Absorption (electromagnetic radiation)

About: Absorption (electromagnetic radiation) is a research topic. Over the lifetime, 76674 publications have been published within this topic receiving 1381221 citations.

Performance Enhancement of the P3HT/PCBM Solar Cells through NIR Sensitization Using a Small-Bandgap Polymer

Abstract: All the attractive and benefi cial features of the organic materials such as their strong absorption coeffi cient and their ability to tailor the bandgap, have brought them into the center of attention for photovoltaic applications. Recently, a large number of organic solar cells with effi ciencies beyond 6% and up to 10% were reported, making this topic more and more promising. [ 1 − 10 ] However, there is still signifi cant room for development, especially with respect to research and development necessary to make highly performing organic solar cells ready for the market. One of the basic concerns of organic solar cells is related to the narrow absorption window of the organic conjugated polymers. Since organic conjugated polymers are dominantly molecular excitonic absorbers, their absorption spectrum is characterized by a few 100 nm width instead of the plateau absorption spectra as seen for inorganic materials. The importance of conjugated polymer’s narrow absorption window and its infl uence on the attainable power conversion effi ciency was

Near-infrared intersubband absorption in GaN/AlN quantum wells grown by molecular beam epitaxy

Abstract: GaN/AlN multiple-quantum-well structures were grown by molecular beam epitaxy. Abrupt interfaces and good periodicity were confirmed. Absorption measurements indicated that intersubband absorptions occurred at wavelengths of 1.3–2.2 μm. Spectral fits by Lorentzians suggested that the well thicknesses fluctuated by two monolayers. The linewidths of the individual fits were as narrow as 80–120 meV. The characteristics of the absorption saturation were investigated at a wavelength of 1.46 μm. A relaxation time of 400 fs and saturation energy density of 0.5 pJ/μm2 were obtained. These results are promising for realizing ultrafast optical switches with energy consumption of the picojoule order.

Natural dyes adsorbed on TiO2 nanowire for photovoltaic applications: enhanced light absorption and ultrafast electron injection.

Abstract: We investigate the electronic coupling between a TiO2 nanowire and a natural dye sensitizer, using state-of-the-art time-dependent first-principles calculations. The model dye molecule, cyanidin, is deprotonated into the quinonoidal form upon adsorption on the wire surface. This results in its highest occupied molecular orbital (HOMO) being located in the middle of the TiO2 bandgap and its lowest unoccupied molecular orbital (LUMO) being close to the TiO2 conduction band minimum (CBM), leading to greatly enhanced visible light absorption with two prominent peaks at 480 and 650 nm. We find that excited electrons are injected into the TiO2 conduction band within a time scale of 50 fs with negligible electron-hole recombination and energy dissipation, even though the dye LUMO is located 0.1-0.3 eV lower than the CBM of the TiO2 nanowire.

Models for Spectral Band Absorption

Abstract: An exhaustive, theoretical study is made of the various models that have been proposed to represent band absorption. These models are compared with each other; a derivation is given of the regions where they predict the same absorption. The regions of validity for various useful approximations to these models are also given. The statistical model is extended to include the random superposition of a finite number of Elsasser bands. Thus a continuous spectrum of absorption curves is obtained between the results for the Elsasser and the pure statistical models. The absorption predicted by the statistical model when there is a specific number of spectral lines in the frequency interval under consideration is compared with the limit as the number of lines approaches infinity. It is shown that the shape of the absorption curve obtained from the statistical model is independent of the distribution of line intensities in the band for most cases of interest. The absorption from the statistical model including the effects of overlapping is shown to depend only on an average equivalent width for a single line. This result is used to derive the band absorption for the statistical model with Lorentz, Doppler, and other line shapes.

QSO Metal Absorption Systems at High Redshift and the Signature of Hierarchical Galaxy Formation

Abstract: In a hierarchical cosmogony, galaxies build up by continuous merging of smaller structures. At z = 3, the matter content of a typical present-day galaxy is dispersed over several individual clumps embedded in sheetlike structures, often aligned along filaments. We have used hydrodynamical simulations to investigate the spatial distribution and absorption properties of metal-enriched gas in such regions of ongoing galaxy formation. The metal and hydrogen absorption features produced by the collapsing structures closely resemble observed QSO absorption systems over a wide range in H I column density. Strong C II and Si IV absorption occurs for lines of sight passing the densest regions close to the center of the protogalactic clumps, while C IV is a good tracer of the prominent filamentary structures and O VI becomes the strongest absorption feature for lines of sight passing through low-density regions far away from fully collapsed objects. The observed column density ratios of the different ionic species at z = 3 can be well reproduced if a mean metallicity [Z/H] = -2.5, relative abundances as found in metal-poor stars, a UV background with intensity J-22 = 3 at the Lyman limit, and either a power-law spectrum (J ∝ ν-1.5) or the spectral shape proposed by Haardt & Madau are assumed. The observed scatter in [C/H] is about a magnitude larger than that in the simulations, which suggests an inhomogeneous metal distribution. Observed and simulated Doppler parameter distributions of H I and C IV absorption lines are in good agreement, which indicates that shock heating due to gravitational collapse is a second important heating agent in addition to photoionization heating. The large velocity spreads seen in some C IV systems may be due to the occasional alignments of the observer's line of sight with expanding large-scale filaments. Both high-ionization multicomponent heavy-element absorbers and damped Lyα systems can arise from groups of moderately sized protogalactic clumps (Mbaryon ~ 109 M☉). Recent detections of star-forming galaxies at similar redshifts are consistent with this picture.