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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - MOSTOPHOS (Modelling stability of organic phosphorescent light-emitting diodes)

Teaser

Summary

The lifetime, reliability, and efficiency of organic light emitting diodes (OLED) are critical factors precluding a number of novel devices from entering the market.Yet, these stability issues of OLEDs are poorly understood due to their notorious complexity, since multiple degradation and failure channels are possible at different length- and timescales. Current experimental and theoretical models of OLED stability are, to a large extent, empirical. They do not include information about the molecular and meso-scales, which prevents their integration into the workflow of the industrial R&D compound design. It is the idea of this project to integrate various levels of theoretical materials characterization into a single software package, to streamline the research workflows in order for the calculations to be truly usable by materials engineers, complementary to experimental measurements. Towards this goal, this project brings together the academic and industrial expertise of the leading experimental and theoretical groups in the field of organic semiconductors. MOSTOPHOS addresses the problem of stability of blue emitting organic LEDs based on phosphorescent dyes in order to achieve all-organic white sources for lighting. The challenge of the project is to provide a theoretical understanding of the dominant degradation mechanisms, that are at the basis of possible improvements. The impact of MOSTOPHOS is not limited to potential innovation in materials. Being primarily a theoretical effort, the project aims at considerably deepening the insights into the microscopic processes at the basis of OLEDs functioning, from a more fundamental level, strongly pushing forward the state-of-art of analysis tools available to the scientific community and to the industry.

Work performed

To this end, both static and polarizable force-fields were developed for the host, phosphorescent guest, and dopant (MPIP). CNR-ISMN has progressed in the modeling of ITO substrate -- towards simulations of ITO/DPBIC interface. BASF has transferred models from former simulation work into the MOSTOPHOS framework and provided compounds for the experimental characterization by TUD. At UPV, two directions were pursued: (1) calculation of exciton transfer rates and (2) analysis of chemical degradation reactions upon exciton transfer. TUE started work on theoretical description of triplet diffusion in a-NPD and TCTA using microscopically calculated morphologies and transfer integrals and an experimental study of triplet-triplet annihilation in CBP:Ir(ppy)3 and TCTA:Ir(ppy)3 with transient photoluminescence. UTV started to develop a continuum model for the macroscopic simulation of OLED including exciton transport and a simplified model has been used to simulate the bilayer aNPD/Alq3 device. TUD has repeated experiments performed at BASF with the BASF materials and achieved similar life-times but slightly lower efficiencies of OLEDs. Sim4tec activities included preparation of the test and measurement tool ``Organic Material Analyzer\'\' (OMA). COSMOlogic has performed general software layout and workflow planning identification of modules, tools, and interfaces, extended the molecular viewer COSMOview for the visualization of large molecules profiling and removing bottlenecks visualization of gro (gromacs) files.

Final results

During the M18 meeting a presentation was given by Prof. Coehoorn with the industrial view and status in the field of OLED. The involvement of two new industrial partners, OSRAM-OLED and FLUXiM, ensures that the consortium is paying strong attention on the impacts of the project. In this respect, OSRAM will help in the definition of a more detailed exploitation plan. Several large European industries related to materials synthesis are impacted by the results of the project, such as MERCK, SAES Getters, CYNORA or Novaled. What will be developed within MOSTOPHOS is also not limited to phosphorescent OLEDs but, with small changes, the software can be adapted to analyze other OLED technologies based on small molecules. For instance it can be applied to other competing technologies for efficient blue light emitting sources such as Thermally Activated Delayed Fluorescence compounds developed at CYNORA.

An International workshop is organized by MOSTOPHOS and EXTMOS in Grenoble in 2017 (https://www.cecam.org/workshop-1383.html). The workshop will constitute one of the major network and training events of the project. Moreover, a summer school will also be organized by MOSTOPHOS researchers in Mittelwihr in 2017 (http://www.softmattergraduate.uni-freiburg.de/summerschool2017).

As part of the scientific output, MOSTOPHOS researchers produced in the first 18 months a total of 25 publications.