Anisotropy of singlet exciton diffusion in organic semiconductor crystals from ab initio approaches

Abstract

Due to its importance for the function of organic optoelectronic devices, accurate simulations of the singlet exciton diffusion are crucial to predict the performance of new materials. We present a protocol which allows for the efficient directional analysis of exciton transport with high-level ab initio methods. It is based on an alternative to the frequently employed rate equation since the latter was found to be erroneous in some cases. The new approach can be used in combination with the master equation which is considerably faster than the corresponding Monte Carlo approach. The long-range character of the singlet exciton coupling is taken into account by an extrapolation scheme. The approach is applied to singlet exciton diffusion in those substances where these quantities are experimentally best established: naphthalene and anthracene. The high quality of the crystals, furthermore, diminish uncertainties arising from the geometrical structures used in the computations. For those systems, our new approach provides exciton diffusion lengths L for naphthalene and anthracene crystals which show an excellent agreement with their experimental counterparts. For anthracene, for example, the computed L value in a direction is computed to 58 nm while the experimental value is 60 ± 10 nm.

Regimes of Exciton Transport in Molecular Crystals in the Presence of Dynamic Disorder

“…Therefore, the exciton transport in anthracene crystals is expected to take place in the incoherent regime, in agreement with several theoretical and experimental studies. [30,31,57,58] For DCVSN5 we estimate instead λ to be 0.328 eV, a figure comparable with the excitonic coupling along the antiparallel π-stacked pair (-0.200 eV) and for which one cannot assume incoherent hopping as the transport mechanism (see below).…”

“…The strongest excitonic interactions take place between adjacent molecules in the ab plane. [28,30] The electronic structure origin of the excitonic coupling fluctuation was previously…”

“…It has been selected because it is a good model for a wide range of active donor materials in the context of organic electronics and its exciton transport properties have been experimentally [23][24][25][26] and theoretically [27][28][29][30][31] characterized. The 5 relatively strong exciton-phonon coupling, due to its small size, is already evident from the absorption spectrum.…”

Quantum-Chemical Studies on Excitation Energy Transfer Processes in BODIPY-Based Donor–Acceptor Systems

“…In this case, the EET rate can be described by a Golden Rule expression which has already been applied successfully to such processes in the past. [6][7][8] k EET = 2π in the electronic ground state with vibronic wave function Ψ AL and energy E AL , etc. The delta distribution term ensures that only energy-conserving processes contribute to the EET rate.…”

QM/MM calculations combined with the dimer approach on the static disorder at organic‐organic interfaces of thin‐film organic solar cells composed of small molecules

“…[2] A more profound understanding of these and other parameters influencing the disorder is needed to rationally design materials with favorable transport properties because small energetic disorder is decisive for efficient exciton and charge transport in molecular semiconducting thin films of optoelectronic devices. [8][9][10] Computational chemistry provides ideal tools to deepen the understanding of the origin of disorder in organic semiconducting materials because the DOS is directly accessible from the calculations. Furthermore, it is in silico also possible to extend the disorder concept to interfaces between 2 semiconducting phases, where optical absorption measurements as well as investigations of charge carrier mobilities are experimentally barely feasible.…”