N-type Organic Semiconductors Research Articles

Photoelectric effect of hybrid ultraviolet-sensitized phototransistors from an n-type organic semiconductor and an all-inorganic perovskite quantum dot photosensitizer.

Low-dimensional all-inorganic perovskite quantum dots (QDs) have been increasingly developed as photo-sensing materials in the field of photodetectors because of their strong light-absorption capability and broad bandgap tunability. Here, solution-processed hybrid phototransistors built by a dithienothiophenoquinoid (DTTQ) n-type organic semiconductor transport channel mixing with a colloidal CsPbBr3 perovskite QD photosensitizer are demonstrated by manipulating the relative volume ratio from 10 : 0 to 9 : 1, 7 : 3, 5 : 5, 3 : 7, 1 : 9, and 0 : 10. This results in a significantly enhanced photodetection performance owing to the advantages of a high UV absorption cross-section based on the perovskite QDs, efficient carrier transport abilities from the DTTQ semiconductor, and the photogating effect between the bulk heterojunction photocarrier transfer interfaces. The optimized DTTQ : QD (3 : 7) hybrid phototransistor achieves a high photoresponsivity (R) of 7.1 × 105 A W-1, a photosensitivity (S) of 1.8 × 104, and a photodetectivity (D) of 3.6 × 1013 Jones at 365 nm. Such a solution-based fabrication process using a hybrid approach directly integrated into a sensitized phototransistor potentially holds promising photoelectric applications towards advanced light-stimulated photodetection.

Significantly enhanced thermal stability from a new kind of n-type organic semiconductor DFA4: a fully fused F8IC

A new n-type organic semiconductor (DFA4) that features a fully-fused tetradecyl cyclic π-backbone was designed and synthesized. OFET and OPV devices based on DFA4 were fabricated and characterized, respectively.

N-Type organic semiconducting polymers: stability limitations, design considerations and applications.

This review outlines the design strategies which aim to develop high performing n-type materials in the fields of organic thin film transistors (OTFT), organic electrochemical transistors (OECT) and organic thermoelectrics (OTE). Figures of merit for each application and the limitations in obtaining these are set out, and the challenges with achieving consistent and comparable measurements are addressed. We present a thorough discussion of the limitations of n-type materials, particularly their ambient operational instability, and suggest synthetic methods to overcome these. This instability originates from the oxidation of the negative polaron of the organic semiconductor (OSC) by water and oxygen, the potentials of which commonly fall within the electrochemical window of n-type OSCs, and consequently require a LUMO level deeper than ∼−4 eV for a material with ambient stability. Recent high performing n-type materials are detailed for each application and their design principles are discussed to explain how synthetic modifications can enhance performance. This can be achieved through a number of strategies, including utilising an electron deficient acceptor–acceptor backbone repeat unit motif, introducing electron-withdrawing groups or heteroatoms, rigidification and planarisation of the polymer backbone and through increasing the conjugation length. By studying the fundamental synthetic design principles which have been employed to date, this review highlights a path to the development of promising polymers for n-type OSC applications in the future.

The Accuracy of a Computational DFT Method for Acrylates-Based N-Type Organic Semiconductors

The Accuracy of a Computational DFT Method for Acrylates-Based N-Type Organic Semiconductors

THEORETICAL INVESTIGATION OF THE EFFECT OF CONJUATION OF THIOPHENE RINGS ON THE CHARGE TRANSPORT OF THIENOCORONENE DERIVATIVES

Based on density functional theory, quantum chemical calculations of the charge-transport rates were performed for five disc-shaped coronene derivatives with varying numbers of fused thiophene rings, using different basis sets 6-31+G(d) and 6-311++G(d,p), hybrid functionals (B3LYP, M06-2X, CAM-B3LYP, WB97XD, M08-HX), and a dispersion-corrected hybrid functional (M06-2X+D3). Our results indicate that increasing the basis set and adding diffusion and polarisation functions had little effect on the molecular reorganisation energy, charge-transport matrix element t, and charge carrier mobility μ. The charge carrier mobility calculated using B3LYP were relatively large, whereas the results calculated using CAM-B3LYP and WB97XD were similar. Among the five coronene derivatives, molecule b with one thiophene ring could be candidates for a n-type organic semiconductor, and molecule c with two thiophene rings can be designed as a p-type semiconductor.

Cocrystal engineering of molecular rearrangement: a “turn-on” approach for high-performance N-type organic semiconductors

From TCAF to binary α-phase cocrystals, an electron mobility of 0.06 cm2 V−1 s−1 was found. Then by molecular rearrangement, β-cocrystals from heterogeneous nucleation growth showed a remarkable mobility up to 0.88 cm2 V−1 s−1.

Charge transport properties in functionalized triphenylene and coronene derivatives: a density functional study using different functionals

We have investigated computationally the effect of π-conjugated extension on the charge transfer properties of triphenylene and coronene; where we have added fused benzene or triazole rings in the parent molecule. The results showed that the six polycyclic aromatic hydrocarbons investigated are semiconductor molecules. The μ- values of molecules naphthotriphenylene (a1), tribenzocoronene (b1), and tristriazolecoronene (b2) were 1.5 to 21.5 times that of the corresponding μ+ values, suggesting that they are n-type organic semiconductors. Compared with the results obtained by the B3LYP and B3LYP + D3 methods, the charge transport mobility obtained using M06-2X, M06-2X + D3, and M08-HX showed the similar calculation results.

Silicon Phthalocyanines for n-Type Organic Thin-Film Transistors: Development of Structure–Property Relationships

Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly design...

Supramolecularly Engineered J-Aggregates Based on Perylene Bisimide Dyes.

The discovery of the self-assembly of cyanine dyes into J-aggregates had a major impact on the development of dye chemistry due to the emergence of new useful properties in the aggregated state. The unique optical features of these J-aggregates are narrowed, bathochromically shifted absorption bands with almost resonant fluorescence with an increased radiative rate that results from the coherently coupled molecular transition dipoles arranged in a slip-stacked fashion. Because of their desirable properties, J-aggregates gained popularity in the field of functional materials and enabled the efficient photosensitization of silver halide grains in color photography. However, despite a good theoretical understanding of structure-property relationships by the molecular exciton model, further examples of J-aggregates remained scarce for a long time as supramolecular designs to guide the formation of dye aggregates into the required slip-stacked arrangement were lacking.Drawing inspiration from the bacteriochlorophyll c self-organization found in the chlorosomal light-harvesting antennas of green sulfur bacteria, we envisioned the use of nature's supramolecular blueprint to develop J-aggregates of perylene bisimides (PBIs). This class of materials is applied in high-performance color pigments and as n-type organic semiconductors in transistors and solar cells. Combining outstanding photochemical and thermal stability, high tinctorial strength and excellent fluorescence, PBIs are therefore an ideal model system for the preparation of J-aggregates with a wide range of potential applications.In this Account, we elucidate how a combination of steric constraints and hydrogen bonding receptor sites can guide the self-assembly of PBI dyes into slip-stacked packing motifs with J-type exciton coupling. We will discuss the supramolecular polymerization of multiple hydrogen-bonded PBI strands in organic and aqueous media and how minor structural modifications in monomeric PBI molecules can be used to obtain near-infrared absorbing J-aggregates, organogels, or thermoresponsive hydrogels. Pushing the boundaries of self-assembly into the bulk, engineering of the substituents' steric requirements by a dendron-wedge approach afforded adjustable numbers of helical strands of PBI J-aggregates in the columnar liquid-crystalline state and the preparation of lamellar phases. To fully explore their potential, we have studied PBI J-aggregates in collaborative work with spectroscopists, physicists, and theoreticians. In this way, exciton migration over distances of up to 180 nm was shown, and insights into the influence of static disorder on the transport of excitation energy in PBI J-aggregates were derived. Furthermore, the application of PBI J-aggregates as functional materials was demonstrated in photonic microcavities, thin-film transistors, and organic solar cells.

Coherent Electron Transport in Air-Stable, Printed Single-Crystal Organic Semiconductor and Application to Megahertz Transistors.

Organic semiconductors (OSCs) have attracted growing attention for optoelectronic applications such as field-effect transistors (FETs), and coherent (or band-like) carrier transport properties in OSC single crystals (SCs) have been of interest as they can lead to high carrier mobilities. Recently, such p-type OSC SCs compatible with a printing technology have been used to achieve high-speed FETs; therefore, developments of n-type counterparts may be promising for realizing high-speed complementary organic circuits. Herein, coherent electron transport properties in a printed SC of a state-of-the-art, air-stable n-type OSC, PhC2 -BQQDI, by means of variable-temperature gated Hall effect measurements and X-ray single-crystal diffraction analyses in conjunction with band structure calculations, are reported. Furthermore, the SC FET is tested for high-speed operations, which obtains a cutoff frequency of 4.3MHz at an operation voltage of 20V in air. Thus, PhC2 -BQQDI is shown as a new candidate for practical applications of SC-based, organic complementary devices.

Cooperative Aggregations of Nitrogen-Containing Perylene Diimides Driven by Rigid and Flexible Functional Groups

Variation of aggregated structures driven by side chains is a crucial issue in organic semiconductors (OSCs) for achieving high carrier mobility and device durability. In this work, phenylalkyl side chains composed of a rigid terminal phenyl group and a flexible alkyl linker were studied based on a state-of-the-art n-type π-electron system, 3,4,9,10-benzo­[de]­isoquinolino­[1,8-gh]­quinolinetetracarboxylic diimide (BQQDI), from the viewpoints of aggregated structures and thin-film transistors. An appropriate length of the alkyl, i.e., propyl, linker led to stable formation of a unique aggregated structure regardless of solution-grown single-crystal and vacuum-deposited polycrystalline thin films likely due to cooperation of rigid phenyl and flexible alkyl moieties. In contrast, a shorter ethyl linker showed polymorphism in the polycrystalline film. An absence of polymorphism did not only result in high mobility and low threshold voltage but also show low contact resistance. Hence, this work proposes opportunities to design n-type OSCs by introduction of both rigid and flexible characters to the side chains.

Molecular alignment on graphene surface determines transport properties of graphene/organic semiconductor transistors

Graphene field-effect transistor structures were used to investigate the role of molecular alignment on charge transport properties of heterostructures comprising a single-layer graphene and variable thickness of N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bisdicarboximide (PDI8-CN2) - an n-type organic semiconductor. Our atomic force microscopy data show that under selected growth conditions PDI8-CN2 grows in a layer-by-layer fashion up to a second monolayer. The first layer comprises flat-lying molecules, whereas the molecules in the second layer orient themselves in an upright orientation. Transconductance measurements show that the flat-lying molecules have little effect on the position of the Fermi level in graphene. Upright oriented molecules in the second layer instead, have a strong effect as to neutralize native p -type doping of graphene and cause a shift of charge-neutrality level towards the Dirac point. We interpret such behavior in terms of different orientation of the surface dipole on layers with different molecular orientations. At the same time the overall mobility of the charge carriers reaches values exceeding 3000 cm 2 /Vs. • PDI8-CN2 grows in a layer-by-layer mode up to a second mono-layer on graphene. • Molecules in the first layer lie flat in the second are upright on the surface. • Flat-lying molecules have little effect on the position of the Fermi level in graphene. • Upright oriented molecules cause a shift of charge-neutrality level towards the Dirac point.

Organic Semiconductors Processed from Synthesis-to-Device in Water.

Organic semiconductors (OSCs) promise to deliver next‐generation electronic and energy devices that are flexible, scalable and printable. Unfortunately, realizing this opportunity is hampered by increasing concerns about the use of volatile organic compounds (VOCs), particularly toxic halogenated solvents that are detrimental to the environment and human health. Here, a cradle‐to‐grave process is reported to achieve high performance p‐ and n‐type OSC devices based on indacenodithiophene and diketopyrrolopyrrole semiconducting polymers that utilizes aqueous‐processes, fewer steps, lower reaction temperatures, a significant reduction in VOCs (>99%) and avoids all halogenated solvents. The process involves an aqueous mini‐emulsion polymerization that generates a surfactant‐stabilized aqueous dispersion of OSC nanoparticles at sufficient concentration to permit direct aqueous processing into thin films for use in organic field‐effect transistors. Promisingly, the performance of these devices is comparable to those prepared using conventional synthesis and processing procedures optimized for large amounts of VOCs and halogenated solvents. Ultimately, the holistic approach reported addresses the environmental issues and enables a viable guideline for the delivery of future OSC devices using only aqueous media for synthesis, purification and thin‐film processing.

Linear acenaphthene-imide-fused pyrazinacene-quinone: synthesis and photophysical properties

ABSTRACT N-type organic semiconductors are of great importance for organic electronics. Nevertheless, the development of n-type organic semiconductors is far lagged than its counterpart of p-type organic semiconductors. Herein, a linear acenaphthene-imide-fused pyrazinacene-quinone (AIPQ) with high planarity is readily prepared via a two-fold condensation reaction. The incorporation of electron-withdrawing groups of imide, imine (C = N), and carbonyl (C = O) groups lowers the LUMO energy level of AIPQ to −4.12 eV, making it a promising candidate for n-type organic semiconductors.

Study on charge mobility of hexathiapentacene and its selenium analogs

The relationship between molecular geometries, crystal structures and charge mobilities of hexathiapentacene (HTP) and three of its derivatives (2Se-HTP, 4Se-HTP, 6Se-HTP) were studied using the density functional theory combined with a hopping mechanism at the molecular and crystal level. The effect of Se substitution on the charge mobility was discussed. The calculated results showed that the derivatives exhibit good planarity and the molecular geometries show little variation during the charge transfer process. The electron mobility is 1.20 cm2 V-1 S-1 for HTP and 2.30 cm2 V-1 S-1 for 6Se- -HTP, which are much larger than the corresponding hole ones, indicating that HTP and 6Se-HTP are good candidates for n-type organic semiconductors. However, 2Se-HTP and 4Se-HTP have comparable hole and electron motilities and are suitable for ambipolar semiconductors.

Conductivity and Photoconductivity of a p-Type Organic Semiconductor under Ultrastrong Coupling.

During the past decade, it has been shown that light-matter strong coupling of materials can lead to modified and often improved properties which has stimulated considerable interest. While charge transport can be enhanced in n-type organic semiconductors by coupling the electronic transition and thereby splitting the conduction band into polaritonic states, it is not clear whether the same process can also influence carrier transport in the valence band of p-type semiconductors. Here we demonstrate that it is indeed possible to enhance both the conductivity and photoconductivity of a p-type semiconductor rr-P3HT that is ultrastrongly coupled to plasmonic modes. It is due to the hybrid light-matter character of the virtual polaritonic excitations affecting the linear response of the material. Furthermore, in addition to being enhanced, the photoconductivity of rr-P3HT shows a modified spectral response due to the formation of the hybrid polaritonic states. This illustrates the potential of engineering the vacuum electromagnetic environment to improve the optoelectronic properties of organic materials.

Selenium-containing core-expanded naphthalene diimides for high performance n-type organic semiconductors

The incorporation of heavy atoms into molecular backbone is an extremely straightforward strategy for fine-tuning the optoelectronic properties of organic semiconductors. However, it is rarely studied in n-type small molecules. Herein, by selenium substitution of NDI3HU-DTYM2, two Se-decorated core-expanded naphthalene diimides (NDI) derivatives DTYM-NDI3HU-DSYM ( 1 ) and NDI3HU-DSYM2 ( 2 ) were synthesized. In comparison with the reference S-containing compound NDI3HU-DTYM2, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of 1 and 2 were fine-tuned with ∆HOMO of about 0.2 eV, ∆LUMO of 0.1 eV and the narrowed HOMO-LUMO gaps. More surprisingly, the as-spun organic thin film transistors (OTFTs) based on 1 and 2 both showed µ e,sat values as high as 1.0 cm2 V−1 s−1, which are 2-fold higher than that of NDI3HU-DTYM2 with the same device structure and measurement conditions. In addition, the single crystal OFET devices based on Se-containing compound NDI2BO-DSYM2 showed a high µ e,sat value of 1.30 cm2 V−1 s−1. The molecular packing of NDI2BO-DSYM2 in single crystals (two-dimensional supramolecular structure formed by intermolecular Se···Se interactions) is quite different from that of a S-containing compound NDI-DTYM2 (one dimensional supramolecular structure formed by intermolecular π-π stacking). Therefore, the Se substitution can cause dramatic change about molecular stacking model, giving rise to high n-type OTFT performance. Our results demonstrated an effective strategy of the heavy atom effect for designing novel organic semiconductors.

Switching of Electron and Ion Conductions by Reversible H2O Sorption in n-Type Organic Semiconductors

Polar H2O molecules generally act as trapping sites and suppress the electron mobility of n-type organic semiconductors, making chemical design of H2O-tolerant and responsive n-type semiconductors an important step toward multifunctional electron-ion coupling devices. The introduction of effective electrostatic interactions between potassium ions (K+) and carboxylate (-COO-) anions into the electron-transporting naphthalenediimide π-framework enables the design of high-performance H2O-tolerant n-type semiconductors with a reversible H2O adsorption-desorption ability, where the electron mobility and K+ ionic conductivity were coupled with the reversible H2O sorption behavior. The reversible H2O adsorption into the crystals enhanced the electron mobility from 0.04 to 0.28 cm2 V-1 s-1, whereas the K+ ionic conductivity decreased from 3.4 × 10-5 to 4.7 × 10-7 S cm-1. Because this reversible electron-ion conducting switch is responsive to H2O sorption behavior, it is a strong candidate for H2O gating carrier transport systems.

High performance n-type organic field-effect transistors based on halogenated derivatives of naphthalene tetracarboxylic diimides

We synthesized three kinds of naphthalene tetracarboxylic diimides (NDIs) containing halogenated phenyl groups by one-step reaction, and they were used as organic semiconductor layers in top-contact Organic field-effect transistors (OFETs). Besides, we adopted SiO2/Si substrates that treated by N-octadecylphosphonic acid (ODPA). In addition, a layer of 4, 4′, 4″-triphenylamine (n-3-methylphenyl-n-phenylamine) triphenylamine (m-MTDATA) was deposited by vacuum between the organic semiconductor layer and the gold electrode as the modification material. It was found through experiments that all the organic materials synthesized by us showed n-type organic semiconductor characteristics. Happily, the device made of NDI-FAN attained the highest electron mobility of 2.2 × 10−1 cm2v−1s−1 at room temperature and in air. The crystallinity and morphology of the films were characterized by x-ray diffraction (XRD) and atomic force microscope (AFM). The results expose that introducing electron withdrawing substituents into naphthalene tetracarboxylic diimides besides inserting ODPA and m-MTDATA are effective ways to achieve high electron mobility.

Trapped Exciton and Large Birefringence in Cl2–NDI Revealed by Optical Spectroscopy

The n-type organic semiconductor, β-phase single crystalline dichloro naphthalene diimide, Cl2–NDI, is investigated in a broad frequency range via optical spectroscopy. The temperature-dependent ab...