Computing Charging and Polarization Energies of Small Organic Molecules Embedded into Amorphous Materials with Quantum Accuracy

Abstract

The ionization potential, electron affinity, and cation/anion polarization energies (IP, EA, P(+), P(−)) of organic molecules determine injection barriers, charge carriers balance, doping efficiency, and light outcoupling in organic electronics devices, such as organic light-emitting diodes (OLEDs). Computing IP and EA of isolated molecules is a common task for quantum chemistry methods. However, once molecules are embedded in an amorphous organic matrix, IP and EA values change, and accurate predictions become challenging. Here, we present a revised quantum embedding method [J. Chem. Theory Comput.20141037203725] that accurately predicts the dielectric permittivity and ionization potentials in three test materials, NPB, TCTA, and C60, and allows straightforward interpretation of their nature. The method paves the way toward reliable virtual screening of amorphous organic semiconductors with targeted IP/EA, polarization energies, and relative dielectric permittivity.

De Novo Calculation of the Charge Carrier Mobility in Amorphous Small Molecule Organic Semiconductors

“…Gaussian DOS, i. e., mean ionization energies and electron affinities, for the different molecular species. This additional quantum chemical challenge is addressed by recent developments for accurate predictions of ionization energies and electron affinities by Armleder et al (2021), which could be integrated in this workflow to facilitate accurate de novo mobility predictions in mixed systems.…”

Systematic kMC Study of Doped Hole Injection Layers in Organic Electronics

“…The simulated systems can be extended from cubic to realistic structures ( Neumann et al, 2013 ), but we note that this approximation is less severe than one might think, because the off-diagonal disorder is captured by the distribution of hopping matrix elements. When applied to novel materials, accurate EAs and IPs can be obtained using ab-initio calculations ( Armleder et al, 2021 ) and the Coulomb interaction of host/dopant pairs can be computed quantum-mechanically ( Symalla et al, 2020a ). In combination with an ab-initio parametrization, this work can help to accelerate computational screening for ideal host/dopant materials in doped injection layers and optimization of material composition and layer arrangements.…”

28‐1: Invited Paper: Bottom‐Up OLED Development by Virtual Design: Systematic Elimination of Performance Bottlenecks Using a Microscopic Simulation Approach

“…Following prior work, we apply a seamless bottom-up multiscale simulation workflow to compute OLED material properties and simulate device characteristics (12,14,15,(24)(25)(26)(27)(28)(29)(30): First, we compute molecule specific forcefields automatically with quantum chemistry. We then apply a simulation protocol mimicking physical vapor deposition to generate atomistic models of pristine or mixed thin films or multilayer structures with atomistic resolution (13,31,32).…”

“…We then apply a simulation protocol mimicking physical vapor deposition to generate atomistic models of pristine or mixed thin films or multilayer structures with atomistic resolution (13,31,32). Based on these morphologies we analyze the electronic structure of compounds in the thin film: While taking into account the unique environment of molecules exclusively on a full-quantum-mechanical level to include local effects in mixed films or at interfaces, we compute distributions of molecular properties such as transport energy levels, electronic couplings or excitation energies (11,12,24,33). Based on these distributions we construct digital twins of OLED devices on the 100nm-scale.…”

“…The key, however, to maximize the impact of computational approaches in OLED R&D, are parameter-free models that predict the impact of molecular properties on device performance without parametrization with experiment (11)(12)(13)(14)(15)(16)(17). Despite recent advances (18) such predictive models to fully connect fundamental chemistry and device design still struggle due to the high level of complexity: a large ensemble of effects and processes needs to be considered, ranging from charge transport in pristine layers via injection processes towards complex excitonic processes in mixed co-emission systems (7,8,(19)(20)(21)(22).…”