Showing papers by "Michael Grätzel published in 2002"

Dye-Sensitized Core−Shell Nanocrystals: Improved Efficiency of Mesoporous Tin Oxide Electrodes Coated with a Thin Layer of an Insulating Oxide

Abstract: Coating nanocrystalline SnO2 electrodes for dye-sensitized solar cell applications with a thin layer of ZnO, TiO2, ZrO2, MgO, Al2O3, Y2O3, or other insulating oxides was found to improve dye adsorption and increase the sensitized photocurrent. The surface of the oxide coating is more basic than SnO2, which renders dye attachment by its carboxyl groups more favorable. At the same time, the photovoltage and fill factor are strongly enhanced, resulting in much better energy conversion efficiencies. This change is ascribed to inhibition of electron back transfer from SnO2 to the redox electrolyte (I3-) by the insulating oxide. The optimum coating thickness is only a few angstroms, suggesting that electron transfer from the excited dye attached to the oxide surface to the underlying SnO2 occurs by tunneling through the insulator layer. Different methods for coating SnO2 nanocrystals with a thin layer of an insulating oxide were compared. The best results were obtained by adding a soluble metal salt to the SnO2...

Quantum dot sensitization of organic-inorganic hybrid solar cells

Abstract: A high surface area pn-heterojunction between TiO2 and an organic p-type charge transport material (spiro-OMeTAD) was sensitized to visible light using lead sulfide (PbS) quantum dots. PbS quantum dots were formed in situ on a nanocrystalline TiO2 electrode using chemical bath deposition techniques.1 The organic hole conductor was applied from solution to form the sensitized heterojunction. The structure of the quantum dots was analyzed using HRTEM technique. Ultrafast laser photolysis experiments suggested the initial charge separation to proceed in the subpicosecond time range. Transient absorption laser spectroscopy revealed that interfacial charge recombination of the initially formed charge carriers is much faster than in comparable dye-sensitized systems.2,3 The sensitized heterojunction showed incident photon-to-electron conversion efficiencies (IPCE) of up to 45% and energy conversion efficiencies under simulated sunlight AM1.5 (10 mW/cm2) of 0.49%.

Design, synthesis, and application of amphiphilic ruthenium polypyridyl photosensitizers in solar cells based on nanocrystalline TiO2 films

Abstract: Reference LPI-ARTICLE-2002-028doi:10.1021/la0110848View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Facile synthesis of nanocrystalline Li4Ti5O12 (spinel) exhibiting fast Li insertion

Abstract: Reference LPI-ARTICLE-2002-023doi:10.1149/1.1432783View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Improvement of the photovoltaic performance of solid-state dye-sensitized device by silver complexation of the sensitizer cis-bis(4,4 ' -dicarboxy-2,2 ' bipyridine)-bis(isothiocyanato) ruthenium(II)

Abstract: The photovoltaic performance of solid-state dye-sensitized solar cells based on 2,2′7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spiro-bifluorene has been improved to 3.2% overall conversion efficiency under air mass (AM) 1.5 illumination by performing the dye adsorption in the presence of silver ions in the dye solution. The enhancement in overall device efficiency is a result of increased open circuit potential and short circuit current. Different spectroscopic methods, such as x-ray photoelectron, Fourier-transform infrared and UV-visible spectroscopy have been employed to scrutinize the impact of the silver on the dye-sensitized device. From spectroscopic evidence it is inferred that the silver is mainly binding to the sensitizer via the amphidentate thiocyanate, allowing the formation of ligand-bridged dye complexes.

Novel ruthenium sensitizers containing functionalized hybrid tetradentate ligands: synthesis, characterization, and INDO/S analysis.

Abstract: Ruthenium sensitizers of the type trans-[Ru(L1)(X)2], trans-[Ru(L2)(X)2], trans-[Ru(L3)(X)2], and trans-[Ru(L4)(X)2] (where L1 = 6,6‘-bis(1-H-benzimidazol-2-yl)-4,4‘-bis(methoxycarbonyl)-2,2‘-bipyridine, L2 = 4,4‘ ‘‘-bis(tert-butyl)-4‘,4‘ ‘-bis[p-(methoxycarbonyl)phenyl]-2,2‘:6‘,2‘ ‘:6‘ ‘,2‘ ‘‘-quaterpyridine, L3 = 4‘,4‘ ‘-bis[3,4-(dimethoxy)phenyl]-2,2‘:6‘,2‘ ‘:6‘ ‘,2‘ ‘‘-quaterpyridine, and L4 = 4‘,4‘ ‘-diethoxycarbonyl-2,2‘:6‘,2‘ ‘:6‘ ‘,2‘ ‘‘-quaterpyridine; X = Cl-, NCS-) were synthesized and characterized by CV, NMR, and UV−vis absorption and emission spectroscopy. The trans-dichloro and dithiocyanate complexes show MLCT transitions in the entire visible and near-IR region. The lowest energy metal-to-ligand charge-transfer transition band of the trans-dichloro complexes is around 14 300 cm-1 in DMF solution, and these complexes show weak and broad emission signals with onset at above 10 500 cm-1. The absorption and emission maxima of the trans-dithiocyanate complexes are blue-shifted compared to thos...

Electrochromic or photoelectrochromic device

Abstract: Electrochromic and photoelectrochromic devices using nanocrystalline semiconductor electrodes with a high specific surface area and surface-absorbed electrochromic molecules are disclosed.

Electron injection kinetics for the nanocrystalline TiO2 films sensitised with the dye (Bu4N)2Ru(dcbpyH)2(NCS)2

Abstract: Transient absorption spectroscopy is employed to determine the electron injection kinetics for nanocrystalline TiO2 electrodes sensitised with the dye (Bu4N)2Ru(dcbpyH)2(NCS)2 2. These kinetics are compared with control data obtained for the more widely studied fully protonated version of this with dye, Ru(dcbpyH2)2(NCS)2 1. In both cases multiphasic, ultrafast electron injection kinetics are observed. However the electron injection kinetics observed for sensitiser 2 are found to be significantly slower than sensitiser 1. Half times for electron injection are observed to be 0.4 and 12 ps with sensitisers 1 and 2, respectively. Prolonged washing of films sensitised with sensitiser 1 in non-acidified ethanol results in retardation of the kinetics, resulting in an injection half time similar to that observed for sensitiser 2. These observations are discussed in terms of the influence of the co-adsorption of protons during the sensitising process, and their relevance to photovoltaic function.

Osteoblast culture on polished titanium disks modified with phosphonic acids

Abstract: Titanium is widely used in dental implants due to its suitable physical properties and its good biocompatibility. However, it is integrated into bone only passively, and the resulting fixation in the bone, which is necessary for the function, is mainly mechanical in nature. With the objective of increasing the chemical interaction between the implant and the bone tissue, several phosphonic acids were synthesized and grafted onto titanium disks. Here we report on the proliferation, differentiation, and protein production of rat osteoblastic cells (CRP10/30) on phosphonic-acid-modified titanium surfaces studied in vitro. No statistical differences were found in osteoblast proliferation among the phosphonic-acid-modified titanium, unmodified titanium, and tissue culture plastic (used as a positive control), indicating that the phosphonic acids used were not cytotoxic to the osteoblasts used. For all surfaces (modified or not), the alkaline phosphatase activity was at least as good as it was on tissue culture plastic. However, the total amount of protein, and especially the collagen type I synthesis, was sensitive to surface modification. On titanium modified with ethane-1,1,2-triphosphonic acid, the total amount of synthesized protein was significantly higher than it was on unmodified titanium surfaces. A significant increase (up to 16%) of collagen type I production was observed on titanium surfaces modified with this acid or with methylenediphosphonic acid compared to unmodified titanium surfaces.

Redox targeting of oligonucleotides anchored to nanocrystalline TiO2 films for DNA detection.

Abstract: Reference LPI-ARTICLE-2002-007doi:10.1002/1439-7641(20020415)3:4 3.0.CO;2-OView record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Packing of ruthenium sensitizer molecules on mostly exposed faces of nanocrystalline TiO2: crystal structure of (NBu4+)2[Ru(H2tctterpy)(NCS)3]2−·0.5 DMSO

Abstract: Reference LPI-ARTICLE-2002-013doi:10.1002/aoc.361View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Synthesis of new polyphosphonic acids

Abstract: A general method for the synthesis of new polyphosphonic acids is described. The hexaisopropyl alkane-1,1,n-triphosphonates (n = 4-5) are formed by the reaction of the salt of tetraisopropyl methylenediphosphonate with diisopropyl n-bromoalkanephosphonates (n = 3-4) while the hexaisopropyl alkane-2,2,n-triphosphonates (n = 5-6) are formed by the reaction of the salt of tetraisopropyl ethane-1,1-diphosphonate with diisopropyl n-bromoalkanephosphonates (n = 3-4). The esters are then hydrolyzed with HCl to give the corresponding phosphonic acids.

Dynamics for solubilization of naphthalene and pyrene into n-decyltrimethylammonium perfluorocarboxylate micelles

Abstract: The entry and exit rate constants of naphthalene and pyrene to and from a micelle (k+ and k-, respectively) have been determined for n-decyltrimethylammonium trifluoroacetate (DeTAPA) and pentafluoropropionate (DeTAPP) micelles by a steady-state fluorescence quenching method. The k- values of naphthalene and pyrene for DeTAPA micelles increased with increasing temperature, whereas the values from DeTAPP micelles had a minimum at 308.2 K. The k+ values of naphthalene and pyrene to DeTAPA micelles also increased with increasing temperature, whereas the values for DeTAPP micelles again showed a minimum at the same temperature. The fluorescence spectra of pyrene have indicated that the molecule is located at the hydrophilic outer site in DeTAPA and DeTAPP micelles rather than at the hydrophobic micellar core site.

Dyes for Semiconductor Sensitization

Abstract: The sections in this article are Introduction General Background Operating Principles of the Dye-Sensitized Solar Cell Incident Photon to Current Efficiency and Open-Circuit Photovoltage Molecular Sensitizers Formation of Complexes Photophysical Properties Ground and Excited State Redox Potentials Requirements of the Sensitizers Absorption Spectral Properties of Metal Complexes Tuning of MLCT Transitions Spectral Tuning in “Push-Pull” Type of Complexes Spectral Tuning in Complexes Containing Hybrid Donor Ligands Influence of Nonchromophoric Ligands on MLCT Transitions Influence of the Position of Carboxyl Groups on MLCT Transitions MLCT Transitions in Geometric Isomers Spectral Tuning in Heteroleptic Sensitizers Hydrophobic Sensitizers Near IR Sensitizers Phthalocyanines Ruthenium Phthalocyanines Phthalocyanines Containing 3d Metals Mononuclear and Polynuclear Metal Complexes of Group VIII Iron Complexes Osmium Complexes Polynuclear Complexes Surface Chelation of Polypyridyl Complexes onto the TiO2 Surface Anchoring Groups Acid-Base Equilibria of the Anchoring Groups Acid-Base Equilibria of the 4,4-Dicarboxy-2,2′-Bipyridine and its Complexes Acid-Base Equilibria of the Phosphonato Group Stability and Performance of the Dyes Stability of the Inorganic Dyes Effect of Protons Carried by the Sensitizer on the Performance Comparison of IPCE Obtained with Various Sensitizers Synthesis and Characterization Synthetic Strategies for Ruthenium Complexes Purification Characterization Conclusion Acknowledgment

Dye-Sensitized Regenerative Solar Cells

Abstract: The sections in this article are Overview Device Concepts Photography and Photoelectrochemistry Sensitization of Powders and Rough Surfaces Substrate Development and Fabrication Dye Sensitization in Heterojunctions Commercial Prospects Conclusion Acknowledgments

Photoinduced electron transfer in dye/semiconductor systems on a sub-10-fs time scale

Abstract: Pump-probe investigation of alizarin adsorbed on the surface of TiO2 colloids reveals a 6 femtosecond electron transfer from the dye molecule to the semiconductor surface, allowing to identify the key factors for this ultrafast electron transfer.