I started my PhD, within the theory group of the Max Planck Institute for Polymer research, in
July 2016. My focus is currently on development of the Kinetic Monte Carlo algorithm, for electronic processes
I obtained my Master of Science degree, in Molecular science, at the Friedrich-Alexander-University of Erlangen-Nuernberg, in 2015. My Master thesis was carried out at the Max Planck Institute for the science of light, in Erlangen. The focus of the thesis was a computational investigation of a
composite nanostructured semiconductor, for the use as a water splitting photocatalyst.
I received my Bachelor of Science (Honours) in chemistry, from the University of Glasgow in 2011.
My Bachelor thesis was concentrated within the area of computational chemistry, namely the
comparison of canonical and local electron correlation descriptions, when considering small
Published in the group
Density of states of OLED hosts from thermally stimulated luminescence
A. Stankevych, A. Vakhnin, D. Andrienko, L. Paterson, I. I. Fishchuk, H. Baessler, A. Koehler, A. Kadashchuk
We have applied the low-temperature fractional thermally stimulated luminescence (TSL) technique to determine the electronic densities of states (DOS) of pristine amorphous films of OLED host materials. The DOS width is determined for two series of hosts namely (i) carbazole-biphenyl (CBP) derivatives: CBP mCBP and mCBP-CN and (ii) carbazole-phenyl (CP) derivatives: mCP and mCP-CN. TSL originates from radiative recombination of charge-carriers thermally released from the lower energy part of the intrinsic DOS that causes charge trapping at very low temperatures. We find that the intrinsic DOS can be approximated by a Gaussian distribution with a deep exponential tail accompanying this distribution in CBP and mCBP films. The DOS profile broadens with increasing molecular dipole moments varying from 0 to 6 Debye in a similar manner within each series in line with the dipolar disorder model. The same molecular dipole moment however leads to a broader DOS of CP compared to CBP derivatives. Using computer simulations we attribute the difference between the series to a smaller polarizability of cations in CP-derivatives leading to weaker screening of the electrostatic disorder by induction.
Computer aided design of stable and efficient OLEDs
L. Paterson, F. May, D. Andrienko
J. Appl. Phys.,
Organic light emitting diodes (OLEDs) offer a unique alternative to traditional display technologies. Tailored device architecture can offer properties such as flexibility and transparency presenting unparalleled application possibilities. The commercial advancement of OLEDs is highly anticipated and continued research is vital for improving device efficiency and lifetime. The performance of an OLED relies on an intricate balance between stability efficiency operational driving voltage and colour coordinate with the aim of optimising these parameters by employing appropriate material design. Multiscale simulation techniques can aid with the rational design of these materials in order to overcome existing shortcomings. For example extensive research has focused on the emissive layer and the obstacles surrounding blue OLEDs in particular; namely the trade-off between stability and efficiency while preserving blue emission. More generally due to the vast number of contending organic materials and with experimental pre-screening being notoriously time-consuming a complementary in silico approach can be considerably beneficial. The ultimate goal of simulations is the prediction of microscopic device properties from chemical composition prior to synthesis. However various challenges must be overcome to bring this to a realisation some of which are discussed in this perspective. Computer aided design is becoming an essential component to future OLED developments and with the field shifting towards machine-learning-based approaches in silico pre-screening is the future of material design.
Perspectives of Unicoloured Phosphor-sensitised Fluorescence (UPSF)
L. Paterson, A. Mondal, P. Heimel, R. Lovrincic, F. May, C. Lennartz, D. Andrienko
Adv. Electron. Mater.,
Unicoloured phosphor-sensitised fluorescence (UPSF) is a dual emitting concept proposed for improving efficiencies and operational lifetimes of blue organic light emitting diodes (OLEDs). To overcome the limitations of the individual emitters it uses a phosphorescent donor to sensitise a fluorescent acceptor. To quantify the potential of the concept we develop a multiscale model of a UPSF OLED. We start from atomistic morphologies parameterise the rates of all processes on the available experimental data and solve the respective master equation with the help of the kinetic Monte Carlo algorithm. Our simulations show that the energy transfer between donor molecules is essential to reproduce the results of the time-resolved photoluminescence experiment. We then expand the scope of experiment by studying the effect of the acceptor concentration as well as Förster and (parasitic) Dexter energy transfer from the donor to acceptor on the characteristics of the UPSF OLED. Our study shows that an appropriate material design can further improve efficiency by more than 30\% and at the same time achieve radiative decay times below 0.02 µs thus significantly extending OLED operational lifetime.