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.

A combined molecular dynamics and experimental study of two-step process enabling low-temperature formation of phase-pure α-FAPbI3.

Abstract: It is well established that the lack of understanding the crystallization process in a two-step sequential deposition has a direct impact on efficiency, stability, and reproducibility of perovskite solar cells. Here, we try to understand the solid-solid phase transition occurring during the two-step sequential deposition of methylammonium lead iodide and formamidinium lead iodide. Using metadynamics, x-ray diffraction, and Raman spectroscopy, we reveal the microscopic details of this process. We find that the formation of perovskite proceeds through intermediate structures and report polymorphs found for methylammonium lead iodide and formamidinium lead iodide. From simulations, we discover a possible crystallization pathway for the highly efficient metastable α phase of formamidinium lead iodide. Guided by these simulations, we perform experiments that result in the low-temperature crystallization of phase-pure α-formamidinium lead iodide.

Light-Enhanced Charge Mobility in a Molecular Hole Transporter

Abstract: We present an investigation into the charge transport through a molecular hole transporter. Under illumination, photoinduced charge transfer occurs from a sensitizer to the hole transporter. The increased hole density results in striking enhancements in film conductivity, up to ${10}^{6}$, and charge carrier mobility, up to ${10}^{3}$. Such enhancements in mobility at low charge densities have not previously been observed in molecular semiconductors, and demonstrate the importance of considering a charge-density dependent mobility in molecular semiconductors employed under photovoltaic operation.

Molecular gelation of ionic liquid–sulfolane mixtures, a solid electrolyte for high performance dye-sensitized solar cells

Abstract: Cyclohexanecarboxylic acid-[4-(3-tetradecylureido)phenyl]amide is an efficient gelator to solidify ionic liquid electrolytes. In this paper we apply this low molecular weight gelator to solidify the newly prepared sulfolane based ionic liquid electrolyte. This solid electrolyte is successfully applied as an electrolyte for dye sensitized solar cells. This solid electrolyte is thermo-reversible, upon heating it will become a liquid and at room temperature it will solidify, facilitating the cell filling by the electrolyte. Applying this solid electrolyte we obtained 7.8% power conversion efficiency under simulated AM 1.5 full sunlight intensity. The devices with liquid and solid electrolytes were analysed by electrochemical impedance spectroscopy to explain the differences in the photovoltaic performance. These cells were also measured under outdoor conditions at Jeddah, Saudi Arabia to explore the feasibility of practical applications of this electrolyte.

Intrinsic and interfacial kinetics of perovskite solar cells under photo and bias-induced degradation and recovery

Abstract: Perovskite solar cells (PSCs) have emerged as a potential candidate for high efficiency low-cost photovoltaic technology. However, the intrinsic and interfacial responses of PSCs under photo and bias-induced degradation and recovery have not been clearly understood. Herein, the influence of illumination and bias on the intrinsic and interfacial characteristics of PSCs is examined by studying the role of trap states, perovskite dielectric relaxation phenomena, transport and recombination characteristics as well as ion movements. We found that under illumination and bias stress conditions, the photo-current at short circuit conditions was decreased in a reversible way and recovered to its initial value after keeping the device in the dark. On the basis of electrical measurements and analysis, we conclude that the full recovery of PSC performance was limited by an increase in the relative dielectric constant, series and shunt resistances and enhanced recombination pathways under stimuli conditions.

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.