Highly efficient deep‐blue organic light‐emitting devices

Abstract— A highly efficient deep‐blue organic light‐emitting device (OLED) incorporating a novel composite hole‐transport layer (c‐HTL) and an emitter based on the new non‐symmetrical mono(styryl)amine fluorescent dopant in the stable host MADN, which achieved a luminance efficiency of 5.4 cd/A with a Commission Internationale d'Eclairage (CIEx,y) of (0.14, 0.13) and an external quantum efficiency of 5.1% at 20 mA/cm² and 6.8 V, is reported. The increased device efficiency is attributed to an improved balance between hole and electron currents in the recombination zone.     

Electrical and optical properties of white organic light‐emitting devices using blue and orange phosphorescent materials

Abstract— Highly efficient white organic light‐emitting devices have been fabricated by doping phosphorescent orange and blue emitters into the separate layers of a single host. The efficiency and electroluminescence spectrum were strongly affected by the sequence of doped layers. The phosphorescent white devices exhibiting high efficiency and reasonable white balances are obtained when the recombination region is overlapped by the blue doped region. By using this principle, a simple structured phosphorescent white device with a peak power efficiency of 40.7 lm/W and Commission International de L'Eclairage coordinates of (0.43, 0.42) have been demonstrated.     

Development of a novel emitting vinyl polymer and its application in organic electroluminescent devices

Abstract— A novel emitting vinyl polymer, poly[4‐(7‐{4‐[N,N‐bis(9,9‐dimethylfluoren‐2‐yl)amino]phenyl}‐2,1,3‐benzothiadiazol‐4‐yl)phenylethylene] (PVFABT), was designed and synthesized. The new vinyl polymer was found to form smooth amorphous films with a high glass‐transition temperature of 199°C. The polymer possesses bipolar character with both electron‐donating and accepting properties. It undergoes reversible anodic oxidation and cathodic reduction to give stable cation and anion radicals. It exhibits intense orange fluorescence in solution and as film. A multilayer organic electroluminescent device using PVFABT as an emitting material emitted orange light, exhibiting high performance.     

Current transport and aging in direct-current powder electroluminescent display devices

Abstract— Direct-current powder electroluminescent (DCPEL) display devices were excited by unipolar voltage pulses, and current flow through the phosphor was recorded. Devices with different formed layer thicknesses were obtained by varying the forming voltage. For a fixed electric field in the formed layer, the phosphor current did not show a substantial increase as the thickness of the formed layer increased. A model is proposed in which tunnel injection from the p-Cu₂S/i-ZnS:Mn interface of a reverse-biased p-Cu₂S/i-ZnS:Mn/n-SnO₂ structure is thought to be the controlling current mechanism. Aging studies revealed that further forming is the dominant degradation mechanism in the early stages, while load-line degradation and softening become the dominant degradation modes as the aging process is continued. The conventional DCPEL device structure was modified by introducing a thin chromium layer just prior to the deposition of the aluminum back electrode. Incorporating chromium reduced the initial series resistance of the device. A hybrid device employing a thin film (1 μm) of ZnS:Mn, sandwiched between two thin dielectric layers (5 nm), was fabricated; ZnS:Mn,Cu powder was sprayed onto the thin-film sandwich. The hybrid structure showed good luminance without forming; however, device degradation with time was still present.     

Preparation and characterization of highly efficient blue TPBI:FIrpic organic light‐emitting devices

Abstract— Blue phosphorescent organic light‐emitting devices (PhOLEDs) using 1,3,5‐tris(N‐phenyl‐ benzimiazole‐2‐yl)benzene [TPBI] as the host and bis((4,6‐difluorophenyl)‐pyridinate‐N,C2′)picolinate [FIrpic] as the dopant in the emitter were fabricated with different treatments of the hole‐transport layers and doping levels. Among the experimental devices, the best electroluminescent characteristics were obtained in the device with the combined hole‐transport layer of N,N′‐diphenyl‐N,N′‐bis‐[4‐ (phenyl‐m‐tolylamino)‐phenyl]‐biphenyl‐4,4′‐diamine [DNTPD]/1, 1‐bis‐(di‐4‐polyaminophen yl)‐ cyclo‐hexane [TAPC] and a doping level of 10‐vol.% FIrpic. The device with a structure of DNTPD/TAPC/TPBI:Firpic (10%) showed a luminance of 1300 cd/m² at an applied voltage of 10 V, a maximum current efficiency of 18 cd/A, and color coordinates of (0.17, 0.43) on the Commission Internationale de I'Eclairage (CIE) chart.     

Interference in thin radiating layers and its application to thin film electroluminescent devices

Results are reviewed of theoretical and experimental studies on interference of light radiated by a thin luminescence layer placed between two reflecting planes which form a Fabry-Perot cavity. This paper considers first the interference effect on the spectral and angular dependences of the emission from the cavity, and then the influence of the method and the intensity of luminescence excitation upon the interference effects. The possibility of producing ‘colour’ thin film electroluminescent devices based on interference of the emission is discussed. Some parameters of such ‘green’ and ‘red’ devices on the basis of the ZnS:Mn films known at present are given.     

Blue electroluminescent materials based on phenylanthracene-substituted fluorene derivatives for organic light-emitting diodes

Two phenylanthracene-substituted fluorene derivatives, 10-(9,9′-dimethyl-2-(10-phenylanthracen-9-yl)-9H-fluoren-7-yl)-phenylanthracene (1) and 2′,7′-di-(10-phenylanthracen-9-yl)-9,9′-spirobi[9H-fluorene] (2) have been designed, synthesized, and characterized. A device using compound 1 as an emitting material exhibited luminous efficiency, power efficiency, external quantum efficiency and CIE coordinates of 3.37 cd/A, 1.50 lm/W, 1.87% at 20 mA/cm² and (0.18, 0.25) at 7 V, respectively. Furthermore, by exploiting this efficient blue fluorescent material as a blue emitting material with the combination of red phosphorescent bis(2-phenylquinoline)acetylacetonate [(pq)₂Ir(acac)], an efficient white OLED (WOLED) with a external quantum efficiency of 1.70%, luminous efficiency of 1.38 cd/A, power efficiency of 0.94 lm/W at 20 mA/cm² and the color coordinates of (0.33, 0.36) at 14 V is demonstrated.     

Novel carbazole/anthracene hybrids for efficient blue organic light-emitting diodes

Two novel carbazole/anthracene hybrided molecules, namely 2-(anthracen-9-yl)-9-ethyl-9H-carbazole (AnCz) and 2,7-di(anthracen-9-yl)-9-ethyl-9H-carbazole (2AnCz), were designed and synthesized via palladium catalyzed coupling reaction. The anthracene was attached either at the 2-site (AnCz) or at both 2,7-sites (2AnCz) of the central carbazole core to tune the conjugation state and the optoelectronic properties of the resultant molecules. Both of them show good solubility in common organic solvents. They also possess relatively high HOMO levels (−5.39 eV, −5.40 eV) that would facilitate efficient hole injection and be favorable for high power efficiencies when used in organic light-emitting devices (OLEDs). AnCz and 2AnCz were used as non-doped emitter to fabricate OLEDs by vacuum evaporation. Good performance was achieved with maximum luminance efficiency of 2.61 cd A⁻¹ and CIE coordinates of (0.15, 0.12) for AnCz, and 9.52 cd A⁻¹ and (0.22, 0.37) for 2AnCz.     

Highly efficient fluorescent blue materials and their applications for top‐emission OLEDs

We developed new fluorescent blue dopants (BDs) for achieving high‐efficient blue organic light‐emitting diode. A new BD showed both high photoluminescent quantum yield >0.9 and highly horizontal orientation (S′ > 0.9) in doped film with keeping a chemical stability by introducing suitable substituents. We developed hole transporting materials and optimized the combination of hole transporting layers to decrease a carrier accumulation at the interface between electron blocking layer and emission layer. We found that the external quantum efficiency dependency from low to high current density was turned flat by promoting hole injection into emission layer. The top‐emission organic light‐emitting diode using the new BD and the optimized device architecture exhibited high efficiency of L/J/CIEy around 200 at CIEy = 0.043.     

Optical characteristics of tandem and microcavity tandem organic light‐emitting devices

Abstract— In pursuit of the further enhancement of the luminance and efficiency of organic light‐emitting devices (OLEDs), it is worthy of exploring what benefits could be obtained by combining two luminance‐enhancement techniques, i.e., microcavity and tandem OLEDs. Furthermore, a deeper understanding of the optics in tandem OLEDs will be useful for the design and optimization of tandem OLEDs. In this paper, the optical characteristics of noncavity and microcavity tandem OLEDs are theoretically and experimentally investigated. By the use of rigorous electromagnetic modeling of OLEDs, the radiation characteristics of tandem OLEDs as a function of device structures are analyzed and correspondingly, the guidelines for optimizing the performance of tandem devices are suggested. By making use of the analytical results, it is shown that with well‐designed microcavity conditions and device structures, a five‐fold enhancement in luminance in the normal direction can be achieved with cavity‐tandem devices having only two emitting units. A very high efficiency of 200 cd/A for a rather broad brightness range of 100–4000 nits is demonstrated with a phosphorescent cavity two‐unit device.     

Bright red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts and broadening

We demonstrated red and yellow organic light-emitting devices (OLEDs) with the structure of ITO/NPB/AlQ:DCJTB/AlQ/LiF/Al, where the NPB, AlQ and DCJTB are 4, 4′-bis[N-(1-naphthyl)-N-henylamino] biphenyl, tris(8-quinolinolato)aluminum and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, respectively. Electroluminescent (EL) behaviors of these devices have been examined with different concentrations of DCJTB doped into AlQ matrix. The emission color of the devices depends on the doping concentrations of DCJTB. For red and yellow OLEDs, a maximum luminescence of 2750 cd/m² and 21,700 cd/m² was obtained, respectively. The peak emission wavelength shift of DCJTB was found to be due to the polarization effects. It is of particular interest that the EL spectrum of DCJTB got broadening with the doping concentrations and current densities of the devices in our experiments.     

Analyzing and tuning emission characteristics of top‐emitting organic light‐emitting devices

Abstract— Top‐emitting organic light‐emitting devices (OLEDs) have several technical merits for application in active‐matrix OLED displays. Generally, stronger microcavity effects inherent with top‐emitting OLEDs, however, complicate the optimization of device efficiency and other viewing characteristics, such as color and viewing‐angle characteristics. In this paper, using the rigorous classical electromagnetic model based on oscillating electric dipoles embedded in layered structures, the emission characteristics of top‐emitting OLEDs as a function of device structures will be analyzed. From comprehensive analysis, trends in the dependence of ewmission characteristics on device structures were extracted, and, accordingly, a general methodology for optimizing viewing characteristics of top‐emitting OLEDs for display applications will be suggested. The effectiveness of the analysis and the methodology was confirmed by experimental results.     

Highly efficient and stable white organic light emitting diode with triply doped structure

A triply doped white organic light emitting diode with red and blue dyes in the light emitting layer and a green dye in another layer is proposed. The device structure was CuPc(12 nm)/NPB(40 nm)/ADN:DCJTB(0.2%):TBPe(1%)(50 nm)/Alq:C545(0.5%)(12 nm)/LiF(4 nm)/Al. Here copper phthalocyanine (CuPc) is a buffer layer, N,N′-di(naphthalene-1-y1)-N,N′-dipheyl-benzidine (NPB) is a hole transporting layer, 9,10-di-(2-naphthyl) anthracene (ADN) is blue emitting layer, tris (8-quinolinolato)aluminium complex (Alq) is an electron transporting layer, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidy1-9-enyl)-4H- pyran (DCJTB), 2,5,8,11-tetra-butylperylene (TBPe), Coumarin6 and deveriative (C545) are red, blue and green dyes, respectively. This device shows a luminance of 21200 cd/m² at driving current of 400 mA/cm² and 1026 cd/m² at 20 mA/cm². Its efficiency is 6 cd/A and 3.11 Lm/W. It also shows a higher operating stability: the half lifetime is 22,245 h at an initial luminance of 100 cd/m², while the driving voltage increased only 0.3 V.     

掺杂荧光染料的高亮度有机蓝光电致发光器件

利用蓝色发光材料DPVBi掺杂高荧光染料rubrene做发光层制备了蓝色发光器件。在掺杂浓度为1.5%(wt)左右的情况下,当改变掺杂层的总的厚度时,器件的亮度、效率和色坐标都有明显的改变。当掺杂层DPVBi和rubrene的厚度为40nm,电子传输层Alq3的厚度为20nm,器件所加的电压是13v时,其最大亮度为14000cd/m2,此时的色坐标为(0.24,0.24),为蓝光发射。这种掺杂明显的提高了蓝光器件的发光效率。使最大效率达到2.5cd/A。     

Reduction of defects and improvement in the performance of blue phosphor for thick‐dielectric electroluminescent displays using Color‐by‐Blue

Abstract— Defect‐free large‐area inorganic thick‐dielectric EL (TDEL) displays using Color by Blue (CBB) technology have been successfully developed. We have achieved the world's highest blue‐phosphor luminance of 900 cd/m² for a single‐pixel device by using CBB and by optimizing the e‐beam gun configuration and the flow rate of H₂S in the vacuum chamber. By analyzing the defects on panels with triple‐pattern phosphors and CBB panels, we also found that the number of defects on CBB panels can be drastically reduced compared with those on triple‐pattern panels. The defect‐free 17‐in. VGA CBB panels show better characteristics, a high peak luminance of 600 cd/m² and a high contrast ratio of 1000:1, compared with those of triple‐pattern panels.     

Device‐dependent angular luminance enhancement and optical responses of organic light‐emitting devices with a microlens‐array film

Abstract— By taking the organic emitter apodization calculated from electromagnetic theory as input, the angular luminance enhancement of organic light‐emitting devices (OLEDs) with a microlens‐array film (MAF) can be further evaluated by the ray‐tracing approach. First, the OLEDs of different Alq³ thickness are fabricated and their angular luminance measurements are compared to simulation results. Second, mode analyses for different layers are performed to estimate the enhancement potential of the MAF‐attached devices. Finally, by decreasing the Alq³ thickness, increasing the viewing angle, and attaching the MAF, the EL spectral peak shifts of the OLEDs seem irregular, but the spectral blue shifts induced by the optical structures are all explained by the optical responses (EL spectra divided by the intrinsic PL spectrum). In conclusion, the organic emitters with higher off‐axis‐angle luminous intensity cause lower out‐coupling efficiency but gain higher enhancement after the MAF is attached. With the choices of apodizations and microstructures, the tailored or customized angular radiation patterns can be also made possible.     

基于Kalman滤波的通用和统一的白噪声估计方法

用射影理论,基于Kalman滤波提出了通用和统一的白噪声估计方法,可统一解决带非零均值相关噪声的线性离散时变随机控制系统的白噪声滤波、平滑和预报问题.提出了输入白噪声估值器和观测白噪声估值器,最优和稳态白噪声估值器,固定点、固定滞后和固定区间白噪声平滑器,白噪声新息滤波器和Wiener滤波器.它可应用于石油地震勘探信号处理和状态估计,为解决信号和状态估计问题,提供了新的途径和工具.关于Bernoulli-Gaussian白噪声估值器的仿真例子说明了其有效性.     

Highly efficient single‐unit white OLED device with emission from both singlet and triplet excitons

We succeeded in developing a single‐unit hybrid organic light‐emitting diode (OLED) device with efficient light emission from both a phosphorescent layer and a fluorescent layer. The single‐unit hybrid OLED achieved a power efficiency higher than that of a two‐unit hybrid tandem OLED with phosphorescent and fluorescent layers.     

Decoupling data-at-rest encryption and smartphone locking with wearable devices

Smartphones store sensitive and confidential data, e.g., business related documents or emails. If a smartphone is stolen, such data are at risk of disclosure. To mitigate this risk, modern smartphones allow users to enable data encryption, which uses a locking password to protect the data encryption key. Unfortunately, users either do not lock their devices at all, due to usability issues, or use weak and easy to guess 4-digit PINs. This makes the current approach of protecting confidential data-at-rest ineffective against password guessing attackers. To address this problem we design, implement and evaluate the Sidekick system — a system that uses a wearable device to decouple data encryption and smartphone locking. Evaluation of the Sidekick system revealed that the proposal can run on an 8-bit System-on-Chip, uses only 4 Kb/20 Kb of RAM/ROM, allows data encryption key fetching in less than two seconds, while lasting for more than a year on a single coin-cell battery.     

Highly efficient white organic light‐emitting diodes with over 100 lm/W for next‐generation solid‐state lighting

High‐performance two‐unit all‐phosphorescent white devices on a built‐up light extraction substrate that comprised high‐index materials were studied. As a result of suitable optical and electrical design, the device showed an extremely high efficacy of 114 lm/W at 1000 cd/m². The device also showed 102 lm/W with long lifetime (LT70) of over 10,000 h at 3000 cd/m². Outstanding external quantum efficiency of almost 50% was also achieved in a flat panel with an emissive area of 25 cm². Color coordinates of the panel met the Energy Star ® criteria of solid‐state lighting with CIE (Commission Internationale de l'Éclairage) 1931 (x, y) = (0.477, 0.423), and the color rendering index was 81.