Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

Excitonic solar cells1—including organic, hybrid organic–inorganic and dye-sensitized cells (DSCs)—are promising devices for inexpensive, large-scale solar energy conversion. The DSC is currently the most efficient2 and stable3 excitonic photocell. Central to this device is a thick nanoparticle film that provides a large surface area for the adsorption of light-harvesting molecules. However, nanoparticle DSCs rely on trap-limited diffusion for electron transport, a slow mechanism that can limit device efficiency, especially at longer wavelengths. Here we introduce a version of the dye-sensitized cell in which the traditional nanoparticle film is replaced by a dense array of oriented, crystalline ZnO nanowires. The nanowire anode is synthesized by mild aqueous chemistry and features a surface area up to one-fifth as large as a nanoparticle cell. The direct electrical pathways provided by the nanowires ensure the rapid collection of carriers generated throughout the device, and a full Sun efficiency of 1.5% is demonstrated, limited primarily by the surface area of the nanowire array.

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Nanowire dye-sensitized solar cells

Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Understanding TiO2 photocatalysis: mechanisms and materials.

The dye-sensitized solar cells (DSC) provides a technically and economically credible alternative concept to present day p–n junction photovoltaic devices. In contrast to the conventional systems where the semiconductor assume both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer, which is anchored to the surface of a wide band semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The use of sensitizers having a broad absorption band in conjunction with oxide films of nanocrstalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar (standard AM 1.5) to current conversion efficiencies (IPCE) over 10% have been reached. There are good prospects to produce these cells at lower cost than conventional devices. Here we present the current state of the field, discuss new concepts of the dye-sensitized nanocrystalline solar cell (DSC) including heterojunction variants and analyze the perspectives for the future development of the technology.

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Dye-sensitized Solar Cells

A new series of panchromatic ruthenium(II) sensitizers derived from carboxylated terpyridyl complexes of tris-thiocyanato Ru(II) have been developed. Black dye containing different degrees of protonation {(C2H5)3NH}[Ru(H3tcterpy)(NCS)3] 1, {(C4H9)4N}2[Ru(H2tcterpy)(NCS)3] 2, {(C4H9)4N}3[Ru(Htcterpy)(NCS)3] 3, and {(C4H9)4N}4[Ru(tcterpy)(NCS)3] 4 (tcterpy = 4,4‘,4‘ ‘-tricarboxy-2,2‘:6‘,2‘ ‘-terpyridine) have been synthesized and fully characterized by UV−vis, emission, IR, Raman, NMR, cyclic voltammetry, and X-ray diffraction studies. The crystal structure of complex 2 confirms the presence of a RuIIN6 central core derived from the terpyridine ligand and three N-bonded thiocyanates. Intermolecular H-bonding between carboxylates on neighboring terpyridines gives rise to 2-D H-bonded arrays. The absorption and emission maxima of the black dye show a bathochromic shift with decreasing pH and exhibit pH-dependent excited-state lifetimes. The red-shift of the emission maxima is due to better π-acceptor properti...

Engineering of Efficient Panchromatic Sensitizers for Nanocrystalline TiO2-Based Solar Cells

The series of Ru(II) polypyridyl compounds shown bind to metal oxide surfaces through the phosphonic acid groups. Ground and excited state properties of the Ru(II) complexes were characterized in fluid solution and when anchored to nanocrystalline ZrO2 and TiO2 thin films. In regenerative solar cells, the complexes bound to TiO2 efficiently convert light into electricity. The position of the phosphonic acid groups on the bipyridine ligand and the introduction of a methylene spacer allow fine-tuning of the light-to-electrical energy conversion efficiencies.

Phosphonate-based bipyridine dyes for stable photovoltaic devices.

Chemoselective platinum(0)-catalysed hydrophosphination of ethyl acrylate

The platinum(0) complex [Pt(tcep)3], tcep = P(CH2CH2CN)3, catalyses the formation of tcep from PH3 and CH2CHCN. The complexes [M(tcep)3] (M = Pt, Pd or Ni) and [MCl(tcep)3] (M = Rh or Ir) are compared for their catalysis of the reaction of PH(CH2CH2CN)2 with CH2CHCN to give tcep and it is shown that the platinum(0) complex is the most efficient. The platinum(0) catalysis has been studied in detail, monitoring the kinetics by 31P-{1H} NMR spectroscopy. It is revealed that the kinetics are a complex function of the concentration of product tcep. Qualitatively, the rates also depend on [CH2CHCN] and [catalyst]. Both 31P-{1H} and 195Pt-{1H} NMR spectroscopy suggests that addition of CH2CHCN to [Pt(tcep)3] gives the complex [Pt(tcep)2(η2-CH2CHCN)] which undergoes phosphine exchange on the NMR time-scale. The binuclear complex [Pt2H2(tcep)2{µ-P(CH2CH2CN)2}2], formed upon addition of PH(CH2CH2CN)2 to trans-[PtHCl(tcep)2] in the presence of base, is shown to be a catalyst precursor for the reaction of PH(CH2CH2CN)2 with CH2CHCN. Two parallel mechanisms involving mononuclear and binuclear intermediates are discussed to rationalise these observations.

Self-replication of tris(cyanoethyl)phosphine catalysed by platinum group metal complexes

Reactions of Diazo Carbonyls with [PtX(CH3)(chiral diphosphine)] (X = Cl, Br, I): Chemoselectivity and Diastereoselectivity of Pt-C and Pt-X Carbene Insertion

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Papers

Engineering of Efficient Panchromatic Sensitizers for Nanocrystalline TiO2-Based Solar Cells

Phosphonate-based bipyridine dyes for stable photovoltaic devices.

Chemoselective platinum(0)-catalysed hydrophosphination of ethyl acrylate

Self-replication of tris(cyanoethyl)phosphine catalysed by platinum group metal complexes

Reactions of Diazo Carbonyls with [PtX(CH3)(chiral diphosphine)] (X = Cl, Br, I): Chemoselectivity and Diastereoselectivity of Pt-C and Pt-X Carbene Insertion