Ordered arrangement of F4TCNQ anions in three-dimensionally oriented P3HT thin films

Abstract

An ordered arrangement of electron-accepting molecular dopant, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), in three-dimensionally (3D) oriented poly(3-hexylthiophene) (P3HT) film was clarified. The 3D oriented P3HT thin films prepared by the friction-transfer technique were doped with F4TCNQ by dipping into an acetonitrile solution. The presence of F4TCNQ anions in the 3D oriented P3HT thin films was investigated by polarized ultraviolet/visible/near-infrared absorption spectroscopy, grazing incidence X-ray diffractometry, polarized Fourier transform infrared spectroscopy (FT-IR), and infrared p-polarized multiple-angle incidence resolution spectroscopy (pMAIRS). The F4TCNQ-doped 3D oriented P3HT films showed anisotropic properties in all characterizations. In particular, the anisotropic molecular vibrations from polarized FT-IR and pMAIRS have clearly revealed orientations of polymeric chains and molecular dopant molecules. Considering the results from several independent techniques indicated that F4TCNQ anions in the 3D oriented P3HT were orderly arranged in a 3D manner with respect to the 3D oriented P3HT such that their molecular long-axis parallel to the P3HT backbone, with in-plane molecular orientation. Additionally, the direction of the optical transition moment of the F4TCNQ anion was found to be parallel to the molecular short-axis.

Critical dopant concentrations govern integer and fractional charge-transfer phases in doped P3HT

“…On the one hand, IPA arrangements of P3HT and F4TCNQ discussed, here. Top: F4TCNQ intercalation with respect to the P3HT backbone and hexyl side-chain; F4TCNQ •− rotation is still subject to debate [19,20]. Bottom: Crystalline and amorphous phases discussed, here.…”

Structural insights into Lewis acid- and F4TCNQ-doped conjugated polymers by solid-state magnetic resonance spectroscopy

“…31,32 In other studies, varied processing conditions were used to tune the ratio of doping by F4TCNQ, which occurred through the integer charge transfer (ICT) or partial charge transfer mechanisms as explained by the location of the dopant molecules in the polymer structure. [33][34][35][36] As partial charge transfer involves orbital hybridization between the dopant and the host material, 37,38 it was shown to be favored when the dopant intercalates between the conjugated backbones of the OSC. 31,39 In contrast to the multitude of doping studies involving F4TCNQ molecules, the doping mechanism employed by the relatively nascent Lewis acid dopant BCF is still unclear and ripe for further investigation.…”

Molecular Doping in the Organic Semiconductor Diindenoperylene: Insights from Many-Body Perturbation Theory

“…1,11,12,20,21 This allows for better control of the distribution, diffusion, and density of dopants within the crystal. 1 Recently, strong organic acceptors like TCNQ (fluorinated tetracyanoquinodimethane) derivatives have been investigated as p-type dopants able to oxidize host OSCs such as pentacene, 9,22 P3HT derivatives, 8,11,16,17 Spiro-TAD, 21 or metal phthalocyanines. 2,6,23,24 The design of these doped OSCs is usually motivated by the canonical condition IE host ≤ EA dopant on the ionization energy (IE) of the host and the electron affinity (EA) of the dopant molecule.…”

“…Organic semiconductors (OSCs) are widely used in optoelectronic devices − because the low-cost, solution-processed synthesis and favorable mechanical properties of OSCs offer improved performance compared with traditional inorganic semiconductors. − Due to the localization of charges in tightly bound states, however, the electrical conductivity of the pristine OSCs is lower than their inorganic counterparts. − , This deficiency in OSCs can potentially be remedied by controllable and effective molecular doping. ,,− , A molecular p-type doping, for instance, can result in a superlinear increase in the conductivity and carrier mobility of OSC hosts. ,,,, This is mainly ascribed to the formation of new hybrid states at the band edge of the doped OSCs, facilitating charge hopping from the host to the dopant. − , Moreover, the symmetry breaking caused by the presence of a molecular dopant within the OSC lattice can alter the electronic structure of the host, offering the possibility to tune its optical properties. − ,− ,,,− This provides a powerful tool for designing new doped OSCs with desired functionalities.…”

“…Instead, OSCs are commonly doped with certain molecules at high dopant concentrations (even one-to-one). ,,,, This allows for better control of the distribution, diffusion, and density of dopants within the crystal . Recently, strong organic acceptors like TCNQ (fluorinated tetracyanoquinodimethane) derivatives have been investigated as p-type dopants able to oxidize host OSCs such as pentacene, , P3HT derivatives, ,,, Spiro-TAD, or metal phthalocyanines. ,,, The design of these doped OSCs is usually motivated by the canonical condition IE host ≤ EA dopant on the ionization energy (IE) of the host and the electron affinity (EA) of the dopant molecule. In other words, the lowest unoccupied molecular orbital (LUMO) of the dopant must be deep enough to withdraw an electron from the highest occupied molecular orbital (HOMO) of the host OSC molecules. ,, Such a favorable energy alignment of the frontier molecular orbitals is expected to result in a partial or integer (negative) charging of the dopant molecules. ,,, …”