A new ambipolar deep blue fluorophore with a non-donor–acceptor structure, MBAn-(4)-tBu (10,10′-bis-(4-tert-butyl-phenyl)-3,3′-dimethyl-9,9′-bianthracene), was designed and synthesized based on 3,3′-dimethyl-9,9′-bianthracene. The twisted conformation of the two anthracene units and the bulky end group substituted with a tert-butyl group in MBAn-(4)-tBu prevented π-conjugation effectively. In particular, MBAn-(4)-tBu in a non-doped device exhibited a maximum external quantum efficiency (EQE) of 3.94% with Commission Internationale de l’Éclairage (CIE) coordinates of (0.16, 0.07) and a narrow full width at half maximum of 49 nm, which was close to the CIE of high definition television standard blue. Furthermore, MBAn-(4)-tBu worked as an excellent fluorescent host for BD1 and DSA-ph dopants to obtain high performance OLEDs with excellent EQEs of 5.26% and 6.96%, respectively. These results demonstrate that the ambipolar 3,3′-dimethyl-9,9′-bianthracene molecule with a non-donor–acceptor structure is advantageous for the fabrication of highly efficient blue fluorescent OLEDs.

•Blue-emitting iridium complexes.•Oxadiazol-substituted amide ancillary ligands.•Efficient organic light-emitting diodes with mild efficiency roll-off.Three novel iridium(III) complexes bearing oxadiazol-substituted amide ligands have been synthesized and characterized, and the photophysical and electrochemical properties have been investigated. All the complexes exhibit blue light emission with major peaks at 472, 468 and 462 nm in acetonitrile solutions, respectively. Both photophysical properties and quantum chemical calculations demonstrate that photoluminescence of these complexes are mainly from cyclometalated ligand-based 3π−π* excited states. Using these complexes as emitters, the organic light-emitting diodes with single- or double-emitting layers were fabricated. The devices with double-emitting layers exhibit good electroluminescence performances with the maximum current efficiencies of 10.5, 6.3 and 4.6 cd A−1, respectively, and mild efficiency roll-off.Download high-res image (187KB)Download full-size image

Inverted organic light-emitting diodes (IOLEDs) on plastic substrates have great potential application in flexible active-matrix displays. High energy consumption, instability and poor electron injection are key issues limiting the commercialization of flexible IOLEDs. Here, we have systematically investigated the electrooptical properties of molybdenum disulfide (MoS2) and applied it in developing highly efficient and stable blue fluorescent IOLEDs. We have demonstrated that MoS2-based IOLEDs can significantly improve electron-injecting capacity. For the MoS2-based device on plastic substrates, we have achieved a very high external quantum efficiency of 7.3% at the luminance of 9141 cd m−2, which is the highest among the flexible blue fluorescent IOLEDs reported. Also, an approximately 1.8-fold improvement in power efficiency was obtained compared to glass-based IOLEDs. We attributed the enhanced performance of flexible IOLEDs to MoS2 nanopillar arrays due to their light extraction effect. The van der Waals force played an important role in the formation of MoS2 nanopillar arrays by thermal evaporation. Notably, MoS2-based flexible IOLEDs exhibit an intriguing efficiency roll-up, that is, the current efficiency increases slightly from 14.0 to 14.6 cd A−1 with the luminance increasing from 100 to 5000 cd m−2. In addition, we observed that the initial brightness of 500 cd m−2 can be maintained at 97% after bending for 500 cycles, demonstrating the excellent mechanical stability of flexible IOLEDs. Furthermore, we have successfully fabricated a transparent, flexible IOLED with low efficiency roll-off at high current density.

By adjusting the conjugation degrees of the phenylquinoline-based cyclometalated ligands, yellow, orange to red phosphorescent iridium(III) complexes [Ir(bzq)2(POXD)] (1, bzq = 7,8-benzoquinoline, POXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-diphenylphosphinic amide), [Ir(pq)2(POXD)] (2, pq = 2-phenylquinoline) and [Ir(piq)2(POXD)] (3, piq = 1-phenylisoquinoline) have been designed and prepared. Their photophysical and electrochemical studies and theoretical calculations were performed, and [Ir(bzq)2(POXD)] was also determined by X-ray crystallography. At room temperature, complexes 1–3 exhibit efficient phosphorescence emissions at about 539, 592 and 614 nm with photoluminescence quantum yields (PLQYs) of 0.21, 0.06 and 0.06 in CH3CN solutions, respectively. In the 5 wt% doped poly(methyl methacrylate) (PMMA) film, the PLQYs (0.35 for complex 1, 0.37 for complex 2 and 0.18 for complex 3, respectively) increase significantly. Organic light emitting diodes (OLEDs) based on these complexes were fabricated to evaluate their potential application. The yellow device in the configuration ITO/2-TNATA (25 nm)/NPB (5 nm)/TCTA (10 nm)/complex 1 (10 wt%):mCP (10 nm)/complex 1 (10 wt%):TPBi (10 nm)/TPBi (40 nm)/Liq (1 nm)/Al (100 nm) shows excellent performance with a maximum luminance of 24 080 cd m−2, maximum current efficiencies of 70.1 cd A−1 and maximum external quantum efficiencies of 21.3% along with low efficiency roll-off.

•Solution-processed hole injection layer of PEDOT:PSS+MoOx is facile prepared.•PEDOT:PSS+MoOx features superior film morphology and electronic properties.•UV OLEDs with 4.4% EQE are demonstrated using solution-processed PEDOT:PSS+MoOx.•Mechanism of PEDOT:PSS+MoOx promoting hole injection is systematically clarified.Hole injection layer (HIL) plays a crucial role in governing external quantum efficiency (EQE) of ultraviolet organic light-emitting diodes (UV OLEDs). We develop a solution-processed aqueous composite HIL of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) incorporated MoOx (PEDOT:PSS+MoOx) and cast successful application to UV OLEDs. PEDOT:PSS+MoOx is characterized in detail with scanning electron microscopy, atomic force microscopy, UV–visible absorption spectra, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and impedance spectroscopy measurements. The results show that PEDOT:PSS+MoOx features superior film morphology and exceptional electronic properties such as enhanced surface work function and promoted hole injection capacity. With PEDOT:PSS+MoOx as HIL, the UV OLED gives maximum EQE of 4.4% and radiance of 12.2 mW/cm2 as well as improved durability. The electroluminescence peaks at 376 nm with full width at half maximum of 34 nm and stable voltage-dependent spectra. Our results pave a way for exploring efficient UV OLEDs with solution-processable techniques.Download high-res image (265KB)Download full-size image

Two novel iridium(III) complexes [Ir(ppy)2(PhOXD)] (1, ppy = 2-phenylpyridine, PhOXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-benzamide) and [Ir(ppy)2(POXD)] (2, POXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-diphenylphosphinic amide) have been designed and synthesized, and their photoluminescence and electrochemistry properties were investigated. At room temperature, complexes 1 and 2 show green emissions at about 502 and 506 nm with photoluminescence quantum yields (PLQYs) of 0.03 and 0.05 in CH2Cl2 solutions, respectively. In the 5 wt% doped poly(methyl methacrylate) (PMMA) film, the PLQYs (0.42 for complex 1, 0.52 for complex 2, respectively) increase significantly. The organic light emitting diodes (OLEDs) with the structure of ITO/HAT-CN (dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile), 10 nm)/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/Ir complexes (10 wt%): mCP (1,3-bis(9H-carbazol-9-yl)benzene, 20 nm)/TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) show good performances. In particular, device G2 based on complex 2 shows superior performances with a peak current efficiency (ηc) of 64.7 cd A−1 and a peak power efficiency (ηp) of 42.5 lm W−1 with low electroluminescence efficiency roll-off. The ηc value still remains over 60.6 cd A−1 even at a luminance of 10000 cd m−2, which indicates that introducing electron transporting 1,3,4-oxadiazole and diphenyl phosphoryl groups into iridium complexes is an effective means of achieving efficient phosphors in OLEDs.

•Cationic iridium complexes.•Blue light emission.•Solution-processed organic light-emitting diodes.•Bis(pyrazole-1-yl)methane.Two new cationic iridium complexes with nonconjugated bis(pyrazole-1-yl)methane as the ancillary ligand have been prepared, and crystal structure, photophysical and electrochemical properties have been investigated. In degassed acetonitrile solutions, these complexes exhibit blue light emission with peaks at 456 and 453 nm, respectively. Both photophysical properties and quantum chemical calculations indicate that photoluminescence of these complexes are mainly from ligand-centered 3π → π*. Solution-processed organic light-emitting diodes based on these complexes exibit blue light emission with the maximum current efficiencies of 7.34 and 5.36 cd A−1, and maximum external quantum efficiencies of 4.06 and 2.66%, respectively.

•Yellow-emitting cationic iridium complexes.•N-heterocyclic carbene-based cyclometalating ligands.•Solution-processed organic light-emitting diodes.Two new cationic iridium complexes bearing cyclometalated carbene ligands have been prepared, and the photophysical and electrochemical properties have been investigated. In degassed acetonitrile solutions, these complexes exhibit yellow light emission with peaks at 591 and 579 nm, respectively. Both photophysical properties and quantum chemical calculations indicate that photoluminescence of these complexes are mainly from triplet charge-transfer excited states. Solution-processed organic light-emitting diodes based on these complexes exhibit yellow electroluminescences with the maximum current efficiencies of 17.42 and 6.36 cd A−1 and Commission Internationale d’Énclairage(x, y) coordinates (CIEx,y) of (0.47, 0.51) and (0.51, 0.47), respectively.

•Li ion doped ZnO was used as cathode buffer in the inverted P3HT:PCBM solar cells.•Li ion doping increased the mobility of ZnO film thus improved the Jsc and FF.•i-PSC using Li ion doped ZnO as cathode buffer resulted in ∼30% enhancement in PCE.We have proposed an approach to improve the photovoltaic performance of inverted polymer solar cells (i-PSC) using lithium ion doped ZnO (LiZnO) as cathode buffer layer (CBL). The LiZnO CBL was prepared using the diffusion technique, performed by inducing the Li ion of 8-hydroxyquinolatolithium (Liq) to diffuse into ZnO film through annealing the bi-layer ZnO/Liq film. Doping concentration of Li ion was controlled by using various thickness of Liq film and annealing temperature. Based on LiZnO CBL, the poly (3-hexylthiophene) [6,6]:-phenyl C61-butyric acid methyl ester (P3HT:PCBM) i-PSC device possessed a optimal power conversion efficiency (PCE) of 4.07%, which was 30% improved than that of the device with neat ZnO as CBL. The enhancement of the device performance could be attributed to the enhanced electron mobility and better band matching of the LiZnO CBL. Our finding indicates that the LiZnO film fabricated with relatively low temperature treatment has great potential for high-performance i-PSCs.In this paper, the photovoltaic performance of the inverted polymer solar cell was significantly improved by using Li ion doped ZnO as cathode buffer layer.

•Temperature-dependent device performance of a squaraine dye based OPV was studied.•Jsc, FF and PCE of the OPV cells increase with increasing the operating temperature.•Voc of the OPV cells decreases with increasing the operating temperature.We have systematically investigated the temperature-dependent device performance of organic photovoltaic (OPV) cells based on a squaraine dye. The 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine:[6,6]-phenyl C71 butyric acid methyl ester (DIBSQ:PC70BM) OPV devices were fabricated and characterized under 100 mW cm−2 (AM1.5G solar spectrum) in a temperature range from 285 to 360 K. The temperature-dependent photovoltaic parameters such as open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE) were studied in detail. The increasing temperature led to an improvement of Jsc and FF, which should be ascribed to the enhanced carrier mobilities and improved electrode/active layer contact thus the improvement of photocurrent extraction at an elevated temperature. However, the Voc decrease in the same period due to the carrier recombination of the OPV device. The increase in the Jsc and FF overtakes the decrease in the Voc with increasing temperature, resulting in a significantly improved PCE at elevated temperature. This study indicated that the DIBSQ based BHJ cells has promising potential for the practical application under changeable temperature environment.The temperature-dependent device performance of organic photovoltaic cells based on a squaraine dye has been systematically investigated.

•Cationic iridium complex.•Blue light emission.•Solution-processed organic light-emitting diodes.•2-(1H-pyrazol-1-yl)pyridine.A cationic iridium complex [Ir(dfpmpy)2(pzpy)](PF6) with 2-(1H-pyrazol-1-yl)pyridine as ancillary ligand has been prepared, and its crystal structure, photophysical and electrochemical properties have been investigated. In degassed CH3CN solution, this complex exhibits blue emission with a peak wavelength of 451 nm. Photophysical property indicates that photoluminescence of complex [Ir(dfpmpy)2(pzpy)](PF6) originates mainly from ligand-centered 3π → π∗ states. In addition, solution-processed organic light-emitting diodes based on [Ir(dfpmpy)2(pzpy)](PF6) have been fabricated. A blue light electroluminescence (484 nm) was observed and a maximum current efficiency of 1.56 cd A−1 corresponding to a maximum power efficiency of 0.33 lm W−1, has been achieved. This demonstrates that this complex is a promising phosphor for achieving efficient electrophosphorescence in the blue light region.A blue emitting cationic iridium complex with 2-(1H-pyrazol-1-yl)pyridine as ancillary ligand were synthesized, and solution-processed organic light-emitting diodes based on this complex exhibit a maximum current efficiency of 1.56 cd A−1 corresponding to a maximum power efficiency of 0.33 lm W−1.

A fiber-shaped polymer light-emitting electrochemical cell (PLEC) was developed by sandwiching an electroluminescent polymer layer between two aligned carbon nanotube (CNT) sheet electrodes. Similar to a conventional planar PLEC, the electroluminescent polymer layer and two carbon nanotube electrodes are closely and stably contacted, so that the injected charges can be rapidly and efficiently transported. Due to their one-dimensional structure, the fiber-shaped PLEC demonstrates unique and promising advantages, e.g., the luminance is almost independent on the observation angle. In addition, the fiber-shaped PLEC is thin, lightweight and flexible, which bespeaks a promising future for various electronic textiles.

•The method of interfacial doping is introduced to fabricate organic light-emitting diodes (OLEDs).•It removed the charge-injection barriers and promoted efficient recombination of excitons in EML.•HTL doped EML which is employed in OLEDs achieved low turn-on voltages, very high efficiencies.Interfacial doping is introduced in order to fabricate both fluorescent and phosphorescent organic light-emitting diodes (FOLEDs and PhOLEDs) with low turn-on voltage, high efficiency and low efficiency roll-off, which employed the doping profile of transporting layer with the host of the light emitting layer (EML). Both hole and electron transport layer doped EML are investigated. Through this method, the injection and transport of carriers can be fine-tuned, and the interfacial energy barriers from the transporting layer to EML are effectively eliminated. Furthermore, a better balance of holes and electrons in the combination zone can be obtained by manipulating the molar ratio of the interfacial doping layer. By combing all these factors, the FOLEDs achieved a very low turn-on voltage of 2.3 V, a high current efficiency of 9.90 cd/A and an external quantum efficiency of 3.12% with low roll-off. In addition, a low turn-on voltage of 2.8 V and a high current efficiency of 54.06 cd/A, which increased by 45% compared to reference device in PhOLEDs have also been achieved.

•Efficient OLED with a doped dual hole-transport layer (dd-HTL) is demonstrated.•dd-HTL engineers hole injection and transport, which improves carrier balance.•Impedance spectroscopy is used to characterize hole injection and transporting.We demonstrate a highly-efficient low-voltage organic light-emitting diode (OLED) by using a doped dual hole-transport layer (dd-HTL) of [NPB: 2 wt% F4-TCNQ]/ [NPB: 5 wt% CuPc]. F4-TCNQ denotes 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, CuPc denotes copper-phthalocyanine, NPB denotes N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine. With tris(8-hydroquinoline) aluminum as emitter, the maximum luminous and power efficiencies achieve 5.4 cd/A and 2.42 lm/W, respectively. Which have been enhanced by 59% and 86%, respectively, in comparison with the counterpart using conventional NPB HTL. By constructing hole-only device and employing current density versus voltage characteristics and impedance spectroscopy analysis, the results indicate that F4-TCNQ doping promotes hole injection and hole transporting, while CuPc doping shows negligible effect on hole injection but traps hole and impedes hole transporting. Consequently, the dd-HTL of [NPB:F4-TCNQ]/[NPB:CuPc] can effectively promoting hole injection and controlling hole transporting, which contributes to reduced driving voltage, improved carrier balance, and enhanced device efficiency.

•Bilayer WOLED with simple structure is demonstrated.•Rubrene doping slightly impedes electron transporting of Alq3.•Impedance spectroscopy is used to characterize electron transport property.A bilayer-structure white organic light-emitting diode (WOLED) using 5,6,11,12-tetraphenylnaphthacene (rubrene) doped tris(8-hydroxy-quinolinato)aluminum (Alq3), [Alq3:rubrene], as electron-transport and yellow-green emitting layer and 2-methyl-9,10-bis(naphthalen-2-yl)anthracene as hole-transport and blue emitting layer is demonstrated. The device shows Commission Internationale de L׳Eclairage color coordinates of (0.34, 0.40) and a maximum luminance of 1132 cd/m2 at 8 V. the electron transporting characteristics of [Alq3:rubrene] and Alq3 are comparatively investigated by using current versus voltage characteristics and impedance spectroscopy measurements such as impedance, phase, and capacitance as a function of bias voltage. Our results indicate that rubrene doping slightly impedes electron transporting of Alq3. This, to a certain extent, counteracts the promotion of device luminance.

Two potential schemes were proposed in this work to realize an organic solid laser pumped by electroluminescence emission in an integrated organic light emitting diode (OLED) employing low threshold laser dyes, [1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl] benzene (DSB) and DSB doped with 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), as the hole injection layer (HIL). Using DSB as HIL was found to improve the efficiency of the device, which exhibited peak efficiencies of 9.59 cd A−1 and 6.93 lm W−1. For the system employing DSB doped with DCJTB as HIL, the mobility of the electron transport layer made a large contribution to the realization of a diode-pumped organic solid-state laser. Moreover, the optical characteristics of organic films pumped by a pulsed Nd:YAG laser at 355 nm were also investigated.

•Color-stability OLED was fabricated with Ir complex-doped electron transport layer.•Ir(ppy)3-doped organic layer utilize excess holes to promote carrier balance.•Ir(ppy)3-doped organic layer reduce electron-transport ability to promote carrier balance.•The highest current efficiency is 37.4 cd/A.•Efficiency roll-up arises instead of traditional roll-off phenomenon.The influence of fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] doped into electron transport layer was investigated by a series of electron-only devices, and the mechanism of the reduced field-dependent electron-transporting properties was also discussed. Utilizing the method of optimized doping concentration, a hybrid white organic light emitting diode with high efficiency, low efficiency roll-off and stable spectra was fabricated. Organic layer doped Ir(ppy)3 serves two functions: emit supernumerary green light with excess holes when the applied bias are low; weaken electron-transport ability when the bias increase. Both the two functions can improve the carrier balance and confine the exciton recombination region. For Device B, the maximum current efficiency and power efficiency reach 37.4 cd/A and 28.6 lm/W, respectively. The Commision Internationale de l’Éclairage (CIE) coordinates vary slightly from (0.48, 0.43) at 1.1 cd/m2 to (0.46, 0.43) at 18,600 cd/m2.

•A gold island structure is proposed to prepare ordered P3HT nanowires.•Dichlorobenzene is an ideal solvent to grow ordered P3HT nanowires.•The length and width of nanowires are measured to be 20–30 μm and 50 nm, respectively.•We successfully fabricate OFETs based on P3HT ordered nanowires.•The mobility and threshold voltage are 0.06 cm2/V s and −13 V, respectively.A gold island structure is proposed to prepare ordered P3HT nanowires. The optical photographs of P3HT nanostructures self-assembly from different solvents show that dichlorobenzene is an ideal solvent to grow ordered P3HT nanowires. From optical and TEM graphs, the length and width of nanowires are measured to be 20–30 μm and 50 nm, respectively. Finally, we successfully fabricate organic field-effect transistors (OFETs) based on P3HT ordered nanowires with uniform density by introducing this method. The mobility and threshold voltage are 0.06 cm2/V s and −13 V, respectively. Our study may provide a thought in developing and optimizing organic electronic devices.

Device stability and life-time rank the key issues for PhOLEDs. We synthesized deuterated Ir(ppy)3-D24. A device based on it has a current density twenty times higher than and a life-time six times longer than devices based on Ir(ppy)3. The more stable C–D bond is found to be the main contributing factor, called the “deuterium effect”.

We have investigated the hole-transporting properties of three different Ir complexes doped 4,4′,4″-tri (N-carbazolyl) triphenylamine (TCTA) using a series of hole-only devices. The improvement of hole-transporting ability was depended on the species of Ir complexes and their doping concentrations. We attributed the improved performance to their strong electron-accepting abilities or hole-transfer capabilities. Yellow organic light-emitting diodes (OLEDs) based on bis(2-phenylbenzothiazolato)(acetylacetonate)iridium bt2Ir(acac) were fabricated by utilizing this method with optimized doping concentration. The best electroluminescent (EL) performance of maximum 83.6 lm/W was obtained for the yellowing-emitting OLED by doping of Firpic into TCTA hole transport layer, compared with the cases of doping of Ir(ppy)3 into TCTA and doping of Ir(bpiq)2acac into TCTA. Moreover, the turn-on voltage of device decreased to 2.2 V, which was corresponding to the optical band gap of the emitter.Graphical abstractThe hole-transporting properties of three different Ir complexes doped 4,4′,4″-tri (N-carbazolyl) triphenylamine (TCTA) using a series of hole-only devices have been investigated. The improvement of hole-transporting ability was attributed the improved performance to their strong electron-accepting abilities or hole-transfer capabilities.Highlights► Ir complex-doped hole transport layer can greatly improve the performance of OLEDs. ► The improved hole-transporting ability depended on the doping concentrate and species of Ir complex. ► The strong electron-accepting or hole-transfer capability contributes to the improvement of hole-transporting. ► A maximum 83.6 lm/W has been obtained for the yellow-emitting OLED by doping of Firpic into TCTA.

•Ten compounds with biphenyl as backbone was asymmetrically modified.•These compounds emit intense pure-blue with high quantum yields up to 80%.•The cyclic voltammograms are completely reversible.•These compounds are useful for blue-emitting, hole-transport and host materials.We report the synthesis and optical properties of a series of ten organic compounds with biphenyl as the backbone and asymmetrically modified by triphenylamines, carbazoles and tetraphenylsilanes (BP 1-10). BP 1-10 were synthesized mainly by Ullmann coupling reaction and Suzuki cross-coupling reaction and characterized by EA, NMR, MS, UV–Vis, DSC, TGA, fluorescence spectra and cyclic voltammetry. They exhibit reversible electrochemical behavior with low oxidation potentials and emit intense pure-blue light with high fluorescence quantum yields (up to 80%). BP 1 was fabricated into multi-layered light-emitting diodes as blue-emitting, host and hole transport materials. Based on the performance of BP 1 and the similarity in chemical structure to those compounds reported in literature, these compounds are expected to be good and versatile hole transport, host and blue emitting materials.

•Molecules with pyridine as the backbone and modified by carbazoles were synthesized.•The molecules exhibit sharp blue fluorescence and excimer orange emission.•Structurally, bromo was identified as a crucial factor to generate excimer emission.•The molecules were made into simple structured OLED devices and emit white emission.Seven compounds with pyridine as the backbone modified by carbazole moiety, bromine atom and fluorine atom were synthesized. Compounds 1, 2, 3 with bromo substitution at the 2-position and carbazole modification at the 5-position of pyridine emit not only a sharp blue singlet fluorescence but also a wide banded excimer-based orange emission. The two colors coming from a single molecule can be used to fabricate a simplified white light emitting device. The electroluminescence based on 1 and 2 exhibits white-light emission with CIE coordinates of x = 0.25 and y = 0.30 for 1 and x = 0.33 and y = 0.37 for 2 at high current densities, very close to pure white emission. In addition, the role of bromo-substitution at pyridine is concluded to be essential to generate molecular interaction thus an excimer emission.

A high color rendering index (CRI) is crucial for organic light-emitting diode (OLED) which can be applied in high-quality lighting sources. We have developed three types of white OLEDs with two-, three- and four-peak electroluminescence spectra. For two-peak OLED, a luminance efficiency of 34.59 cd A−1 at 100 cd m−2 with a CRI of 45 is obtained. For three-peak OLED, CRI above 85 and a maximum luminance efficiency of 27.29 cd A−1 are realized. Four-peak OLED yields color-temperature tunable white emission in the luminance range of 100 cd m−2 to 5000 cd m−2, a sunlight-like spectrum with a CRI of 89 at 5000 cd m−2. The wide color-temperature span of the four-peak OLED could meet the requirements for lighting in dwellings.

We have developed two kinds of cyclic arylamines functioning as hole-transporting and light-emitting materials of organic light emitting diodes (OLEDs), respectively. The hole-transporting cyclic arylamine (C1)-based device exhibited an improved maximum luminance efficiency of 4.21 cd/A, utilizing a single light-emitting layer of tris(8-hydroxyquinolinato) aluminum. While the maximum luminance efficiencies for N,N′-bis-(naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and 4,4′,4″-tris-N-naphthyl-N-phenylamino-triphenylamine/NPB-based devices were 2.28 and 3.02 cd/A, respectively. In addition, a non-doped deep-blue (448 nm) light-emitting device was obtained, employing cyclic arylamine (C2) as emission layer. And the exciplex formation occurred at C1/C2 interface or in the emission layer of C2 doped C1, which leaded to a wide EL emission. Furthermore, we have developed a very simple bluish-white OLED using C2 (5 wt.%) doped C1, which showed particularly wide full width at half maximum of 135 nm.Highlights► We synthesized two versatile cyclic arylamines for organic light-emitting diodes. ► Cyclic arylamine (C1)-based device exhibited good hole-transporting characteristics. ► We developed a non-doped deep-blue device at 448 nm using cyclic arylamine (C2). ► A simple bluish-white OLED was fabricated with full width at half maximum of 135 nm.

The research of high-brightness organic light-emitting diodes, as an important branch of organic light-emitting diodes (OLEDs), makes it possible for achieving high-brightness lighting source and lasing. Heat dissipation and efficiency roll off, as two main factors, affect the brightness of the OLEDs heavily. In this paper, high-brightness OLEDs are obtained by utilizing pulse voltage, small areas and micro-cavity structure to minimize the effect of the two factors. The major advances, ongoing challenges and future perspectives of this research frontier are also critically discussed.

We have fabricated high-efficient white organic light-emitting diodes (WOLEDs) using two types of electron transport materials with different electron mobility. The effect of the electron mobility on the device performance is discussed. In addition, to generate the desired white emission and high color rendering index, we perform the structure design of OLED, in which the functions of co-host of blue and green dopants on chromatic-stability are investigated. Experimental results find that the maximum color rendering index reaches as high as 91 at the voltage of 8 V.

Two novel iridium(III) complexes [Ir(ppy)2(PhOXD)] (1, ppy = 2-phenylpyridine, PhOXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-benzamide) and [Ir(ppy)2(POXD)] (2, POXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-diphenylphosphinic amide) have been designed and synthesized, and their photoluminescence and electrochemistry properties were investigated. At room temperature, complexes 1 and 2 show green emissions at about 502 and 506 nm with photoluminescence quantum yields (PLQYs) of 0.03 and 0.05 in CH2Cl2 solutions, respectively. In the 5 wt% doped poly(methyl methacrylate) (PMMA) film, the PLQYs (0.42 for complex 1, 0.52 for complex 2, respectively) increase significantly. The organic light emitting diodes (OLEDs) with the structure of ITO/HAT-CN (dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile), 10 nm)/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/Ir complexes (10 wt%): mCP (1,3-bis(9H-carbazol-9-yl)benzene, 20 nm)/TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) show good performances. In particular, device G2 based on complex 2 shows superior performances with a peak current efficiency (ηc) of 64.7 cd A−1 and a peak power efficiency (ηp) of 42.5 lm W−1 with low electroluminescence efficiency roll-off. The ηc value still remains over 60.6 cd A−1 even at a luminance of 10000 cd m−2, which indicates that introducing electron transporting 1,3,4-oxadiazole and diphenyl phosphoryl groups into iridium complexes is an effective means of achieving efficient phosphors in OLEDs.

A fiber-shaped polymer light-emitting electrochemical cell (PLEC) was developed by sandwiching an electroluminescent polymer layer between two aligned carbon nanotube (CNT) sheet electrodes. Similar to a conventional planar PLEC, the electroluminescent polymer layer and two carbon nanotube electrodes are closely and stably contacted, so that the injected charges can be rapidly and efficiently transported. Due to their one-dimensional structure, the fiber-shaped PLEC demonstrates unique and promising advantages, e.g., the luminance is almost independent on the observation angle. In addition, the fiber-shaped PLEC is thin, lightweight and flexible, which bespeaks a promising future for various electronic textiles.

A high color rendering index (CRI) is crucial for organic light-emitting diode (OLED) which can be applied in high-quality lighting sources. We have developed three types of white OLEDs with two-, three- and four-peak electroluminescence spectra. For two-peak OLED, a luminance efficiency of 34.59 cd A−1 at 100 cd m−2 with a CRI of 45 is obtained. For three-peak OLED, CRI above 85 and a maximum luminance efficiency of 27.29 cd A−1 are realized. Four-peak OLED yields color-temperature tunable white emission in the luminance range of 100 cd m−2 to 5000 cd m−2, a sunlight-like spectrum with a CRI of 89 at 5000 cd m−2. The wide color-temperature span of the four-peak OLED could meet the requirements for lighting in dwellings.

Device stability and life-time rank the key issues for PhOLEDs. We synthesized deuterated Ir(ppy)3-D24. A device based on it has a current density twenty times higher than and a life-time six times longer than devices based on Ir(ppy)3. The more stable C–D bond is found to be the main contributing factor, called the “deuterium effect”.

Two potential schemes were proposed in this work to realize an organic solid laser pumped by electroluminescence emission in an integrated organic light emitting diode (OLED) employing low threshold laser dyes, [1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl] benzene (DSB) and DSB doped with 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), as the hole injection layer (HIL). Using DSB as HIL was found to improve the efficiency of the device, which exhibited peak efficiencies of 9.59 cd A−1 and 6.93 lm W−1. For the system employing DSB doped with DCJTB as HIL, the mobility of the electron transport layer made a large contribution to the realization of a diode-pumped organic solid-state laser. Moreover, the optical characteristics of organic films pumped by a pulsed Nd:YAG laser at 355 nm were also investigated.