Polythiophenes are one of the most important classes of conjugated polymers, with a wide range of applications, such as conducting films, electrochromics, and field‐effect transistors, which have been the subject of a number of older and more recent reviews. Much less attention has been paid to the light‐emitting properties of this class of materials, although their unique properties present a number of opportunities unavailable from more popular polymeric light emitters such as polyfluorene or poly(p‐phenylene vinylene). This article reviews achievements to date in applications of thiophene‐based polymers and oligomers as electroluminescent materials. We demonstrate the basic principles of controlling the optical properties of polythiophenes through structural modifications and review the most important light‐emitting materials created from thiophene derivatives. Special attention is paid to consequences of structural variations on the performance of light‐emitting diodes fabricated with these materials.

Bright and stable blue emitters with narrow full‐width at half‐maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al3+) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead‐halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion‐exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red‐emitting CdSe@ZnS NCs result in UV‐pumped white light‐emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU‐R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low‐cost, earth‐abundant, solution‐processable Al‐doped perovskite NCs can be promising candidate materials for blue down‐conversion layer in backlit displays.

A new method of fabricating small metal-molecule-metal junctions is developed, approaching the single-molecule limit. The conductance of different conjugated molecules in a broad temperature, source-drain, and gate voltage regime is reported. At low temperature, all investigated molecules display sharp conductance steps periodic in source-drain voltage. The position of these steps can be controlled by a gate potential. The spacing corresponds to the energy of the lowest molecular vibrations. These results show that the low-bias conductance of molecules is dominated by resonant tunneling through coupled electronic and vibration levels.

Multi-resonance induced by boron and nitrogen atoms in opposite resonance positions endows a thermally activated delayed fluorescence (MR-TADF) emitter with a strikingly small full width at half maximum of only 26 nm and excellent photoluminescence quantum yield of up to 97.48 %. The introduction of a carbazole unit in the para position of the B-substituted phenyl-ring can significantly boost up the resonance effect without compromising the color fidelity, subsequently enhancing the performances of the corresponding pure blue TADF-OLED, with an outstanding external quantum efficiency (EQE) up to 32.1 % and low efficiency roll-off, making it one of the best TADF-OLEDs in the blue region to date. Furthermore, utilizing this material as host for a yellow phosphorescent emitter, the device also shows a significantly reduced turn-on voltage of 3.2 V and an EQE of 22.2 %.

A series of alkyl chain end-capped oligofluorene−thiophenes have been prepared with high yields using Suzuki or Stille coupling reactions. The electronic and optical properties of the thin films deposited at different substrate temperatures have been investigated. Morphological studies using transmission electron microscopy (TEM) revealed well-interconnected microcrystalline domains in these thin films. X-ray diffraction measurements of the vacuum-evaporated films showed enhanced crystalline order with increasing substrate deposition temperature. Thermal analysis as well as electrochemical measurements of the materials indicated that the new oligomers have high thermal and oxidative stability. Highly ordered polycrystalline vacuum-evaporated films with charge carrier mobility as high as 0.12 cm2 V-1 s-1 have been achieved with 5,5‘-bis(7-hexyl-9H-fluoren-2-yl)-2,2‘-bithiophene (DHFTTF). Thin film field-effect transistor (TFT) devices made from these materials showed remarkable stability even after UV (366 nm) irradiation for more than 48 h in air. The semiconductors exhibit high on/off ratios (up to 105) and no significant decrease in mobility and on/off ratio over several months in air with exposure to ambient light. Finally, bright emission colors from greenish yellow to orange-red were observed in this new series of oligomer solid films excited with UV light (366 nm). In addition, a comparative study of the newly synthesized oligomers with α,α‘-dihexylsexithiophene (DH6T), one of the most widely investigated oligothiophenes, is presented. The current approach to the molecular design can be applied toward the rational design of new TFT materials.

The development of new organic semiconductors with improved electrical performance and enhanced environmental stability is the focus of considerable research activity. This communication presents the design, synthesis, and device stability data for novel bis-5'-alkylthiophen-2'yl-2,6-anthracene organic semiconductors. When incorporated into thin-film field-effect transistors, mobilities as high as 0.5 cm2/Vs and on/off current ratios greater than 107 are observed. We have investigated device stability in terms of both shelf life and operating lifetime. Devices incorporating the reported semiconductors display an average field-effect mobility of 0.4 cm2/Vs for DHTAnt and an on/off current ratio of 106 even after 15 months of storage. Furthermore, there is no decrease in performance during continuous operation of the devices over several thousand cycles.

Postdeposition solvent annealing of water-dispersible conducting polymers induces dramatic structural rearrangement and improves electrical conductivities by more than two orders of magnitude. We attain electrical conductivities in excess of 50 S∕cm when polyaniline films are exposed to dichloroacetic acid. Subjecting commercially available poly(ethylene dioxythiophene) to the same treatment yields a conductivity as high as 250 S∕cm. This process has enabled the wide incorporation of conducting polymers in organic electronics; conducting polymers that are not typically processable can now be deposited from solution and their conductivities subsequently enhanced to practical levels via a simple and straightforward solvent annealing process. The treated conducting polymers are thus promising alternatives for metals as source and drain electrodes in organic thin-film transistors as well as for transparent metal oxide conductors as anodes in organic solar cells and light-emitting diodes.electrical conductivity | solar cells | thin-film transistors | light-emitting diodes | polyaniline

nanotube is observed and the lower side of the wall corresponds to the outside of the nanotube. The thickness of the wall is about 3.3 nm and it consists of many parallel graphene layers. Each layer, however, curves and wrinkles to some extent, indicating lower crystallinity of the present nanotubes than the ones prepared by other methods, such as arc discharge synthesis. It should be noted that this image does not exhibit any clear difference in crystallinity between pure carbon layers (upper half of the wall) and N-doped layers (the lower half). In the case of nanotubes from P-A CVD, their HRTEM images (not shown here) were found to be very similar to the image of Figure 4, and again there was no crystallinity difference between N-doped and undoped multiwalls.In conclusion, this study has demonstrated the fabrication of aligned carbon nanotubes with double coaxial structure of N-doped and undoped multiwalls. It can be determined whether the N-doped layer belongs to the inner or outer multiwalls by changing the sequence of the two-step CVD process. Moreover, the thickness of both the N-doped and pure carbon layers is controllable by changing each CVD period. The use of the AAO film as a template enables us for the first time to precisely control the nitrogen location in N-doped carbon nanotubes. Since nitrogen doping would enhance the electron-conducting properties of carbon nanotubes, the present carbon nanotubes may exhibit excellent performance as field electron emitters. The present technique opens up a novel route for the synthesis of heteroatom-doped carbon nanotubes with double coaxial structure and furthermore this will lead to the production of coaxial heterojunctions (pn, npn, or pnp) by stacking N-and B-doped layers. ExperimentalBy anodic oxidation of an aluminum plate, an AAO film with a channel diameter of 30 nm and a thickness of about 70 lm was prepared. Details are given elsewhere [13]. The resultant AAO film was placed on a quartz boat in a horizontal quartz reactor (inside diameter 55 mm). The reactor temperature was then increased to 800 C under N 2 flow. When the temperature reached 800 C, propylene gas (1.2 % in N 2 ) was passed through the reactor at a total flow rate of 1000 cm 3 (STP)/min. After the 2 h carbon deposition from propylene, the reactor was cooled down to room temperature and the carbon-coated AAO film taken out. In the second step, the carbon-coated film was placed in the reactor again and acetonitrile vapor (4.2 % in N 2 of 500 cm 3 (STP)/min) was allowed to flow over the film at 800 C. The vapor was generated by bubbling N 2 through acetonitrile liquid in a saturator kept at 0 C. This acetonitrile CVD was performed for 5 h. After this two-step sequential CVD process, the doubly coated AAO film was treated with 10 M NaOH solution at 150 C for 6 h to remove the alumina template, thereby liberating the nanotubes from the template AAO film.The carbon-coated AAO films and the corresponding carbon nanotubes were analyzed by X-ray photoelectron spectroscopy (XPS). The samples were...