Article

Kramers-Kronig relations in optical data inversion.

Physical review. B, Condensed matter (Impact Factor: 3.66). 11/1991; 44(15):8301-8303. DOI: 10.1103/PhysRevB.44.8301
Source: PubMed

ABSTRACT Some remarks are made on the use of Kramers-Kronig relations in optical data inversion. It is shown that symmetry relations imposed on the optical constant should be taken into account when modeling the tails of the absorption and extinction curves.

1 Follower
 · 
78 Views
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Organic solar cells (OSCs) combine the advantages of low-cost and large-area fabrication with the use of nonhazardous and environmentally friendly materials. Over the last few years, power conversion efficiencies improved continuously, now exceeding 10% in single-junction solar cells. Improvements often originated from the synthesis of new absorber materials that allowed for an enhanced spectral coverage of the solar spectrum or enabled higher internal quantum efficiencies. In the lab, screening and optimization of new materials and cell architectures often follow a trial and error approach, although only very little amounts of material are available.An alternative and material saving route to optimized OSCs is a comprehensive optoelectronic device simulation that reduces the experimental parameter space. This becomes particularly important for sophisticated device architectures, such as tandem solar cells. However, in order to carry out meaningful optical simulations, a profound knowledge of the refractive indices is mandatory.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kramers-Kronig analysis is commonly used to estimate the optical properties of new materials. The analysis typically uses data from far infrared through near ultraviolet (say, 40--40,000 cm$^{-1}$ or 5 mev--5 eV) and uses extrapolations outside the measured range. Most high-frequency extrapolations use a power law, 1/$\omega^n$, transitioning to $1/\omega^{4}$ at a considerably higher frequency and continuing this free-carrier extension to infinity. The mid-range power law is adjusted to match the slope of the data and to give pleasing curves, but the choice of power (usually between 0.5 and 3) is arbitrary. Instead of an arbitrary power law, it is is better to use X-ray atomic scattering functions such as those presented by Henke and co-workers. These basically treat the solid as a linear combinations of its atomic constituents and, knowing the chemical formula and the density, allow the computation of dielectric function, reflectivity, and other optical functions. The "Henke reflectivity" can be used over photon energies of 10 eV--34 keV, after which a $1/\omega^{4}$ continuation is perfectly fine. The bridge between experimental data and the Henke reflectivity as well as two corrections that needed to be made to the latter are discussed.
    Physical Review B 11/2014; 91(3). DOI:10.1103/PhysRevB.91.035123 · 3.66 Impact Factor

Full-text

Download
5 Downloads
Available from
Nov 5, 2014