In the OLED industry, materials and devices are often optimized independently, making the process time-consuming and expensive. To address this, we are developing a toolchain for parameter-free simulation-aided OLED design from molecule all the way up to device. In this toolchain, the molecular level properties are calculated using accurate quantum chemistry simulations in a realistic morphology. These nanoscale morphologies are then scaled to device-scale morphologies that can be used as input for the device level simulations. In this talk, we will show how this approach enables optimizing the molecular and stack properties simultaneously and ultimately can reduce time-to-market and costs.
An experimental and modelling study has been carried out of the current-voltage-luminance (J-V-L) characteristics of blue
polyfluorene-based organic light emitting devices, with a PEDOT:PSS anode and a Ba/Al cathode. The polymer contains copolymerized
hole transporting units that facilitate hole injection. The luminous efficacy for perpendicular emission as a
function of the voltage shows a pronounced peak; for an 80 nm thick device, it is equal to 3.3 cd/A at 8 V. At the peak
voltage, the external quantum efficiency is 2.2 %. We are working on a comprehensive device model that should provide a
framework within which these results can be understood, and present in this paper our intermediate results. Hole and electron
transport were studied using devices with a Au and Al cathode and anode, respectively. For hole-only devices a fair
description of the temperature and layer thickness dependent J-V curves could be obtained by using a 'conventional' model
for the mobility, involving a Poole-Frenkel factor for the field-dependence. For electron-only devices, the analysis is
complicated by the presence of an approximately 0.5 eV injection barrier. We have found a parametrization scheme that
provides a good description of the experimental J-V curves. A double carrier model that is based on the results of these
studies of single-carrier devices provides a good description of the J-V curves of double carrier devices. We have developed
a numerical model for the light outcoupling from the optical cavity. For the model parameters assumed, the calculated peak
position and shape of the lumunous efficacy as a function of V are in good agreement with the experimental results at room
temperature. An analysis is given of the factors that determine the peak height. We argue that a solid physical basis for the
model used to describe the electron injection and mobility is still lacking, so that continued electron transport studies will be
required.
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