Search

Rhythmic lighting with varying color-temperature and brightness like that of diurnal sunlight has now been recognized to be extremely crucial to human health. In this study, we demonstrate a high-efficiency and high light-quality organic light-emitting diode (OLED) with color temperature tunable from the 1700 K of dusk-hue, 1900 K of candles and 2500 K of incandescent bulbs to 3000 K of warm-white light. The color-temperature tunable OLED device was achieved by utilizing a hybrid system and inserting a carrier modulation layer (CML) between the emission layers. In addition, the electron-rich charge transport properties of EML-1, facilitated via a 3 : 1 composition ratio of the 3P-T2T host to TPD-15 co-host, played a crucial role in tuning the desirable low-color temperature of the fabricated OLED devices. The current efficiency, power efficacy, and spectrum resemblance index (SRI) of the studied OLED are 40.2 cd/A, 40.3 lm W−1 and 82.2 at 1000 cd m−2, respectively. The resultant devices show great potential to advance the study and development of physiologically friendly lighting and enable a successful commercial OLED lighting product in the market.

Organic materials are used in novel optoelectronic devices because of the ease and high compatibility of their fabrication processes. Here, we demonstrate a low-driving-voltage cathodic-controlled organic upconverter with a mapping application that converts near-infrared images to produce images of visible blood vessels. The proposed upconverter has a multilayer structure consisting of a photosensitive charge-generation layer (CGL) and a phosphorescent organic light-emitting diode (OLED) for producing clear images with a high resolution of 600 dots per inch. In this study, temperature-dependent electrical characterization was performed to analyze the interfacial modification of the cathodic-controlled upconverter. The result shows that the upconverter demonstrated a high conversion efficiency of 3.46% because of reduction in the injection barrier height at the interface between the CGL and the OLED.

Highly efficient electrophosphorescent organic light-emitting diodes (PHOLEDs) containing mixed hosts of bis(3,5-di(9H-carbazol-9-yl)phenyl)diphenylsilane (SimCP2) and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7) and a soluble derivative of the green emitter fac-tris(2-phenylpyridine)iridium (III) [(Ir(ppy)3 ] have been demonstrated. All organic layers were mixed in a single layer for solution processing during the fabrication of the PHOLEDs. The amorphous mixed host of SimCP2:OXD-7:Ir(ppy)3 exhibited ambipolar charge transport as well as high hole and electron mobilities on the order of 10-7 cm2 /Vs from space-charge-limited current measurement. The values of both the hole and electron mobilities were 100 times greater than that of the widely used poly(9-vinylcarbazole) (PVK):OXD-7:Ir(ppy)3 host, resulting in efficient charge balance in the SimCP2 host. Based on a simple fabrication process of single-layer PHOLED, a green device with the maximum luminous and power efficiencies of 42 cd/A and 20 lm/W, respectively, was obtained at 600 cd/m2.

We have developed a high efficiency and deep blue organic light-emitting diodes (OLEDs) incorporating a 4-hydroxy-8-methyl-1,5-naphthyridine aluminum chelate (AlmND3) as the emitter and electron transporting layer (ETL). The blue AlmND3 emitter, with an electron withdrawing group added to the well-known green fluorophore tris(8-hydroxyquinolinato)aluminum (Alq3) , exhibited ambipolar charge transport as well as high electron and hole mobilities on the order of 10-5 cm2/V·s, as deduced time-of-flight measurements. The magnitude of the electron mobility was 10 times greater than that of the widely used Alq3 ETL, resulting in efficient charge balance in the AlmND3 device. Based on a simple configuration of double heterojunction device, a blue device with the maximum external quantum efficiency of 1.58% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.16, 0.08) was achieved at a brightness of 200 cd/m2 . This study has revealed the fundamental nature of charge transport in hydroxynaphthyridine metal chelate and shed a new light on the design of high performance blue OLEDs.

In this study, we compared the use of neat bathocuproine (BCP) and BCP:C60 mixed buffer layers in chloroboron subphthalocyanine (SubPc)/C60 bilayer organic photovoltaic (OPV) devices and analyzed their influence on device performance. Replacing the conventional BCP with BCP:C60 enabled manipulating the optical field distribution for optimizing the optical properties of the devices. Estimation of the interfacial barrier indicated that the insertion of the BCP:C60 between the C60 and electrode can effectively reduce the barrier for electrons and enhance electron collection at the electrode. Temperature-dependent measurements of the OPV devices performed to calculate the barrier height at the SubPc/C60 interface suggested that band bending was larger when the BCP:C60 buffer layer was used, reflecting increased exciton dissociation efficiency. In addition, the device lifetime was considerably improved when the BCP:C60 buffer layer was used. The device performance was stabilized after the photodegradation of the active layers, thereby increasing the device lifetime compared with the use of the neat BCP buffer layer. Atomic force microscopy images showed that the neat BCP was easily crystallized and could degrade the cathodic interface, whereas the blend of C60 and BCP suppressed the crystallization of BCP. Therefore, the optimal buffer layer improved both the device performance and the device lifetime.

Time-of-flight (TOF) measurements typically require a sample thickness of several micrometers for determining the carrier mobility, thus rendering the applicability inefficient and unreliable because the sample thicknesses are orders of magnitude higher than those in real optoelectronic devices. Here, we use subphthalocyanine (SubPc):C70 as a charge-generation layer (CGL) in the TOF measurement and a commonly hole-transporting layer, N,N’-diphenyl-N,N’-bis(1,1’-biphenyl)-4,4’-diamine (NPB), as a standard material under test. When the NPB thickness is reduced from 2 to 0.3 μm and with a thin 10-nm CGL, the hole transient signal still shows non-dispersive properties under various applied fields and thus the hole mobility is determined accordingly. Only 1-μm NPB is required for determining the electron mobility by using the proposed CGL. Both the thicknesses are the thinnest value reported to data. In addition, the flexibility of fabrication process of small molecules can deposit the proposed CGL underneath and atop the material under test. Therefore, this technique is applicable to small-molecule and polymeric materials. We also propose a new approach to design the TOF sample using an optical simulation. These results strongly demonstrate that the proposed technique is valuable tool in determining the carrier mobility and may spur additional research in this field.

Transparent organic upconversion devices are shown in a night-vision demonstration of a real object under near-infrared (NIR) illumination in the dark. An extraordinarily high current gain - reflecting the on-off switching effect - greater than 15 000 at a driving voltage of 3 V is demonstrated, indicating the high sensitivity to NIR light and potential of using the proposed upconverter in practical applications. A maximum luminance exceeding 1500 cd m(-2) at 7 V is achieved. Unlike previous studies, where 2D aperture projection is reported, the current study shows 3D images of real objects under NIR illumination in the dark.

In this study, we demonstrate electrophosphorescent organic light-emitting diodes (PHOLEDs) with a simple structure and high efficiency, utilizing fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)3) as a green phosphorescent emitter. The device structure (ITO/TAPC/TAPC:Ir(ppy)3/TPBi:Ir(ppy)3/TPBi /LiF/Al) was fabricated by the hole transporting layer of 1,1-bis((di-4-tolylamino)phenyl)cyclohexane (TAPC; T1 = 2.87 eV) and the electron transporting layer of 2,2,2-(1,3,5-benzenetriyl)tris[1-phenyl-1H-benzimidazole] (TPBI; T1 = 2.74 eV) to assemble a double emitting zone without common host materials. The emitting region with a TAPC/TPBI bilayer interface was able to provide an effective energy transference of Ir(ppy)3 (T1 = 2.4 eV). Thus, the green PHOLED exhibited high current efficiency (70 cd/A at 100 cd/m 2 ) and low roll-off in these devices.

Acenes can be thought of as one-dimensional strips of graphene and they have the potential to be used in the next generation of electronic devices. However, because acenes larger than pentacene have been found to be unstable, it was generally accepted that they would not be particularly useful materials under normal conditions. Here, we show that, by using a physical vapour-transport method, platelet-shaped crystals of hexacene can be prepared from a monoketone precursor. These crystals are stable in the dark for a long period of time under ambient conditions. In the crystal, the molecules are arranged in herringbone arrays, quite similar to that observed for pentacene. A field-effect transistor made using a single crystal of hexacene displayed a hole mobility significantly higher than that of pentacene. This result suggests that it might be instructive to further explore the potential of other higher acenes.

Single-layer blue phosphorescence organic light emitting diodes (OLEDs) with either small-molecule or polymer hosts are fabricated using solution process and the performances of devices with different hosts are investigated. The small-molecule device exhibits luminous efficiency of 14.7 cd/A and maximum power efficiency of 8.39 lm/W, which is the highest among blue phosphorescence OLEDs with single-layer solution process and small molecular hosts. Using the same solution process for all devices, comparison of light out-coupling enhancement, with brightness enhancement film (BEF), between small-molecule and polymer based OLEDs is realized. Due to different dipole orientation and anisotropic refractive index, polymer-based OLEDs would trap less light than small molecule-based OLEDs internally, about 37% better based simulation results. In spite of better electrical and spectroscopic characteristics, including ambipolar characteristics, higher carrier mobility, higher photoluminescence quantum yield, and larger triplet state energy, the overall light out-coupling efficiency of small molecule-based devices is worse than that of polymer-based devices without BEF. However, with BEF for light out-coupling enhancement, the improved ratio in luminous flux and luminous efficiency for small molecule based device is 1.64 and 1.57, respectively, which are significantly better than those of PVK (poly-9-vinylcarbazole) devices. In addition to the theoretical optical simulation, the experimental data also confirm the origins of differential light-outcoupling enhancement. The maximum luminous efficiency and power efficiency are enhanced from 14.7 cd/A and 8.39 lm/W to 23 cd/A and 13.2 lm/W, respectively, with laminated BEF, which are both the highest so far for single-layer solution-process blue phosphorescence OLEDs with small molecule hosts.

Single-layer and efficient blue phosphorescence organic light-emitting diodes (PHOLEDs) utilizing a small molecule host, bis[3,5-di(9H-carbazol-9-yl)phenyl]diphenylsilane (SimCP2), as the host material were investigated. All active components including SimCP2, 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7), and iridium(III) bis[(4,6-di-fluorophenyl)-pyridinato-N,C 2] picolinate (FIrpic) were mixed in an organic solution for wet processing in the fabrication of single-layer PHOLEDs. The device's performance significantly exceeds other small-molecule-host, single-layer, blue PHOLEDs fabricated by the solution process. With minimum efficiency roll-off, a maximum current efficiency of 13.6 cd/A, power efficiency of 8 lm/W, external quantum efficiency of 4.71%, and Commission Internationale de L'Eclairage (CIE x,y ) coordinates of (0.15,0.36) at 600 cd/m2 have been achieved. In addition, the device performance of the solution-processed single-layer PHOLED is much greater than that of its vacuum-deposited counterparts.

To optimize the performance of organic light-emission devices (OLEDs), optical simulation or electrical simulation is often used to help designing the device structures. However, employing electrical or optical simulation separately to optimize the device might lead to incorrect conclusions. A few researches have combined optical and electrical simulations to design OLED structures by merely inserting the maximum carrier recombination rate calculated from electrical simulation into optical simulation programs, which is still insufficient for optimization of OLEDs due to lack of considering the influence of optical interference positions. In this paper, we investigate the OLED performance by using three simulation methods, pure optical, pure electrical, or combination of both, to design the devices. Using the models incorporating both electrical and optical simulations, we found that the optimal emission position occurs neither at the place with the best optical interference nor at the point where carrier recombination rate is the maximum. In order to verify the simulation results, we design the testing devices, red fluorescence OLEDs of bi-layer structures, with various positions of recombination emission. It is found that the position of recombination emission has major impact on the device performance of OLEDs, which lead to some important design rules. With integration of electrical and optical simulations, the real emission position could be predicted with excellent agreements to the experimental results. Applying this method to design the red fluorescent bi-layer OLEDs, the device with very high efficiency of 8.44 cd/A was achieved.

In this paper, a novel electron donor, bis4-[N-(1-naphthyl)phenylamino]phenylfumaronitrile (NPAFN), was demonstrated as a potential for application in high open-circuit voltage (V OC) organic photovoltaic (OPV) cells. Devices based on NPAFN/C60 heterojunction were firstly manipulated to their optimum optical property by tuning the thickness of C60 without compromising the transport property. With the appropriate thickness of C60, the electrical configuration of the devices was improved when the thickness of NPAFN was less than 6.3 nm. The optimum efficiency was 2.1% with a V OC of 0.87 V when the thickness of NPAFN was 5 nm. In addition, the increase in V OC by increasing the thickness of NPAFN was observed and discussed.

The synthesis, thermal and photophysical properties, and solution-processed organic field effect transistors fabricated from a soluble tetraceno[2,3-b]thiophene precursor 1. Compound 1 was synthesised in 9.8% through 6 steps. The TGA profiles showed that a 9.1% weight loss occurred at ca. 130 °C, corresponding to an expulsion of a carbonyl group. The photogeneration of tetraceno[2,3-b]thiophene from 1 in the solution state could be fitted into a first-order rate law with a rate constant (k) of 2.05 × 10−2s−1 in a yield of 55.6% (±0.9%) under a 1.25 mW cm−2 UV lamp. The platelet micro crystals of 1, formed either by heat or by light, were confirmed by XRD to be identical to a simulated one from reported X-ray crystallographic data. The field effect mobility across a single crystal was measured to be 4.75 × 10−1 cm2 V−1s−1 with on/off ratio 105. The high purity of single crystals formed both by heat and by light are supported by an EPR analysis. This is the first report of a solution-processed single-crystal OFET of linear acenes without bulky substituent groups. In another experiment, the devices made directly from an amorphous thin film of 1, prepared by spin-coating, exhibited a charge mobility 3.0 × 10−4 cm2 V−1s−1 with on/off ratio 103.

— A new type of single-layer blue-phosphorescence organic light-emitting devices (OLEDs) containing poly(9-vinylcarbazole) (PVK) and small-molecule-based amorphous ambipolar bis(3,5-di(9H-carbazol-9-yl)phenyl) diphenylsilane (SimCP2) as the co-host material have been demonstrated. All active materials [PVK, SimCP2, Flrpic (blue-phosphorescence dopant), and OXD-7 (electron transport)] were mixed in a single layer for solution processing in the fabrication of OLEDs. The SimCP2 small-molecule host has adequate high electron and hole-carrier mobiltieis of ∼10−4 cm2/V-sec and a sufficiently large triplet state energy of ∼2.70 eV in confining emission energy on FIrpic. Based on such an architecture for single-layer devices, a maximum external quantum efficiency of 6.2%, luminous efficiency of 15.8 cd/A, luminous power efficiency of 11 lm/W, and Commision Internale de l'Eclairage (CIEx,y) coordinates of (0.14,0.32) were achieved. Compared with those having PVK as the single-host material, the improvement in the device performance is attributed to the balance of hole and electron mobilities of the co-host material, efficient triplet-state energy confinement on FIrpic, and the high homogeneity of the thin-film active layer. Flexible blue-phosphorescence OLEDs based on solution-processed SimCP2 host material (withou PVK) have been demonstrated as well.