Accurate and fast modeling of opto-electronic processes in organic light-emitting diodes

February 7, 2024

Mahyar Taherpour defends his PhD thesis at the Department of Applied Physics and Science Education/Department of Chemical Engineering and Chemistry on February 8th.

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For his PhD thesis, Mahyar Taherpour looked at ways to enhance modeling techniques to investigate optoelectronic processes in organic light-emitting diodes (OLEDs), with a specific emphasis on second-generation OLEDs that utilize phosphorescent emitters. The main objective of the research was to improve the accuracy and efficiency of master equation (ME) and kinetic Monte Carlo (KMC) methods, offering viable alternatives to current modeling techniques.

As part of the research, Mahyar Taherpour considered exciton diffusion and generation, triplet-triplet annihilation (TTA), triplet-polaron quenching (TPQ), and the transport of charges within the phosphorescent emission layers of OLEDs.

Foundations

He started by looking at the foundational principles necessary for understanding the newly developed methodologies, as well as modeling optoelectronic processes such as TTA, TPQ, exciton diffusion and generation, and charge transport, employing the ME approach.

Following this, he established a new method and performed a mathematical analysis of a potential improvement of the standard KMC method to achieve greater accuracy and reduced computational time. This method is called multiverse kinetic Monte Carlo (MKMC).

Organic emission layers

Next, a novel ME modeling technique was used to describe Förster-type TTA among emitter molecules in organic emission layers, showcasing the accuracy of the approach against KMC simulations. The methodology significantly decreases computational time while providing comparable precision, shedding light on the role of positional triplet correlations.

The approach was then extended to a simplified model for TPQ, demonstrating accurate results compared to KMC simulations and significantly faster computational speeds.

Charge transport

Thereafter, Taherpour applied the ME methods to model charge transport, analyzing scenarios with on-site and long-range Coulomb interactions between charges. He identified conditions where the positional correlation between charges becomes pivotal and marks progress toward simulating charge transport with Coulomb interactions.

This component of the work serves as a first step toward developing a more generally applicable method to simulate charge transport using the ME approach, including Coulomb interactions.

Processes

Finally, Taherpour used the MKMC method to investigate various processes within OLEDs, such as charge transport with and without Coulomb interactions, exciton diffusion, and TTA. This showcased how accuracy in calculated quantities can be enhanced, reducing simulation times considerably without significant computational overhead.

Title of PhD thesis: Accurate and fast modeling of opto-electronic processes in organic light-emitting diodes: From master equation to multiverse kinetic Monte Carlo modelling. Supervisors: Peter Bobbert and Reinder Coehoorn.