We fabricated a unique ternary organic hybrid microwire radial heterojunction by a facile method. First, 4,4′,4′′-tri(N-carbazolyl)triphenylamine (TCTA) microwires were prepared by solvent-evaporation-assisted self-assembly. Then, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles were adsorbed onto the surface of the TCTA microwires, forming interesting corncob-like binary hybrid microwires. Finally, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) was adsorbed on the surface of the binary hybrid microwires to form ternary hybrid microwire radial heterojunctions. The thermally activated delayed fluorescence (TADF) material 4CzIPN was introduced into the donor–acceptor (D–A) system to form the ternary hybrid microwire radial heterojunction for the first time. The morphology has been confirmed by fluorescence microscopy, SEM and TEM. Interestingly, we found that this ternary hybrid microwire exhibited efficient photoconductivity by fabricating a bottom contact device; the photocurrent increased by more than 3 times compared with the reference device without 4CzIPN. By examining some reference devices, it can be inferred that the enhancement of the photoconductivity originates from the reversed intersystem crossing (RISC) process in 4CzIPN. This process can promote the formation of triplet excitons, thereby increasing the charge carrier concentration in the conductive channel of the microwire radial heterojunction. These high photoconductivity ternary microwires provide an efficient approach to improve the performance of photovoltaic devices and show promise for applications in organic integrated optoelectronics.

Organic nano/micro one-dimensional (1D) materials are generally considered as promising materials for flexible, portable optoelectronic devices due to their well-known distinctive feature. Over the past few years, numerous organic nano/micro 1D photosensitive resistors have been developed; however, as one of the important photoelectronic components for fabricating organic nano/microelectronic circuits, organic nano/micro 1D photodiodes have not been reported yet. Herein, on the basis of our previous work about an organic photosensitive radial heterostructure microwire, we tried to prepare another kind of radial heterostructure microwire and explore its photodiode properties. Excitingly, the organic radial heterostructure microwire using aluminum tris(8-hydroxyquinoline) as the core and poly(3-hexyl thiophene) as the shell, which was prepared by a solution-based method, showed excellent performance with a large rectification ratio, a high on/off ratio and a good photoresponsivity under ambient conditions. Our work has developed a convenient method to prepare microwire photodiodes based on an all-organic heterojunction.

Herein, we report a facile self-assembly strategy to prepare a novel 1D organic semiconductor/graphene microribbon heterojunction by coating a layer of graphene sheets on the organic semiconductor microribbon. The organic semiconductor microribbon composed of a p-type small molecule 3,7-bis(5-(2-ethylhexyl)thiophen-2-yl)dithieno[2,3-b:2′,3′-e]pyrazine (BEHT-DTP) was prepared by evaporation-induced self-assembly. Subsequently the graphene nanosheets, as an electron acceptor, were self-assembled onto the surface of a BEHT-DTP microribbon in aqueous solution to form a 1D p–n junction. The device based on the single microribbon heterojunction demonstrated enhanced photoconductivity properties. This preliminary work points out a new path to fabricate 1D organic nano/micro-heterojunctions, avoiding complex molecular design and equipment.

Core–shell gold nanoparticles have been doped into the solution-processed electron-transporting layer (ETL) of polymer light-emitting diodes (PLEDs). By using this doping strategy, metal-enhanced fluorescence was realized in the device. The doped device has obtained enhanced luminance, enhanced luminous efficiency and a reduced turn-on voltage compared with that using the non-doped ETL.

Being incompatible with host materials in a physically blended emitting layer, phosphorescent dyes are prone to form aggregates induced by Joule heat in devices under work. In this work, a new and efficient blue phosphorescent dye Cz-C8-FIrpic was designed and synthesised by incorporating 9-phenyl-9H-carbazole into a commonly used blue emissive iridium complex bis(4,6-(difluorophenyl)pyridine-N,C2′)picolinate (FIrpic) via an alkyl chain linkage. This phosphorescent dye exhibits similar photophysical properties to the units of FIrpic and 9-phenyl-9H-carbazole in solutions. In solid films of Cz-C8-FIrpic, the energy transfer from 9-phenyl-9H-carbazole to FIrpic units is effective. The Cz-C8-FIrpic doped emissive layer was investigated by AFM, STEM-EDS, transient photoluminescence decay curves and molecular dynamics simulations. The results show that in the Cz-C8-FIrpic doped film the phase aggregation of FIrpic units is less severe than that in the typically used FIrpic film. In addition, the optimized Cz-C8-FIrpic based device achieved a maximum luminance of 25142 cd m−2, a maximum EQE of 8.5% and a maximum current efficiency of 22.5 cd A−1 which is about 15% higher than that of the control device based on FIrpic. We conclude that grafting a typically used dye to functional groups with alkyl chains is useful to restrict phase separation in physically blended emitting layers, and thus can achieve high electroluminescence performances.

Diphenylamino- or cabazolyl-endcapped silafluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been designed, synthesized, and characterized. Double layer electroluminescent devices of these silafluorene derivatives exhibited efficient blue emission. The non-doped double layer OLEDs containing TDMS, TDPS, CDMS, or CDPS exhibited better electroluminescence efficiencies than those of the devices using the reference emitter DPFL-NPB, among which the best device was with TDPS, which showed a maximum current efficiency of 1.62 cd A−1 and an external quantum efficiency (EQE) of 1.36%. The solution processed device using TDPS as dopant exhibited a high performance with an EQE of 2.48% and an obviously low turn-on voltage of 4 V, when compared to the results of the reference device. The replacement of the carbon atom of the fluorene unit with a silicon atom could lower the energy gap effectively and improve the thermal stability as well as optical performances. The results indicate that the end-capped arylamino groups affect the organic light-emitting diode (OLED) performances greatly and aryl or alkyl substitution on the 9-position of a silafluorene unit is also crucial to the OLED performances of this kind of silafluorene.

Organic semiconductor materials with one-dimensional (1D) radial (core–shell) heterojunction structures are highly desired for their expected excellent optoelectronic properties. However, currently, such structures are still in a fledgling period for optoelectronic applications due to the absence of both good materials and suitable preparation methods. Here we have synthesized a p-type organic semiconductor based on a new electron-donating unit (dithienopyrazine) and utilized it as a shell material to construct organic 1D radial p–n heterojunctions. This p-type compound shows a higher oxidation potential and is more resistant to photooxidation in air than its analogs with the commonly-used benzodithiophene unit. Moreover, we prepared organic microwires with radial heterojunctions via a solution-processed method by self-assembly of our p-type material on the surface of n-type cores. Thus, photoconductive devices based on an individual microwire with the radial heterojunction can be fabricated and demonstrate a high photoconductivity. Our work provides a path for preparing 1D radial heterojunctions suitable for optoelectronic applications.

Two kinds of host materials, 4,4′-(diphenylgermanediyl)bis(N,N-diphenylaniline) and bis(4-(9H-carbazol-9-yl)phenyl)diphenylgermane (DCzGe), for blue phosphorescent organic light emitting diodes (PhOLEDs) were designed by incorporating electron donating groups (carbazole and triphenylamine) into tetraphenylgermane, which is a new type of core moiety that has never been studied for use in this field. This molecular structure endows the compounds with a wide energy bandgap, high thermal/morphological stability and good solution processability. Based on the theoretic calculations, DCzGe was selected and synthesized as a host material which demonstrates a wide bandgap (Eg: 3.56 eV) and a high triplet energy (ET: 3.02 eV). It also exhibits a high glass transition temperature (110 °C), which is beneficial for resisting the Joule heat in devices. All solution processed, blue emitting PhOLEDs were fabricated by using a mixed host combining DCzGe and an electron-transporting material, with a maximum luminance of 10000 cd m−2 and a maximum current efficiency of 15.2 cd A−1. Furthermore, the devices showed a very low current efficiency roll-off, which remained as high as 15.2 cd A−1 at the luminance of 1000 cd m−2, and the roll-off is only 2.6% even at the higher luminance of 2000 cd m−2.

Two blue-emitting fluorescent polymers PTPATPPO and PTPATPP with small singlet–triplet splitting comprising triphenylamine and triphenylphosphine/triphenylphosphine oxide moieties have been designed and synthesized. An appropriate overlap between the HOMO and the LUMO in these compounds was realized. This design strategy endows the two blue-emitting polymers with a high triplet energy of 2.45 and 2.46 eV, a shallow HOMO level of −5.21 and −5.23 eV, and a bipolar feature to act as good host materials. Monochromic organic light-emitting devices (OLEDs) using these polymers as emitters show sky-blue emissions with Commission Internationale de l'Eclairage (CIE) coordinates of (0.24, 0.32) and (0.24, 0.31) together with a maximum current efficiency of 3.63 cd A−1. Moreover, the single-emitting-layer two-element fluorescent–phosphorescent (F–P) hybrid white OLEDs based on PTPATPPO or PTPATPP as both hosts and blue-emitting fluorophores were fabricated by a solution process. Among the two polymers, PTPATPPO-based F–P hybrid white OLEDs show better performance with a maximum current efficiency of 10.5 cd A−1, a maximum external quantum efficiency of 6.1%, CIE coordinates of (0.40, 0.34), and a maximum luminance of 11962 cd m−2.

Fluorescent organic nanoparticles have a much better photostability than molecule-based probes. Here, we report a simple strategy to detect chemicals and biomolecules by a binary nanoparticle system based on fluorescence resonance energy transfer (FRET). Poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO, energy donor) and poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV, energy acceptor) are utilized to prepare the binary nanoparticle system through a reprecipitation method. Since the FRET process is strongly distance-dependent, a change in the interparticle distance between the two kinds of nanoparticles after introduction of analytes will alter the FRET efficiency. The response of the binary nanoparticle system to cationic polyelectrolytes was investigated by monitoring the FRET efficiency from PFO to MEH-PPV nanoparticles and the fluorescence color of the nanoparticle solutions. Furthermore, the cationic polyelectrolyte pretreated binary nanoparticle system can be used to detect DNA by desorption of nanoparticles from the polyelectrolyte’s chains and the detection concentration can go down to 10–14 M. Thus, the binary nanoparticle system shows great promise for applications in chemical sensing or biosensing.Keywords: conjugated polymer; fluorescence; fluorescence resonance energy transfer; organic nanoparticles; polyelectrolyte; reprecipitation;

A series of fluorene derivatives end-capped with diphenylamino and oxadiazolyl were synthesized, and their photophysical and electrochemical properties are reported. Aggregation-induced emission (AIE) effects were observed for the materials, and bipolar characteristics of the molecules are favored with measurement of carrier mobility and calculation of molecular orbitals using density functional theory (DFT). Using the fluorene derivatives as emitting-layer, nondoped organic light-emitting devices (OLEDs) have been fabricated by spin-coating in the configuration ITO/PEDOT:PSS(35 nm)/PVK(15 nm)/PhN-OF(n)-Oxa(80 nm)/SPPO13(30 nm)/Ca(8 nm)/Al(100 nm) (n = 2–4). The best device with PhN-OF(2)-Oxa exhibits a maximum luminance of 14 747 cd/m2, a maximum current efficiency of 4.61 cd/A, and an external quantum efficiency (EQE) of 3.09% in the blue region. Investigation of the correlation between structures and properties indicates that there is no intramolecular charge transfer (ICT) increase in these molecules with the increase of conjugation length. The device using material of the shortest conjugation length as emitting-layer gives the best electroluminescent (EL) performances in this series of oligofluorenes.Keywords: AIE-active; blue; fluorene; nondoped; organic light-emitting devices

The small-molecule hole-blocking material SPPO13 has been doped with a non-conjugated polymer to act as the hole-blocking layer in solution-processed OLEDs. Such a doping strategy can significantly improve the electron injection in devices, resulting in an enhanced luminous efficiency and a reduced turn-on voltage.

A novel alcohol-soluble electron-transporting small-molecule material comprising oxadiazole and arylphosphine oxide moieties, ((1,3,4-oxadiazole-2,5-diyl)bis(4,1-phenylene))bis(diphenylphosphine oxide) (OXDPPO), has been synthesized and characterized. Its single crystal structure, together with the photophysical, electrochemical and thermal properties, has been investigated. This material not only possesses a wide bandgap with a low HOMO level but also exhibits a strong π–π stacking with a distance of 3.35 Å. Moreover, this compound shows excellent thermal stability with a high glass transition temperature of 104 °C and a decomposition temperature of 384 °C. The unique solubility in 2-propanol makes it a good candidate for fabricating fully solution-processed multilayer organic light-emitting diodes (OLEDs). Efficient solution-processed white OLEDs have been fabricated with this compound as an electron-transporting layer (ETL). It was found that this ETL can greatly balance the electrons and holes in devices with the high work-function metal cathode (Al) and an increase in luminous efficiency of ∼70-fold can be achieved. The maximum luminous efficiency of devices with an ETL/Al configuration is even higher than that of devices using a Ca cathode.

By attaching two electron-withdrawing trifluoromethyl (CF3) groups to the 2-phenylbenzothiazole cyclo-metalated ligand, a bis-trifluoromethyl-functionalized orange-emitting phosphorescent iridium(III) complex bis-(6-(trifluoromethyl)-2-(4-(trifluoromethyl)phenylbenzothiozolato))iridium(acetylacetonate) [(F3BT-CF3P)2Ir(acac)] was successfully synthesized. The optical, electrochemical and electroluminescence (EL) properties of this new complex were studied. The experimental results support the theoretical expectation that incorporating electron-withdrawing trifluoromethyl groups at the 4-site of the phenyl ring directly bonded to the metal center, and at the 6-site of 2-phenylbenzothiazole, cause a bathochromic shift in the emission peak and bring the emission color much closer to long-wavelength orange light. Moreover, such trifluoromethyl substituents can hinder the π–π stacking or self-polarization effect occurring from the aggregation of the molecules. The new iridium complex gives an unchanged luminescence spectrum, regardless of whether it is in solution, in untreated film or in film doped at different concentrations. Using this iridium complex as a dopant emitter, solution-processed single emissive layer orange and two-element white OLEDs with good performance can be obtained. Highly efficient orange electroluminescence was obtained with a maximum efficiency of 10.5 cd A−1 and CIE coordinates (0.48, 0.51). When combined with a commercial sky-blue phosphorescent emitter, (CF3BT–CF3P)2Ir(acac) can be utilized to achieve two-element white OLEDs that exhibited a high efficiency of 28.3 cd A−1. Such OLEDs retain high efficiency at a luminance suitable for lighting (e.g. 5000 cd m−2).

Solution-processed white organic light emitting diodes (WOLEDs) with quaternary ammonium salt doped water/alcohol soluble conjugated polyelectrolyte, poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluoren)] dibromide (PFNBr), as electron transport material has been fabricated. Compared with the undoped devices, the performances of such devices with a doped electron transport layer have been dramatically improved to be nearly twice high in luminous efficiency and nearly one-third in response time when the weight ratio of PFNBr to tetraethylammonium bromide (TEAB) was 10:3. Four kinds of quaternary ammonium salts have been investigated to be dopants in the conjugated polyelectrolyte electron transport layer. It has been shown that both the anions and the cations of quaternary ammonium salts can influence the device performance. The dopant who has both a smaller anion and a smaller cation size can exhibit a better device performance. In addition, ultraviolet photoelectron spectroscopy measurement and single-carrier device testing have been employed to investigate the reason why such quaternary ammonium salt dopants can make an obvious improvement in the device performance of WOLEDs. These findings will be beneficial to the progress in design and fabrication of solution-processed WOLEDs suitable for lighting.Keywords: conjugated polyelectrolyte; dopant; electron transport material; quaternary ammonium salt; solution-processing; white organic light-emitting diodes;

Solution-processed organic field-effect transistors (OFETs) were fabricated based on a hygroscopic biomaterial, egg-white albumin, as the gate dielectric and poly(3-hexylthiophene) as the semiconductor. With increasing humidity, such OFETs can show improved performance exhibiting a very low driving voltage, together with enhanced carrier mobility and suppressed off-state current.

•An orange–red iridium(III) complex (CF3BT-N)2Ir(acac) for single emissive layer monochromatic and white OLEDs by solution processing was synthesized.•(CF3BT-N)2Ir(acac) exhibit unchanged EL emission under different doping concentrations in monochromatic OLEDs.•A high luminous efficiency of 14.6 cd A−1 together with good CIE coordinates were obtained for WOLEDs.A novel iridium(III) complex bis(2-(naphthalen-1-yl)-6-(trifluoromethyl)benzothiazole)iridium(acetylacetonate) (CF3BT-N)2Ir(acac) with an orange–red emission was synthesized. The incorporation of CF3 and naphthalene groups into benzimidazole to act as a new ligand causes a significant change of both HOMO and LUMO energy levels of the iridium complex compared with the yellow emissive parent compound comprising the 2-phenylbenzimidazole ligand. As a result, a bathochromic shift by as much as 50 nm of the phosphorescence emission peak can be achieved. Electronic properties of (CF3BT-N)2Ir(acac) were examined by time-dependent density functional theory (TD-DFT) calculations. The influence of such substituent groups on the photophysical, electrochemical and electroluminescent properties of iridium complex was studied. Furthermore, two- and three-element solution-processed white organic light-emitting diodes (WOLEDs) with high performance can be realized by using this kind of orange–red phosphorescent emitter in conjunction with other phosphors in a single emissive layer. A maximum luminous efficiency of 10.9 cd A−1 with CIE coordinates of (0.27, 0.37) was obtained for the two-element WOLEDs. For the three-element WOLED, a maximum luminance of 22716 cd m−1 and a maximum luminous efficiency of 14.6 cd A−1 with CIE coordinates of (0.33, 0.42) can be achieved.

A new method is reported for preparing solution-processed molybdenum oxide (MoO3) hole selective layer (HSL). Via combustion processing at low annealing temperatures, the obtained MoO3 HSL exhibits a high charge-transporting performance similar to poly(ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) but overcoming its defect to device stability. The combustion precursor solution using ammonium heptamolybdate as the metal source, acetylacetone as a ‘fuel’, and nitric acid as an oxidizer can largely reduce the temperature for transformation of the polyoxomolybdate to α-phase MoO3. Furthermore, when a small amount of PEDOT:PSS has been introduced into the combustion precursor solution to improve the film morphology, the derived film can exhibit a flat and continuous surface morphology with coexistence of α- and β-MoO3 after being annealed at a low temperature (150 °C). The simplicity, rapidness, and effectiveness of our method together with the low annealing temperature needed make it promising for the roll-to-roll manufacture of polymer solar cells.Keywords: device stabilities; hole selective layers; polymer; polymer solar cells; polyoxomolybdates; solution-processing;

Fluorescent organic nanoparticles (FONs) as a new class of nanomaterials can provide more advantages than molecule based probes. However, their applications in specific metal ion detection have rarely been exploited. We design and synthesize a branched small-molecule compound with triazole as a core and benzothiadiazole derivative as branches. By a facile reprecipitation method, nanoparticles (NPs) of this compound can be prepared in aqueous solutions, which can show high selectivity and sensitivity to Fe(III) ions based on fluorescence quenching. In addition, the fluorescence intensity of these NPs is resistant to pH changes in solutions. Such characters of this kind of NPs can be utilized in Fe3+ impurity detection in a promising cathode material (LiFePO4) for lithium ion batteries. When exposed to Fe3+, both the triazole and benzothiadiazole groups contribute to the fluorescence quenching of NPs, but the former one plays a more important role in Fe3+ impurity detection. The sensing mechanism has also been investigated which indicates that a Fe-organic complex formation may be responsible for such sensing behavior. Our findings demonstrate that specific metal ion detection can be realized by FONs and have extended the application field of FONs for chemical sensing in aqueous solutions.Keywords: branched small molecule; fluorescence; ion detection; lithium iron(II) phosphate; lithium-ion battery; organic nanoparticles;

Two classical conjugated polymers, poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), commonly used in organic optoelectronic devices are endowed with a new function for radical sensing. The synergetic effect between MEH-PPV and PFO nanoparticles (NPs) plays an important role in the detection of hydroxyl radicals and sulfate anion radicals. When exposed to free radicals, MEH-PPV NPs are subjected to attack by the radicals and undergo molecular structure changes. Thus, a strong-polarity shell can be formed on the radical treated MEH-PPV NPs. When such radical treated MEH-PPV NPs come into close contact with PFO NPs, a new phenomenon whereby PFO alters its fluorescence emission intensity of the 0–2 transition relative to the 0–0 transition band is observed. The relative intensity ratio of these two transition bands can serve as an index for the hydroxyl radical concentration. Therefore, radical detection can be realized by measuring the solid state fluorescence, which is highly desired in off-site laboratory determination since solid samples are more convenient for storage and transport than solutions. Our results can open a way for the application of conjugated polymer nanoparticles in chemical/biological sensing.

Organic semiconductor nanoparticles are expected to be used in organic optical and electronic devices due to their unique optical and electrical properties. However, no method has been reported for the preparation of high-quality organic nanoparticle films without remaining additives and being capable of dealing with binary nanoparticle blends. We developed a simple approach to fabricate high-quality organic semiconductor nanoparticle films from their aqueous solutions by solvent-evaporation-induced self-assembly. Only volatile solvents are employed in the nanoparticle solutions, so the self-assembled nanoparticle films are free of additives. Moreover, this method is also suitable for fabricating thin films containing binary nanoparticles. Therefore, it paves the way for potential applications of organic semiconductor nanoparticles in nanoscale optical and electronic devices.

Two classical conjugated polymers, poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), commonly used in organic optoelectronic devices are endowed with a new function for radical sensing. The synergetic effect between MEH-PPV and PFO nanoparticles (NPs) plays an important role in the detection of hydroxyl radicals and sulfate anion radicals. When exposed to free radicals, MEH-PPV NPs are subjected to attack by the radicals and undergo molecular structure changes. Thus, a strong-polarity shell can be formed on the radical treated MEH-PPV NPs. When such radical treated MEH-PPV NPs come into close contact with PFO NPs, a new phenomenon whereby PFO alters its fluorescence emission intensity of the 0–2 transition relative to the 0–0 transition band is observed. The relative intensity ratio of these two transition bands can serve as an index for the hydroxyl radical concentration. Therefore, radical detection can be realized by measuring the solid state fluorescence, which is highly desired in off-site laboratory determination since solid samples are more convenient for storage and transport than solutions. Our results can open a way for the application of conjugated polymer nanoparticles in chemical/biological sensing.

By attaching two electron-withdrawing trifluoromethyl (CF3) groups to the 2-phenylbenzothiazole cyclo-metalated ligand, a bis-trifluoromethyl-functionalized orange-emitting phosphorescent iridium(III) complex bis-(6-(trifluoromethyl)-2-(4-(trifluoromethyl)phenylbenzothiozolato))iridium(acetylacetonate) [(F3BT-CF3P)2Ir(acac)] was successfully synthesized. The optical, electrochemical and electroluminescence (EL) properties of this new complex were studied. The experimental results support the theoretical expectation that incorporating electron-withdrawing trifluoromethyl groups at the 4-site of the phenyl ring directly bonded to the metal center, and at the 6-site of 2-phenylbenzothiazole, cause a bathochromic shift in the emission peak and bring the emission color much closer to long-wavelength orange light. Moreover, such trifluoromethyl substituents can hinder the π–π stacking or self-polarization effect occurring from the aggregation of the molecules. The new iridium complex gives an unchanged luminescence spectrum, regardless of whether it is in solution, in untreated film or in film doped at different concentrations. Using this iridium complex as a dopant emitter, solution-processed single emissive layer orange and two-element white OLEDs with good performance can be obtained. Highly efficient orange electroluminescence was obtained with a maximum efficiency of 10.5 cd A−1 and CIE coordinates (0.48, 0.51). When combined with a commercial sky-blue phosphorescent emitter, (CF3BT–CF3P)2Ir(acac) can be utilized to achieve two-element white OLEDs that exhibited a high efficiency of 28.3 cd A−1. Such OLEDs retain high efficiency at a luminance suitable for lighting (e.g. 5000 cd m−2).

Organic semiconductor materials with one-dimensional (1D) radial (core–shell) heterojunction structures are highly desired for their expected excellent optoelectronic properties. However, currently, such structures are still in a fledgling period for optoelectronic applications due to the absence of both good materials and suitable preparation methods. Here we have synthesized a p-type organic semiconductor based on a new electron-donating unit (dithienopyrazine) and utilized it as a shell material to construct organic 1D radial p–n heterojunctions. This p-type compound shows a higher oxidation potential and is more resistant to photooxidation in air than its analogs with the commonly-used benzodithiophene unit. Moreover, we prepared organic microwires with radial heterojunctions via a solution-processed method by self-assembly of our p-type material on the surface of n-type cores. Thus, photoconductive devices based on an individual microwire with the radial heterojunction can be fabricated and demonstrate a high photoconductivity. Our work provides a path for preparing 1D radial heterojunctions suitable for optoelectronic applications.

Two kinds of host materials, 4,4′-(diphenylgermanediyl)bis(N,N-diphenylaniline) and bis(4-(9H-carbazol-9-yl)phenyl)diphenylgermane (DCzGe), for blue phosphorescent organic light emitting diodes (PhOLEDs) were designed by incorporating electron donating groups (carbazole and triphenylamine) into tetraphenylgermane, which is a new type of core moiety that has never been studied for use in this field. This molecular structure endows the compounds with a wide energy bandgap, high thermal/morphological stability and good solution processability. Based on the theoretic calculations, DCzGe was selected and synthesized as a host material which demonstrates a wide bandgap (Eg: 3.56 eV) and a high triplet energy (ET: 3.02 eV). It also exhibits a high glass transition temperature (110 °C), which is beneficial for resisting the Joule heat in devices. All solution processed, blue emitting PhOLEDs were fabricated by using a mixed host combining DCzGe and an electron-transporting material, with a maximum luminance of 10000 cd m−2 and a maximum current efficiency of 15.2 cd A−1. Furthermore, the devices showed a very low current efficiency roll-off, which remained as high as 15.2 cd A−1 at the luminance of 1000 cd m−2, and the roll-off is only 2.6% even at the higher luminance of 2000 cd m−2.

Two blue-emitting fluorescent polymers PTPATPPO and PTPATPP with small singlet–triplet splitting comprising triphenylamine and triphenylphosphine/triphenylphosphine oxide moieties have been designed and synthesized. An appropriate overlap between the HOMO and the LUMO in these compounds was realized. This design strategy endows the two blue-emitting polymers with a high triplet energy of 2.45 and 2.46 eV, a shallow HOMO level of −5.21 and −5.23 eV, and a bipolar feature to act as good host materials. Monochromic organic light-emitting devices (OLEDs) using these polymers as emitters show sky-blue emissions with Commission Internationale de l'Eclairage (CIE) coordinates of (0.24, 0.32) and (0.24, 0.31) together with a maximum current efficiency of 3.63 cd A−1. Moreover, the single-emitting-layer two-element fluorescent–phosphorescent (F–P) hybrid white OLEDs based on PTPATPPO or PTPATPP as both hosts and blue-emitting fluorophores were fabricated by a solution process. Among the two polymers, PTPATPPO-based F–P hybrid white OLEDs show better performance with a maximum current efficiency of 10.5 cd A−1, a maximum external quantum efficiency of 6.1%, CIE coordinates of (0.40, 0.34), and a maximum luminance of 11962 cd m−2.

Being incompatible with host materials in a physically blended emitting layer, phosphorescent dyes are prone to form aggregates induced by Joule heat in devices under work. In this work, a new and efficient blue phosphorescent dye Cz-C8-FIrpic was designed and synthesised by incorporating 9-phenyl-9H-carbazole into a commonly used blue emissive iridium complex bis(4,6-(difluorophenyl)pyridine-N,C2′)picolinate (FIrpic) via an alkyl chain linkage. This phosphorescent dye exhibits similar photophysical properties to the units of FIrpic and 9-phenyl-9H-carbazole in solutions. In solid films of Cz-C8-FIrpic, the energy transfer from 9-phenyl-9H-carbazole to FIrpic units is effective. The Cz-C8-FIrpic doped emissive layer was investigated by AFM, STEM-EDS, transient photoluminescence decay curves and molecular dynamics simulations. The results show that in the Cz-C8-FIrpic doped film the phase aggregation of FIrpic units is less severe than that in the typically used FIrpic film. In addition, the optimized Cz-C8-FIrpic based device achieved a maximum luminance of 25142 cd m−2, a maximum EQE of 8.5% and a maximum current efficiency of 22.5 cd A−1 which is about 15% higher than that of the control device based on FIrpic. We conclude that grafting a typically used dye to functional groups with alkyl chains is useful to restrict phase separation in physically blended emitting layers, and thus can achieve high electroluminescence performances.

Diphenylamino- or cabazolyl-endcapped silafluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been designed, synthesized, and characterized. Double layer electroluminescent devices of these silafluorene derivatives exhibited efficient blue emission. The non-doped double layer OLEDs containing TDMS, TDPS, CDMS, or CDPS exhibited better electroluminescence efficiencies than those of the devices using the reference emitter DPFL-NPB, among which the best device was with TDPS, which showed a maximum current efficiency of 1.62 cd A−1 and an external quantum efficiency (EQE) of 1.36%. The solution processed device using TDPS as dopant exhibited a high performance with an EQE of 2.48% and an obviously low turn-on voltage of 4 V, when compared to the results of the reference device. The replacement of the carbon atom of the fluorene unit with a silicon atom could lower the energy gap effectively and improve the thermal stability as well as optical performances. The results indicate that the end-capped arylamino groups affect the organic light-emitting diode (OLED) performances greatly and aryl or alkyl substitution on the 9-position of a silafluorene unit is also crucial to the OLED performances of this kind of silafluorene.

Organic nano/micro one-dimensional (1D) materials are generally considered as promising materials for flexible, portable optoelectronic devices due to their well-known distinctive feature. Over the past few years, numerous organic nano/micro 1D photosensitive resistors have been developed; however, as one of the important photoelectronic components for fabricating organic nano/microelectronic circuits, organic nano/micro 1D photodiodes have not been reported yet. Herein, on the basis of our previous work about an organic photosensitive radial heterostructure microwire, we tried to prepare another kind of radial heterostructure microwire and explore its photodiode properties. Excitingly, the organic radial heterostructure microwire using aluminum tris(8-hydroxyquinoline) as the core and poly(3-hexyl thiophene) as the shell, which was prepared by a solution-based method, showed excellent performance with a large rectification ratio, a high on/off ratio and a good photoresponsivity under ambient conditions. Our work has developed a convenient method to prepare microwire photodiodes based on an all-organic heterojunction.

We fabricated a unique ternary organic hybrid microwire radial heterojunction by a facile method. First, 4,4′,4′′-tri(N-carbazolyl)triphenylamine (TCTA) microwires were prepared by solvent-evaporation-assisted self-assembly. Then, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles were adsorbed onto the surface of the TCTA microwires, forming interesting corncob-like binary hybrid microwires. Finally, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) was adsorbed on the surface of the binary hybrid microwires to form ternary hybrid microwire radial heterojunctions. The thermally activated delayed fluorescence (TADF) material 4CzIPN was introduced into the donor–acceptor (D–A) system to form the ternary hybrid microwire radial heterojunction for the first time. The morphology has been confirmed by fluorescence microscopy, SEM and TEM. Interestingly, we found that this ternary hybrid microwire exhibited efficient photoconductivity by fabricating a bottom contact device; the photocurrent increased by more than 3 times compared with the reference device without 4CzIPN. By examining some reference devices, it can be inferred that the enhancement of the photoconductivity originates from the reversed intersystem crossing (RISC) process in 4CzIPN. This process can promote the formation of triplet excitons, thereby increasing the charge carrier concentration in the conductive channel of the microwire radial heterojunction. These high photoconductivity ternary microwires provide an efficient approach to improve the performance of photovoltaic devices and show promise for applications in organic integrated optoelectronics.