Ab Initio Treatment of Disorder Effects in Amorphous Organic Materials: Toward Parameter Free Materials Simulation

Abstract

Disordered organic materials have a wide range of interesting applications, such as organic light emitting diodes, organic photovoltaics, and thin film electronics. To model electronic transport through such materials it is essential to describe the energy distribution of the available electronic states of the carriers in the material. Here, we present a self-consistent, linear-scaling first-principles approach to model environmental effects on the electronic properties of disordered molecular systems. We apply our parameter free approach to calculate the energy disorder distribution of localized charge states in a full polaron model for two widely used benchmark-systems (tris(8-hydroxyquinolinato)aluminum (Alq3) and N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD)) and accurately reproduce the experimental charge carrier mobility over a range of 4 orders of magnitude. The method can be generalized to determine electronic and optical properties of more complex systems, e.g. guest-host morphologies, organic-organic interfaces, and thus offers the potential to significantly contribute to de novo materials design.

Effects of energy correlations and superexchange on charge transport and exciton formation in amorphous molecular semiconductors: An ab initio study

“…In the center of this subsystem, 1000 molecules were selected, for which the electron and hole site energies were obtained using the quantum patch embedding method described in Ref. [5]. The remaining 2500 molecules in the spherical subsystem were used as an electrostatic background.…”

“…An acceleration in this understanding has occurred by the employment of ab initio calculations of the morphology and the intermolecular charge hopping rates of these semiconductors [1][2][3][4][5][6]. Recently, we developed an ab initio model for hole transport in two amorphous molecular semiconductors often used as hole transporters in OLEDs: α-NPD [N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1, 1'-biphenyl)-4,4'-diamine] and TCTA [tris(4-carbazoyl-9-ylphenyl)amine] [7].…”

Full quantum treatment of charge dynamics in amorphous molecular semiconductors

“…With a stochastic expansion method [23], simulated morphologies of the materials in relatively small simulation boxes are stochastically expanded to a collection of sites representing molecular centers of mass in boxes of size 100 × 100 × 100 nm 3 , large enough to allow reliable evaluation of μ by solving a master equation. A Gaussian DOS is taken for the site energies of electrons and holes, with standard deviations σ equal to those of ab initio calculations of the energies of the lowest unoccupied and highest occupied molecular orbitals (LUMO and HOMO) [24], respectively, of 1000 molecules in the simulated morphology (the values are, respectively, σ = 0.087, 0.100, and 0.156 eV for electrons in the three materials and σ = 0.087, 0.136, and 0.122 eV for holes [16]). We neglect spatial correlations in the site energies; they only weakly increase μ in the considered materials [16].…”

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

“…of samples with dimensions of about 10 4 − 10 6 nm 3 . Note that the most popular ones are optimized for other purposes 26 and that, to date, the literature appears to be not only scarce of efforts for obtaining the first objective, exception made for the notable work of Andrienko, Lennartz, Wenzel and collaborators, 19,20,24,[27][28][29][30] but also almost absent of attempts of reducing the computational cost via the derivation of simpler potentials.…”