Optical constants (n, k) extraction from R, T measurements in organic thin film
Résumé
several layers of organic materials, typically requires an accurate determination of optical constants
(n,k) [1]. Several approaches have been proposed to this aim, mostly using spectrophotometric
measurements, such as ellipsometry [2] and reflectance and transmittance [3]. The real challenge for
both techniques is the n and k extraction from measurements, especially when n and k are potentially
of the same order of magnitude, and/or strongly varying with the wavelength, as in most organic
materials used in OPV [4]. Indeed, for these materials, the simplest extraction techniques cannot be
used. The ‘envelope’ method [5] for example is limited to low absorbing materials. Moreover, multiwavelength
approaches usually require to know a-priori an equation for the dispersion model ([6])
(Cauchy equations, Sellmeier relations or a limited number of Lorentz oscillators). In consequence, a
brute-force numerical inversion method has to be use to deduce (n,k) from measurements, which is
known to lead to multiple solutions [7], requiring additional information to select the true (n,k) value
from all multiple solutions.
The aim of this paper is to propose an original and complete methodology to extract n and k from R, T
measurements without making any a-priori assumption.
Origine : Fichiers produits par l'(les) auteur(s)
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