2,069 research outputs found
Modeling, synthesis, and characterization of thin film copper oxide for solar cells
The modeling, growth, and characterization of
Copper Oxide thin films for solar cell applications are
reported. Cu_2O has several attractive properties which
include its direct band gap (Eg=2.17 eV) for use in photoelectrolysis
of water and use in tandem multi-junction
cells. Detailed balance calculations predict efficiencies on
the order of 20% while Cu_2O cells have yet to even pass
2% efficiency. The device physics model reveals that
defects, particularly at the heterojunction interface, are the
main reason for lowered efficiencies. Epitaxial Cu_2O (100)
thin films on MgO are fabricated using RF Oxygen plasma
MBE. The films are quite smooth and showed mobilites in
the range of 10-100 cm^2/V*sec and carrier concentrations
in the range of 10^(14)-10^(17). Finally, the epitaxial growth of
Cu_2O on a MgO template is demonstrated
Increased cell efficiency in InGaAs thin film solar cells with dielectric and metal back reflectors
Compound single junction and multijunction solar
cells enable very high photovoltaic efficiencies by virtue of
employing different band gap materials in seriesconnected
tandem cells to access the full solar spectrum.
Researchers focused on improving the electrical properties
of solar cells by optimizing the material growth conditions,
however relatively little work to date has been devoted
to light trapping and enhanced absorption in III-V
compound solar cells using back reflectors. We studied
absorption enhancement in InGaAs and InGaAsP thin film
solar cells by means of numerical modeling. Flat dielectric
and metal back reflectors that might be introduced into the
solar cell via wafer-bonding, epitaxial lift-off or deposition
techniques have been shown to increase the short circuit
current and the photovoltaic efficiency of solar cells
Size-dependent oxygen-related electronic states in silicon nanocrystals
Silicon nanocrystals embedded in SiO2 were isolated with a selective etching procedure, and the isolated nanocrystals' excitonic emission energy was studied during controlled oxidation. Nanocrystals having initial diameters, d(0), of similar to 2.9-3.4 nm showed a photoluminescence (PL) blueshift upon oxidatively induced size reduction, as expected from models of quantum confinement. Oxidation of smaller Si nanocrystals (d(0)similar to 2.5-2.8 nm) also initially resulted in a PL blueshift, but a redshift in the PL was then observed after growth of similar to 0.3 monolayers of native oxide. This decrease in excitonic emission energy during oxidation is consistent with the theoretically predicted formation of an oxygen-related excitonic recombination state
Comparison of the device physics principles of planar and radial p-n junction nanorod solar cells
A device physics model has been developed for radial p-n junction nanorod solar cells, in which densely packed nanorods, each having a p-n junction in the radial direction, are oriented with the rod axis parallel to the incident light direction. High-aspect-ratio (length/diameter) nanorods allow the use of a sufficient thickness of material to obtain good optical absorption while simultaneously providing short collection lengths for excited carriers in a direction normal to the light absorption. The short collection lengths facilitate the efficient collection of photogenerated carriers in materials with low minority-carrier diffusion lengths. The modeling indicates that the design of the radial p-n junction nanorod device should provide large improvements in efficiency relative to a conventional planar geometry p-n junction solar cell, provided that two conditions are satisfied: (1) In a planar solar cell made from the same absorber material, the diffusion length of minority carriers must be too low to allow for extraction of most of the light-generated carriers in the absorber thickness needed to obtain full light absorption. (2) The rate of carrier recombination in the depletion region must not be too large (for silicon this means that the carrier lifetimes in the depletion region must be longer than ~10 ns). If only condition (1) is satisfied, the modeling indicates that the radial cell design will offer only modest improvements in efficiency relative to a conventional planar cell design. Application to Si and GaAs nanorod solar cells is also discussed in detail
Spectral tuning of plasmon-enhanced silicon quantum dot luminescence
In the presence of nanoscale silver island arrays, silicon quantum dots exhibit up to sevenfold luminescence enhancements at emission frequencies that correspond to the collective dipole plasmon resonance frequency of the Ag island array. Using electron-beam lithography to alter the pitch and particle diameter, this wavelength-selective enhancement can be varied as the metal array resonance wavelength is tuned from 600 to 900 nm. The luminescence intensity enhancement upon coupling is attributed to an increase in the radiative decay rate of the silicon quantum dots
Meson multiplicity in nucleus-nucleus collisions above 4 GeV/amu
Dependence of meson multiplicity on energy for 1486 cosmic ray nucleus-emulsion nucleus interactions is examined. Comparison is made to predictions of the Multi-Chain Model
Bicarbonate or Carbonate Processes for Coupling Carbon Dioxide Capture and Electrochemical Conversion
Designing a scalable system to capture CO₂ from the air and convert it into valuable chemicals, fuels, and materials could be transformational for mitigating climate change. Climate models predict that negative greenhouse gas emissions will be required by the year 2050 in order to stay below a 2 °C change in global temperature. The processes of CO₂ capture, CO₂ conversion, and finally product separation all require significant energy inputs; devising a system that simultaneously minimizes the energy required for all steps is an important challenge. To date, a variety of prototype or pilot-level CO₂ capture and/or conversion systems have been designed and built targeting the individual objectives of either capture or conversion. One approach has focused on CO₂ removal from the atmosphere and storage of pure pressurized CO₂. Other efforts have concentrated on CO₂ conversion processes, such as electrochemical reduction or fermentation. Only a few concepts or analyses have been developed for complete end-to-end processes that perform both CO₂ capture and transformation
Photoluminescence-based measurements of the energy gap and diffusion length of Zn_3P_2
The steady-state photoluminescence spectra of zinc phosphide (Zn_3P_2) wafers have revealed a fundamental indirect band gap at 1.38 eV, in close proximity to the direct band gap at 1.50 eV. These values are consistent with the values for the indirect and direct band gaps obtained from analysis of the complex dielectric function deduced from spectroscopic ellipsometric measurements. Bulk minority carrier lifetimes of 20 ns were observed by time-resolved photoluminescence decay measurements, implying minority-carrier diffusion lengths of ≥ 7 µm
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