Theoretical comparative studies on transport properties of pentacene, pentathienoacene, and 6,13‐dichloropentacene

Abstract

Pentacene derivative 6,13-dichloropentacene (DCP) is one of the latest additions to the family of organic semiconductors with a great potential for use in transistors. We carry out a detailed theoretical calculation for DCP, with systematical comparison to pentacene, pentathienoacene (PTA, the thiophene equivalent of pentacene), to gain insights in the theoretical design of organic transport materials. The charge transport parameters and carrier mobilities are investigated from the first-principles calculations, based on the widely used Marcus electron transfer theory and quantum nuclear tunneling model, coupled with random walk simulation. Molecular structure and the crystal packing type are essential to understand the differences in their transport behaviors. With the effect of molecule modification, significant one-dimensional π-stacks are found within the molecular layer in PTA and DCP crystals. The charge transport along the a-axis plays a dominant role for the carrier mobilities in the DCP crystal due to the strong transfer integrals within the a-axis. Pentacene shows a relatively large 3D mobility. This is attributed to the relatively uniform electronic couplings, which thus provides more transport pathways. PTA has a much smaller 3D mobility than pentacene and DCP for the obvious increase of the reorganization energy with the introduction of thiophene. It is found that PTA and DCP exhibit lower HOMO (highest occupied molecular orbital) levels and better environmental stability, indicating the potential applications in organic electronics.

Polaron Diffusion in Pentathienoacene Crystals

“…. This order of magnitude agrees with other results presented in the literature 15,16,20,42,43 . Moreover, it is worthwhile to stress that intrinsic charge mobility is difficult to obtain experimentally.…”

“…Recently, Zhang and colleagues have theoretically investigated the charge transport parameters and carrier mobilities in pentacene and pentathienoacene (PTA) crystals within the framework of Marcus' semi-classical theory and quantum nuclear tunneling model, coupled with random walk simulation 15 . In their work, a systematic comparative study was also carried out for pentacene and PTA to gain insights into the theoretical design of these materials.…”

Raman antenna effect from exciton–phonon coupling in organic semiconducting nanobelts

“…As DCP has a similar chromophore to pentacene, the optical transition dipole moment of DCP aligns with the molecular short-axis. 27,33,34 That is, the optical transition dipole moment of DCP has the same direction as the collective vibrations along M-axis, and forms an angle of ~65° with X-axis (the long-axis of nanobelt). Therefore, the intramolecular exciton-phonon coupling is stronger along the M-axis and leads to larger resonant effects for the 1361 cm -1 mode.…”

“…25,26 Both experimental and calculated results have shown that the existence of large π-π overlap between adjacent molecules in DCP nanobelts leads to highly anisotropic carrier transport in bulk DCP crystals. 26,27 Together with the good ambient stability as well as the easy syntheses and purification, DCP presents itself as an ideal candidate for studying the anisotropic coupling of exciton and molecular vibrations, which is fundamentally important for understanding the interaction between light and organic semiconductors at molecular scale.…”

Indolocarbazole (IC) Derivatives as Promising p‐type Organic Semiconductors: A First‐Principle Study of Their Anisotropic Charge Mobilities

“…where V eff is the effective electronic coupling, and k B is Boltzmann constant, and λ is the reorganization energy. Though band model and hopping model are two widely used methodologies to explain charge transport mechanism in organic semiconductors, the later is often used near room temperature in the cases of localized charge carriers with intermolecular electron coupling being far less than the electron‐vibration coupling ,,,,,…”