Michael Grätzel

Bio: Michael Grätzel is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Dye-sensitized solar cell & Perovskite (structure). The author has an hindex of 248, co-authored 1423 publications receiving 303599 citations. Previous affiliations of Michael Grätzel include University of California, Berkeley & Siemens Energy Sector.

Effect of sensitizer adsorption temperature on the performance of dye-sensitized solar cells.

Abstract: Employing a mesoscopic titania photoanode whose bilayer structure was judiciously selected to fit the optoelectronic characteristics of the Ru-based heteroleptic complex Na-cis-Ru(4,4'-(5-hexyltiophen-2-yl)-2,2'-bipyridine)(4-carboxylic-acid-4'-carboxylate-2,2'-bipyridine)(thiocyanate)(2), coded as C101, we investigated the effect of temperature for dye adsorption on the photovoltaic performance of dye-sensitized solar cells (DSCs). We found a significant efficiency enhancement upon lowering the temperature applied during the sensitizer uptake from solution. When the dye adsorption was performed at 4 °C, the photovoltaic performance parameters measured under standard reporting conditions (AM1.5 G sunlight at 1000 W/m(2) intensity and 25 °C), i.e., the open circuit voltage (V(oc)), the short circuit photocurrent density (J(sc)), the fill factor (FF), and consequently the power conversion efficiency (PCE), improved in comparison to cells stained at 20 and 60 °C. Results from electrochemical impedance spectroscopy (EIS) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) show that the self-assembled layer of C101 formed at lower temperature impairs the back-electron transfer from the TiO(2) conduction band to the triiodide ions in the electrolyte more strongly than the film produced at 60 °C. Profiting from the favorable influence that the low-temperature dye uptake exerts on photovoltaic performance, we have realized DSCs showing a power conversion efficiency of 11.5%.

Electronic and Optical Properties of the Spiro-MeOTAD Hole Conductor in Its Neutral and Oxidized Forms: A DFT/TDDFT Investigation

Abstract: The molecular structures and electronic and optical properties of 2,2′7,7′-tetrakis-(N,N-di-p-methoxyphenyl amine)-9,9′-spirobifluorene (spiro-MeOTAD) in different oxidation states have been investigated by means of DFT/TDDFT methods. Spiro-MeOTAD has been demonstrated to be an efficient hole-transport material (HTM) in organic light-emitting devices (OLEDs) and in solid-state dye-sensitized solar cells (ssDSCs), and to date spiro-MeOTAD, has yielded the highest ssDSC efficiency. The spiro-MeOTAD radical cation exhibits long-term stability, even though the 2+ and 4+ formal oxidation states are accessible. DFT and TDDFT allow the characterization of the excited states involved in the absorption processes of the spiro-MeOTAD-derived cations, an important aspect considering that the oxidized species absorb in the visible region. The excellent agreement between theory and experiment for both neutral spiro-MeOTAD and its oxidized forms opens the possibility for identifying the features that make it an efficien...

A High-Efficiency Panchromatic Squaraine Sensitizer for Dye-Sensitized Solar Cells

Abstract: Keywords: dyes/pigments ; light harvesting ; sensitizers ; solar cells ; squaraines ; Films Reference EPFL-ARTICLE-171211doi:10.1002/anie.201101362View record in Web of Science Record created on 2011-12-16, modified on 2017-12-03

Comprehensive control of voltage loss enables 11.7% efficient solid-state dye-sensitized solar cells

Abstract: The relatively large voltage loss (Vloss) in excitonic type solar cells severely limits their power conversion efficiencies (PCEs). Here, we report a comprehensive control of Vloss through efficacious engineering of the sensitizer and redox mediator, making a breakthrough in the PCE of dye-sensitized solar cells (DSSCs). The targeted down-regulation of Vloss is successfully realized by three valid channels: (i) reducing the driving force of electron injection through dye molecular engineering, (ii) decreasing the dye regeneration overpotential through redox mediator engineering, and (iii) suppressing interfacial electron recombination. Significantly, the “trade-off” effect between the dye optical band gap and the open-circuit voltage (VOC) is minimized to a great extent, achieving a distinct enhancement in photovoltaic performance (PCE > 11.5% with VOC up to 1.1 V) for liquid junction cells. The solidification of the best-performing device leads to a PCE of 11.7%, which is so far the highest efficiency obtained for solid-state DSSCs. Our work inspires further development in highly efficient excitonic solar cells by comprehensive control of Vloss.

Low-Temperature Nb-Doped SnO2 Electron-Selective Contact Yields over 20% Efficiency in Planar Perovskite Solar Cells

Abstract: Low-temperature planar organic–inorganic lead halide perovskite solar cells have been at the center of attraction as power conversion efficiencies go beyond 20%. Here, we investigate Nb doping of SnO2 deposited by a low-cost, scalable chemical bath deposition (CBD) method. We study the effects of doping on compositional, structural, morphological, and device performance when these layers are employed as electron-selective layers (ESLs) in planar-structured PSCs. We use doping concentrations of 0, 1, 5, and 10 mol % Nb to Sn in solution. The ESLs were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and ultraviolet–visible spectroscopy. ESLs with an optimum 5 mol % Nb doping yielded, on average, an improvement of all the device photovoltaic parameters with a champion power conversion efficiency of 20.5% (20.1% stabilized).

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Environmental Applications of Semiconductor Photocatalysis

Abstract: The civilian, commercial, and defense sectors of most advanced industrialized nations are faced with a tremendous set of environmental problems related to the remediation of hazardous wastes, contaminated groundwaters, and the control of toxic air contaminants. For example, the slow pace of hazardous waste remediation at military installations around the world is causing a serious delay in conversion of many of these facilities to civilian uses. Over the last 10 years problems related to hazardous waste remediation have emerged as a high national and international priority.