Since the report of the first diketopyrrolopyrrole (DPP)-based polymer semiconductor, such polymers have received considerable attention as a promising candidate for high-performance polymer semiconductors in organic thin-film transistors (OTFTs). This Progress Report summarizes the advances in the molecular design of high-mobility DPP-based polymers reported in the last few years, especially focusing on the molecular design of these polymers in respect of tuning the backbone and side chains, and discussing the influences of structural modification of the backbone and side chains on the properties and device performance of corresponding DPP-based polymers. This provides insights for the development of new and high-mobility polymer semiconductors.

The integration of graphene nanosheets on the macroscopic level using a self-assembly method has been recognized as one of the most effective strategies to realize the practical applications of graphene materials. Here, a facile and scalable method is developed to synthesis two types of graphene-based networks, manganese dioxide (MnO₂)–graphene foam and carbon nanotube (CNT)–graphene foam, by solution casting and subsequent electrochemical methods. Their practical applications in flexible all-solid-state asymmetric supercapacitors are explored. The proposed method facilitates the structural integration of graphene foam and the electroactive material and offers several advantages including simplicity, efficiency, low-temperature, and low-cost. The as-prepared MnO₂–graphene and CNT–graphene electrodes exhibit high specific capacitances and rate capability. By using polymer gel electrolytes, a flexible all-solid-state asymmetric supercapacitor was synthesized with MnO₂–graphene foam as the positive electrode and CNT-graphene as the negative electrode. The asymmetric supercapacitors can be cycled reversibly in a high-voltage region of 0 to 1.8 V and exhibit high energy density, remarkable rate capability, reasonable cycling performance, and excellent flexibility.

Two aggregation-induced emission active luminogens (TPE–pTPA and TPE–mTPA) were successfully synthesized. For comparison, another six similar compounds were prepared. Because of the introduced hole-dominated triphenylamine (TPA), fluorene groups with high luminous efficiency, and unconjugated linkages, the π conjugation length of the obtained luminogens is effectively restricted to ensure their blue emission. The undoped organic light-emitting diodes based on TPE–pTPA and TPE–mTPA exhibited blue or deep-blue emissions, low turn-on voltages (3 V), and high electroluminescence efficiencies with L_max, η_C,max, and η_P,max values of up to 26 697 cd m⁻², 3.37 cd A⁻¹, and 2.40 Lm W⁻¹.

The advantages of organic field-effect transistors, such as low cost, mechanical flexibility and large-area fabrication, make them potentially useful for electronic applications such as flexible switching backplanes for video displays, radio frequency identifications and so on. A large amount of molecules were designed and synthesized for electron transporting (n-type) and ambipolar organic semiconductors with improved performance and stability. In this review, we focus on the advances in performance and molecular design of n-type and ambipolar semiconductors reported in the past few years.

The interface between the organic semiconductor and dielectric plays an important role in determining the device performance of organic field-effect transistors (OFETs). Although self-assembled monolayers (SAMs) made from organosilanes have been widely used for dielectric modification to improve the device performance of OFETs, they suffer from incontinuous and lack uniform coverage of the dielectric layer. Here, it is reported that by introduction of a solution-processed organozinc compound as a dielectric modification layer between the dielectric and the silane SAM, improved surface morphology and reduced surface polarity can be achieved. The organozinc compound originates from the reaction between diethylzinc and the cyclohexanone solvent, which leads to formation of zinc carboxylates. Being annealed at different temperatures, organozinc compound exists in various forms in the solid films. With organozinc modification, p-type polymer FETs show a high charge carrier mobility that is about two-fold larger than a control device that does not contain the organozinc compound, both for devices with a positive threshold voltage and for those with a negative one. After organozinc compound modification, the threshold voltage of polymer FETs can either be altered to approach zero or remain unchanged depending on positive or negative threshold voltage they have.

With the aim to develop new tetraphenylethylene (TPE)-based conjugated hyperbranched polymer, TPE units, one famous aggregation-induced emission (AIE) active group, are utilized to construct hyperbranched polymers with three other aromatic blocks, through an “A₂+B₄” approach by using one-pot Suzuki polycondensation reaction. These three hyperbranched polymers exhibit interesting AIEE behavior and act as explosive chemsensors with high sensitivity both in the nanoparticles and solid states. This is the first report of the AIE activity of the TPE-based conjugated hyperbranched polymers. Their corresponding PLED devices also demonstrate good performance.

2,4,6-Tri(2-thienyl)pyridine is used to synthesize the new conjugated polymer PBDTTPy for OFET applications. The concept of introducing electron-deficient pyridine repeating units and meta-linked structures into a conjugated polymer to reduce its HOMO energy level and thereby increase its ambient stability is tested. The absorption spectrum of the polymer thin film displays a large bathochromic shift compared with its solution absorption spectrum. The polymer PBDTTPy shows a typical amorphous structure in the solid state. The first OFET device based on a conjugated polymer with meta-linked trithienylpyridine units is reported. PBDTTPy exhibits p-type transport under ambient conditions in a bottom-gate, top-contact OFET device with a mobility of 2.4 × 10⁻⁴ cm² V⁻¹ s⁻¹.

Particular attention has been focused on n-channel organic thin-film transistors (OTFTs) during the last few years, and the potentially cost-effective circuitry-based applications in flexible electronics, such as flexible radiofrequency identity tags, smart labels, and simple displays, will benefit from this fast development. This article reviews recent progress in performance and molecular design of n-channel semiconductors in the past five years, and limitations and practicable solutions for n-channel OTFTs are dealt with from the viewpoint of OTFT constitution and geometry, molecular design, and thin-film growth conditions. Strategy methodology is especially highlighted with an aim to investigate basic issues in this field.

Graphene, a two-dimensional material, is regarded as one of the most promising candidates for future nanoelectronics due to its atomic thickness, excellent properties and widespread applications. As the first step to investigate its properties and finally to realize the practical applications, graphene must be synthesized in a controllable manner. Thus, controllable synthesis is of great significance, and received more and more attention recently. This Progress Report highlights recent advances in controllable synthesis of graphene, clarifies the problems, and prospects the future development in this field. The applications of the controllable synthesis are also discussed.

Oligoarenes as an alternative group of promising semiconductors in organic optoelectronics have attracted much attention. However, high-performance and low-cost opto-electrical devices based on linear asymmetric oligoarenes with nano/microstructures are still rarely studied because of difficulties both in synthesis and high-quality nano/microstructure growth. Here, a novel linear asymmetric oligoarene 6-methyl-anthra[2,3-b]benzo[d]thiophene (Me-ABT) is synthesized and its high-quality microribbons are grown by a solution process. The solution of Me-ABT exhibits a moderate fluorescence quantum yield of 0.34, while the microribbons show a glaucous light emission. Phototransistors based on an individual Me-ABT microribbon prepared by a solution-phase self-assembly process showed a high mobility of 1.66 cm² V⁻¹ s⁻¹, a large photoresponsivity of 12 000 A W⁻¹, and a photocurrent/dark-current ratio of 6000 even under low light power conditions (30 µW cm⁻²). The measured photoresponsivity of the devices is much higher than that of inorganic single-crystal silicon thin film transistors. These studies should boost the development of the organic semiconductors with high-quality microstructures for potential application in organic optoelectronics.

A new series of full hydrocarbons, namely 4,4′-(9,9′-(1,3-phenylene)bis(9H-fluorene-9,9-diyl))bis(N,N-diphenylaniline) (DTPAFB), N,N′-(4,4′-(9,9′-(1,3-phenylene)bis(9H-fluorene-9,9-diyl))bis(4,1-phenylene))bis(N-phenylnaphthalen-1-amine) (DNPAFB), 1,3-bis(9-(4-(9H-carbazol-9-yl)phenyl)-9H-fluoren-9-yl)benzene, and 1,3-bis(9-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-9H-fluoren-9-yl)benzene, featuring a highly twisted tetrahedral conformation, are designed and synthesized. Organic light-emitting diodes (OLEDs) comprising DNPAFB and DTPAFB as hole transporting layers and tris(quinolin-8-yloxy)aluminum as an emitter are made either by vacuum deposition or by solution processing, and show much higher maximum efficiencies than the commonly used N,N′-di(naphthalen-1-yl)-N,N′-diphenylbiphenyl-4,4′-diamine device (3.6 cd A⁻¹) of 7.0 cd A⁻¹ and 6.9 cd A⁻¹, respectively. In addition, the solution processed blue phosphorescent OLEDs employing the synthesized materials as hosts and iridium (III) bis[(4,6-di-fluorophenyl)-pyridinato-N, C²] picolinate (FIrpic) phosphor as an emitter present exciting results. For example, the DTPAFB device exhibits a brightness of 47 902 cd m⁻², a maximum luminescent efficiency of 24.3 cd A⁻¹, and a power efficiency of 13.0 lm W⁻¹. These results show that the devices are among the best solution processable blue phosphorescent OLEDs based on small molecules. Moreover, a new approach to constructing solution processable small molecules is proposed based on rigid and bulky fluorene and carbazole moieties combined in a highly twisted configuration, resulting in excellent solubility as well as chemical miscibility, without the need to introduce any solubilizing group such as an alkyl or alkoxy chain.

A series of fused thiophenes composed of fused α-oligothiophene units as building blocks, end-capped with either styrene or 1-pentyl-4-vinylbenzene groups, has been synthesized through Stille coupling reactions. The compounds have been fully characterized by means of ¹H NMR spectrometry, high-resolution mass spectrometry, and elemental analysis. The molecules present a trans–trans configuration between their double bonds, which has been verified and confirmed by Fourier-transform infrared spectroscopy and single-crystal X-ray diffraction analysis. The X-ray crystal structures showed π–π overlap and sulfur–sulfur interactions between the adjacent molecules. The decomposition temperatures were all found to be above 300 °C, indicating that compounds of this series possess excellent thermal stability. The fact that no phase transition occurs at low temperature indicates that they should be well-suited for application in devices. Moreover, they possess low HOMO energy levels, based on cyclic voltammetry measurements, and suitable energy gaps, as determined from their thin-film UV/Vis spectra. Thin-film X-ray diffraction analysis and atomic force microscopy revealed high crystallinity on supporting substrates. In addition, as the substrate temperature has a significant influence on the morphology and the degree of crystallinity, the device performance could be optimized by varying the substrate temperature. These materials were found to exhibit optimal field-effect performance, with a mobility of 0.17 cm² V⁻¹ s⁻¹ and an on/off ratio of 10⁵, at a substrate temperature of 70 °C.

The synthesis, characterization, and field-effect transistor (FET) properties of a new class of thieno[3,2-b]thieno[2′,3′:4,5]thieno[2,3-d]thiophene derivatives are described. The optical spectra of their films show the presence of stronger interactions between molecules in the solid state. Thermal analyses reveal that the three materials are thermally stable and have no phase transitions at low temperature. The crystal structures are determined, and show π-stacked structures and intermolecular S···S contacts. These organic materials exhibit p-type FET behavior with hole mobilities as high as 0.14 cm² V⁻¹ s⁻¹ and an on/off current ratio of 10⁶. These results indicate that thieno[3,2-b]thieno [2′,3′:4,5]thieno[2,3-d]thiophene, as a linear π-conjugated system, is an effective building block for developing high-performance organic semiconductors.

A new hyperbranched polymer (HB-car), constructed fully by carbazole moieties, is successfully synthesized through a one-pot Suzuki coupling reaction. The resultant polymer is well-characterized, and its hole-transporting ability is studied carefully. The device, in which HB-car is utilized as a hole-transporting layer and tris-(8-hydroxyquinoline) aluminum as an electron-emitting layer as well as electron-transporting layer, gives a much higher efficiency (3.05 cd A^–1), than that of a poly(N-vinylcarbazole) based device (2.19 cd A^–1) under similar experimental conditions. The remarkable performance is attributed to its low energy barrier and enhanced hole-drifting ability in the HB-car based device. In addition, for the first time, a field-effect transistor (FET) based on the hyperbranched polymer is fabricated, and the organic FET device shows that HB-car is a typical p-type FET material with a saturation mobility of 1 × 10^–5 cm² V^–1 s^–1, a threshold voltage of –47.1 V, and an on-to-off current ratio of 10³.

Single-walled carbon nanotubes (SWNTs) are a promising material for future nanotechnology. However, their applications are still limited in success because of the co-existence of metallic SWNTs and semiconducting SWNTs produced samples. Here, electrochemical etching, which shows both diameter and electrical selectivity, is demonstrated to remove SWNTs. With the aid of a back-gate electric field, selective removal of metallic SWNTs is realized, resulting in high-performance SWNT field-effect transistors with pure semiconducting SWNT channels. Moreover, electrochemical etching is realized on a selective area. These findings would be valuable for research and the application of SWNTs in electrochemistry and in electronic devices.

A series of fluorene-based oligomers with novel spiro-annulated triarylamine structures, namely DFSTPA, TFSTPA, and TFSDTC, are synthesized by a Suzuki cross-coupling reaction. The spiro-configuration molecular structures lead to very high glass transition temperatures (197–253 °C) and weak intermolecular interactions, and consequently the structures retain good morphological stability and high fluorescence quantum efficiencies(0.69–0.98). This molecular design simultaneously solves the spectral stability problems and hole-injection and transport issues for fluorene-based blue-light-emitting materials. Simple double-layer electroluminescence (EL) devices with a configuration of ITO/TFSTPA (device A) or TFSDTC (device B)/ TPBI/LiF/Al, where TFSTPA and TFSDTC serve as hole-transporting blue-light-emitting materials, show a deep-blue emission with a peak around 432 nm, and CIE coordinates of (0.17, 0.12) for TFSTPA and (0.16, 0.07) for TFSDTC, respectively, which are very close to the National Television System Committee (NTSC) standard for blue (0.15, 0.07). The maximum current efficiency/external quantum efficiencies are 1.63 cd A⁻¹/1.6% for device A and 1.91 cd A⁻¹/2.7% for device B, respectively. In addition, a device with the structure ITO/DFSTPA/Alq₃/LiF/Al, where DFSTPA acts as both the hole-injection and -transporting material, is shown to achieve a good performance, with a maximum luminance of 14 047 cd m⁻², and a maximum current efficiency of 5.56 cd A⁻¹. These values are significantly higher than those of devices based on commonly usedN,N′-di(1-naphthyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (NPB) as the hole-transporting layer (11 738 cd m⁻² and 3.97 cd A⁻¹) under identical device conditions.

A series of novel branched polythiophene derivatives bearing different densities of vinylene-bridges as linking chains were synthesized by a general synthetic strategy. The organic field-effect transistors, which were fabricated by spin-coating the polymer solutions onto octadecyltrichlorosilane-modified SiO₂/Si substrates with top-contact configuration, afforded a high mobility of 8.0 × 10⁻³ cm² V⁻¹ s⁻¹ with an on/off ratio greater than 10⁴ and a threshold voltage of about −3 V in saturation regime. The devices based on these polymers possessed better performance than those of polymers without conjugated bridges and polymers with longer conjugated bridges. These results demonstrated that the combination of conjugated polythiophene backbones and vinylene-bridges would improve the carrier mobility. As an emerging class of conjugated materials, polymers with vinylene-bridges as linking chains would open up new opportunities in organic electronics, and their applications in organic electronics are promising. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1381–1392, 2009

A novel conjugated polymer, poly(thienylene-vinylene-thienylene) with cyano substituent (CN-PTVT) was synthesized via Stille coupling for the application in air stable field-effect transistor and polymer solar cell. The polymer was characterized by ¹H NMR, elemental analysis, UV-vis absorption and photoluminescence spectroscopy, TGA, cyclic voltammetry and XRD analysis. CN-PTVT exhibits a good thermal stability with 5% weight loss at 306 °C. The FET hole mobility of the polymer reached 5.9 × 10⁻³ cm² V⁻¹ s⁻¹ with I_on/I_off ratio of 4.9 × 10⁴, which is one of the highest performance among the air-stable amorphous polymers. The polymer solar cell based on CN-PTVT as donor and PCBM as acceptor shows a relatively high open-circuit voltage of 0.82 V and a power conversion efficiency of 0.3% under the illumination of AM1.5, 100 mW/cm². © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4028–4036, 2009

Poly(3-[2-(5-hexyl-2-thienyl) ethenyl]-2,2′-bithiophene) (P2, see Scheme 1) with conjugated thienylvinyl side chain was synthesized by copolymerization of the thiophene units with and without conjugated side chain with Pd-catalyzed Stille coupling method. For comparison, P1 with the hexyl side chain instead of conjugated side chain was also synthesized. P2 film shows broad absorption in the visible region with absorption edge at about 700 nm. The solution-processed polymer field-effect transistors were fabricated and characterized with bottom gate/top contact geometry. The organic field-effect transistors (OFET) based on P2 showed an average hole mobility of about 0.034 cm²/Vs (the highest value reached 0.061 cm²/Vs) upon annealing at about 180 °C for 30 min, with a threshold voltage of −1.15 V and an on/off ratio of 10⁴ with n-octadecyltrichlorosilane (OTS) modified SiO₂ substrate. In comparison, the OFET based on P1 displayed a hole mobility of 8.9 × 10^–4 cm²/Vs and an on/off ratio of 10⁴ with OTS modified SiO₂ substrate. The results indicate that the polythiophene derivative with conjugated thienylvinyl side chain is a promising polymer for the application in polymer field-effect transistors. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5304–5312, 2009

A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3-b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single-crystal X-ray studies demonstrated that the length of the substituent side chains greatly affects the solid-state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low-lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di-n-hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91 %. Solution-processed green phosphorescent organic light-emitting diodes with the di-n-butyl derivative as the host material exhibited a maximum brightness of 14 185 cd m⁻² and a luminescence efficiency of 12 cd A⁻¹.