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.

Working Principles of Perovskite Photodetectors: Analyzing the Interplay Between Photoconductivity and Voltage‐Driven Energy‐Level Alignment

Abstract: Organic-inorganic lead halide perovskites have recently received significant attention as active materials for high-performance photovoltaics and photo-detectors. However, the understanding of their operation mechanism remains limited. High-gain, low-voltage CH3NH3PbI3 photodetectors in various architectures are demonstrated herein. Photomultiplication in all structures with direct contact of fluorine-doped tin oxide (FTO) and perovskite with the highest responsivity 208 A W-1 corresponding to an incident photon-to-current efficiency of 47 000% is observed. Studying the dynamics and temperature dependence, a slow process with an activation energy of 420 +/- 90 meV in the time scale of seconds is found, which is essential to photocurrent multiplication. A model based on ion migration to explain the observed transients and the photomultiplication is developed. The accumulation of negative ionic charge at the FTO/perovskite interface under reverse bias lowers the FTO work function allowing for direct hole injection into the perovskite valence band. Under illumination, the conductivity of perovskite is increased and the device behaves similar to a photoconductor.

Characterization of Hole Transport in a New Class of Spiro‐Linked Oligotriphenylamine Compounds

Abstract: Reference LPI-ARTICLE-2000-035View record in Web of Science Record created on 2006-02-21, modified on 2016-08-08

Oxygen Evolution from Water via Redox Catalysis

Abstract: The decomposition of water by sunlight is a fascinating concept in view of today's energy debate. Evolution of O/sub 2/ according to 4Ce/sup 4 +/ + 2H/sub 2/O ..-->.. 4Ce/sup 3 +/ + 4H/sup +/ + O/sub 2/ or 4Ru(bpy)/sub 3//sup 3 +/ + 2H/sub 2/O ..-->.. 4Ru(bpy)/sub 3//sup 2 +/ + 4H/sup +/ + O/sub 2/ could be a first step in this direction. Suitable redox catalysts are P + O/sub 2/ and IrO/sub 2/. Ce/sup 3 +/ and Ru(bpy)/sub 3//sup 2 +/ can be photochemically reoxidized with evolution of H/sub 2/.

Light-induced reactivity of gold and hybrid perovskite as a new possible degradation mechanism in perovskite solar cells

Abstract: We suggest a new degradation mechanism of commonly used gold electrodes in hybrid perovskite solar cells (PSCs) originating from chemical interaction between gold and highly reactive iodine-containing byproducts formed in the course of perovskite decomposition. Intensive UV-irradiation of perovskite would typically lead to the release of volatile I2 and CH3NH3I (MAI) resulting in the formation of recently reported highly reactive polyiodide melts (RPMs) with the general formula MAI–nI2. These RPMs react aggressively with metallic gold at room temperature causing the formation of [AuI2]− and [AuI4]− complexes and, consequently, precipitation on the gold interface of a new (MA)2Au2I6 phase with a tetragonal symmetry. The high rate and depth of this reaction renders gold an easy target for attack under these particular conditions despite its notorious chemical inertness, thus making gold unsuitable for widespread use in iodine-based perovskite solar cells; other cheaper and more stable materials are needed as a better choice for further development in this area.

Self-assembled hierarchical nanostructured perovskites enable highly efficient LEDs via an energy cascade

Abstract: Metal halide perovskites have established themselves as extraordinary optoelectronic materials, exhibiting promise for applications in large area illumination and displays. However, low luminescence, low efficiencies of the light-emitting diodes (LEDs), and complex preparation methods currently limit further progress towards applications. Here, we report on a new and unique mesoscopic film architecture featuring the self-assembly of 3D formamidinium lead bromide (FAPbBr3) nanocrystals of graded size, coupled with microplatelets of octylammonium lead bromide perovskites, which enables an energy cascade, yielding very high-performance light-emitting diodes with emission in the green spectral region. These hierarchically structured perovskite films exhibit photoluminescence quantum yields of over 80% and LEDs associated with record high efficiencies in excess of 57.6 cd A−1 with an external quantum efficiency above 13%. Additionally, due to low turn-on voltages (∼2.2 V) the LEDs have power efficiencies exceeding 58 lumens per watt, obtained without any light-outcoupling structures.

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.