Optical constants (n, k) extraction from R, T measurements in organic thin film

Abstract

International audienceseveral 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 spectrophotometricmeasurements, such as ellipsometry [2] and reflectance and transmittance [3]. The real challenge forboth techniques is the n and k extraction from measurements, especially when n and k are potentiallyof the same order of magnitude, and/or strongly varying with the wavelength, as in most organicmaterials used in OPV [4]. Indeed, for these materials, the simplest extraction techniques cannot beused. The ‘envelope’ method [5] for example is limited to low absorbing materials. Moreover, multiwavelengthapproaches 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, abrute-force numerical inversion method has to be use to deduce (n,k) from measurements, which isknown to lead to multiple solutions [7], requiring additional information to select the true (n,k) valuefrom all multiple solutions.The aim of this paper is to propose an original and complete methodology to extract n and k from R, Tmeasurements without making any a-priori assumption

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Last time updated on 12/11/2016

This paper was published in HAL-UJM.

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