Selfconsistent Model of Photoconversion Efficiency for Multijunction Solar Cells

To accurately calculate efficiencies $\eta$ of experimentally produced multijunction solar cells (MJSCs) and optimize their parameters, we offer semi-analytical photoconversion formalism that incorporates radiative recombination, Shockley-Read-Hall (SRH) recombination, surface recombination at the front and back surfaces of the cells, recombination in the space charge region (SCR) and the recombination at the heterojunction boundaries. Selfconsistent balance between the MJSC temperature and efficiency was imposed by jointly solving the equations for the photocurrent, photovoltage, and heat balance. Finally, we incorporate into the formalism the effect of additional photocurrent decrease with subcell number increase. It is shown that for an experimentally observed Shockley-Read-Hall lifetimes, the effect of re-absorption and re-emission of photons on MJSC efficiency can be neglected for non-concentrated radiation conditions. A significant efficiency $\eta$ increase can be achieved by improving the heat dissipation using radiators and bringing the MJSC emissivity to unity, that is closer to black body radiation rather than grey body radiation. Our calculated efficiencies compare well with other numerical results available and are consistent with the experimentally achieved efficiencies. The formalism can be used to optimize parameters of MJSCs for maximum photoconversion efficiency.Comment: 40th IEEE Photovoltaic Specialists Conference, June 8-13, 2014, Denver, Colorado, III-V Epitaxy and Solar Cells, F30 16

First-principles calculation of the temperature dependence of the optical response of bulk GaAs

A novel approach has been developed to calculate the temperature dependence of the optical response of a semiconductor. The dielectric function is averaged over several thermally perturbed configurations that are extracted from molecular dynamic simulations. The calculated temperature dependence of the imaginary part of the dielectric function of GaAs is presented in the range from 0 to 700 K. This approach that explicitly takes into account lattice vibrations describes well the observed thermally-induced energy shifts and broadening of the dielectric function.Comment: 6 pages, 3 figure

Ab initio optical properties of Si(100)

We compute the linear optical properties of different reconstructions of the clean and hydrogenated Si(100) surface within DFT-LDA, using norm-conserving pseudopotentials. The equilibrium atomic geometries of the surfaces, determined from self-consistent total energy calculations within the Car-Parrinello scheme, strongly influence Reflectance Anisotropy Spectra (RAS), showing differences between the p(2x2) and c(4x2)reconstructions. The Differential Reflectivity spectrum for the c(4x2) reconstruction shows a positive peak at energies < 1 eV, in agreement with experimental results.Comment: fig. 2 correcte

Adsorption of benzene on Si(100) from first principles

Adsorption of benzene on the Si(100) surface is studied from first principles. We find that the most stable configuration is a tetra-$\sigma$-bonded structure characterized by one C-C double bond and four C-Si bonds. A similar structure, obtained by rotating the benzene molecule by 90 degrees, lies slightly higher in energy. However, rather narrow wells on the potential energy surface characterize these adsorption configurations. A benzene molecule impinging on the Si surface is most likely to be adsorbed in one of three different di-$\sigma$-bonded, metastable structures, characterized by two C-Si bonds, and eventually converts into the lowest-energy configurations. These results are consistent with recent experiments.Comment: 4 pages, RevTex, 2 PostScript gzipped figure