Modeling of organic light-emitting diodes: from molecule to device (MODEOLED)

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The project MODEOLED involves a transnational academic-industrial collaboration between two Dutch and two German groups active in research on white organic light-emitting diodes (OLEDs). Present-day white OLEDs for high-efficiency lighting applications consist of stacked layers of different organic molecules, where each layer has a specific function. Highly positively and negatively doped injection layers contacted by electrodes inject holes and electrons, which move into the stack and meet to form excitons. In special emissive organic layers for the three primary colors, often doped with phosphorescent dyes, the excitons decay radiatively under emission of a photon which ideally should have a broad and balanced emission spectrum. Presently, the design of white OLEDs proceeds by trial and error. The goal of MODEOLED is to develop and apply predictive modeling to predict the properties of white OLEDs solely on the basis of the molecular structure of the specific materials and processing methods. This will lead to rational design strategies of white OLEDs and OLED materials leading to improved understanding and significant reduction in R&D cost for developers.A multi-scale modeling approach will be followed, where each group brings in a specific expertise. The approach starts with determining the microscopic morphology of the materials with Monte-Carlo modeling (expertise of KIT). Next, the reorganization energies related to the excitation of molecules by charges and excitons and the inter-molecular transfer integrals of these excitations will be calculated by Quantum-Chemistry methods (expertise of BASF). This information will be used in large-scale Monte-Carlo simulations of the motion and interaction of charges and excitons in application-relevant white multilayer OLEDs (expertise of EUT). The predicted current-voltage characteristics and light-emission profiles within the OLED stack will be verified experimentally (expertise of Philips). The comparison will lead to a critical evaluation and improvement of the predictive power of the modeling. The scientific questions will focus on the excitonic processes in the doped emissive layers (motion of excitons, and exciton-exciton as well as exciton-charge interactions) and on the working of the doped injection layers, i.e. on key processes in the most complex materials included in OLEDs.