Simulating Next-Generation OLEDs

Thermally activated delayed fluorescence (TADF)-based organic LED (OLED) molecules retain the lightweight mechanical flexibility and inexpensive production of earlier generations of OLEDs, whilst being more environmentally friendly by avoiding their reliance on precious metals such as platinum1.

Electronic structure calculations which capture host-guest effects and thermal disorder at finite temperatures are required to optimise the use of TADF emitters in technologies such as low-energy lighting, wearable electronics and smartphones.

Density functional theory (DFT) methods have frequently been used to probe the electronic structure of OLED molecules, but novel device-realistic calculations necessitate the simulation of large ensembles of TADF molecules.

Such system scales cannot be accessed using 'traditional' DFT codes for which computation time scales cubically with the number of atoms2.

This project aims to develop workflows for the calculation of key design parameters for TADF-based devices, such as the singlet-triplet splitting, which use the cutting-edge DFT codes BigDFT3, MADNESS4 and MRChem5.

MADNESS and MRChem enable calculations up to a user-specified precision through adaptive resolution, whilst BigDFT facilitates the study of systems of sizes up to 1000s of atoms through the implementation of a linear-scaling DFT algorithm. All three tools efficiently exploit high-performance computing resources using parallelisation.

Large-scale calculations will help to bridge the lengthscale gap between quantum mechanical DFT-based OLED simulations and system sizes which are accessible experimentally2.

Thus, the workflows developed here will facilitate the interpretation of experimental data, such as X-ray photoelectron spectra for complex structures for which peak assignment using nearest-neighbour considerations is ineffective and comparison with reference spectra is challenging.

As such, this project will involve collaboration with experimentalists including Professor Anna Regoutz at the University of Oxford, as well as the developers of the DFT codes used, such as Professor Luca Frediani at UiT The Arctic University of Norway (MRChem) and Dr Luigi Genovese at CEA Grenoble (BigDFT).

First simulating the prototypical TADF emitter 2CzPN1 in the gas-phase, this project aims to explore a wide range of TADF emitters and the impacts of phase, environmental effects and conformational disorder on their efficiency.

The overall goal is to design a workflow for screening potential TADF emitters for their in-device efficiency, as well as optimising the design of devices using established TADF molecules.

This would help to enable the creation of more energy-efficient OLED devices, contributing to the worldwide drive towards environmentally friendly electronics.

Given its focus on study organic molecular systems using DFT, this project falls primarily within the EPSRC computational and theoretical chemistry research area.

However, as an interdisciplinary project, also spanning computational physics and materials science, the outputs of this project align with other EPSRC research areas.

Workflows for identifying and optimising the use of TADF emitters will contribute to research into materials for energy applications, whilst simulations of host-guest complexes will be of interest to synthetic supramolecular chemistry researchers. 1Uoyama et al., Nature, 492, 234-238 (2012) 2Ratcliff et al., WIREs Comput.

Mol.

Sci., 7(1), e1290 (2017) 3Genovese et al., Comptes Rendus Mécanique, 339(2-3), 149-164 (2011) 4Harrison et al., SIAM J. Sci. Comput., 38(5), 123-142 (2016) 5Wind et al., J. Chem. Theory Comput., 19(1), 137-146 (2023)