I joined the Max Planck Institute for Polymer Research as a PostDoc in September 2009.
Within the reserach interest of our group at MPIP, my current focus is on the determination of
intermolecular transport properties from density-functional theory. Particular emphasis is
placed on method development for fast evaluation of parameters governing charge/exciton
transport in
organic semiconductors.
I obtained my PhD in Physics in February 2009 from the University of Muenster. In the theory group of Prof. Johannes Pollmann, I
studied "Self-interaction corrections to density-functional theory for solids, surfaces, and
nanotubes". From March to August 2009, I worked on the project "Controlling surface plasmon
polaritions by purposefully designed surface structues" together with Prof. Alexei Maradudin at
the University of California, Irvine. The project was
supported by a postdoctoral fellowship of the DAAD.
2015
![[pdf]](../../images/icon.pdf.red.gif)
Impact of Mesoscale Order on Open-Circuit Voltage in Organic Solar Cells
C. Poelking, M. Tietze, C. Elschner, S. Olthof, D. Hertel, B. Baumeier, F. Wuerthner, K. Meerholz, K. Leo, D. Andrienko
Nature Materials,
14,
434-439,
2015,
[doi]
[abstract]
Structural order in organic solar cells is paramount: It reduces energetic disorder boosts charge and exciton mobilities and assists exciton splitting. Due to spatial localization of electronic states microscopic descriptions of photovoltaic processes tend to overlook the influence of structural features at a mesoscale. Long-range electrostatic interactions nevertheless probe this ordering making local properties depend on the mesoscopic order. To account for this a technique that addresses spatially aperiodic excitations in a periodic polarizable environment is developed. We show that structural order can reverse the role of donor and acceptor as conditioned by gas-phase energy levels. This finding resolves the controversy between experimental and theoretical results for the band shape and level alignment in efficient photovoltaic systems. Furthermore we rationalize the acceptor-donor-acceptor paradigm for molecular design of the successful DCVnT series of dyes which makes optimal use of these long-range effects. Comparing atomistic simulations to UPS experiments we provide an alternative interpretation for the empirical link between molecular energy levels and open-circuit voltage.
2014
Electronic excitations in push-pull oligomers and their complexes with fullerene from Many-Body Green's function theory with polarizable embedding
B. Baumeier, M. Rohlfing, D. Andrienko
J. Chem. Theory Comput.,
10,
3104-3110,
2014,
[doi]
Parametrization of extended Gaussian disorder models from microscopic charge transport simulations
P. Kordt, O. Stenzel, B. Baumeier, V. Schmidt, D. Andrienko
J. Chem. Theory Comput.,
10,
2508-2513,
2014,
[doi]
[abstract]
Simulations of organic semiconducting devices using drift-diffusion equations are vital for the understanding of their functionality as well as for the optimization of their performance. Input parameters for these equations are usually determined from experiments and do not provide a direct link to the chemical structures and material morphology. Here we demonstrate how such a parametrization can be performed by using atomic-scale (microscopic) simulations. To do this a stochastic network model parametrized on atomistic simulations is used to tabulate charge mobility in a wide density range. After accounting for finite-size effects at small charge densities the data is fitted to the uncorrelated and correlated extended Gaussian disorder models. Surprisingly the uncorrelated model reproduces the results of microscopic simulations better than the correlated one compensating for spatial correlations present in a microscopic system by a large lattice constant. The proposed method retains the link to the material morphology and the underlying chemistry and can be used to formulate structure-property relationships or optimize devices prior to compound synthesis.
A general framework for consistent estimation of charge transport properties via random walks in random environments
O. Stenzel, C. Hirsch, V. Schmidt, T. Brereton, D. Kroese, B. Baumeier, D. Andrienko
Multiscale Model. Simul.,
12,
1108-1134,
2014,
[doi]
Two Channels of Charge Generation in Perylene Monoimide Solid-State Dye-Sensitized Solar Cells
I. Howard, M. Meister, B. Baumeier, H. Wonneberger, N. Pschirer, R. Sens, I. Bruder, L. Chen, K. Muellen, D. Andrienko, F. Laquai
Adv. Energy Mater.,
4,
1300640,
2014,
[doi]
Efficient simulation of Markov chains using segmentation
T. Brereton, O. Stenzel, B. Baumeier, D. Andrienko, V. Schmidt, D. Kroese
Methodol. Comput. Appl.,
16,
465-484,
2014,
[doi]
[abstract]
A methodology is proposed that is suitable for efficient simulation of continuous-time Markov chains that are nearly-completely decomposable. For such Markov chains the effort to adequately explore the state space via Crude Monte Carlo (CMC) simulation can be extremely large. The purpose of this paper is to provide a fast alternative to the standard CMC algorithm which we call Aggregate Monte Carlo (AMC). The idea of the AMC algorithm is to reduce the jumping back and forth of the Markov chain in small subregions of the state space. We accomplish this by aggregating such problem regions into single states. We discuss two methods to identify collections of states where the Markov chain may become trapped: the stochastic watershed segmentation from image analysis and a graph-theoretic decomposition method. As a motivating application we consider the problem of estimating the charge carrier mobility of disordered organic semiconductors which contain low-energy regions in which the charge carrier can quickly become stuck. It is shown that the AMC estimator for the charge carrier mobility reduces computational costs by several orders of magnitude compared to the CMC estimator.
2013
Observing Charge Dynamics in Surface Reactions by Time-Resolved Stark Effects
M. Meister, B. Baumeier, N. Pschirer, R. Sens, I. Bruder, F. Laquai, D. Andrienko, I. Howard
J. Phys. Chem. C,
117,
9171-9177,
2013,
[doi]
[abstract]
Surfaces facilitate chemical reactions occurring in biological and synthetic systems with wide-ranging applications from energy conversion to catalysis and sensing. Microscopic understanding of the structure and dynamics that underpin these reactions is keenly pursued with novel experimental techniques such as sum frequency generation and laser-assisted photoemission spectroscopy. Herein we demonstrate a method for interpreting the time-resolved observation of the Stark effect to provide an in situ optical probe of the charge dynamics during an interfacial reaction. The analysis holds broad potential for investigating charge migration in surface-bound catalysts and sensors as well as photocenter and retinal proteins even when the Stark parameters of the material are unknown. We demonstrate the analysis with respect to the energy conversion reaction in solid-state dye-sensitized solar cells.
2012
Challenges for in silico design of organic semiconductors
B. Baumeier, F. May, C. Lennartz, D. Andrienko
J. Mater. Chem.,
22,
10971-10976,
2012,
[doi]
[abstract]
We outline the objectives of microscopic simulations of charge and energy transport processes in amorphous organic semiconductors describe the current status of techniques used to achieve them and list the challenges such methods face when aiming at quantitative predictions.
Stochastic modeling of molecular charge transport networks
B. Baumeier, O. Stenzel, C. Poelking, D. Andrienko, V. Schmidt
Phys. Rev. B,
86,
184202,
2012,
[doi]
[abstract]
We develop a stochastic network model for charge transport simulations in amorphous organic semiconductors which generalizes the correlated Gaussian disorder model to realistic morphologies charge transfer rates and site energies. The network model includes an iterative dominance-competition model for positioning vertices (hopping sites) in space distance-dependent distributions for the vertex connectivity and electronic coupling elements and a moving-average procedure for assigning spatially correlated site energies. The field dependence of the hole mobility of the amorphous organic semiconductor tris-(8-hydroxyquinoline)aluminum which was calculated using the stochastic network model showed good quantitative agreement with the prediction based on a microscopic approach.
Design rules for charge-transport efficient host materials for phosphorescent OLEDs
F. May, M. Al-Helwi, B. Baumeier, W. Kowalsky, E. Fuchs, C. Lennartz, D. Andrienko
J. Am. Chem. Soc.,
134,
13818-13822,
2012,
[doi]
[abstract]
The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies the alignment of levels with respect to the emitter the ability to form and sustain amorphous order material processability and an adequate charge carrier mobility. A possible design strategy is to choose a pi-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents however induce large spatial separations between conjugated cores can substantially reduce intermolecular electronic couplings and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 28-bis(triphenylsilyl)dibenzofuran an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies especially for electrons while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole-Frenkel slope supporting our conclusions. By linking electronic structure molecular packing and mobility we provide a pathway to the rational design of hosts with high charge mobilities.
Frenkel and charge-transfer excitations in donor-acceptor complexes from many-body Green's functions theory
B. Baumeier, D. Andrienko, M. Rohlfing
J. Chem. Theory Comput.,
8,
2790-2795,
2012,
[doi]
[abstract]
Excited states of donor-acceptor dimers are studied using many-body Green's functions theory within the GW approximation and the BetheâÃÂÃÂSalpeter equation. For a series of prototypical small-molecule based pairs this method predicts energies of local Frenkel and intermolecular charge-transfer excitations with the accuracy of tens of meV. Application to larger systems is possible and allowed us to analyze energy levels and binding energies of excitons in representative dimers of dicyanovinyl-substituted quarterthiophene and fullerene a donor-acceptor pair used in state of the art organic solar cells. In these dimers the transition from Frenkel to charge transfer excitons is endothermic and the binding energy of charge transfer excitons is still of the order of 1.5 eV. Hence even such an accurate dimer-based description does not yield internal energetics favorable for the generation of free charges either by thermal energy or an external electric field. These results confirm that for qualitative predictions of solar cell functionality accounting for the explicit molecular environment is as important as the accurate knowledge of internal dimer energies.
Can lattice models predict density of states of amorphous organic semiconductors?
F. May, B. Baumeier, C. Lennartz, D. Andrienko
Phys. Rev. Lett.,
109,
136401,
2012,
[doi]
[abstract]
We extend existing lattice models of amorphous semiconductors by accounting for changes in molecular polarizability upon charging/excitation. A compact expression of this contribution to the density of states is provided. Although the lattice model and the description based on a microscopic morphology both qualitatively predict an additional broadening shift and an exponential tail (traps) of the density of states a quantitative agreement between the two cannot be achieved.
Comparative study of microscopic charge dynamics in crystalline acceptor-substituted oligothiophenes
M. Schrader, R. Fitzner, M. Hein, C. Elschner, B. Baumeier, M. Riede, K. Leo, P. Baeuerle, D. Andrienko
J. Am. Chem. Soc.,
134,
6052-6056,
2012,
[doi]
[abstract]
By performing microscopic charge transport simulations for a set of crystalline dicyanovinyl-substituted oligothiophenes we find that the internal acceptor-donor-acceptor molecular architecture combined with thermal fluctuations of dihedral angles results in large variations of local electric fields substantial energetic disorder and pronounced Poole-Frenkel behavior which is unexpected for crystalline compounds. We show that the presence of static molecular dipoles causes large energetic disorder which is mostly reduced not by compensation of dipole moments in a unit cell but by molecular polarizabilities. In addition the presence of a well-defined pi-stacking direction with strong electronic couplings and short intermolecular distances turns out to be disadvantageous for efficient charge transport since it inhibits other transport directions and is prone to charge trapping.
Excited states of dicyanovinyl-substituted oligothiophenes from many-body Green's functions theory
B. Baumeier, D. Andrienko, Y. Ma, M. Rohlfing
J. Chem. Theory Comput.,
8,
997-1002,
2012,
[doi]
[abstract]
Excited states of dicyanovinyl-substituted oligothiophenes are studied using many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation. By varying the number of oligomer repeat units we investigate the effects of resonant-antiresonant transition coupling dynamical screening and molecular conformations on calculated excitations. We find that the full dynamically screened Bethe-Salpeter equation yields absorption and emission energies in good agreement with experimental data. The effect of resonant-antiresonant coupling on the first singlet excitation monotonically decreases with increasing size of the molecule while dynamical screening effects uniformly lower the excitation energies.
2011
Microscopic simulations of charge transport in disordered organic semiconductors
V. Ruehle, A. Lukyanov, F. May, M. Schrader, T. Vehoff, J. Kirkpatrick, B. Baumeier, D. Andrienko
J. Chem. Theory Comput.,
7,
3335-3345,
2011,
[doi]
[abstract]
Charge carrier dynamics in an organic semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements reorganization energies and driving forces which vary as a function of position and orientation of the molecules. The exact evaluation of these contributions in a molecular assembly is computationally prohibitive. Various often semiempirical approximations are employed instead. In this work we review some of these approaches and introduce a software toolkit which implements them. The purpose of the toolkit is to simplify the workflow for charge transport simulations provide a uniform error control for the methods and a flexible platform for their development and eventually allow in silico prescreening of organic semiconductors for specific applications. All implemented methods are illustrated by studying charge transport in amorphous films of tris-(8-hydroxyquinoline)aluminum a common organic semiconductor.
Toward quantitative structure-property relationships for charge transfer rates of polycyclic aromatic hydrocarbons
M. Misra, D. Andrienko, B. Baumeier, J.-L. Faulon, O. A. von Lilienfeld
J. Chem. Theory Comput.,
7,
2549-2555,
2011,
[doi]
[abstract]
Quantitative structure-property relationships (QSPRs) have been developed and assessed for predicting the reorganization energy of polycyclic aromatic hydrocarbons (PAHs). Preliminary QSPR models based on a combination of molecular signature and electronic eigenvalue difference descriptors have been trained using more than 200 PAHs. Monte Carlo cross-validation systematically improves the performance of the models through progressive reduction of the training set and selection of best performing training subsets. The final biased QSPR model yields correlation coefficients q2 and r2 of 0.7 and 0.8 respectively and an estimated error in predicting reorganization energy of ±0.014 eV.
2010
Charge transport in columnar mesophases of carbazole macrocycles
T. Vehoff, B. Baumeier, D. Andrienko
J. Chem. Phys.,
133,
134901,
2010,
[doi]
Charge transport in organic crystals: role of disorder and topological connectivity
T. Vehoff, B. Baumeier, A. Troisi, D. Andrienko
J. Am. Chem. Soc.,
132,
11702-11708,
2010,
[doi]
Density-functional based determination of intermolecular charge transfer properties for large-scale morphologies
B. Baumeier, J. Kirkpatrick, D. Andrienko
Phys. Chem. Chem. Phys.,
12,
11103-11113,
2010,
[doi]
