Quantitative Hole Mobility Simulation and Validation in Substituted Acenes

Abstract

Knowledge of the full phonon spectrum is essential to accurately calculate the dynamic disorder (σ) and hole mobility (μ h ) in organic semiconductors (OSCs). However, most vibrational spectroscopy techniques under-measure the phonons, thus limiting the phonon validation. Here, we measure and model the full phonon spectrum using multiple spectroscopic techniques and predict μ h using σ from only the Γ-point and the full Brillouin zone (FBZ). We find that only inelastic neutron scattering (INS) provides validation of all phonon modes, and that σ in a set of small molecule semiconductors can be miscalculated by up to 28% when comparing Γ-point against FBZ calculations. A subsequent mode analysis shows that many modes contribute to σ and that no single mode dominates. Our results demonstrate the importance of a thoroughly validated phonon calculation, and a need to develop design rules considering the full spectrum of phonon modes.

Catching the Killer: Dynamic Disorder Design Rules for Small‐Molecule Organic Semiconductors

“…[40] We demonstrated nearly quantitative matching to INS spectra over three orders of energy for a variety of common small molecule OSCs using these techniques. [8,11,31,41] The first step in DCS-Flow is to relax the structure. This relaxed structure is also used for the left side of the workflow.…”

“…[38] Specifically, the notion that a single "killer" mode is responsible for limiting charge mobility has become popular. [9,39] Although the simplicity of this idea is seductive, the most accurate predictions of μ within transient localization theory included the entire spectrum of phonon modes, [8,11] which suggests that consideration of the full spectrum of phonon modes is a requirement to generate practical synthetic design rules. As we will demonstrate, each molecule contains thousands of phonon modes that are difficult or impossible to compare, even between similar materials.…”

“…[ 8–10 ] Although several works have used transient localization theory to predict electronic properties, design rules that effectively predict high μ for new structures remain elusive. [ 8,10–12 ]…”

“…[8][9][10] Although several works have used transient localization theory to predict electronic properties, design rules that effectively predict high μ for new structures remain elusive. [8,[10][11][12] Computation of μ within the transient localization framework requires accurate simulations of both the phonons and transfer integrals. This theory of charge transport has been validated against a wide variety of experiments.…”

Elucidating correlated defects in metal organic frameworks using theory-guided inelastic neutron scattering spectroscopy

“…In the ESI, † we present a comparison between optical spectroscopy methods (Raman and infrared) and INS, so the differences are made clear to the reader. 43 Finally, owing to the high neutron scattering cross-section of the 1 H nucleus, INS is particularly sensitive to the molecular environment of organic linkers and node ligands. Because the 1 H atoms are present in a wide range of locations in the structural organic backbone, they are remarkably sensitive to subtle changes in the intermolecular environment.…”