Decoding the Vertical Phase Separation and Its Impact on C8-BTBT/PS Transistor Properties

Disentangling the details of the vertical distribution of small semiconductor molecules blended with polystyrene (PS) and the contact properties are issues of fundamental value for designing strategies to optimize small-molecule:polymer blend organic transistors. These questions are addressed here for ultrathin blends of 2,7-dioctyl[1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene (C8-BTBT) and PS processed by a solution-shearing technique using three different blend composition ratios. We show that friction force microscopy (FFM) allows the determination of the lateral and vertical distribution of the two materials at the nanoscale. Our results demonstrate a three-layer stratification of the blend: a film of C8-BTBT of few molecular layers with crystalline order sandwiched between a PS-rich layer at the bottom (a few nm thick) acting as a passivating dielectric layer and a PS-rich skin layer on the top (∼1 nm) conferring stability to the devices. Kelvin probe force microscopy (KPFM) measurements performed in operating organic field-effect transistors (OFETs) reveal that the devices are strongly contact-limited and suggest contact doping as a route for device optimization. By excluding the effect of the contacts, field-effect mobility values in the channel as high as 10 cm² V^–1 s^–1 are obtained. Our findings, obtained via a combination of FFM and KPFM, provide a satisfactory explanation of the different electrical performances of the OFETs as a function of the blend composition ratio and by doping the contacts

Chiral Organization and Charge Redistribution in Chloroaluminum Phthalocyanine on Au(111) Beyond the Monolayer

The nontrivial effect of molecular dipoles on the surface work function of metals is explored for the unidirectional ordered arrays forming the first and second layers of chloroaluminum phthalocyanine on Au(111). This phthalocyanine is a nonplanar molecule with permanent electric dipole perpendicular to its molecular π-plane that can adopt two distinct configurations (Cl-up and Cl-down) when adsorbed on surfaces. The ordered array forming the first layer is known to consist of all Cl-up molecules, whereas the less-studied second layer is formed by molecules in the Cl-down configuration. The inverted orientation of the molecules in these two layers constitutes our benchmark system to investigate the influence of the dipole array orientation on the surface work function. The present study includes an experimental and theoretical approach that combines diverse imaging and spectroscopic scanning probe microscopies, in ultrahigh vacuum, with first-principles density functional theory-based atomistic simulations. Experiment and theory show a chiral organization transferred from the first layer to the growing film that is reflected in the electronic structure. We demonstrate that the obtained surface work function changes are smaller in magnitude than expected from a dipolar approximation because of charge rearrangement at and beyond the monolayer. We provide understanding of the crucial interplay between the interlayer and organic/metal interactions and quantify their effect on the electron density distribution and on the work function changes

Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO₃ Surfaces

The (001)­SrTiO₃ crystal surface can be engineered to display a self-organized pattern of well-separated and nearly pure single-terminated SrO and TiO₂ regions by high temperature annealing in oxidizing atmosphere. By using surface sensitive techniques we have obtained evidence of such a surface chemical self-structuration in as-prepared crystals and unambiguously identified the local composition. The contact surface potential at regions initially consisting of majority single terminations (SrO and TiO₂) is determined to be Φ­(SrO) < Φ­(TiO₂), in agreement with theoretical predictions, although the measured difference ΔΦ ≤ 100 meV is definitely below calculations for ideally pure single-terminated SrO and TiO₂ surfaces. These relative values are maintained if samples are annealed in UHV up to 200 °C. Annealing in UHV at higher temperature (400 °C) preserves the surface morphology of self-assembled TiO₂ and SrO rich regions, although a non-negligible chemical intermixing is observed. The most dramatic consequence is that the surface potential contrast is reversed. It thus follows that electronic and chemical properties of (001)­SrTiO₃ surfaces, widely used in oxide thin film growth, can largely vary before growth starts in a manner strongly dependent on temperature and pressure conditions

Threshold-Voltage Shifts in Organic Transistors Due to Self-Assembled Monolayers at the Dielectric: Evidence for Electronic Coupling and Dipolar Effects

The mechanisms behind the threshold-voltage shift in organic transistors due to functionalizing of the gate dielectric with self-assembled monolayers (SAMs) are still under debate. We address the mechanisms by which SAMs determine the threshold voltage, by analyzing whether the threshold voltage depends on the gate-dielectric capacitance. We have investigated transistors based on five oxide thicknesses and two SAMs with rather diverse chemical properties, using the benchmark organic semiconductor dinaphtho­[2,3-b:2′,3′-<i>f</i>]­thieno­[3,2-<i>b</i>]­thiophene. Unlike several previous studies, we have found that the dependence of the threshold voltage on the gate-dielectric capacitance is completely different for the two SAMs. In transistors with an alkyl SAM, the threshold voltage does not depend on the gate-dielectric capacitance and is determined mainly by the dipolar character of the SAM, whereas in transistors with a fluoroalkyl SAM the threshold voltages exhibit a linear dependence on the inverse of the gate-dielectric capacitance. Kelvin probe force microscopy measurements indicate this behavior is attributed to an electronic coupling between the fluoroalkyl SAM and the organic semiconductor

Electron Accumulative Molecules

With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N­(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N­(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M­(C₂B₉H₁₁)­(C₂B₉H₁₀)-NC₅H₄-C₅H₄N-M′(C₂B₉H₁₁)­(C₂B₉H₁₀)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi­(metallacarboranyl)­viologen [3,3′-M­(8-(NC₅H₄-C₅H₄N-1,2-C₂B₉H₁₀)­(1′,2′-C₂B₉H₁₁)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount

Electron Accumulative Molecules

With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N­(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N­(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M­(C₂B₉H₁₁)­(C₂B₉H₁₀)-NC₅H₄-C₅H₄N-M′(C₂B₉H₁₁)­(C₂B₉H₁₀)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi­(metallacarboranyl)­viologen [3,3′-M­(8-(NC₅H₄-C₅H₄N-1,2-C₂B₉H₁₀)­(1′,2′-C₂B₉H₁₁)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount

Electron Accumulative Molecules

With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N­(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N­(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M­(C₂B₉H₁₁)­(C₂B₉H₁₀)-NC₅H₄-C₅H₄N-M′(C₂B₉H₁₁)­(C₂B₉H₁₀)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi­(metallacarboranyl)­viologen [3,3′-M­(8-(NC₅H₄-C₅H₄N-1,2-C₂B₉H₁₀)­(1′,2′-C₂B₉H₁₁)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount

Electron Accumulative Molecules

With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N­(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N­(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M­(C₂B₉H₁₁)­(C₂B₉H₁₀)-NC₅H₄-C₅H₄N-M′(C₂B₉H₁₁)­(C₂B₉H₁₀)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi­(metallacarboranyl)­viologen [3,3′-M­(8-(NC₅H₄-C₅H₄N-1,2-C₂B₉H₁₀)­(1′,2′-C₂B₉H₁₁)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount

Electron Accumulative Molecules

With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N­(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N­(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M­(C₂B₉H₁₁)­(C₂B₉H₁₀)-NC₅H₄-C₅H₄N-M′(C₂B₉H₁₁)­(C₂B₉H₁₀)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi­(metallacarboranyl)­viologen [3,3′-M­(8-(NC₅H₄-C₅H₄N-1,2-C₂B₉H₁₀)­(1′,2′-C₂B₉H₁₁)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount

Electron Accumulative Molecules

With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B–N­(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B–N­(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M­(C₂B₉H₁₁)­(C₂B₉H₁₀)-NC₅H₄-C₅H₄N-M′(C₂B₉H₁₁)­(C₂B₉H₁₀)] (M = M′ = Co, Fe and M = Co and M′ = Fe) and semi­(metallacarboranyl)­viologen [3,3′-M­(8-(NC₅H₄-C₅H₄N-1,2-C₂B₉H₁₀)­(1′,2′-C₂B₉H₁₁)] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can find important application in any area where ET is paramount