I joined the theory group at the Max Planck Institute for Polymer Research (MPI-P) as a Postdoctoral fellow in October 2020. In my current research, I focus on the design of stable blue thermally activated delayed fluorescence organic molecules for organic light-emitting diodes (OLED) via virtual screening.
I obtained my Ph.D. in chemistry from École polytechnique fédérale de Lausanne (EPFL) in 2020, working in the group of Prof. Clémence Corminboeuf. During my Ph.D., my research interest lies in understanding the charge transport behaviors of organic semiconductors. In particular, I focused on revealing the structure-property-packing relationship of organic hole transport materials incorporated in perovskite solar cells. In addition, I participated in a wide variety of projects regarding aggregation-induced emission systems, DNA/carbon nanotubes interactions and the OLED host-dopant system. I received my master degree in materials science and engineering from National Taiwan University, under the supervision of Prof. Chin-Lung Kuo. During that time, I mainly focused on the lithiation mechanism of anode materials in lithium-ion batteries.
In June 2022 Kun-Han was appointed associate professor at the National Tsing Hua University.
2023
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Electronic coarse-graining of long conjugated molecules: Case study of non-fullerene acceptors
A. Zhugayevych, K.-H. Lin, D. Andrienko
J. Chem. Phys.,
159,
024107,
2023,
[doi]
[abstract]
By considering only one electronic state per molecule charge transport models of molecular solids neglect intramolecular charge transfer. This approximation excludes materials with quasi-degenerate spatially separated frontier orbitals such as non-fullerene acceptors (NFAs) and symmetric thermally activated delayed fluorescence emitters. By analyzing the electronic structure of room-temperature molecular conformers of a prototypical NFA ITIC-4F we conclude that the electron is localized on one of the two acceptor blocks with the mean intramolecular transfer integral of 120 meV which is comparable with intermolecular couplings. Therefore the minimal basis for acceptor–donor–acceptor (A–D–A) molecules consists of two molecular orbitals localized on the acceptor blocks. This basis is robust even with respect to geometry distortions in an amorphous solid in contrast to the basis of two lowest unoccupied canonical molecular orbitals withstanding only thermal fluctuations in a crystal. The charge carrier mobility can be underestimated by a factor of two when using single site approximation for A–D–A molecules in their typical crystalline packings.
Ambipolar charge transport in a non-fullerene acceptor
F. H. Hasenburg, K.-H. Lin, B. van der Zee, P. W. M. Blom, D. Andrienko, G.-J. A.H. Wetzelaer
APL Materials,
11,
021105,
2023,
[doi]
[abstract]
Charge transport is one of the key factors in the operation of organic solar cells. Here we investigate the electron and hole transport in the non-fullerene acceptor (NFA) IT-4F by a combination of space-charge-limited current measurements and multiscale molecular simulations. The electron and hole mobilities are fairly balanced amounting to 2.9 x 10-4 cm2 V-1 s-1 for electrons and 2.0 x 10-5 cm2 V-1 s-1 for holes. Orientational ordering and electronic couplings facilitate a better charge-percolating network for electrons than for holes while ambipolarity itself is due to sufficiently high electron affinity and low ionization energy typical for narrow-gap NFAs. Our findings provide a molecular-level understanding of balanced hole and electron transport in an archetypical NFA which may play a key role in exciton diffusion and photogenerated hole transfer in organic solar cells.
Elimination of Charge-Carrier Trapping by Molecular Design
O. Sachnik, X. Tan, C. Haese, N. Kinaret, K.-H. Lin, D. Andrienko, R. Graf, G.-J. A. H. Wetzelaer, J. J. Michels, Paul W. M. Blom
Nature Materials,
2023,
[doi]
2022
Virtual screening for organic solar cells and light emitting diodes
N. C. Forero-Martinez, K.-H. Lin, K. Kremer, D. Andrienko
Advanced Science,
2200825,
2022,
[doi]
[abstract]
The field of organic semiconductors is multifaceted and the potentially suitable molecular compounds are very diverse. Representative examples include discotic liquid crystals dye-sensitized solar cells conjugated polymers and graphene-based low-dimensional materials. This huge variety not only represents enormous challenges for synthesis but also for theory which aims at a comprehensive understanding and structuring of the plethora of possible compounds. Eventually computational methods should point to new better materials which have not yet been synthesized. In this perspective it is shown that the answer to this question rests upon the delicate balance between computational efficiency and accuracy of the methods used in the virtual screening. To illustrate the fundamentals of virtual screening chemical design of non-fullerene acceptors thermally activated delayed fluorescence emitters and nanographenes are discussed.
2021
Virtual screening of TADF emitters for single-layer OLEDs
K.-H. Lin, G.-J. A. H. Wetzelaer, P. W. M. Blom, D. Andrienko
Frontiers in Chemistry,
9,
2021,
[doi]
[abstract]
Thermally-activated delayed fluorescence (TADF) is a concept which helps to harvest triplet excitations boosting the efficiency of an organic light-emitting diode. TADF can be observed in molecules with spatially separated donor and acceptor groups with a reduced triplet-singlet energy level splitting. TADF materials with balanced electron and hole transport are attractive for realizing efficient single-layer organic light emitting diodes greatly simplifying their manufacturing and improving their stability. Our goal here is to computationally screen such materials and provide a comprehensive database of compounds with a range of emission wavelengths ionization energies and electron affinities.
Chemical design rules for non-fullerene acceptors in organic solar cells
A. Markina, K.-H. Lin, W. Liu, C. Poelking, Y. Firdaus, D. R. Villalva, J. I. Khan, S. H. K. Paleti, G. T. Harrison, J. Gorenflot, W. Zhang, S. De Wolf, I. McCulloch, T. D. Anthopoulos, D. Baran, F. Laquai, D. Andrienko
Adv. Energy Mater.,
2102363,
2-11,
2021,
[doi]
[abstract]
Efficiencies of organic solar cells have practically doubled since the development of non-fullerene acceptors (NFAs). However generic chemical design rules for donor-NFA combinations are still needed. Such rules are proposed by analyzing inhomogeneous electrostatic fields at the donor–acceptor interface. It is shown that an acceptor–donor–acceptor molecular architecture and molecular alignment parallel to the interface results in energy level bending that destabilizes the charge transfer state thus promoting its dissociation into free charges. By analyzing a series of PCE10:NFA solar cells with NFAs including Y6 IEICO and ITIC as well as their halogenated derivatives it is suggested that the molecular quadrupole moment of 75 Debye A balances the losses in the open circuit voltage and gains in charge generation efficiency.
Glass transition temperature prediction of disordered molecular solids
K.-H. Lin, L. Paterson, F. May, D. Andrienko
npj Computational Materials,
7,
2021,
[doi]
[abstract]
Glass transition temperature Tg is the key quantity for assessing morphological stability and molecular ordering of films of organic semiconductors. A reliable prediction of Tg from the chemical structure is however challenging as it is sensitive to both molecular interactions and analysis of the heating or cooling process. By combining a new fitting protocol with an automated determination of interaction parameters we predict Tg with a mean absolute error of ca 20 deg C for a set of organic compounds with Tg in the 50-230 deg C range. Our study establishes a reliable and automated pre-screening procedure for design of amorphous organic semiconductors essential for the optimization and development of organic light emitting diodes.
Molecular Library of OLED Host Materials - Evaluating the Multiscale Simulation Workflow
A. Mondal, L. Paterson, J. Cho, K.-H. Lin, B. van der Zee, G.-J. A. H. Wetzelaer, A. Stankevych, A. Vakhnin, J.-J. Kim, A. Kadashchuk, P. W. M. Blom, F. May, D. Andrienko
Chem. Phys. Rev.,
2,
031304,
2021,
[doi]
[abstract]
Amorphous small-molecule organic materials are utilized in organic light emitting diodes (OLEDs) with device performance relying on appropriate chemical design. Due to the vast number of contending materials a symbiotic experimental and simulation approach would be greatly beneficial in linking chemical structure to macroscopic material properties. We review simulation approaches proposed for predicting macroscopic properties. We then present a library of OLED hosts containing input files results of simulations and experimentally measured references of quantities relevant to OLED materials. We find that there is a linear proportionality between simulated and measured glass transition temperatures despite a quantitative disagreement. Computed ionization energies are in excellent agreement with the ultraviolet photoelectron and photoemission spectroscopy in air measurements. We also observe a linear correlation between calculated electron affinities and ionization energies and cyclic voltammetry measurements. Computed energetic disorder correlates well with thermally stimulated luminescence measurements and charge mobilities agree remarkably well with space charge–limited current measurements. For the studied host materials we find that the energetic disorder has the greatest impact on the charge carrier mobility. Our library helps to swiftly evaluate properties of new OLED materials by providing well-defined structural building blocks. The library is public and open for improvements. We envision the library expanding and the workflow providing guidance for future OLED material design.
