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Perovskite light‐emitting diodes (PeLEDs) for full‐color displays based on inkjet printing technology are increasingly attractive. For potential applications, fabricating high‐quality perovskite films with defined‐pixel sizes is crucially important. The key issue is how to control the contact properties between the perovskite ink and a hole transport layer (HTL). In this study, a novel strategy is proposed by using the poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethylammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] dibromide (PFN‐Br) polar polymer to modify the HTL surface, instead of conventional O2 plasma method. The PFN‐Br can enhance the surface energy of HTLs, including PVK, Poly‐TPD, TFB, etc., and improve the wettability of perovskite inks on the HTL due to its polar quaternary ammonium groups. Besides, the PFN‐Br acts as the easier nucleation to induce a tiny crystallization of perovskites. On the other hand, the diphenyl phosphate liver (DPA) is first used to mix in perovskite inks to optimize the perovskite film phase distribution and the elimination of uncoordinated Pb2+, resulting from interactions between PEA+ and DPA, Pb2+ and DPA, respectively. As a result, a defined‐pixel matrix green quasi‐2D PeLED with the peak external quantum efficiency over 10% via inkjet printing technique is achieved, which is the most efficient matrix green PeLEDs fabricated by inkjet printing technique so far. [ABSTRACT FROM AUTHOR]

The quality of high‐resolution luminescent films is key for high‐definition and near‐eye displays, but is limited by the apparent boundary effects at sub‐micrometer scales, such as boundary quenching in inorganic light‐emitting diodes and the coffee ring effect in inkjet printing. This study demonstrates that the electroplating of electrified electrode microarrays is not limited by boundary effects, enabling the deposition of luminescent dyes as high‐quality films with uniform and smooth morphologies as well as strong electroluminescence. As radial diffusion is the key to boundary effect in electroplating technology, small pixels tend to weaken the boundary effects and ease the overlap of diffusion layers. When the pixel size is lower than the critical value, the boundary effects can be eliminated. The smallest pixel width attempted is 3 µm, and prototype devices of monochrome and red‐green‐blue‐colored pixel arrays are successfully fabricated on glass and flexible backplanes without bad pixels and lines, indicating the high potential of the electroplating technique to achieve high‐resolution and immersive virtual reality for fine displays. [ABSTRACT FROM AUTHOR]

Unlike the traditional fabrication of distributed Bragg reflector (DBR) structure via atomic layer deposition or spin-coating, here the 1–6 pairs of magnesium fluoride (MgF2)/zinc sulfide (ZnS) alternative dielectric layers were grown via thermal evaporation. The absorption, transmission, reflection, and photoluminescence (PL) spectra were evaluated. 5 pair MgF2/ZnS denotes the largest reflectance (88.5% at 535 nm) together with a stopband at 450–650 nm among the 1– 6 pair dielectric layers, exhibiting the potential for using as DBR. Relative to the bare 4,4'-bis(carbazol-9-yl)biphenyl(CBP):(4s,6s)−2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN) film, the PL intensity of CBP:4CzIPN/5 pair MgF2/ZnS DBR is enhanced and splitted into two peaks. The 5 pair alternative dielectric film presents more uniform aggregation over 4 pair MgF2/ZnS. The cross-sectional scanning electron microscopic image denotes explicit layering for the MgF2 and ZnS. The organic light-emitting diode (OLED) incorporating 5 pair MgF2/ZnS DBR layers illustrates significantly improved electroluminescent (EL) performance due to the photons concentrated in the direction perpendicular to the DBR. The slightly narrowed EL spectrum is originated from the microcavity effect between the two Al electrodes. Here we develop a universal method for the DBR fabrication suitable to most of OLEDs. [ABSTRACT FROM AUTHOR]

Polymer insulator is employed as efficient hole injection layer (HIL) in lead halide perovskites light‐emitting diodes (PeLEDs) for the first time, by revealing that metal–insulator–semiconductor (MIS) contact is responsible for the hole‐injection mechanism in PeLEDs with indium tin oxide (ITO)/insulator/perovskite structure. For MIS contact of ITO/insulator/perovskite, the electric field is concentrated in the insulator layer, thereby reducing the tunneling distance from ITO to perovskite. By studying the transient current response, it is confirmed that the accumulation of both electrons and ions at the insulator/perovskite interface is responsible for the screening of electric field. With polystyrene (PS) as hole injection layer, the device exhibits a much better device performance than that of PeLEDs with regular polyvinylcarbazole (PVK) HIL, even though the resistivity of PS is 5 orders of magnitude higher than that of PVK, which confirms the universal applicability of MIS contact. By optimizing the thickness of PS layer, the performance of FAPbBr3‐based device achieves a turn‐on voltage of 2.8 V, a peak luminous efficiency of 44.7 cd A−1, and an external quantum efficiency of 10.6%. [ABSTRACT FROM AUTHOR]

Traditional inkjet printing color quantum dot technology is to print red, green and blue quantum dot inks respectively, while perovskite material is ionic compound, and changing the halogen component can change the light color, which provides a new method for inkjet printing to realize color display. Here, we report a method for implementing blue devices by ion exchange between halogen‐containing inks and underlying perovskite quantum dot films by inkjet‐printing. This method can also be used for full‐color devices. [ABSTRACT FROM AUTHOR]

The aggregation-induced emission (AIE) phenomenon is important in organic light-emitting diodes (OLEDs), for it can potentially solve the aggregation-caused quenching problem. However, the performance of AIE fluorophor-based OLEDs (AIE OLEDs) is unsatisfactory, particularly for deep-blue devices (CIEy < 0.15). Here, by enhancing the device engineering, a deep-blue AIE OLED exhibits low voltage (i.e., 2.75 V at 1 cd m−2), high luminance (17 721 cd m−2), high efficiency (4.3 lm W−1), and low efficiency roll-off (3.6 lm W−1 at 1000 cd m−2), which is the best deep-blue AIE OLED. Then, blue AIE fluorophors, for the first time, have been demonstrated to achieve high-performance hybrid white OLEDs (WOLEDs). The two-color WOLEDs exhibit i) stable colors and the highest efficiency among pure-white hybrid WOLEDs (32.0 lm W−1); ii) stable colors, high efficiency, and very low efficiency roll-off; or iii) unprecedented efficiencies at high luminances (i.e., 70.2 cd A−1, 43.4 lm W−1 at 10 000 cd m−2). Moreover, a three-color WOLED exhibits wide correlated color temperatures (10 690-2328 K), which is the first hybrid WOLED showing sunlight-style emission. These findings will open a novel concept that blue AIE fluorophors are promising candidates to develop high-performance hybrid WOLEDs, which have a bright prospect for the future displays and lightings. [ABSTRACT FROM AUTHOR]

Abstract: High efficiency all phosphorescent white electroluminescence was realized by double doping of blue-light-emitting bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) and red iridium complex Ir(DMFPQ)2pbm into conjugated polymer host poly(9,9-dioctylfluorene) (PFO). Effects of hole-transport layer (HTL) on the performances of white polymer light-emitting diodes (WPLEDs) were investigated. First of all, PVK as the HTL was essential, because the back energy transfer from FIrpic to PFO caused by the low-lying triplet energy level of PFO was suppressed by PVK. Furthermore, performances of the WPLEDs were enhanced by introducing CBP into PVK owing to improved balance of electron and hole current. The resulting all phosphorescent WPLEDs have a peak luminous efficiency of 15.5cd/A and a peak power efficiency of 6lm/W. Commisssion Internationale de L’Eclairage (CIE) coordinates of (0.41, 0.38) were realized at a current density of 18mA/cm2. The obtaining of the efficient all phosphorescent white electroluminescence with PFO as host polymer will broaden the approaches of white light generation and be a big promote for the application of phosphorescent WPLEDs. [Copyright &y& Elsevier]

This tutorial reviewpresents some recent developments in the design, synthesis and implementation of organic solution-processable molecular fluorophores for non-doped electroluminescent light-emitting devices. After a brief presentation of the basic principles of operation and main characteristics of electroluminescent devices, some examples of active emitters representative of the main classes of non-doped molecular electrofluorophores will be discussed. Emphasis is placed on the relationships between the molecular structure and the electronic properties of molecular emitters, in which high photoluminescence efficiency, synthetic accessibility and processability are combined by design with additional functions such as hole and/or electron injection and transport. [ABSTRACT FROM AUTHOR]

Two novel diketopyrrolopyrrole-based alternating copolymers, poly(2,7-(9,9-diethyl)-fluorenylvinylene-alt-2,5-bis(4'-octyloxyphe- nylmethyl)-3,6-bis(4-vinylenephenyl)pyrrolo[3,4-c]pyrrole-1,4-dione) (P1) and poly(1,4-(2,5-dioctyl- oxy)-phenylenevinylene-alt-2,5-bis(4'-octyloxyphenylmethyl)-3,6-bis(4-vinylenephenyl)pyrrolo[3,4-c]pyrrole-1,4-dione) (P2) were synthesized through Wittig polycondensation in good yields. P1 and P2 were characterized by NMR, FT-IR, UV-Vis, photoluminescence (PL) and electroluminescence (EL). EL devices with ITO/PEDOT/polymer/CsF/Al exhibited red-emitting light with the maximum EL wavelength at 620 nm and 682 nm. The results show that PL quantum yield of the polymers in thin film can be improved through N-alkylation of diketopyrrolopyrrole (DPP) with bulky substituent. EL performance of P2 was better than P1, which might be due to 1,4-dioctyloxybenzene of P2 enhancing the hole-transporting to make more charge balance. EL devices of P1 and P2 possessed low turn on voltage (2.4 V and 2.1 V, respectively), which was an advantage for PLED. [ABSTRACT FROM AUTHOR]

High efficiency of near infrared polymer light-emitting diodes with bilayer structure was obtained. The diode structure is ITO/PEDOT/L1/L2/Ba/Al, where L1 is phenyl-substituted poly [p-phenylphenylene vinylene] derivative (P-PPV), L2 is 9,9-dioctylfluorene (DOF) and 4,7-bis(3-hexylthiophen)-2-yl-2,1,3-naphthothiadiazole (HDNT) copolymer (PFHDNT10). The electroluminescence (EL) spectrum of diodes from PFHDNT10 is at 750 nm located in the range of near infrared. The maximum external quantum efficiency is up to 2.1% at the current density of 35 mA/cm². The improvement of the diode's performances was considered to be the irradiative excitons confined in the interface between L1 and L2 layers. [ABSTRACT FROM AUTHOR]

Discusses the utilization of Dioctylfluorene (DOF) and 4,7-dithien-2-yl2,1,3-benzothiadiazole (DBT) copolymers synthesized in our lab with different compositions of DBT (1%, 5%, 15% and 25%) to fabricate bilayered light emitting diodes. Fabrication of the external quantum efficiency (QE) of the diode from the copolymer with 15% DBT content reaches 1.4% (ph/el), over 1.0 cd/A in luminance efficiency at the driving voltage of 4.2 V; How the highest luminance can reach 3780 cd/m² at 8.2 V; Conclusion that devices emit a saturated red light centered at 675 nm with chromaticity coordinate changed from x = 0.66, y = 0.32 for PDOF-DBT1 (1% DBT) to x = 0.70, y = 0.28 for PDOF-DBT25 (25% DBT).

We report the effects of ultraviolet (UV) irradiation and storage on the performance of ZnO-based inverted quantum-dot light-emitting diodes (QLEDs). The effects of UV irradiation on the electrical properties of ZnO nanoparticles (NPs) were investigated. We demonstrate that the charge balance was enhanced by improving the electron injection. The maximum external quantum efficiency (EQE) and power efficiency (PE) of QLEDs were increased by 26% and 143% after UV irradiation for 15 min. In addition, we investigated the storage stabilities of the inverted QLEDs. During the storage period, the electron current from ZnO gradually decreased, causing a reduction in the device current. However, the QLEDs demonstrated improvements in maximum EQE by 20.7% after two days of storage. Our analysis indicates that the suppression of exciton quenching at the interface of ZnO and quantum dots (QDs) during the storage period could result in the enhancement of EQE. This study provides a comprehension of the generally neglected factors, which could be conducive to the realization of high-efficiency and highly storage-stable practical applications. [ABSTRACT FROM AUTHOR]

International Conference on Display Technology 2020 (V olume 52, Issue S1) 565 Bifacial Passivation towards Efficient FAPbBr 3 -based Inverted Perovskite Light-emitting Diodes Miaozi Li, Junbiao Peng, Jian Wang* *Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China. P-9.1: Bifacial Passivation towards Efficient FAPbBr3-based Inverted Perovskite Light-emitting Diodes. The synergetic interplay of organic/inorganic hybrid ETL and organic halide salt surface modification substantially shrinks the grain size to facilitate the radiative recombination, and suppresses the non-radiative recombination both at the interface of ETL/perovskite and HTL/perovskite, and in the perovskite layer. [Extracted from the article]

Metal halide perovskite materials occupy an increasingly important position in the field of optoelectronic materials due to their excellent light absorption properties, long carrier dispersion length and high mobility. However, the instability of perovskite materials is still a major factor constraining its development. So, its' important to improve the stability of perovskite materials in air and even to produce high‐performance LEDs in air. Here, we proposed a simple way to improve the stability of perovskite quantum dots and achieved the preparation of perovskite light‐emitting diodes in air. And green PQDs‐LED devices are fabricated by inkjet printing. [ABSTRACT FROM AUTHOR]

Abstract: The efficient red phosphorescence polymer light-emitting diodes (PLEDs) based on aluminum (Al) cathode were demonstrated. The devices composed of neutral aminoalkyl substituted polyfluorene, poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) as the host and bis(1-(3-(9,9-dimethyl-fluorene-2-yl)phenyl)isoquinoline-C2,N′) iridium (III) (3-(pyridin-2′-yl)-1,2,4-triazole) [Ir(DMFPQ)2pt] as the dopant. High external quantum efficiency of 5.6% (at 16.8V) and a luminance of 1400cd/m2 (at 19.6V) were obtained from the device with Al cathode only. The performances (quantum efficiency and luminance) of the devices could be comparable to those of the devices with a low work-function metal cathode (such as calcium and barium). We believe that the reason for the high performances was due to the effective electron injection from Al into PFN. [Copyright &y& Elsevier]

Abstract: A new bilayer cathode has been developed for varieties of RGB emitting polymers to form an effective electron injector. An effective electron injection from high work function metal, such as Al cathode can be realized by incorporation of a thin layer of amino-ended alkyl-substituted polyfluorene copolymer and corresponding ammonium salt-cationic polyelectrolyte between metal cathode and emitting layer. The performance of polymer light emitting-diodes (PLEDs) fabricated with such bilayer cathodes can be enhanced to the levels comparable or even higher than that obtained by using Ca and Ba as the cathode (for red QE=2–3%, for green 5–8%, for blue 1–2% respectively). The new electron-injection layer can be processed from environment-friendly solvents such as alcohol or water in which most of light-emitting polymers are insoluble. The mechanism of lowering the barrier height for electron injection from Al is discussed based on I-V characteristics, build-in potential, and X-ray diffraction data. [Copyright &y& Elsevier]

Abstract: Polymer light-emitting diodes (PLEDs) have attracted great interests recent years due to their potential application in next generation large-area flat-panel displays. For these devices, however, achieving efficient electron injection from air- and chemicals-stable cathode remains a great challenge. Here we demonstrate for first time that by incorporation of a thin layer of amino-alkyl-substituted polyfluorene copolymer spin-coated from alcohol or water solution, Au, a most noble metal with high work-function, can be a good electron injection cathode. This new type of bilayer cathode can significantly enhance electron injection to red, green and blue electroluminescent (EL) polymers, thereby resulting in high efficiency polymer LEDs, which are comparable to that of using low work-function metals, such as Ca and Ba as cathode. The use of most stable metals such as Au as cathode will open a door for fabrication and patterning of air-stable flat panel displays. [Copyright &y& Elsevier]

Abstract: Polymer light-emitting diodes (PLEDs) were prepared using an environment-friendly alcohol-soluble quaternized aminoalkyl-substituted conjugated polyfluorene co-polymerizing 2,1,3-benzothiadiazole monomer (PFNBr-BTDZ05) as an emitter, a high work-function Au metal as a cathode. The device structure used here is indium–tin–oxide (ITO)/poly(N-vinylcarbazole) (PVK)/PFNBr-BTDZ05/Au, where PVK is an anode buffer layer acting as the hole injection. The maximal external quantum and luminance efficiencies of 0.73% and 0.86 cd/A are obtained, and the maximal luminance is nearly 700 cd/m2 at 13 V, which was the highest brightness value reported in PLEDs with the Au metal cathode. This conjugated polyelectrolyte has such excellent electron injection ability that the device with the structure of ITO/poly(ethylene dioxythiophene)/poly(2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene)/PFNBr-BTDZ05/Al exhibits a high external quantum efficiency of 7.0%. The electron-injecting mechanism of PFNBr-BTDZ05 was discussed. [Copyright &y& Elsevier]

Abstract Inverted polymer/quantum-dots (QDs) hybrid white light emitting diodes with high efficiency and color stability were fabricated. The white devices show high luminous efficiency of 5.3 cd/A, external quantum efficiency of 3.0%, by using polyetherimide (PEI) to modify zinc oxide layer as the electron injection layer and blue emitting polymer of poly (dibenzothiophene-S,S-dioxide-co-9,9-dioctyl-2,7-fluorene) (PFSO) doped with green and red quantum-dots (G-QDs, R-QDs) as the emitting layer. Pure white emission at Commission Internationale de L'Eclairage coordinates of (0.31, 0.32) was achieved by adjusting weight ratio of PFSO: G-QDs: R-QDs to be 10.0: 3.6: 2.2. In addition, the electroluminescence (EL) spectra of the white device are quite stable in the wide brightness range between 1.0 × 102 cd/m2 and 1.0 × 104 cd/m2. The possible reason was that the PEI could reduce the energy barrier height between the cathode and emitting layer, and facilitate electron injection into the emitting layer. It's confirmed that both Forest energy transfer and charge trapping mechanisms work in the EL process and the latter is dominant. Highlights • Efficient blue polymer doped with quantum dots is used as the emitting layer. • Polyetherimide is introduced to reduce the electron injection barrier. • White spectra of electroluminescence is stable. • This device shows a peak luminous efficiency of 5.3 cd/A. [ABSTRACT FROM AUTHOR]

Compared to the single-unit organic light-emitting device (OLED), the tandem OLED connects multiple light-emitting units in series through the charge generation layer (CGL), thereby improving the device's current efficiency and lifetime. In this paper, we found that an ultra-thin Yb metal layer with low work function, high transmittance, and large atomic radii can be added to the CGL as an ion-blocking layer to prolong tandem OLEDs' lifetime. A green light tandem OLED utilizing Bphen:Cs 2 CO 3 /Yb/HAT-CN/NPB as the CGL exhibited an impressively longer lifetime (T 90) of 308 h at an initial brightness of 10000 cd/m2, which is 362 times longer than that of a device without a Yb layer inserted (T 90 = 0.85 h) and is 6.3 times greater than that of a single-unit OLED (T 90 = 49 h). In addition, the tandem OLED with Yb can achieve a maximum current efficiency (CE max) of 113.5 cd/A and a maximum power efficiency (PE max) of 68.6 lm/W, which are 2.3 times and 1.28 times higher, respectively, compared to those achieved by a single-unit OLED. The insertion of the Yb metal layer promotes the injection of electrons from HAT-CN to Bphen:Cs 2 CO 3 and can well curb the performance degradation caused by the diffusion of the two materials at this interface, thereby greatly improving the device lifetime. In particular, the performance and lifetime of the tandem OLED, composed of this CGL, remain largely unaffected when varying the Yb thickness within the range of 2∼4 nm, indicating that the device has a wide process window. Lastly, a high-performance white light tandem OLED with a Yb layer was obtained, achieving a CE max of 75.2 cd/A, a PE max of 40.9 lm/W, and a T 90 lifetime of 65 h at the initial brightness of 10000 cd/m2. The results indicate that metal Yb is suitable for the evaporation process of organic materials and can withstand a significant margin of error, showing great potential in the production of tandem OLEDs. [Display omitted] • A green light tandem OLED with a Yb layer in the CGL (Bphen:Cs 2 CO 3 /Yb/HAT-CN/NPB) obtained CE max of 113.5 cd/A and PE max of 68.6 lm/W, and an impressively longer lifetime (T 90) of 308 h, approximately 362 times longer than without and 6.3 times longer than that of a single-unit OLED. • Within the range of 2–4 nm, Yb thickness has little impact on the tandem OLED's performance and lifetime, implying a wide process window and tolerance for a significant margin of error. • The insertion of an ultra-thin Yb metal layer in the CGL as an ion-blocking layer curbs device performance degradation by inhibiting the diffusion of Bphen:Cs 2 CO 3 and HAT-CN at the interface. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract There has been an increasing demand for high-performance and cost-effective organic electron-transport materials for organic light-emitting diodes (OLEDs). In this contribution, we present a simple compound 3-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1,10-phenanthroline through the facile Pd-catalyzed coupling of a triphenyltriazine boronic ester with 3-bromo-1,10-phenanthroline. It shows a high T g of 112 °C. The ultraviolet photoelectron spectroscopy measurements reveal a deep HOMO level of −6.5 eV. The LUMO level is derived as −3.0 eV, based on the optical bandgap. The low-temperature solid-state phosphorescent spectrum gives a triplet energy of ∼2.36 eV. n-Doping with 8-hydroxyquinolatolithium (Liq, 1:1) leads to considerably improved electron mobility of 5.2 × 10−6–5.8 × 10−5 cm2 V−1 s−1 at E = (2–5) × 105 V cm−1, in contrast with the triarylphosphine oxide-phenantroline molecular conjugate we reported previously. It has been shown that through optimizing the device structure and hence suppressing polaron-exciton annihilation, introducing this single Liq-doped electron-transport layer could offer high-efficiency and stable phosphorescent OLEDs. [ABSTRACT FROM AUTHOR]

A bifacial modification technique has been developed to improve the device performance of the perovskite light-emitting diodes (PeLEDs). For the bottom modification, to reduce the acidity of the hole injection layer (HIL) poly(3,4-ethyl-enedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), environmental-friendly L- (+)-Arginine (Arg) is added to alleviate the erosion of indium in ITO electrode. As the result, the peak current efficiency (CE) is enhanced from 6.1 to 16.3 cd A−1, and the maximum external quantum efficiency (EQE) goes from 1.7% to 4.4%. For the top modification, (3-Aminopropyl)triethoxysilane (APTES) is introduced to passivate the surface defects of the perovskite film by coordinating with Pb2+ and suppressing the creation of metallic Pb atoms. With additional APTES on top, the peak CE reaches 31.8 cd A−1, and the maximum EQE reaches 7.7%. [Display omitted] • A bifacial modification technique is developed to passivate both the bottom and the top surfaces of the perovskite film. • L- (+)-Arginine (Arg) is utilized to neutralize the acidic hole-injection-layer PEDOT:PSS. • (3-Aminopropyl)triethoxysilane (APTES) is introduced to passivate the surface defects of the perovskite film. [ABSTRACT FROM AUTHOR]

Light out-coupling is an important strategy for the performance enhancement of white organic light-emitting diodes (OLEDs). Polydimethylsiloxane (PDMS), as a famous transparent elastomer, has the potential of using as a light extraction structure for OLED devices. Here, wrinkle-patterned PDMS films were in-situ fabricated via breath figure method together with spin coating process in a highly humid environment onto the glass side of the ITO substrate. The effect of solvent additive on the wrinkle morphology were investigated. The PDMS films were introduced into two different white OLED devices to extract the light of the substrate mode at the substrate-air interface. The maximum luminance improves 30.7% and 50.4%, respectively. While OLEDs also show appreciable enhancement with 31% and 11% in external quantum efficiencies due to luminance increase. Additionally, finite-difference time-domain (FDTD) simulations were performed to get insight into the mechanism of the light extraction enhancement due to the PDMS wrinkle structure. The reduced total internal reflections at the substrate-glass interface seems to increase the light out-coupling. We infer from these results that wrinkle-patterned PDMS films help to extract more light confined to the interior of white OLEDs, thereby improving the device performance. This work provides a relatively simple method to efficiently extract light from white OLEDs. [Display omitted] • Wrinkle-patterned PDMS films were in-situ fabricated via breath figure method together with spin coating. • Wrinkle structure can be attached to the light emitting surface of the OLEDs. • 7.5% and 50.4% max luminance enhancement are achieved for two different white OLEDs. • FDTD simulations were performed to explore the light extraction enhancement mechanism by the PDMS wrinkle. [ABSTRACT FROM AUTHOR]

In this manuscript, we reported the effects of solvent vapor annealing on performances of blue polymer light-emitting diodes, where the blue light-emitting poly(dibenzothiophene- S , S -dioxide- co -dioctyl-2,7-fluorene) that comprising dibenzothiophene- S , S -dioxide with molar ratio of 10% was used as the emissive layer, and toluene or chloroform was use as the annealing solvents. It was noted that the performances of PLED in terms of both luminous efficiency and brightness were obviously enhanced by solvent vapor annealing treatment, which can be correlated to the improved film morphology. The formation of β -phase lead to more balanced electron and hole flux as evaluated by single carrier devices. The best device performance with luminous efficiency of 4.8 cd/A was realized, which increased about 70% relative to that of 2.77 cd/A for the pristine device. These observations demonstrated that the solvent vapor annealing approach can be an effective strategy to improve performances of polymer light-emitting diodes. [ABSTRACT FROM AUTHOR]

A series of blue emitters incorporatingspiro[fluorene-9,9′-thioxanthene]or spiro[fluorene-9,9′-thioxanthene-S,S-dioxide] as the core and phenylcarbazole or triphenylamineas the arms were designed and synthesized. Their spiro conformationis beneficial for their thermal stability and for reducing the trendof aggregation quenching. By tuning the valence of the sulfur atom,highly efficient local excited (LE) state deep blue emitters and charge-transfer(CT) state blue emitters are obtained. The devices based on the LEemitters TPA-S and CzB-S as the nondoped emissive layer exhibit highexternal quantum efficiency of 1.76% and 2.03% and Commission Internationalede l’Eclairage (CIE) coordinates of (0.158, 0.039) and (0.160,0.054), respectively, and their CIEyvaluesare among the smallest ever reported for the deep blue OLEDs and arereadily very close to that of the inorganic light-emitting diode [CIE(0.16, 0.02)]. The nondoped device based on the CT emitter TPA-SO2as the emissive layer also exhibits a high current efficiency of 5.46cd A–1and CIE coordinates of (0.154, 0.168). Tofully utilize the 25% singlet and 75% triplet excitons, fluorescent/phosphorescenthybrid white organic light-emitting diodes in a single-emissive-layerarchitecture were also fabricated with TPA-SO2 as the blue emitteras well as the host of orange phosphorescent emitter to give forward-viewingpower efficiency of 47.9 lm W–1, which is the highestvalue ever reported for the devices in a similar architecture withoutusing any out-coupling technology. [ABSTRACT FROM AUTHOR]

Abstract: Highly efficient and bright hybrid white organic light emitting diodes (WOLEDs) based on simple architectures have been successfully fabricated and characterized. The optimized device can reach a maximum forward-viewing power efficiency (PE) of 20.2lm/W, a peak forward-viewing current efficiency (CE) of 30.7cd/A, an extremely high brightness of 95,683cd/m2, and a Commission International de l’E clairage chromaticity coordinates of (0. 436, 0.425) at 12V. Even at the illumination-relevant brightness of 1000cd/m2, a forward-viewing PE of 17.0lm/W and CE of 30.7cd/A are obtained. Moreover, it is found that the device not only suffers slight efficiency roll-off but also exhibits a stable color during a large range of brightness, indicating that the device can satisfy the future commercial requirements. Undoubtedly, the results will be beneficial to the design of both material and device architecture for high-performance WOLEDs and next-generation solid-state lighting sources. [Copyright &y& Elsevier]

Highlights: [•] A very simplified HWOLED with P–F structure has been successfully developed. [•] The forward-viewing CE and PE are as high as 59.4cd/A and PE of 58.4lm/W, respectively. [•] A simple but effective way towards high-efficiency HWOLEDs has been demonstrated. [•] The origin of this high-efficiency device is explored comprehensively. [Copyright &y& Elsevier]

Abstract: Solvent treatment was discovered as an efficient anode modification approach to improve the performance of polymer light-emitting diodes. By simply spin-coating several drops of the polar solvent on top of the PEDOT:PSS hole injection layer, the maximum luminance efficiency was increased by as much as 83% without sacrificing the operation voltage. The combination effects of the reduced work function and the lowered resistivity of PEDOT:PSS film, decreased the hole leakage current, leading to a more balanced charge density inside the emission layer, thereby enhancing the device performance. [Copyright &y& Elsevier]

Abstract: Two novel blue light-emitting sextuple hydrogen-bonding self-assembly molecular duplexes bearing 4-phenoxy-1,8-naphthalimide fluorophores, namely PhNIHB and 2TPhNIHB, have been synthesized and characterized. Compared with their small molecular counterparts PhNI and 2TPhNI, the objective compounds exhibit 13–22nm blue-shifted fluorescent emission, and much higher photoluminescence quantum yields (0.34 vs 0.18 for PhNIHB; 0.42 vs 0.27 for 2TPhNIHB) in solid state; and their thermal and morphological stability have been improved as well. Employing 2TPhNIHB or 2TPhNI as emitter, non-doped solution-processed light-emitting diodes with structure of ITO/PEDOT: PSS (40nm)/PVK (40nm)/blue emitter (70–80nm)/CsF (1.5nm)/Al (120nm) have been fabricated. The 2TPhNI-based device gives yellow emission [CIE (0.38, 0.49)] with poor maximum luminous efficiency (LEmax) of 0.13cd/A and external quantum efficiency (EQEmax) of 0.06%. The 2TPhNIHB-based device, however, gives blue-green emission [CIE (0.25, 0.34)], with much higher efficiency relative to 2TPhNI-based one (LEmax of 0.37cd/A and EQEmax of 0.35%). The effective isolation of the naphthalimide fluorescent cores as well as the suppressed formation of exciplex at the PVK/emitter interface by these oligoamide motifs are suggested to be responsible for the improved EL performance. [Copyright &y& Elsevier]

Abstract: By simply spin-coating the solvents, such as ethanol and methanol, on top of the organic active layer, the performance of polymer organic light-emitting diodes is significantly enhanced. The quantum efficiency is increased by as large as 58% for low work function Ba/Al cathode devices after solvent treatment. An interface dipole between the organic layer and the metal layer induced by the solvent, either from the intrinsic dipole or the interaction between the solvent and the cathode metal, is responsible for the device performance improvement. The interface dipole layer, which is confirmed by the Kelvin Probe Force Microscopy and the photovoltaic measurements, lifts the vacuum level on the metal side, thereby reducing the electron injection barrier at the organic/metal interface, and leading to better device performance. [Copyright &y& Elsevier]

Abstract: Two novel diketopyrrolopyrrole (DPP)-based copolymers P1–2 were prepared by doping red emitting DPP monomer (1mol%) into benzothiadiazole, alkoxybenzene and 9,9-dialkylfluorene-based copolymers through base-free Suzuki polymerization. P1 contained the pendants of electron-transport oxadiazole and hole-transport carbazole, but P2 did not contain them. P1 had higher glass transition temperature than P2. The electroluminescence (EL) devices of P1 and P2 (ITO/PEDOT:PSS/polymer/CsF/Al) exhibited red emission with external quantum efficiency of 0.63% and 0.18%, and with brightness of 2681 and 885cd/m2, respectively. The results show that the EL properties of P1 are much better than that of P2 due to the introduction of oxadiazole and carbazole as the pendants. The pendants could restrain aggregation which might induce fluorescence quenching and are of benefit to keep high charge mobility. The efficient energy transfer existed among the pendants, polymer backbone and DPP unit. These factors should be responsible for the higher EL performance of P1. [Copyright &y& Elsevier]

Abstract: Substitution at the 4-position of 1,8-naphthalimide with electron-donating phenoxy or tert-butyl modified phenoxy groups, novel naphthalimide derivatives were obtained which emitted blue fluorescence with emission peaks of 425–444 nm in chloroform solution under UV irradiation, with highest relative photoluminescence quantum efficiency of 0.82. When in solid film, only compounds that contained ortho-tert-butylphenoxy substituents displayed blue photoluminescence of 438–451 nm, with highest absolute fluorescence quantum yield of 0.29; whereas other compounds showed greenish blue fluorescence at 471–478 nm, with highest absolute fluorescence quantum yield of 0.42. Cyclic voltammetry studies revealed that the molecules have low-lying energy levels of the lowest unoccupied molecular orbital (LUMO) ranging from −3.29 eV to −3.24 eV, and energy levels of the highest occupied molecular orbital (HOMO) ranging from −6.26 eV to −6.16 eV, suggesting they may possess good electron-transporting or hole-blocking properties. The findings indicate that the molecules offer potential as dopants as well as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue or greenish blue organic light-emitting diodes. [Copyright &y& Elsevier]

Abstract: Two novel diketopyrrolopyrrole (DPP) and p-phenylenevinylene alternating copolymers, poly(1,4-(2,5-dicyano)-phenylenevinylene-alt-2,5-dioctyl-3,6-bis(4-vinylenephenyl)pyrrolo[3,4-c]pyrrole-1,4-dione) (P1) and poly(1,4-(2,5-diethoxy)-phenylenevinylene-alt-2,5-dioctyl-3,6-bis(4-vinylenephenyl)pyrrolo[3,4-c]pyrrole-1,4-dione) (P2), were synthesized through Wittig reaction in good yields, and were characterized by FTIR, NMR. Two polymers possessed moderate molecular weights and polydispersities, well-defined structures, and were readily soluble in common organic solvents. In particular, P1 and P2 exhibited excellent thermal stability with T d =393 and 398°C at 5% weight loss, respectively. Both P1 and P2 in solution and in thin films exhibited strong red photoluminescence. Both electroluminescence devices using ITO/PEDOT/polymer/Ba/Al configuration with P1 and P2 as the emitting layer showed nearly pure red emission with the emission peaks at 646nm for P1 and 648nm for P2, and exhibited low turn-on voltages of 4.5 and 3.4V, respectively. The results show that P1 and P2 are promising candidates for red emissive materials in polymer light-emitting diodes. [Copyright &y& Elsevier]

Abstract: We report highly efficient white polymer light-emitting devices (WPLEDs) using a newly synthesized, deep-blue emitting fluorene-co-dibenzothiophene-S,S-dioxide copolymer as host, doped with two narrow-bandgap iridium complexes. Despite the low-lying triplet energy levels of the host, phosphorescent quenching by the polyfluorene copolymer host was significantly suppressed with poly(N-vinylcarbazole) (PVK) as hole-injecting, anode buffer layer. The energy transfer process had been studied via transient photoluminescence spectra and confirmed that PVK layer is responsible for the efficient electrophosphorescence in the devices. As a result of balanced red–green–blue (RGB) emission from the host and the triplet emitters, white emission with Commission Internationale de L’Eclairage (CIE) coordinates of (0.278, 0.312) was achieved, with a peak luminous efficiency of 15.1cdA−1 and a color rendering index (CRI) of 79–86. [Copyright &y& Elsevier]

Abstract: Here we report a new approach for the preparation of anode buffer layer for efficient polymer light-emitting devices (PLEDs) by using glycerol to modify relative low conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). This new type of anode buffer layer allows for a 50–90% increase in device performance for green emitting phosphorescent PLEDs in terms of luminous efficiency, and external quantum efficiency, while 90–150% in power efficiency, as compared to devices fabricated using commercially available PEDOT:PSS. The green emitting phosphorescent PLEDs with this modified anode buffer exhibit very high efficiencies, representing a significant step forward to matching and exceeding the efficiencies reported to date with vacuum-deposited small molecular devices. We anticipate that these findings can provide a simple experimental procedure for improvement of PLEDs. [Copyright &y& Elsevier]

Abstract: The synthesis of the tris-cyclometalated iridium(III) complex [Ir(DCP)3] (HDCP=1-(N,N-diphenyl-amino)-4-(4-chlorophenyl)-phthalazine) from hydrated iridium(III) chloride and the ligand HDCP under mild reaction conditions was described. The photophysical, electrochemical and electrophosphorescent properties of this complex were investigated. Organic light-emitting diodes (OLEDs) using the complex as a dopant and a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) as a host exhibited bright red emission at 620nm with the Commission Internationale de l’Eclairage (CIE) coordinate of (0.67, 0.32). A maximum external quantum efficiency of 13.6% photos/electron with a luminous efficiency of 7.4cd/A at a current density of 0.73mA/cm2, and a maximum luminance of 2941cd/m2 at 99mA/cm2 were obtained in the device at 4wt% doping concentration. [Copyright &y& Elsevier]

Abstract: A series of new heteroleptic iridium complexes bearing fluorenyl-modified 1-phenylisoquinoline as the first ligand and different ancillary ligands has been prepared and characterized. These complexes bis(1-(3-(9,9-dimethyl-fluoren-2-yl)phenyl)isoquinoline-C2,N′)iridium(III)acetylacetonate(Ir(DMFPQ)2acac)), bis(1-(3-(9,9-dimethyl-fluoren-2-yl)phenyl)isoquinoline-C2,N′)iridium(III)(3-(pyridin-2-yl)-1,2,4-triazolate)(Ir(DMFPQ)2pt) and bis(1-(3-(9,9-dimethyl-fluoren-2-yl)phenyl)isoquinoline-C2,N′)iridium(III)(2-(2-pyridyl)benzimidazolate)(Ir(DMFPQ)2pbi) showed red phosphorescent emissions of 615–630nm in dichloromethane solution. The device fabricated with these complexes doped into a host polyfluorene (PFO) blend with 30% of an electron transport material 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) showed high device efficiencies. Ir(DMFPQ)2acac exhibited red emission with an external quantum efficiency(η ext) of 14.3% and luminous efficiency(η c) of 7.8cd/A at 1.2mA/cm2 and the maximum brightness reached 10006cd/m2 (Commission Internationale de I’Eclairage(CIE) chromaticity coordinates: (0.67,0.32)) at 412mA/cm2. Ir(DMFPQ)2pt showed a η ext of 13.0% and η c of 9.2cd/A at 17mA/cm2, 1532cd/m2, and the maximum brightness reached 15085cd/m2 (CIE: 0.64,0.34) at 360mA/cm2. [Copyright &y& Elsevier]

Abstract: A new yellow-emitting iridium complex Ir(3-piq)2pt with 3-phenylisoquinoline(3-piq) as cyclometalated ligand by introducing 2-(2H-1,2,4-triazol-3-yl)pyridine (pt) as ancillary ligand was synthesized. Efficient yellow polymer light-emitting devices (PLEDs) with the new iridium complex Ir(3-piq)2pt in device structure ITO/PEDOT/PVK/Ir-complex (x%):PFO (or +PBD (30%))/Ba/Al (with or without PBD electron transports additive) were fabricated. The device doped with 4% Ir(3-piq)2pt displayed a quantum efficiency of 9.4% (16.2cd/A) at 5.06mA/cm2 with PBD additive. A white emission was also obtained at a doping concentration of 0.5% Ir(3-piq)2pt with no PBD added. CIE coordinate (0.34 and 0.31) close to National Television Standards Committee (NTSC) white standard, external quantum efficiency of 2.25%, and luminance of 2250cd/m2 at applied voltage of 15V were obtained. The results indicated that introducing triazole group based ancillary ligand into iridium complexes could enhance the electron-transporting ability of the iridium complexes. [Copyright &y& Elsevier]

Abstract: PLED based flat panel displays with RGBW sub-pixel format utilizing a white emitter as the fourth primary, was analyzed theoretically and experimentally. Instead of the traditional white point characterization method, uniform luminance color space was introduced to characterize the display performance in a more realistic way. In the uniform luminance color space, after the power efficiency of the white emitter exceeds a threshold determined by the green emitter’s efficiency, the RGBW display becomes more energy efficient than the RGB display. To simulate the display performance in different applications, such as computer desktop visualization, or video application, the color usage frequency with Gaussian distribution was adopted. As the color usage frequency distribution gets closer to that in the real images, the full color pixel’s power efficiency of the RGBW display is more and more dependent on the EL performance of the white emitter. With a highly efficient white emitter as W sub-pixel, the RGBW display will be the preferable choice for displaying video information. [Copyright &y& Elsevier]

Abstract: Here we report efficient and color-stable white polymer light-emitting devices (WPLEDs) based on a newly synthesized efficient blue emitting polymer poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)fluorene)-co-(3,7-dibenziothiene-S,S-dioxide10)] (PPF-3,7SO10) which dually function as host material and blue emitter, with appropriate blending ratio with two typical electroluminescent polymers, green emitting poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) and orange–red emitter poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH–PPV) with appropriate blending ratio. In a single active layer WPLEDs with a blending ratio of 100:0.8:0.5 (B:G:R) by weight, white light emission with CIE coordinate of (0.34, 0.35) was realized. The resulted device shows a high luminous efficiency (LE) of 8.7cdA−1, which could be further enhanced to 14.0cdA−1 with incorporation of a thin hole transporting layer poly (vinylcarbazole) (PVK) at the anode side. The obtained luminous efficiency is listed as one of the highest reported value for WPLEDs based on all fluorescent polymer emitters. The devices had appropriate color temperature of 2500–6500K and high color rendering index (CRI) of 72–79, and are characterized with stable electroluminescent spectra upon change of current density, stress and annealing at high temperature, thus can find application in solid-state lighting. [Copyright &y& Elsevier]

Abstract: A novel ligand 9-(4-(4-chlorophenyl)phthalazin-1-yl)-9H-carbazole (HCPC) was designed and prepared, and the corresponding tris-cyclometalated iridium(III) complex Ir(CPC)3 was readily synthesized by the reaction of the ligand with IrCl3 · 3H2O at 80°C for 20h. A highly efficient organic light-emitting device using this complex as a dopant was obtained. The device fabricated by solution process showed a maximum luminance of 2948cd/m2 at a current density of 115.6mA/cm2 and a maximum external quantum efficiency of 20.2% at 0.18mA/cm2. [Copyright &y& Elsevier]

Abstract: We demonstrate highly efficient white emission polymer light-emitting diodes (WPLEDs) from multilayer structure formed by solution processed technique, in which alcohol/water-soluble polymer, poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) was incorporated as electron-injection layer and Al as cathode. It was found that the device performance was very sensitive to the solvents from solution of which the PFN electron-injection layer was cast. Devices with electron-injection layer cast from methanol solution show degraded performance while the best device performance was obtained when mixed solvent of water and methanol with ratio of 1:3 was used. We attribute the variation in device performance to washing out the electron transport material in the emissive layer due to rinse effect. As a result of alleviative loss of electron transport material in the emissive layer, the optimized device with a peak luminous efficiency of 18.5cdA−1 for forward-viewing was achieved, which is comparable to that of the device with same emissive layer but with low work-function metal Ba cathode (16.6cdA−1). White emission color with Commission International de I’Eclairage coordinates of (0.321, 0.345) at current 10mAcm−2 was observed. [Copyright &y& Elsevier]

Abstract: Asymmetrically 9,10-disubstituted anthracene derivatives 1a/1b have been synthesized and characterized. The new compounds exhibit a high solubility and can be easily purified by chromatographic methods. Thin solid films based on these compounds combine intrinsic amorphous morphology with pure blue emission and high solid-state photoluminescent efficiencies. These materials have been used as solution-processed active emitters in electroluminescent devices leading to interesting device performances. The effect of partial fluorination of a sub-unit of one of the compounds on the properties of the material is discussed. [Copyright &y& Elsevier]

Abstract: Full color reproduced by white OLED (organic light emitting diodes) coupled with transmission color filters for the application in flat panel display was analyzed theoretically and experimentally. A white emitter made up of three primary emission peaks was found to be superior to a white emitter made up of complementary colors, i.e. two emission peaks. However, though the full color reproduction by white emitter possesses the merit of manufacturing simplicity, it is much worse than the color reproduction by three individual primary color sub-pixels, in terms of power efficiency and the power consumption. Adjusted to the same external quantum efficiency, the full color pixel made of three primary color sub-pixels is 10 times more efficient than that made of white emitter coupled with color filters. [Copyright &y& Elsevier]

Abstract: 1.5in. diagonal red, green, and blue monochrome passive-matrix (PM) polymer light-emitting diodes (PLED) flat panel displays (FPDs) with format 96×64 were fabricated by spin-coating technology with device structure of ITO/PEDOT/Emissive layer/Ba/Al. During spin-coating process, by rearranging the location and the direction of the panel with respect to the center of the spinner, the piling of organic materials under the cathode separator was significantly reduced, resulting in a more uniform light emission. The final display showed neither dead pixels nor dead lines. Current efficiencies of 1.37, 9.5 and 1.44cd/A, and CIE color coordinates of (0.62,0.37), (0.37,0.60) and (0.15,0.13), for red, green, and blue monochrome displays, respectively, have been achieved. Further, 1.5in. full color PM PLED FPDs with format 96×RGB×64 was successfully fabricated by inkjet printing technology. The current efficiency was about 0.75cd/A at full screen white with color coordinates located at (0.34,0.35). A color gamut of 50% NTSC was obtained. For all the displays, the 5-point uniformity was more than 80%. [Copyright &y& Elsevier]

Abstract: Efficient polymer white-light-emitting diodes (WPLEDs) have been fabricated with a single layer of fluorescent polymer blend. The device structure consists of ITO/PEDOT/PVK/emissive layer/Ba/Al. The emissive layer is a blend of poly(9,9-dioctylfluorene) (PFO), phenyl-substituted PPV derivative (P-PPV) and a copolymer of 9,9-dioctylfluorene and 4,7-di(4-hexylthien-2-yl)-2,1,3-benzothiadiazole (PFO-DHTBT), which, respectively, emits blue, green and red light. The emission of pure and efficient white light was implemented by tuning the blend weight ratio of PFO: P-PPV: PFO-DHTBT to 96:4:0.4. The maximum current efficiency and luminance are, respectively, 7.6cd/A at 6.7V and 11930cd/m2 at 11.2V. The CIE coordinates of white-light emission were stable with the drive voltages. [Copyright &y& Elsevier]

Abstract: A series of random conjugated copolymers (PFO-HBT) derived from 9,9-dioctylfluorene (DOF) and 2-hexylbenzotriazole (HBT) is prepared by the palladium-catalyzed Suzuki coupling reaction with the feed HBT molar ratio around 1%, 5% and 15%. By copolymerizing 2-hexylbenzotriazole into the backbone of polyfluorene, an efficient colorfast blue light-emitting polymer system is developed. The device with the structure of ITO (indium tin oxide)/PEDOT/PVK/PFO-HBT1/Ba/Al exhibits the highest external quantum efficiency 1.62% with luminance efficiency of 2.69cd/A, power efficiency of 1.25lm/W and the CIE coordinates of (0.15, 0.17). The EL spectra are stable at the increased current density and continuous operation without significant change of CIE. [Copyright &y& Elsevier]

Abstract: Bis(2-(2-hydroxyphenyl)benzthiazolate)zinc(II), [Zn(BTZ)2]2, is amongst the best white-light emissive as well as electron transport materials used in organic light-emitting diodes (OLEDs). In order to gain a deeper understanding for its carrier transport properties, we adopt the density-functional theory (DFT) with generalized gradient approximation (GGA) to calculate the electronic band structure and the density of states (DOS) by the Becke exchange plus Lee–Yang–Parr correlation (BLYP) functional. The intermolecular interaction related to transport behavior has been analyzed from the bandwidths and band gaps. Within the effective mass approximation, we find that the mobility of electron is about two times larger than that for the hole. Furthermore, if we consider the bands near Fermi level, we conclude that the interband gaps within the unoccupied bands are generally smaller than those for the occupied bands, which indicate that the electron can hop through scattering from one band to another, much easier than the hole. These facts indicate that, in [Zn(BTZ)2]2, the electron are the dominant carriers in transport, in contrast to most organic materials. [Copyright &y& Elsevier]

Solution-processed colloidal quantum dot light-emitting diodes (QLED) have attracted many attentions with significant progress in recent years. However, QLED devices still face some challenges. The energy barrier between Cd-base quantum dots (QDs) and commonly used hole transport materials is larger than that between QDs and electron transport materials, which leads to the imbalance of carriers in the light emitting layer (EML) and the low performance of QLED devices. Herein, we report a simple strategy to improve the device performance by doping small molecule transport material 4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC) into red CdSe/ZnS QDs. The optimized red QLED devices with TAPC-doped emissive layer at a ratio of 3.2 wt% achieve 20.0 cd/A of maximum current efficiency, 16.6 lm/W of power efficiency and 15.7% of external quantum efficiency, which is 30%, 58% and 33% higher than the control device. The improved performance of devices can be ascribed to the increase of hole current density, decrease of leakage electrons and more balanced quantity of carriers in EML. This work put forward a viewpoint to improve the performance of QLED devices via doping high hole mobility materials into emission layer. [Display omitted] • Small molecule hole transport material TAPC is doped into red CdSe/ZnS QDs to enhance the device performance. • The EML solution consists of QD octane solution and TAPC o-xylene solution. • The introduction of TAPC leads to the reduction of leakage electrons and the improvement of hole density. [ABSTRACT FROM AUTHOR]

High performance quantum dot light emitting diodes (QD-LED) are being considered as a next-generation technology for energy efficient solid-state lighting and displays. In recent years, cadmium (Cd)-based QLEDs have made great progress in performance, which is close to commercial applications. However, the performance of environmentally friendly Cd-free QD-LED still needs to be improved. In this letter, using InP/ZnS quantum dots (QDs), an environmentally friendly red QDs material, as the light emitting layer, low-cost all-solution processed red InP/ZnS QD-LED are fabricated. The optimized device with a hybrid multilayered structure employing an organic double hole transport layer (HTL) with doping small molecules (TFB/PVK:TAPC) and an inorganic ZnMgO nanoparticles (NPs) electron transport layer (ETL), here TFB, PVK and TAPC represent poly [(9,9-dioctylfluorenyl-2,7-diyl)- co -(4,4'-(N -(p -butylphenyl))-diphenylamine)], poly (9-vinlycarbazole) and 1,1-bis [4-[N,N′-di (p -tolyl)amino]phenyl]-cyclohexane, respectively. The best device exhibits a peak current efficiency (CE) of 7.58 cd A−1, which is 2.4 times higher than the control device using PVK (HTL) and ZnO (ETL). At the same time, turn-on voltage dropped from 2.8 V (control devices) to 2.4 V. These superb QD-LED performances originate not only from the improved hole injection by the introduction of a double hole layer and the reduced the quenching of excitons by using ZnMgO NPs ETL but also from increasing the hole mobility with doping of small molecule materials in PVK to balance the carrier transportation. This work provides a simple and feasible idea with optimization the carrier transport for realizing high-efficiency QD-LED devices. [Display omitted] • For the first time, systematically optimizing both HTL and ETL in InP-based red QD-LED, which is simple but effective. • A double layer of TFB/PVK HTLs are introduced, and doping TAPC with high hole mobility into PVK. • Device with peak CE of 7.58 cd A−1 was obtained, which total nearly 140% improvement compare with control device. • All solution-process technique can reduce fabrication cost. [ABSTRACT FROM AUTHOR]