metal coordination geometry.

A novel cage organotellurate(IV) macrocyclic host encapsulating a bromide anion guest: [Li(THF)4][(PriTe)12O16Br4(Li(THF)Br)4)Br].2THF.

The first structural report of an unprecedented organotellurate(IV) inorganic-organic hybrid macrocyclic host encapsulating a bromide anion guest is described.