28 research outputs found
Performance Analysis of Ultrathin Cu(In,Ga)Se2 Solar Cells with Backwall Superstrate Configuration Using AMPS-1D
This study used AMPS-1D to peform numerical simulations and model the behavior of back-wall superstrate solar cells based on Cu(In,Ga)Se2 (CIGS) thin films to investigate optimal conditions and obtain maximum efficiency. The effects of absorber thickness and density of interface defects were examined along with the work function of the transparent conductive oxide (WTCO) to investigate their influence on the output parameters. Measurements of device performance (J-V) and Quantum Efficiency (QE) showed that the performance of the cell improved as the thickness of the CIGS layer decreased because photons were absorbed near the junction. The device achieved an efficiency of 16.4% using an optimal thickness for the CIGS layer on the order of 0.3µm, defect densities in the range of 1013-1015cm-3, doping concentration of the n-TCO back contact on the order of 1019cm-3, and WTCO in the range of 4.5-5.2eV. These results show that the generated electron-hole pairs had a high probability of separation and demonstrate the potential of this device structure
Exchange energies in CoFeB/Ru/CoFeB Synthetic Antiferromagnets
The interlayer exchange coupling confers specific properties to Synthetic
Antiferromagnets that make them suitable for several applications of
spintronics. The efficient use of this magnetic configuration requires an
in-depth understanding of the magnetic properties and their correlation with
the material structure. Here we establish a reliable procedure to quantify the
interlayer exchange coupling and the intralayer exchange stiffness in synthetic
antiferromagnets; we apply it to the ultrasmooth and amorphous
CoFeB (5-40 nm)/Ru/ CoFeB material
platform. The complex interplay between the two exchange interactions results
in a gradient of the magnetization orientation across the thickness of the
stack which alters the hysteresis and the spin wave eigenmodes of the stack in
a non trivial way. We measured the field-dependence of the frequencies of the
first four spin waves confined within the thickness of the stack. We modeled
these frequencies and the corresponding thickness profiles of these spin waves
using micromagnetic simulations. The comparison with the experimental results
allows to deduce the magnetic parameters that best account for the sample
behavior. The exchange stiffness is established to be 16 2 pJ/m,
independently of the CoFeB thickness. The interlayer
exchange coupling starts from -1.7 mJ/m for the thinnest layers and it can
be maintained above -1.3 mJ/m for CoFeB layers as thick as 40 nm. The
comparison of our method with earlier characterizations using the sole
saturation fields argues for a need to revisit the tabulated values of
interlayer exchange coupling in thick synthetic antiferromagnets
Inducing or suppressing the anisotropy in multilayers based on CoFeB
Controlling the uniaxial magnetic anisotropy is of practical interest to a
wide variety of applications. We study CoFeB single films
grown on various crystalline orientations of LiNbO substrates and on
oxidized silicon. We identify the annealing conditions that are appropriate to
induce or suppress uniaxial anisotropy. Anisotropy fields can be increased by
annealing up to 11 mT when using substrates with anisotropic surfaces. They can
be decreased to below 1 mT when using isotropic surfaces. In the first case,
the observed increase of the anisotropy originates from the biaxial strain in
the film caused by the anisotropic thermal contraction of the substrate when
back at room temperature after strain relaxation during annealing. In the
second case, anisotropy is progressively removed by applying successive
orthogonal fields that are assumed to progressively suppress any chemical
ordering within the magnetic film. The method can be applied to CoFeB/Ru/CoFeB
synthetic antiferromagnets but the tuning of the anisotropy comes with a
decrease of the interlayer exchange coupling and a drastic change of the
exchange stiffness
Unidirectionality of spin waves in Synthetic Antiferromagnets
We study the frequency non-reciprocity of the spin waves in symmetric
CoFeB/Ru/CoFeB synthetic antiferromagnets stacks set in the scissors state by
in-plane applied fields. Using a combination of Brillouin Light Scattering and
propagating spin wave spectroscopy experiments, we show that the acoustical
spin waves in synthetic antiferromagnets possess a unique feature if their
wavevector is parallel to the applied field: the frequency non-reciprocity can
be so large that the acoustical spin waves transfer energy in a unidirectional
manner for a wide and bipolar interval of wavevectors. Analytical modeling and
full micromagnetic calculations are conducted to account for the dispersion
relations of the optical and acoustical spin waves for arbitrary field
orientations. Our formalism provides a simple and direct method to understand
and design devices harnessing propagating spin waves in synthetic
antiferromagnets
Measuring a population of spin waves from the electrical noise of an inductively coupled antenna
We study how a population of spin waves can be characterized from the
analysis of the electrical microwave noise delivered by an inductive antenna
placed in its vicinity. The measurements are conducted on a synthetic
antiferromagnetic thin stripe covered by a micron-sized antenna that feeds a
spectrum analyser after amplification. The antenna noise contains two
contributions. The population of incoherent spin waves generates a fluctuating
field that is sensed by the antenna: this is the "magnon noise". The antenna
noise also contains the contribution of the electronic fluctuations: the
Johnson-Nyquist noise. The latter depends on all impedances within the
measurement circuit; this includes the antenna self-inductance. As a result,
the electronic noise contains information about the magnetic susceptibility,
though it does not inform on the absolute amplitude of the magnetic
fluctuations. For micrometer-sized systems at thermal equilibrium, the
electronic noise dominates and the pure magnon noise cannot be determined. If
in contrast the spinwave bath is not at thermal equilibrium with the
measurement circuit, and if the spinwave population can be changed then one
could measure a mode-resolved effective magnon temperature provided specific
precautions are implemented
Selective emitters diffusion using an air belt furnace
A new and simple process for the selective emitter realization was developed
on multicrystalline silicon wafers. This material is in competition with
single-crystal silicon since it is able to lead to similar performances with
a reduction in the cost of solar cell realization.
This work is centred on the study of emitter area of a photovoltaic cell and
the possibilities to obtain a selective emitter in only one step while
avoiding the use of chemicals.
This would make substantial economies on the rejections treatment which
became a capital environmental factor. A structure with selective emitter
consists of a heavy doping under the metallic contacts, leaving weak the
surface concentration between the grid lines.
This allows a good surface passivation while keeping a good contact
resistance for screen printed lines.
The advantages of such a structure could be observed by quantum efficiency
measurements yield where the benefit appears in the UV-VIS range of the
solar spectrum
One-Step Chemiluminescent Assay for Hydrogen Peroxide Analysis in Water
The detection of hydrogen peroxide is of great importance in the environmental field. For this, a homogeneous technique has been developed here for sensitive and rapid quantification of hydrogen peroxide. In this technique, hemoglobin was used as a bioreceptor, where heme groups acted as electroactive centers to catalyze hydrogen peroxide reduction. The chemiluminescence reagent luminol is also a peroxidase substrate and can be oxidized by hemoglobin—thus generating a CL signal. The principle of the designed biosensor was based on the competition between hydrogen peroxide and luminol towards hemoglobin. Under optimized conditions, the chemiluminescent signal decreased with increasing hemoglobin concentrations within the linear range of 0.5 to 12 mM, with a correlation coefficient R2 of 0.99762. The limit of detection was calculated to be as low as 0.308 mM. The selectivity of the biosensor was successfully demonstrated against different interferents. The developed strategy provides a one step, simple, and low-cost bioanalytical method which can be applied for the monitoring of other peroxidase substrates