Ambipolar Transport Materials Research Articles

Structural, electronic, and optical properties of some new dithienosilole derivatives

Structural, electronic, and optical properties of a series of organic semiconductors based on dithienosilole (DTS) and its derivatives were theoretically studied using density functional theory (DFT) and time-dependent-DFT (TD-DFT) methods. Our calculated results suggest that two phenyl groups substituted at silicon atom, as well as functional groups at 1,1′-positions, are an efficient way to induce substantial changes in the optical and electronic properties of DTS compounds. By substituting the functional groups at 1,1′-positions of DTS dimeric compound, we successfully make changes in the charge transport rate of the designed compounds, especially a remarkable reduction in hole reorganization energies. Introduction of pyridyl groups is efficient to lower the LUMO level, and optical band gap energies, to increase the charge and the balance transport rate between hole and electron for producing the ambipolar transport materials promising for use not only in the OLED but also in DSSC devices.

Density functional theory calculations of charge transport properties of ‘plate-like’ coronene topological structures

Charge transport rate is one of the key parameters determining the performance of organic electronic devices. In this paper, we used density functional theory (DFT) at the M06-2X/6−31 $$+$$ G(d) level to compute the charge transport rates of nine coronene topological structures. The results show that the energy gap of these nine coronene derivatives is in the range 2.90–3.30 eV, falling into the organic semiconductor category. The size of the conjugate ring has a large influence on the charge transport properties. Incorporation of methyl groups on the rigid core of tetrabenzocoronene and hexabenzocoronene is more conducive to the hole transport of the molecule than incorporating methoxyl groups. The derivatisation of a ‘long plate-like’ coronene with methoxyl groups facilitates both hole and electron transport. This class of molecules can thus be used in the design of ambipolar transport semiconductor materials. JCSC-D-16-01407 SYNOPSIS Density functional theory was used to compute the charge transport rates of three series nine coronene topological structures at the M06-2X/6−31+G(d) level. Tetrabenzocoronene (series a) and hexabenzocoronene (series b) could be candidates for a hole-transporting (p-type) organic semiconductor material, and ‘long plate-like’ coronene topological structures (series c) could be used as an ambipolar transport material.

Study of a ternary blend system for bulk heterojunction thin film solar cells**This publication was made possible by PDRA (Grant No. PDRA1-0117-14109) from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors.

In this research, we report a bulk heterojunction (BHJ) solar cell consisting of a ternary blend system. Poly(3-hexylthiophene) P3HT is used as a donor and [6,6]-phenyl C61-butyric acid methylester (PCBM) plays the role of acceptor whereas vanadyl 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine (VOPcPhO) is selected as an ambipolar transport material. The materials are selected and assembled in such a fashion that the generated charge carriers could efficiently be transported rightwards within the blend. The organic BHJ solar cells consist of ITO/PEDOT:PSS/ternary BHJ blend/Al structure. The power conversion efficiencies of the ITO/ PEDOT:PSS/P3HT:PCBM/Al and ITO/PEDOT:PSS/ P3HT:PCBM:VOPcPhO/Al solar cells are found to be 2.3% and 3.4%, respectively.

Theoretical investigation on charge transport parameters of two novel heterotetracenes as ambipolar organic semiconductors

In the current work, the charge transport parameters of two novel dicyanovinyl heterotetracenes as potential ambipolar transport materials, 2-((10H-benzo[4,5]thieno[3,2-b]indol-2-yl)methylene)malononitrile (BTMN) and 2-((11H-benzo[a]carbazol-9-yl)methylene)malononitrile (BCMN), have been investigated at the molecular and crystal levels by means of the first-principles density functional theory (DFT) calculations and the incoherent charge-hopping model combining with the quantum-mechanical charge transfer approach. Based on the random-walk simulation of charge diffusion coefficient, the 3D-average mobilities of hole and electron at T=300K are predicted to be 6.387×10−2 and 1.936×10−2cm2V−1s−1 for BTMN crystal, while they are as high as 2.404×10−1 and 1.418×10−1cm2V−1s−1 for BCMN crystal. The predicted high and balanced carrier mobility for BCMN crystal suggests its potential application as ambipolar charge transport materials under favorable device conditions. However, this claim needs experimental verification. The temperature dependence of mobility shows that the carrier transport in both systems behaves in a “bandlike” manner over a wide range of temperatures when the nuclear tunneling effect is considered, as indicated by a decrease in mobility with the increasing temperature, in contradiction to the classical Marcus–Hush description. In addition, the simulation for the angle dependence of mobility shows that the hole transport is remarkable anisotropic in both crystals, and the maximum μh is 0.518cm2V−1s−1 for BTMN and 0.368cm2V−1s−1 for BCMN, which appears along the crystallographic a-axis direction due to the close face-to-face molecular stack and intermolecular π–π interaction that result to the large electronic coupling values.

From electronic excited state theory to the property predictions of organic optoelectronic materials

We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.

Theoretical study of photophysical properties of 1,4-dihydropyrrolo[3,2-b]pyrrole-cored branched molecules with thienylenevinylene arms toward broad absorption spectra for solar cells

A series of oligo(thienylenevinylene) derivatives with 1,4-dihydropyrrolo[3,2-b]pyrrole as core has been investigated at the PBE0/6-31G(d) and the TD-PBE0/6-31+G(d,p) levels to design materials with high performances such as broad absorption spectra and higher balance transfer property. The results show that position and amount of arm affect the electronic density contours of frontier molecular orbitals significantly. The molecule with four arms owns the narrowest energy gap and the largest maximum absorption wavelength, and the molecule with two arms in positions a and c has the broadest absorption region among the designed molecules. Calculated reorganization energies of the designed molecules indicate that the molecules with two arms can be good potential ambipolar transport materials under proper operating conditions.

Perylene diimide copolymers with dithienothiophene and dithienopyrrole: Use in n-channel and ambipolar field-effect transistors

Solution-processable polymers consisting of perylene diimide (PDI) acceptor moieties alternating with dithienothiophene (DTT), N-dodecyl-dithienopyrrole (DTP), or oligomers of these donor groups have been synthesized. We have, in addition to varying the donor, varied the N,N′ substituents of the PDIs. The thermal, optical, electrochemical, and charge-transport properties of the polymers have been investigated. The polymers show broad absorption extending from 300 to 1000 nm with optical band gaps as low as 1.2 eV; the band gap decreases with increasing the conjugation length of donor block, or by replacement of DTT by DTP. The electron affinities of the polymers, estimated from electrochemical data, range from −3.87 to −4.01 eV and are slightly affected by the specific choice of donor moiety, while the estimated ionization potentials (−5.31 to −5.92 eV) are more sensitive to the choice of donor. Bottom-gate top-contact organic field-effect transistors based on the polymers generally exhibit n-channel behavior with electron mobilities as high as 1.7 × 10–2 cm2/V/s and on/off ratios as high as 106; one PDI-DTP polymer is an ambipolar transport material with electron mobility of 4 × 10–4 cm2/V/s and hole mobility of 4 × 10–5 cm2/V/s in air. There is considerable variation in the charge transport properties of the polymers with the chemical structures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Design of donors with broad absorption regions and suitable frontier molecular orbitals to match typical acceptors via substitution on oligo(thienylenevinylene) toward solar cells

A series of oligo(thienylenevinylene) derivatives with or without thieno[3,2-b]thiophene analogs as cores and three types substituent has been investigated at the PBE0/6-31G(d) and the TD-PBE0/6-31+G(d,p) levels to design materials with high performance such as suitable frontier molecular orbital (FMO) energies to match those of [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) and its derivatives, broad absorption spectra, higher and balance transfer property, and better stability. The results reveal that fused cores have slight effects on photophysical properties of investigated derivatives. The electron-withdrawing or push-pull substituents result in red shifts of absorption spectra and better stabilities for investigated derivatives. The calculated reorganization energies of designed derivatives suggest them to be good potential ambipolar transport materials under the proper operating conditions. The promising donors for PCBM, bisPCBM, PC70BM, and indene-C(60) bisadduct (ICBA) as acceptors are recommended theoretically for solar cells based on the proper match for FMOs between donors and acceptors. Moreover, we have also predicted the mobility of designed molecule with better performance.

Toward design of high-performance optoelectronic materials: comparative theoretical studies on the photophysical and charge transport properties of fluorene-based compounds

As an important building block for optoelectronic applications, various chemical modifications at C9-position of fluorene have been proposed to enhance its performance by suppressing the well-known keto effect. In order to identify different substitution effects on the photophysical and charge transport properties of fluorene, we systematically study the electronic structures and photophysical behaviors of fluorene (FR) and its three dimerized counterparts, namely, 9,9′-spirobifluorene (SBF), 9,9′-bifluorenylidene (BFD), and bis(biphenyl-2-2-diyl)allene (BDA), by employing density functional theory calculations. The changes in bond length alternation indicate that the geometrical relaxations of the fluorene unit in its dimerized derivatives are smaller than FR compound. This fact was further proved by the nonradiative decay rate estimated of the first excited singlet state for each compound. Meanwhile, the vibration relaxation analyses suggest that the bridge between two fluorene fragments plays an important role in the nonradiative decay process. In addition, the injection abilities were evaluated in terms of the ionization potentials and electron affinities, and the carrier transport properties were discussed in the framework of Marcus theory. We find BFD could be a better ambipolar transport material, and BDA can be used as a high-efficient luminescent building unit with excellent hole transport property.

Designing of the white-light emission from a single-polymer system: Quantum theoretical study

Quantum-chemical calculations are applied to study the white-light emission from a single-polymer system with simultaneous blue (polyfluorene as a blue host) and orange (2,1,3-benzothiadiazole-based derivative as an orange dopant) emissions. Particular attention is paid to the variation in electronic and optical properties upon the structure tuning in pristine 2,1,3-benzothiadiazole-based derivative. Importantly, by the introduction of electron-donating groups on terminal N,N-disubstituted amino groups, the electronic and optical properties of designed 2,1,3-benzothiadiazole-based derivative have been tuned, making them to be potential candidates as orange dopants in white organic light-emitting devices based on polymers with polyfluorene as a blue-light-emitting host. Furthermore, designed 2,1,3-benzothiadiazole-based derivatives have a possibility to be good hole or ambipolar transport materials in organic light-emitting diodes from the charge hopping model. Finally, we find that the designed 2,1,3-benzothiadiazole-based derivative exhibit improved stability.

Density functional theory study on electron and hole transport properties of organic pentacene derivatives with electron‐withdrawing substituent

Attaching electron-withdrawing substituent to organic conjugated molecules is considered as an effective method to produce n-type and ambipolar transport materials. In this work, we use density functional theory calculations to investigate the electron and hole transport properties of pentacene (PENT) derivatives after substituent and simulate the angular resolution anisotropic mobility for both electron and hole transport. Our results show that adding electron-withdrawing substituents can lower the energy level of lowest unoccupied molecular orbital (LUMO) and increase electron affinity, which are beneficial to the electron injection and ambient stability of the material. Also the LUMO electronic couplings for electron transport in these pentacene derivatives can achieve up to a hundred meV which promises good electron transport mobility, although adding electron-withdrawing groups will introduce the increase of electron transfer reorganization energy. The final results of our angular resolution anisotropic mobility simulations show that the electron mobility of these pentacene derivatives can get to several cm(2) V(-1) s(-1), but it is important to control the orientation of the organic material relative to the device channel to obtain the highest electron mobility. Our investigation provide detailed information to assist in the design of n-type and ambipolar organic electronic materials with high mobility performance.

The effect of diphenylamine on the electronic, optical, and charge transport properties of BTD-based derivative: Insights from theory

Abstract Theoretical investigations have been performed to explore the variation in electronic, optical, and charge transport properties upon the change of the chemical composition along the backbone in 2,1,3-benzothiadiazole (BTD)-based derivative. Narrow difference between hole and electron transportations with the charge hopping model indicates studied BTD-based derivative can be used as good ambipolar transport material in organic light-emitting diodes.

A theoretical study of ambipolar organic transport material: 1,4-Bis(pentafluorobenzyl)[60]-fullerene

A novel C 60 derivative-1,4-bis(pentafluorobenzyl)[60]-fullerene (C 60(CH 2C 6F 5) 2) has been recently synthesized and can be utilized for high-performance organic photovoltaic devices. Its charge transport properties have been systemically investigated by band model and hopping model, respectively. Both models demonstrate that both electron and hole are favor of transporting, and C 60(CH 2C 6F 5) 2 has the potential to be used as ambipolar transport material. The density of states, frontier molecular orbitals, and transfer integrals in main pathways show that it is the fullerene–fullerene face-to-face interaction, not C 6F 5–fullerene interaction determines the charge transport properties.

Theoretical investigation on the white-light emission from a single-polymer system with simultaneous blue and orange emission (Part II)

We report here a theoretical investigation of the white-light emission from a single-polymer system with simultaneous blue (polyfluorene as a blue host) and orange (2,1,3-benzothiadiazole(BTD)-based derivative as an orange dopant) emission. With use of quantum-chemical approaches, our studies are focused on the variation in electronic and optical properties as a function of the chemical composition of the backbone in BTD-based derivatives. Furthermore, the results show that the electronic and optical properties of designed BTD-based derivatives can be tuned by the introduction of suitable electron-donating groups on terminal N, N-disubstituted amino groups, implying good candidates as orange dopants in WPLEDs with polyfluorene as a blue-light-emitting host. In addition, low reorganization energy values of holes or narrow differences between hole and electron transportations within the framework of the charge hopping model suggest designed BTD-based derivatives to be good hole transport or ambipolar transport materials in organic light-emitting diodes. It is also found that the designed BTD-based derivatives containing fluorene-based unit exhibit higher stability.