Ionization Energies, Electron Affinities, and Polarization Energies of Organic Molecular Crystals: Quantitative Estimations from a Polarizable Continuum Model (PCM)-Tuned Range-Separated Density Functional Approach

Abstract

We propose a new methodology for the first-principles description of the electronic properties relevant for charge transport in organic molecular crystals. This methodology, which is based on the combination of a nonempirical, optimally tuned range-separated hybrid functional with the polarizable continuum model, is applied to a series of eight representative molecular semiconductor crystals. We show that it provides ionization energies, electron affinities, and transport gaps in very good agreement with experimental values, as well as with the results of many-body perturbation theory within the GW approximation at a fraction of the computational costs. Hence, this approach represents an easily applicable and computationally efficient tool to estimate the gas-to-crystal phase shifts of the frontier-orbital quasiparticle energies in organic electronic materials.

Toward Design of Novel Materials for Organic Electronics

“…Due to this strong dependence, small errors in the calculation of the energy disorder lead to large errors in the predicted charge carrier mobility, demanding high accuracy of all models involved in the simulation workflow. [112] Combining such approaches with accurate embedding schemes, it becomes possible to calculate solid state properties, such as thin film ionization energies or electron affinities [17,104,113] energy disorder parameters for electrons, holes, or excited states of a pristine material or a mixture of materials, distributions of electronic couplings for charge or exciton transport [114a] and optical film properties such as absorption spectra. [110,111] Recent advances toward quantitative electronic structure methods were made using methods like GW [104] or self-consistently tuned range-separated functionals.…”

Characterization of intrinsic hole transport in single-crystal spiro-OMeTAD

“…24 More details on the optimization of the range-separation parameter have been well documented in the literature. 37 The electronic band structures were calculated with the CRYSTAL14 package 38 by using the B3LYP functional (we note that long-range-corrected functionals with tunable ω are currently not available for periodic systems and those with default values of ω lead to convergence issues with the spiro-OMeTAD single crystal used in our calculations). However, given that the transfer integrals calculated at the B3LYP level agree very well with the Opt-ωB97X-D results (see Table 1), the band structures calculated with the B3LYP functional are reliable.…”

Prediction of excited‐state properties of oligoacene crystals using polarizable continuum model‐tuned range‐separated hybrid functional approach

“…Previous theoretical studies of excited‐state properties of oligoacenes have been performed using high‐level post‐Hartree‐Fock (PHF) methods, but mostly with isolated molecules or small clusters. These PHF methods are too expensive to deal with large clusters or extended systems such as crystals and the studies are therefore limited to the molecular level where the solid polarization effect is completely ignored . Many‐body perturbation theory based on the GW approximation and the Bethe‐Salpeter equation (BSE) has been used to characterize the excited states for acenes from molecules, dimers and trimers to crystals .…”

“…Its nonlocal Fock‐like exchange component can benefit the inclusion of long‐range contributions. However, the “optimal” fractions of eX generally depend on the molecular systems and even different phases of the same molecule . Furthermore, the calculated electronic‐coupling parameter, band gap, UV‐vis absorption spectrum, and reflectivity in molecular crystals and solids are found to be very sensitive to the amount of eX.…”

“…Furthermore, the calculated electronic‐coupling parameter, band gap, UV‐vis absorption spectrum, and reflectivity in molecular crystals and solids are found to be very sensitive to the amount of eX. Unfortunately, none of the conventional density functionals can consistently yield accurate TDDFT optical spectra for various types of semiconductors and reasonably capture polarization effects in organic molecular crystals . Notably, the theoretical evaluation of exciton binding energies using TDDFT in organic solids remains challenging as the conventional functionals typically predict the quasiparticle gap similar to the optical gap and thus yield negligible exciton binding energies .…”