Analysis of the emission profile in organic light-emitting devices

Abstract

In this paper, numerical algorithms for extraction of optoelectronic material and device parameters in organic light-emitting devices (OLEDs) are presented and tested for their practical use. Of particular interest is the extraction of the emission profile and the source spectrum. A linear and a nonlinear fitting method are presented and applied to emission spectra from OLEDs in order to determine the shape of the emission profile and source spectrum. The motivation of the work is that despite the existence of advanced numerical models for optical and electronic simulation of OLEDs, their practical use is limited if methods for the extraction of model parameters are not well established. Two fitting methods are presented and compared to each other and validated on the basis of consistency checks. Our investigations show the impact of the algorithms on the analysis of realistic OLED structures. It is shown that both fitting methods p form reasonably well, even if the emission spectra to be analyzed are noisy. In some cases the nonlinear method performs slightly better and can achieve a perfect resolution of the emission profile. However, the linear method provides the advantage that no assumption on the mathematical shape of the emission profile has to be made.

Numerical analysis of exciton dynamics in organic light-emitting devices and solar cells

“…5(a) we determine such profiles by an optical inverse outcoupling algorithm. 6,7 This method is implemented in SETFOS and is based on a weighting of the different emission contributions for dipoles located at various positions in the layer. The energy dissipation into evanescently coupled modes is also considered.…”

“…The method is suitable for extracting a single or multiple emission zones from spectral and/or angular emission measurements. 7 We reported an extension of this method in Ref. 8, which takes an additional weighting into account based on the position-dependent dynamics of the emissive dipoles.…”

Analytical estimation of emission zone mean position and width in organic light-emitting diodes from emission pattern image-source interference fringes

“…3,14 Indeed, in the last couple of years numerous authors have presented methods to recover EZ properties from a variety of optical measurements, such as electroluminescence (EL) spectra, emission patterns, external efficiencies, and photoluminescence lifetimes. 12,[15][16][17][18][19][20][21] These methods heavily utilize fitting procedures, which may yield highly resolved evaluation, however, usually require extensive data sets, and naturally rely on advanced numerical techniques, which tend to obscure the underlying physical phenomena. 19,22,23 In recent work, we have presented a different approach to this problem, developing analytical closed-form formulae to extract the emission zone location from measured emission pattern extrema, assuming the excitons are concentrated in a very narrow region.…”

Spatial resolution of methods for measuring the light-emission profile in organic light-emitting diodes

“…The light-emission profile can also be obtained from an analysis of measured spectral intensities. [9][10][11][12][13][14][15][16][17][18]20 We recently proposed a comprehensive novel approach to solve this "inverse outcoupling problem." 20 Crucial elements are (i) the use of the full angular and polarization dependent emission spectra, extracted using a glass hemisphere, (ii) the use of a combined classical and quantum-mechanical microcavity model for properly treating the radiative decay probability and light-outcoupling efficiency, and (iii) the use of a flexible and problem-specific fit function describing the profile.…”

“…13 A different approach, allowing more flexibility in the profile shape, involves the use of a dense set of dipoles distributed uniformly across the emitting layer. [17][18][19] In Refs. 18 and 19, the contribution of the ensemble of dipoles is regularized, leading to a more smooth light emission profile.…”