Structure of pentacene thin films

Abstract

Grazing incidence x-ray diffraction, x-ray reflectivity and atomic force microscopy have been performed to study the structure of pentacene thin films on oxidized Si substrates from submonolayer to multilayer coverages. The volume of the unit cell in the thin film phase is almost identical to that of the bulk phase, thus the molecular packing efficiency is effectively the same in both phases. The structure forming from the first monolayer remains the same for films at least 190Å thick. The in-plane structure of the submonolayer islands also remains unchanged within a substrate temperature range of 0<Tsub<45°C while the island size changes by more than a factor of 4.

Influence of alkyl chain substitution on sexithienyl-metal interface morphology and energetics

“…This angle is larger than the one reported for DH6T on silicon oxide ͑21.3°͒. 9 However, rodlike molecules are prone to exhibit a number of different crystal structure polymorphs ͑with dif- 17 whose existence critically depends on the nature of the substrate and deposition conditions. We therefore assume that multilayer DH6T exists in a different polymorph on ML-DH6T/Ag͑111͒ than it does on SiO 2 ; in addition, some alkyl chains may not be in the all-trans conformation.…”

Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method

“…In addition to the changed thin film morphology, certain molecular organic semiconductors can form various molecular packing structures (polymorphs) by changing film formation processes 19,20 . Since the electronic wavefunction overlap that determines the charge transfer integral is a very sensitive function of the precise molecular packing, the various polymorphs generally have different carrier mobilities with some having a higher mobility than their equilibrium structures 10,[19][20][21][22][23] .…”

Triplet diffusion in singlet exciton fission sensitized pentacene solar cells

“…Also, Ruiz et al showed that the orientation of the long axis of pentacene molecules in monolayers is approximately out of the substrate plane for layer thickness of up to 19 nm. 24 Density functional theory calculations suggest that the charge transfer state in a pentacene/C 60 molecular couple has its minimum energy for exactly this "head-to-tail" orientation. 25 Therefore, lower g Pent for 30 and 50 nm thick layers might be partially due to a change in the interfacial molecular orientation of pentacene.…”

“…Due to the distribution of the optical field, low-energy photons are preferentially absorbed closer to the interface between pentacene and ITO and at this interface, the pentacene can stack such that transport is favored in horizontal direction rather than the preferential vertical direction. 24 In addition, the excitons generated in regions with different stacking directions may have varying dissociation efficiencies as the charge transfer state energy of the pentacene/C 60 molecular couple is minimized for the configuration, where the short molecular axis of pentacene is interfaced with C 60 . 25 Furthermore, because the pentacene crystal diameter in our films (250 6 100 nm, obtained with atomic force microscopy) is comparable to the wavelength of incident light, we may need to consider two separated polarization phases each with its own optical constants and generation profiles.…”