Parasitic absorption

From a theoretical point-of view, significantly higher current densities are feasible, but require further improved front TCO films and perfect mirrors as back reflectors. This is illustrated by the dotted curve in Fig. 8.28, which shows simulations of quantum efficiency for a 1 pm thick pc-Si H solar cell. These simulations reveal a current potential of 29.2 mA cm-2 by improved optical components like reduced parasitic absorption in the front TCO, ideal Lambertian light scattering, dielectric back reflectors, and antireflection coatings on the front side [147]. However, this still has to be achieved experimentally. 

As in any other laser, the lasing threshold in a semiconductor laser diode is reached when the gain of the active material overcomes the losses of the laser cavity. These losses have two basic origins, namely the finite reflectivity of the mirrors mid distributed losses due to scattering and parasitic absorption in the active medium. In contrast to other lasers, the mirrors in typical semiconductor lasers are simply formed by cleaved or etched crystal facets. Therefore, the reflectivity (Fresnel reflectivity) is rather low, about 20% in the case of the nitrides. 

We were inclined to conclude that... the water-uranium system would sustain a chain reaction. Placzek said that our conclusion was wrong because in order to make a chain reaction go, we would have to eliminate the absorption of [neutrons by the] water that is, we would have to reduce the amount of water in the system, and if we reduced the water in the system, we would increase the parasitic absorption of [neutrons by] uranium [because with less water fewer neutrons would be slowed]. He recommended that we abandon the water-uranium system and use helium for slowing down the neutrons. To Fermi this sounded funny, and Fermi referred to helium thereafter invariably as Placzek s helimn. 

The breeder is an arrangement in which 23 undergoes flssion and the neutrons produced thereby are absorbed by thorium. When this thorium decays it produces again 23 via Pa. Since the rj of 23 is, according to Anderson and May, 2.37 the net increase in the number of neutrons per 23 destroyed is 1.37. If all these neutrons were absorbed in thorium, we would obtain 1.37 23 atoms per 23 destroyed. It is well to remember, however, that if only as many as 15% of the 2.37 neutrons emitted are lost by escape from the system or parasitic absorption by other materials or otherwise, the efficiency of the breeder goes down to 1 and no increase in the amount of 23 results. 

The reason that we gave the nitrate precedence over other salts is that we expect it to reduce the corrosion of the walls and also because it does not give products under radiation which may gum the system. The sulfate which has negligible absorption may precipitate sulphur although it is not clear that this cannot be avoided by the addition of peroxide. The parasitic absorption of the fluoride, the use of which was propsed by Allen, is also negligible but there is a strong opinion (Hiskey) that it will be difficult to avoid precipitation of the peroxide at such concentrations of the hydrofluoric acid which are tolerable from the point of view of corrosion. If the uranium is used in the form of a solution in Bi or fluorocarbons it may be necessary to eliminate the products of nuclear reactions of these substances along with the fission products. 

It has been found in this connection that the 17 of or, in other words, the number of neutrons emitted per fission of a atom is about 2.37, thus providing a net 35 increase of 1.37 neutrons per fission. If all of these neutrons are absorbed in fertile material such as, fer example, thorium atoms, 1.37 atoms are produced for each atom consumed or destroyed by the chain reaction. However, it will be noted that the loss of as 0 much as 15 percent of the 2.37 neutrons by escape from the system or by parasitic absorption of other materials than the thorium results in a net increase of zero thus preventing the breeding of thermally fissionable material. An enumeration of the losses follows ... 

Stainless-steel cladding results in parasitic absorption of neutrons, which reduces the neutron economy of the reactor. 

Others 0.20 0.20 Parasitic absorption by structure material and coolant... 

A representative application of the MSR concept is thorium reactor, and MSRE (Molten-Salt Reactor Experiment) with thermal output of 8 MW was developed by Oak Ridge National Laboratory in the USA and had been operated from 1966 to 1969. In the thorium reactor, the breeding of fissile nuclide, can be achieved through prevention of parasitic absorption by... 

The thermal absorption of thorium is three times that of Due to this, the deleterious effects of parasitic absorption are less in thorium systems, and one can consider the use of light water coolant. This opens the way to in-core boiling. The reactor then has to be vertical, and then it becomes possible to design for 100% heat removal by natural circulation and passive safety. The possibility of positive void coefficient of reactivity has been countered by the lattice being under moderated with a burnable absorber in the fuel cluster. 

Margulis GY, Hardin BE, Ding IK, Hoke ET, McGehee MD (2013) Parasitic absorption and internal quantum efficiency measurements of solid-state dye sensitized solar cells. Adv Energ Mater 3(7) 959-966... 

The reactivity difference between an air (nitrogen) and a helium atmosphere in the reactor has been calculated to be 0.l6. The principal effect of nitrogen in the lattice is to Increase the parasitic absorptions and thus reduce the thermal utilization, f The thermal neutron absorption cross section of helium is zero. 

Abstract We review the methods used to simulate the optoelectronic response of organic solar cells and focus on the application of one-dimensional drift-diffusion simulations. We discuss how the important physical processes are treated and review some of the experiments necessary to determine the input parameters for device simulations. To illustrate the usefulness of drift-diffusion simulations, we discuss several case studies, addressing the influence of charged defects on transport in bipolar and unipolar devices, the influence of defects on recombination, device performance and ideality factors. To illustrate frequency domain simulations, we show how to determine the validity range of Mott-Schottky plots for thin devices. Finally, we discuss an example where optical simulations are used to calculate the parasitic absorption in contact layers. 

In Sect. 2.1 we discussed the many applications of optical modelling for organic solar cells. The case study we chose to present as one application of optical modelling of organic solar cells is the analysis of parasitic absorption losses in the different layers of the solar cell stack. One example is shown in Fig. 8. We calculated the absorptance of each layer in a layer stack glass/ITO (160 nm)/poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT PSS) (30 nm)/poly[(4,40-bis (2-ethylhexyl)dithieno [3,2-h 20,30- 7 silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,l,3-benzothiadiazole)-5,50-diyl] (SiPCPDTBT) [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) (100 nm)/Ca (20 nm)/Al(100 nm). The transfer matrix formalism... 

Because of the small reactivity margin available for breeding in a thermal reactor, the use of the thorium cycle has mainly been associated with reactors with very good neutron economy based on low parasitic absorption, such as the high-temperature gas-cooled reactor, where graphite is used in place of metal for the fuel cladding, or heavy water reactors, with very low moderator absorption. A special case is the molten salt breeder reactor, where circulation of the fissile and fertile materials allows continuous removal not only of Pa but also of fission products. 

In the early days of the SGHWR project it was realized that the nuclear performance of the reactor would be dominated by the choice of lattice parameters. Since the parasitic absorption present in the structural materials tends to be fixed by asking the mechanical designer to minimize his requirements, the nuclear designer has essentially three main parameters at his disposal ... 

The first two solutions have been adopted for enriched SGHWR designs. The third solution Is appropriate to the natural fuelled version. The fourth solution was felt to be basically Incompatible with the objective of obtaining high efficiency fuel management schemes since it relies on parasitic absorptions. In the sections which follow. It will be shown how these general approaches have been adapted to the needs of particular situations. 

In addition, in the top parts of the fuel rods of the control assembly, depleted uranium is used instead of steel to avoid high local power peaks in the uppermost fuel pellets, and to improve economics by reducing parasitic absorption (which would occur in the steel) and reducing axial neutron leakage ... 

The polarizability of the particle is dependent on the size as well as the refractive index of the medium as is evident from Eq. 5. This in turn results in a higher scattering cross-section because of its dependence on a as shown in Eq. 4. Larger particles along with larger surface coverage lead to increased parasitic absorption and reflection reducing the desired optical absorption in semiconductor layer. 

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