4,058 research outputs found
Light emission as a solar cell analysis technique
In order to determine if a solar cell would indeed emit usable light as expected, a gallium arsenide solar cell was forward biased and examined with an infrared viewer. The light emitted from the solar cell was not uniform, ever though the I-V curve of the solar cell displayed no defects
Modelling and design of high performance indium phosphide solar cells
A first principles pn junction device model has predicted new designs for high voltage, high efficiency InP solar cells. Measured InP material properties were applied and device parameters (thicknesses and doping) were adjusted to obtain optimal performance designs. Results indicate that p/n InP designs will provide higher voltages and higher energy conversion efficiencies than n/p structures. Improvements to n/p structures for increased efficiency are predicted. These new designs exploit the high absorption capabilities, relatively long diffusion lengths, and modest surface recombination velocities characteristic of InP. Predictions of performance indicate achievable open-circuit voltage values as high as 943 mV for InP and a practical maximum AM0 efficiency of 22.5 percent at 1 sun and 27 C. The details of the model, the optimal InP structure and the effect of individual parameter variations on device performance are presented
A new structure for comparing surface passivation materials of GaAs solar cells
The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described
Window structure for passivating solar cells based on gallium arsenide
Passivated gallium arsenide solar photovoltaic cells with high resistance to moisture and oxygen are provided by means of a gallium arsenide phosphide window graded through its thickness from arsenic rich to phosphorus rich
Elementary Excitations of a Bose-Einstein Condensate in an Effective Magnetic Field
We calculate the low energy elementary excitations of a Bose-Einstein
Condensate in an effective magnetic field. The field is created by the
interplay between light beams carrying orbital angular momentum and the trapped
atoms. We examine the role of the homogeneous magnetic field, familiar from
studies of rotating condensates, and also investigate spectra for vector
potentials with a more general radial dependence. We discuss the instabilities
which arise and how these may be manifested.Comment: 8 pages, 4 figure
The azimuthal component of Poynting's vector and the angular momentum of light
The usual description in basic electromagnetic theory of the linear and angular momenta of light is centred upon the identification of Poynting's vector as the linear momentum density and its cross product with position, or azimuthal component, as the angular momentum density. This seemingly reasonable approach brings with it peculiarities, however, in particular with regards to the separation of angular momentum into orbital and spin contributions, which has sometimes been regarded as contrived. In the present paper, we observe that densities are not unique, which leads us to ask whether the usual description is, in fact, the most natural choice. To answer this, we adopt a fundamental rather than heuristic approach by first identifying appropriate symmetries of Maxwell's equations and subsequently applying Noether's theorem to obtain associated conservation laws. We do not arrive at the usual description. Rather, an equally acceptable one in which the relationship between linear and angular momenta is nevertheless more subtle and in which orbital and spin contributions emerge separately and with transparent forms
Negative experimental evidence for magneto-orbital dichroism - supplemental information
A light beam can carry both spin angular momentum (SAM) and orbital angular
momentum (OAM). SAM is commonly evidenced by circular dichroism (CD)
experiments {\em i. e.} differential absorption of left and right-handed
circularly polarized light. Recent experiments, supported by theoretical work,
indicate that the corresponding effect with OAM instead of SAM is not observed
in chiral matter.
Isotropic materials can show CD when subjected to a magnetic field (MCD). In
Ref. ~\onlinecite{Mathevet2012} we report a set of experiments, under well
defined conditions, searching for magnetic orbital dichroism (MOD),
differential absorption of light as a function of the sign of its OAM. We
experimentally demonstrate that this effect, if any, is smaller than a few
of MCD for the Nd:YAG transition.
This transition is essentially of electric dipole nature. We give an intuitive
argument suggesting that the lowest order of light matter interaction leading
to MOD is the electric quadrupole term.
We give here more experimental details and extra measurements.Comment: 6 pages, 7 figures. Supplemental material for a publication in Optics
Expres
Polarisation rotation of slow light with orbital angular momentum in ultracold atomic gases
We consider the propagation of slow light with an orbital angular momentum
(OAM) in a moving atomic medium. We have derived a general equation of motion
and applied it in analysing propagation of slow light with an OAM in a rotating
medium, such as a vortex lattice. We have shown that the OAM of slow light
manifests itself in a rotation of the polarisation plane of linearly polarised
light. To extract a pure rotational phase shift, we suggest to measure a
difference in the angle of the polarisation plane rotation by two consecutive
light beams with opposite OAM. The differential angle is
proportional to the rotation frequency of the medium
and the winding number of light, and is inversely proportional to the
group velocity of light. For slow light the angle should
be large enough to be detectable. The effect can be used as a tool for
measuring the rotation frequency of the medium.Comment: 5 pages, 1 figur
Analysis and Prediction of Energy Production in Concentrating Photovoltaic (CPV) Installations
A method for the prediction of Energy Production (EP) in Concentrating
Photovoltaic (CPV) installations is examined in this study. It presents a new method that
predicts EP by using Global Horizontal Irradiation (GHI) and the Photovoltaic
Geographical Information System (PVGIS) database, instead of Direct Normal Irradiation
(DNI) data, which are rarely recorded at most locations. EP at four Spanish CPV
installations is analyzed: two are based on silicon solar cells and the other two on
multi-junction III-V solar cells. The real EP is compared with the predicted EP. Two
methods for EP prediction are presented. In the first preliminary method, a monthly
Performance Ratio (PR) is used as an arbitrary constant value (75%) and an estimation of
the DNI. The DNI estimation is obtained from GHI measurements and the PVGIS
database. In the second method, a lineal model is proposed for the first time in this paper to
obtain the predicted EP from the estimated DNI. This lineal model is the regression line
that correlates the real monthly EP and the estimated DNI in 2009. This new method
implies that the monthly PR is variable. Using the new method, the difference between the
predicted and the real EP values is less than 2% for the annual EP and is in the range of
5.6%–16.1% for the monthly EP. The method that uses the variable monthly PR allows the
prediction of the EP with reasonable accuracy. It is therefore possible to predict the CPV
EP for any location, using only widely available GHI data and the PVGIS database
A three solar cell system based on a self-supporting, transparent AlGaAs top solar cell
Development of a three solar cell stack can lead to practical efficiencies greater than 30 percent (1x,AM0). A theoretical efficiency limitation of 43.7 percent at AM0 and one sun is predicted by this model. Including expected losses, a practical system efficiency of 36.8 percent is anticipated. These calculations are based on a 1.93eV/1.43eV/0.89eV energy band gap combination. AlGaAs/GaAs/GaInAsP materials can be used with a six-terminal wiring configuration. The key issues for multijunction solar cells are the top and middle solar cell performance and the sub-bandgap transparency. AstroPower has developed a technique to fabricate AlGaAs solar cells on rugged, self-supporting, transparent AlGaAs substrates. Top solar cell efficiencies greater than 11 percent AM0 have been achieved. State-of-the-art GaAs or InP devices will be used for the middle solar cell. GaInAsP will be used to fabricate the bottom solar cell. This material is lattice-matched to InP and offers a wide range of bandgaps for optimization of the three solar cell stack. Liquid phase epitaxy is being used to grow the quaternary material. Initial solar cells have shown open-circuit voltages of 462 mV for a bandgap of 0.92eV. Design rules for the multijunction three solar cell stack are discussed. The progress in the development of the self-supporting AlGaAs top solar cell and the GaInAsP bottom solar cell is presented
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