105 research outputs found
Simulating multiple quantum well solar cells
The quantum well solar cell (QWSC) has been proposed as a route to higher
efficiency than that attainable by homojunction devices. Previous studies have
established that carriers escape the quantum wells with high efficiency in
forward bias and contribute to the photocurrent. Progress in resolving the
efficiency limits of these cells has been dogged by the lack of a theoretical
model reproducing both the enhanced carrier gen- eration and enhanced
recombination due to the quantum wells. Here we present a model which
calculates the incremental generation and recombination due to the QWs and is
verified by modelling the experimental light and dark current-voltage
characteristics of a range of III-V quantum well structures. We find that
predicted dark currents are significantly greater than experiment if we use
lifetimes derived from homostructure devices. Successful simulation of light
and dark currents can be obtained only by introducing a parameter which
represents a reduction in the quasi-Fermi level separation.Comment: Preprint submitted to the 28th IEEE Photovoltaic Specialists
Conference, Anchorage, Alaska, USA, Sept. 2000, pp. 1304-130
Charge transport in hybrid nanorod-polymer composite photovoltaic cells
ABSTRACT Charge transport in composites of inorganic nanorods and a conjugated polymer is investigated using a photovoltaic device structure. We show that t he current-voltage (I-V) curves in the dark can be modelled using the Shockley equation modified to include series and shunt resistance at low current levels, and using an improved model that incorporates both the Shockley equation and the presence of a space charge limited region at high currents. Under illumination the efficiency of photocurrent generation is found to be dependent on applied bias. Furthermore, the photocurrent-light intensity dependence was found to be sublinear. An analysis of the shunt resistance as a function of light intensity suggests that the photocurrent as well as the fill factor is diminished as a result of increased photoconductivity of the active layer at high light intensity. By studying the intensity dependence of the open circuit voltage for nanocrystals with different diameters and thus band gaps, it was inferred that Fermi-level pinning occurs at the interface between the aluminum electrode and the nanocrystal.
Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases
The production of peroxide and superoxide is an inevitable consequence of
aerobic metabolism, and while these particular "reactive oxygen species" (ROSs)
can exhibit a number of biological effects, they are not of themselves
excessively reactive and thus they are not especially damaging at physiological
concentrations. However, their reactions with poorly liganded iron species can
lead to the catalytic production of the very reactive and dangerous hydroxyl
radical, which is exceptionally damaging, and a major cause of chronic
inflammation. We review the considerable and wide-ranging evidence for the
involvement of this combination of (su)peroxide and poorly liganded iron in a
large number of physiological and indeed pathological processes and
inflammatory disorders, especially those involving the progressive degradation
of cellular and organismal performance. These diseases share a great many
similarities and thus might be considered to have a common cause (i.e.
iron-catalysed free radical and especially hydroxyl radical generation). The
studies reviewed include those focused on a series of cardiovascular, metabolic
and neurological diseases, where iron can be found at the sites of plaques and
lesions, as well as studies showing the significance of iron to aging and
longevity. The effective chelation of iron by natural or synthetic ligands is
thus of major physiological (and potentially therapeutic) importance. As
systems properties, we need to recognise that physiological observables have
multiple molecular causes, and studying them in isolation leads to inconsistent
patterns of apparent causality when it is the simultaneous combination of
multiple factors that is responsible. This explains, for instance, the
decidedly mixed effects of antioxidants that have been observed, etc...Comment: 159 pages, including 9 Figs and 2184 reference
Review of physics
Some of the topics on K/sup +or-/p physics are discussed. The application of quark-parton model ideas to low-p/sub T/ hadronic interactions appears to be a fruitful approach. In particular two- particle correlations place stringent restrictions on the possible dynamical mechanisms. The presence of a strange quark in K/sup +or-/p interactions greatly extends the possible tests. Inclusive resonance production is also discussed. Mention is also made of the use of bubble chamber data as a standard of known physics with which to compare any new effects. (15 refs)
Classical Behaviour of Output Light Emitted by the Edge of a Luminescent Solar Concentrator
A straightforward technique for measuring the output light from one edge of a luminescent solar concentrator (LSC) was recently developed. A set of measurements was performed both on conventional LSCs and thin film composite LSCs, showing interesting differences between two types of devices. In order to investigate the origin of this behaviour, different models have been developed
by our groups. In this work we present the experimental setup and main results, together with a simple three-dimensional Monte Carlo code, modelling light re-emission by a LSC and distribution of output light from the edge under examination. Light is described by means of classical non-interacting particles undergoing classical optics laws at glass-to-air interfaces. Simulation results agree well with the experimental data and explain the output light distribution close to the edge under examination.JRC.F.8-Renewable Energy (Ispra
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