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 …

I and i

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.

Fast parallel algorithms for short-range molecular dynamics

Objective comparisons of electrocatalyst activity and stability using standard methods under identical conditions are necessary to evaluate the viability of existing electrocatalysts for integration into solar-fuel devices as well as to help inform the development of new catalytic systems. Herein, we use a standard protocol as a primary screen for evaluating the activity, short-term (2 h) stability, and electrochemically active surface area (ECSA) of 18 electrocatalysts for the hydrogen evolution reaction (HER) and 26 electrocatalysts for the oxygen evolution reaction (OER) under conditions relevant to an integrated solar water-splitting device in aqueous acidic or alkaline solution. Our primary figure of merit is the overpotential necessary to achieve a magnitude current density of 10 mA cm–2 per geometric area, the approximate current density expected for a 10% efficient solar-to-fuels conversion device under 1 sun illumination. The specific activity per ECSA of each material is also reported. Among HER...

Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices

介绍了Kirk—Othmer Encyclopedia of Chemical Technology（化工技术百科全书）（第五版）电子图书网络版数据库，并对该数据库使用方法和检索途径作出了说明，且结合实例简单地介绍了该数据库的检索方法。

Kirk-Othmer Encyclopedia of Chemical Technology数据库介绍及实例

Bismuth vanadate (BiVO4) has a band structure that is well-suited for potential use as a photoanode in solar water splitting, but it suffers from poor electron-hole separation. Here, we demonstrate that a nanoporous morphology (specific surface area of 31.8 square meters per gram) effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE). We enhanced the propensity for surface-reaching holes to instigate water-splitting chemistry by serially applying two different oxygen evolution catalyst (OEC) layers, FeOOH and NiOOH, which reduces interface recombination at the BiVO4/OEC junction while creating a more favorable Helmholtz layer potential drop at the OEC/electrolyte junction. The resulting BiVO4/FeOOH/NiOOH photoanode achieves a photocurrent density of 2.73 milliamps per square centimenter at a potential as low as 0.6 V versus RHE.

https://science.sciencemag.org/content/sci/early/2014/02/12/science.1246913.full.pdf

Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar Water Splitting

Effect of c-Si base layer thickness on efficiency limits of thin - film c-Si solar cells on glass

Hydrogenated amorphous silicon (a-Si:H) films are grown at different hydrogen dilutions. For high dilutions we observe a discrepancy in the surface roughness analysis between real-time spectroscopic ellipsometry (RTSE) and atomic force microscopy (AFM) measurements. With RTSE a much higher roughness layer thickness is measured than with AFM. Additionally we observe what appears to be a strong roughening phase in the first 30-50 nm of film growth for all conditions. A mechanism that involves the formations of a hydrogenrich overlayer and etching of higher hydrides in this overlayer is suggested.



This mechanism explains the difference in RTSE roughness layer thickness evolution. At higher hydrogen dilutions, we obtain a thicker overlayer dominated by lower hydrides. RTSE interprets this overlayer as additional surface roughness and consequently overestimates the surface roughness for higher dilutions. The initial strong roughening phase is related to the built-up of this over-layer. In this phase, we obtain much denser films compared to the bulk film. The presence of columnar growth at higher dilutions is attributed to reduced surface mobility under these conditions (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of hydrogen dilution on surface roughness development of a‐Si:H thin films grown by remote plasma deposition

In this paper, we investigate the light scattering properties of our randomly textured back reflector (BR) for n-i-p thin-film microcrystalline silicon μc-Si:H) solar cells. The texture-etched ZnO:Al (AZO) covered with Ag is used as BR. The substrate temperature during the sputtering of AZO and the etching time are crucial for the morphology of the BR. An optimized substrate temperature can improve the morphology of etched AZO and optical performance of the BR, thereby increasing the photocurrent of solar cells. After Ag evaporation we obtain small features superimposed on the large features of the etched AZO. As a result the angle distribution becomes much wider. Large features of BR can preferentially scatter light into larger angles. The optimized BR has a wide surface angle distribution with an average angle of 27 ° and exhibiting a peak at 32 °. The optimized BR has a very broad reflective angular intensity distribution in air (AIDair) with peak at around 45 ° for incident light from 400 nm to 800 nm, and has a very high haze in reflection. With this optimized BR we obtained 7.68% efficiency for rf-PECVD deposited n-i-p μc-Si:H thin film solar cells. The Jsc is 25.2 mA/cm2 with a very high quantum efficiency in the long wavelength region. And the VHF-PECVD deposited n-i-p μc-Si:H thin film solar cells prove that the optimized BR does not deteriorates the solar cells electrical performance and the obtained the best efficiency is 8.9%.

Textured substrate for high-efficiency n-i-p μc-Si:H solar cells

We present results of computer simulations of the light induced degradation of amorphous silicon solar cells. It is now well established that when amorphous silicon is illuminated the density of dangling bond states increases. Dangling bond states produce amphoteric electronic mid-gap states which act as efficient charge trapping and recombination centres. The increase in dangling bond states causes a decrease in the performance of amorphous silicon solar cells. To show this effect, a modelling approach has been developed which uses the density of localised states with exponentially increasing band-tails and dangling bond defect states distribution chosen according to the defect pool model. The calculation of the evolution of dangling bond state density during illumination has been achieved through a dynamic scaling relation derived from a defect creation model. The approach considers the amphoteric nature of the dangling bond state and thus accounts for the contributions of the different charge states of the dangling bond during the degradation process. This paper attempts to describe the simulation approach which calculates the defect density as a function of energy, position in the solar cell and illumination time. In excellent agreement with other workers, our simulation results show that the increase in the density of neutral dangling bond states during illumination is higher than of the charged states.

/pdf/modelling-the-light-induced-metastable-effects-in-amorphous-220seiglju.pdf

Modelling the light induced metastable effects in amorphous silicon

Photovoltaic (PV) electricity generation is currently the fastest growing technology for energy production. PV technology is for more than 90% based on silicon as source material and this material is one of the most expensive components of silicon based solar cells. Thin-film silicon based solar cells are low-cost alternatives. This contribution discusses the most important features of amorphous silicon based thin-film solar cells. In addition, solar cells based on a heterojunction between amorphous silicon and crystalline silicon are discussed. This solar-cell technology has how attracted much attention due to the high performance and several industrial benefits resulting from low-temperature processing.

Miro Zeman

Papers

Effect of c-Si base layer thickness on efficiency limits of thin - film c-Si solar cells on glass

Influence of hydrogen dilution on surface roughness development of a‐Si:H thin films grown by remote plasma deposition

Textured substrate for high-efficiency n-i-p μc-Si:H solar cells

Modelling the light induced metastable effects in amorphous silicon

Thin-film silicon technology for highly-efficient solar cells