Theoretical study on charge transport of quinacridone polymorphs

The charge carrier transporting ability in the polymorphism of quinacridone (QA) has been studied using density‐functional theory and Marcus charge transport theory. The theoretical results indicated quinacridone has good electron transport ability and electron mobilities of all the polymorphism are at 10^?2 magnitude. But its hole mobility, which varied with the different molecular packing, is at range of 10^?1–10^?3 magnitude. The difference of charge carrier mobilities among the polymorphism is originated from the different packing mode. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

P4VP and oligo(phenylenevinylene)‐perylenebisimide mixed donor‐acceptor supramolecular comb polymer complexes with improved charge carrier mobility

Random donor‐acceptor (D‐A) supramolecular comb polymers were formed when hydroxyl functionalized donor and acceptor small molecules based on Oligo(phenylenevinylene) (named OPVCN‐OH ) and Perylenebisimide (named UPBI‐PDP ), respectively, were complexed with Poly(4‐vinyl pyridine) (P4VP). A series of random D‐A supramolecular comb polymers were formed by varying the ratios of UPBI‐PDP and OPVCN‐OH with P4VP. A 100% P4VP‐donor polymer complex [ P4VP(OPV_1.00 )] and a 100% P4VP‐acceptor polymer complex [ P4VP(UPBI_1.00 )] were also synthesized and characterized. Complex formation was confirmed by FT‐IR and ¹H NMR spectroscopy. Solid state structural studies carried out using small angle X‐ray scattering and wide angle X‐ray diffraction experiments revealed altered packing of the D and A molecules in the complexes. Transmission electron microscopy images showed lamellar structures in the < 10 nm scale for the P4VP(OPV_1.00 ), P4VP(UPBI_1.00 ), and mixed P4VP (D‐A) complexes. The effect of the nanoscopic D‐A self‐assembly on the bulk mobility of the materials was probed using SCLC measurements. The mixed D‐A random complexes exhibited ambipolar charge transport characteristics with higher values for the average bulk hole mobility estimate. P4VP(OPV_0.25 + UPBI_0.75) exhibited an average hole mobility in the order of 10^?2cm² V^?1 s^?1 and electron mobility 10^?5cm² V^?1 s^?1. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2403–2412     

Electronic structure and microscopic charge‐transport properties of a new‐type diketopyrrolopyrrole‐based material

Recently, diketopyrrolopyrrole (DPP)‐based materials have attracted much interest due to their promising performance as a subunit in organic field effect transistors. Using density functional theory and charge‐transport models, we investigated the electronic structure and microscopic charge transport properties of the cyanated bithiophene‐functionalized DPP molecule (compound 1 ). First, we analyzed in detail the partition of the total relaxation (polaron) energy into the contributions from each vibrational mode and the influence of bond‐parameter variations on the local electron–vibration coupling of compound 1 , which well explains the effects of different functional groups on internal reorganization energy (λ). Then, we investigated the structural and electronic properties of compound 1 in its isolated molecular state and in the solid state form, and further simulated the angular resolution anisotropic mobility for both electron‐ and hole‐transport using two different simulation methods: (i) the mobility orientation function proposed in our previous studies (method 1); and (ii) the master equation approach (method 2). The calculated electron‐transfer mobility (0.00003–0.784 cm² V^?1 s^?1 from method 1 and 0.02–2.26 cm² V^?1 s^?1 from method 2) matched reasonably with the experimentally reported value (0.07–0.55 cm² V^?1 s^?1). To the best of our knowledge, this is the first time that the transport parameters of compound 1 were calculated in the context of band model and hopping models, and both calculation results suggest that the intrinsic hole mobility is higher than the corresponding intrinsic electron mobility. Our calculation results here will be instructive to further explore the potential of other higher DPP‐containing quinoidal small molecules. © 2015 Wiley Periodicals, Inc.     

The influence of electron deficient unit and interdigitated packing shape of new polythiophene derivatives on organic thin‐film transistors and photovoltaic cells

A series of new polythiophene derivatives containing a thiazole ring as an electron deficient unit were successfully synthesized via Stille coupling reactions. Synthesized polymers were classified into two types (H‐shape packing and A‐shape packing) based on their interdigitated packing structure induced by different side chain configurations. The thiophene derivatives that contained a thiazole unit ( PT50Tz50 , PTz100 , and PTTz ) exhibited much better thermal stability than did the full thiophene polymers ( PT100 and PTT ). The polymers containing the thiazole unit ( PTz100 and PTTz ) showed a red‐shifted absorption spectrum with clear vibronic structure. In addition, the XRD and AFM results showed that the polymers containing the thiazole unit and interdigitated H‐shape exhibited much better ordered and connected intermolecular structures than did other polymers. The improved intermolecular ordering and surface morphologies directly facilitated charge carrier transport in thin film transistor (TFT) devices, without introducing charge traps, and yielded higher solar cell performance. Among these polymers, the PTTz copolymer exhibited the best TFT performance (μ = 0.050 cm² V^?1 s^?1, on/off ratio = 10⁶, and V_th = ?2 V) and solar cell performance (PCE = 1.39%, J_sc = 6.58 mA cm^?2, and V_oc = 0.58 V). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Significant Difference in Semiconducting Properties of Isomeric All‐Acceptor Polymers Synthesized via Direct Arylation Polycondensation

The direct arylation polycondensation (DArP) appeared as an efficient method for producing semiconducting polymers but often requires acceptor monomers with orienting or activating groups for the reactive carbon‐hydrogen (C‐H) bonds, which limits the choice of acceptor units. In this study, we describe a DArP for producing high‐molecular‐weight all‐acceptor polymers composed of the acceptor monomers without any orienting or activating groups via a modified method using Pd/Cu co‐catalysts. We thus obtained two isomeric all‐acceptor polymers, P1 and P2, which have the same backbone and side‐chains but different positions of the nitrogen atoms in the thiazole units. This subtle change significantly influences their optoelectronic, molecular packing, and charge‐transport properties. P2 with a greater backbone torsion has favorable edge‐on orientations and a high electron mobility μ_e of 2.55 cm² V^?1 s^?1. Moreover, P2‐based transistors show an excellent shelf‐storage stability in air even after the storage for 1 month.     

Thienoacene‐Fused Pentalenes: Syntheses,Structures, Physical Properties and Applications for Organic Field‐Effect Transistors

Three soluble and stable thienoacene‐fused pentalene derivatives ( 1 – 3 ) with different π‐conjugation lengths were synthesized. X‐ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field‐effect transistors (OFETs) were also investigated. The highest field‐effect hole mobility of 0.016, 0.036 and 0.001 cm² V^?1 s^?1 was achieved for solution‐processed thin films of 1 – 3 , respectively.     

Effect of thiophene spacers in benzodithiophene‐based polymers for organic electronics

Poly{2,6‐bis(thiophene‐2‐yl)‐4,8‐bis(5‐dodecylthiophen‐2‐yl)benzo[1,2‐b :4,5‐b' ]dithiophene} [poly(Th‐bDTBDT‐Th)] was successfully synthesized through Stille coupling polymerization. The addition of the thiophene spacer groups between the benzodithiophene units resulted in improved performance in optoelectronic devices. This was attributed to the reduced lamellae stacking distance in thin film with prominent π–π stacking peak indicating close assembly of poly(Th‐bDTBDT‐Th). Spacing between the benzodithiophene units in poly(Th‐bDTBDT‐Th) helped the close packing of dodecyl chains and generated improved π stacking interaction. For poly(Th‐bDTBDT‐Th), the measured average field effect mobility was 2.32 × 10^?3 cm² V^?1 s^?1 and average hole mobility in vertical direction was 2.92 × 10^?5 cm² V^?1 s^?1. Charge transport in both directions was improved by one order of magnitude with the presence of the thiophene spacer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3942–3948     

Simultaneous morphological stability and high charge carrier mobilities in donor–acceptor block copolymer/PCBM blends

Donor–acceptor block copolymers (BCP), incorporating poly(3‐hexylthiophene) (P3HT), and a polystyrene copolymer with pendant fullerenes (PPCBM) provide desired stable nanostructures, but mostly do not exhibit balanced charge carrier mobilities. This work presents an elegant approach to match hole and electron transport in BCP by blending with molecular PCBM without causing any macrophase separation. An insufficient electron mobility of PPCBM can be widely compensated by adding PCBM which is monitored by the space‐charge limited current method. Using X‐ray diffraction, atomic force microscopy, and differential scanning calorimetry, we verify the large miscibility of the PPCBM:PCBM blend up to 60 wt % PCBM load forming an amorphous, molecularly mixed fullerene phase without crystallization. Thus, blending BCP with PCBM substantially enhances charge transport achieving an electron mobility of μ_e=(3.2 ± 1.7) × 10^?4 cm²V^?1s^?1 and hole mobility of μ_h=(1.8 ± 0.6) × 10^?3 cm²V^?1s^?1 in organic field‐effect transistors (OFET). The BCP:PCBM blend provides a similarly high ambipolar charge transport compared to the established P3HT:PCBM system, but with the advantage of an exceptionally stable morphology even for prolonged thermal annealing. This work demonstrates the feasibility of high charge transport and stable morphology simultaneously in a donor–acceptor BCP by a blend approach. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1125–1136     

A Planarized Triphenylborane Mesogen: Discotic Liquid Crystals with Ambipolar Charge‐Carrier Transport Properties

A discotic liquid‐crystalline (LC) material, consisting of a planarized triphenylborane mesogen, was synthesized. X‐ray diffraction analysis confirmed that this compound forms a hexagonal columnar LC phase with an interfacial distance of 3.57 Å between the discs. At ambient temperature, this boron‐centered discotic liquid crystal exhibited ambipolar carrier transport properties with electron and hole mobility values of approximately 10^?3 and 3×10^?5 cm² V^?1 s^?1, respectively.     

EDOT‐diketopyrrolopyrrole copolymers for high bulk hole mobility and near infrared absorption

To obtain novel low‐bandgap materials with tailored hole‐transport properties and extended absorption, electron rich 3,4‐ethylenedioxythiophene is introduced as a comonomer in diketopyrrolo[3,4‐c]pyrrole copolymers with different aryl flanking units. The polymers are characterized by absorption and photoluminescence spectroscopy, dynamic scanning calorimetry, cyclic voltammetry, and X‐ray diffraction. The charge transport properties of these new materials are studied carefully using an organic field effect transistor geometry where the charge carriers are transported over a narrow channel at the semiconductor/dielectric interface. These results are compared to bulk charge carrier mobilities using space‐charge limited current (SCLC) measurements, in which the charge carrier is transported through the complete film thickness of several hundred nanometers. Finally, charge carrier mobilities are correlated with the electronic structure of the compounds. We find that in particular the thiophene‐flanked copolymer PDPP[T]₂‐EDOT is a very promising candidate for organic photovoltaics, showing an absorption response in the near infrared region with an optical bandgap of 1.15 eV and a very high bulk hole mobility of 2.9 × 10^?4 cm² V^?1 s^?1 as measured by SCLC. This value is two orders of magnitudes higher than SCLC mobilities reported for other polydiketopyrrolopyrroles and is in the range of the well‐known hole transporting polymer poly(3‐hexylthiophene). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 639–648     

Determination of Electron and Hole Mobility of Regioregular Poly(3‐hexylthiophene) by the Time of Flight Method

Time of flight method (TOF) is used to measure the electron and hole mobility of a spin coated regioregular poly(3‐hexylthiophene) (P3HT) film. We find that both electron and hole have the same mobility (about 3.8～3.9×10^?4 cm²/Vs) at an applied field of 120 kV/cm. It is demonstrated in this paper that the electron‐hole recombination process may prevent the electron transport in the material due to the fact that the carrier recombination time is much shorter than the transit time.     

Syntheses and Properties of Graphyne Fragments: Trigonally Expanded Dehydrobenzo[12]annulenes

We present herein the synthesis and properties of the largest hitherto unknown graphyne fragment, namely trigonally expanded tetrakis(dehydrobenzo[12]annulene)s (tetrakis‐DBAs). Intramolecular three‐fold alkyne metathesis reactions of hexakis(arylethynyl)DBAs 9 a and 9 b using Fürstner’s Mo catalyst furnished tetrakis‐DBAs 8 a and 8 b substituted with tert‐butyl or branched alkyl ester groups in moderate and fair yields, respectively, demonstrating that the metathesis reaction of this protocol is a powerful tool for the construction of graphyne fragment backbones. For comparison, hexakis(arylethynyl)DBAs 9 c – g have also been prepared. The one‐photon absorption spectrum of tetrakis‐DBA 8 a bearing tert‐butyl groups revealed a remarkable bathochromic shift of the absorption cut‐off (λ_cutoff) compared with those of previously reported graphyne fragments due to extended π‐conjugation. Moreover, in the two‐photon absorption spectrum, 8 a showed a large cross‐section for a pure hydrocarbon because of the planar para‐phenylene‐ethynylene conjugation pathways. Hexakis(arylethynyl)‐DBAs 9 c – e and 9 g and tetrakis‐DBA 8 b bearing electron‐withdrawing groups aggregated in chloroform solutions. Comparison between the free energies of 9 e and 8 b bearing the same substituents revealed the more favorable association of the latter due to stronger π–π interactions between the extended π‐cores. Polarized optical microscopy observations, DSC, and XRD measurements showed that 8 b and 9 e with branched alkyl ester groups displayed columnar rectangular mesophases. By the time‐resolved microwave conductivity method, the columnar rectangular phase of 8 b was shown to exhibit a moderate charge‐carrier mobility of 0.12 cm² V^?1 s^?1. These results indicate that large graphyne fragments can serve as good organic semiconductors.     

Crystalline Supramolecular Nanofibers Based on Dehydrobenzoannulene Derivatives

Supramolecular nanofibers (SNFs) composed of low‐molecular‐weight π‐conjugated molecules exhibit attractive optical and electrical properties and are expected to be the next optoelectronic materials. In this work, five crystalline SNFs have been constructed from three dehydrobenzoannulene (DBA) derivatives. The DBAs were designed to assemble in one dimension in a strategy based on anisotropic crystal growth. The crystallinity of the SNFs allowed the molecular arrangements in the SNFs to be determined. Therefore the mechanism of construction and correlations between the molecular arrangements and optical and electrical properties could be considered. The results clearly indicate that the properties of the SNFs are affected by the chemical structures and molecular arrangements. Moreover, one of the SNFs exhibits a high charge‐carrier mobility (Σμ=0.61 cm² V^?1 s^?1) because of its crystallinity and appropriate molecular arrangement. This systematic experimental study based on a proposed strategy has provided information for improving the electrical properties of SNFs. This strategy will lead to highly functional SNFs.     

Structure Investigations on 4‐Halo‐1,2,3,5‐dithiadiazolyl Radicals XCNSSN• (X = F,Cl, Br): The Shortest Intradimer S···S Distance in Dithiadiazolyl Dimers

Crystals of the 4‐halo‐1,2,3,5‐dithiadiazolyl radicals (X = F, Cl, Br) were obtained by sublimation at 80 °C and 10^?2 Torr, and the structures were determined by X‐ray diffraction. The fluoro derivative crystallizes as a cisoid dimer in the space group P2₁/n, whereas the chloro and bromo derivatives crystallize isomorphous as twisted dimers in the space group C2/c. The chloro and bromo derivatives show the shortest intradimer S···S contacts of all known 1,2,3,5‐dithiadiazolyl dimers. In addition the obtained structure of ClCN₂S₂^? represents the fifth polymorph of ClCN₂S₂^? characterized by X‐ray crystallography. The structures and the packing including secondary interactions are discussed.     

Formation and Geometrical Control of Polygon‐Like Metal‐Coordination Assemblies

Polygon‐like [2+2]‐ and [3+3]‐type metal complexes were prepared from dipyrrin dimers connected by acute‐angled spacers. The electrical conduction depends strongly on the packing alignment of the compounds, revealing the presence of effective hopping pathways for holes with relatively high mobility up to 0.11 cm² V^?1 s^?1 along the aligned axis of [3+3]‐type metal‐bridged assemblies. These observations correlated with the geometrical control of the π‐conjugated metal complexes in the cyclic structures, which enables their ordered arrangement in the assemblies.     

High‐performance field‐effect transistors based on furan‐containing diketopyrrolopyrrole copolymer under a mild annealing temperature

Two furan‐flanked polymers poly{3,6‐difuran‐2‐yl‐2,5‐di(2‐octyldodecyl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐alt‐thienylenevinylene} (PDVFs), with a highly π‐extended diketopyrrolopyrrole backbone, are developed for solution‐processed high‐performance polymer field‐effect transistors (FETs). Atomic force microscopy and grazing incidence X‐ray scattering analyses indicate that PDVF‐8 and PDVF‐10 films exhibit a similar nodular morphology with the ultrasmall lamellar distances of 16.84 and 18.98 Å, respectively. When compared with the reported polymers with the same alkyl substitutes, this is the smallest d‐spacing value observed to date. This closed lamellar crystallinity facilitates charge carrier transport. Therefore, polymer thin‐film transistors fabricated from as‐spun PDVF‐8 films exhibit a high hole mobility exceeding 1.0 cm² V^?1 s^?1 with a current on/off ratio above 10⁶. After annealing treatment at 100 °C in air, the highest hole mobility of PDVF‐8‐based FETs was significantly improved to 1.90 cm² V^?1 s^?1, which is among the highest values of the reported FET devices fabricated from polymer thin films based on this mild annealing temperature. In contrast, long alkyl‐substituted PDVF‐10 exhibited a relatively low hole mobility of 1.65 cm² V^?1 s^?1 mainly resulting from low molecular weight. This work demonstrated that PDVFs would be promising semiconductors for developing cost‐effective and large‐scale production of flexible organic electronics. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1970–1977     

Two‐Step direct arylation for synthesis of naphthalenediimide‐based conjugated polymer

A naphthalenediimide (NDI)‐based conjugated polymer was synthesized by a two‐step direct C‐H arylation sequence. In the first step, two ethylenedioxythiophene units were coupled to NDI by direct arylation. In the second step, the direct arylation polycondensation of the monomer, formed in the first step, with 2,7‐dibromo‐9,9‐dioctylfluorene afforded the corresponding NDI‐based conjugated polymer ( PEDOTNDIF ) with molecular weight of 21,500 in 91% yield. The optical and electrochemical properties of the polymer were evaluated. The polymer showed ambipolar behavior in organic field‐effect transistors (OFETs). The electron mobility of PEDOTNDIF was estimated to be 2.3 × 10^?6 cm² V^?1 s^?1 using an OFET device with source‐drain (S‐D) Au electrodes. A modified OFET device with S‐D MgAg electrodes increased the electron mobility for PEDOTNDIF to 1.0 × 10^?5 cm² V^?1 s^?1 due to the more suitable work function of these electrodes, which reduced the injection barrier to the semiconducting polymer. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1401–1407     

Diketopyrrolopyrrole‐based acceptor–acceptor conjugated polymers: The importance of comonomer on their charge transportation nature

Besides the donor–acceptor (D–A) type, acceptor–acceptor (A–A) polymers are another class of important alternative conjugated copolymers, but have been less studied in the past. In this study, two kinds of A–A polymers, P1 and P2 , have been designed and synthesized based on diketopyrrolopyrrole in combination with the second electron‐deficient unit, perylenediimide or thieno[3,4‐c]pyrrole‐4,6‐dione. UV–vis absorption spectroscopy revealed that these two kinds of polymers have a band gap of 1.28–1.33 eV. Their highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are around ?5.6 and ?4.0 eV for P1 polymers, whereas ?5.4 and ?3.7 eV for P2 polymers, respectively. Density functional theory study disclosed that P1 backbone is in a vastly twisting state, whereas that of P2 is completely planar. Furthermore, organic field‐effect transistor devices were fabricated using these two kinds of polymers as the active material. Of interest, the devices based on P1 polymers displayed n‐channel behaviors with an electron mobility in the order of 10^?4 cm² V^?1 s^?1. In contrast, the P2 ‐based devices exhibited only p‐channel charge transportation characteristics with a hole mobility in the order of 10^?3 cm² V^?1 s^?1. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2356–2366     

Synthesis,morphology, and field‐effect transistor characteristics of new crystalline–crystalline diblock copolymers of poly(3‐hexylthiophene‐block‐steryl acrylate)

We report the synthesis, morphology, and charge‐transporting characteristics of new crystalline–crystalline diblock copolymers, poly(3‐hexylthiophene‐block‐stearyl acrylate) (P3HT‐b‐PSA). Three different diblock copolymers, P1 , P2 , and P3 , with P3HT/PSA polymerization degree block ratios of 60/26, 60/50, and 60/360, respectively, were prepared for investigating the morphology‐property relationship and the dependence of optoelectronic properties on the block copolymer structure. Small‐ and wide‐angle X‐ray scattering indicated the presence of both P3HT and PSA crystalline domains and the presence of microphase separation among blocks. The transmission electron microscopy and atomic force microscopy results revealed that the diblock copolymers cast from chlorobenzene, tended to form needle‐like morphologies. The field‐effect mobilities of the diblock copolymers deposited on untreated SiO₂ substrates, decreased with increasing PSA block length. In a sharp contrast, the mobilities enhanced with increasing PSA content when the P3HT‐b‐PSA was deposited on phenyltrichlorosilane (PTS)‐treated substrates. The copolymers with a 60/360 P3HT/PSA ratio showed a good mobility of 4 × 10^?3 cm² V^?1 s^?1 and a high on/off ratio of 7 × 10⁶ on PTS‐treated substrates. This study highlighted the importance of the block ratio, the substrate and self‐assembly structures on the charge transport characteristics of the crystalline–crystalline conjugated diblock copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

RGB Small Molecules Based on a Bipolar Molecular Design for Highly Efficient Solution‐Processed Single‐layer OLEDs

In this paper, we describe a bipolar molecular design for small molecule solution‐processed organic light emitting diodes (OLEDs). Combining the rigidity of the conjugated emissive cores and the flexibility of the peripheral alkyl‐linked carbazole groups, two series of highly efficient bipolar RGB (red, green, blue) emitters have been synthesized and characterized. The emissive cores are composed of electron‐withdrawing groups; the carbazole groups endow the materials electron‐donating units. Such bipolar structures are advantageous for the carrier injection and balance. Four peripheral carbazole groups are introduced in T‐series materials (TCDqC, TCSoC, TCBzC, TCNzC), and another four in O‐series materials (OCDqC, OCSoC, OCBzC, OCNzC). With the single‐layer device configuration of ITO/PEDOT:PSS/emitting layer/CsF/Al, two green devices exhibited excellent performance with a maximum luminescence efficiency of over 6.4 cd A^?1, and a high maximum luminance of more than 6700 cd m^?2. In addition, compared with the T‐series, the luminescence efficiency of blue and red devices based on O‐series materials increased from 1.6 to 2.8 cd A^?1 and 0.2 to 1.3 cd A^?1, respectively. To our knowledge, the performance of the blue device based on OCSoC is among the best of the blue small‐molecule solution‐processed single‐layer devices reported so far.