基于Firpic发光的高效率蓝色有机发光器件

为了充分利用发光层中主客体间的能量转移和空穴阻挡层（HBL）的空穴阻挡作用,制作了结构为ITO/m-MTDATA（25 nm）/NPB（15 nm）/Ir（ppz）3（10 nm）/Simcp：Firpic（30 nm,6%）/HBL（35 nm）/LiF（1 nm）/Al（200 nm）的高效率蓝光器件,研究了3种类...     

基于过渡金属氧化物薄膜为连接层的叠层有机电制发光器件的数值模型

By utilizing a two-step process to express the charge generation and separation mechanism of the transition metal oxides （TMOs） interconnector layer, a numerical model was proposed for tandem organic light emitting diodes （OLEDs） with a TMOs thin film as the interconnector layer. This model is valid not only for an n-type TMOs interconnector layer, but also for a p-type TMOs interconnector layer. Based on this model, the influences of different carrier injection barriers at the interface of the electrode/organic layer on the charge generation ability of interconnector layers were studied. In addition, the distribution characteristics of carrier concentration, electric field intensity and potential in the device under different carrier injection barriers were studied. The results show that when keeping one carrier injection barrier as a constant while increasing another carrier injection barrier, carri- ers injected into the device were gradually decreased, the carrier generation ability of the interconnector layer was gradually reduced, the electric field intensity at the interface of the organic/electrode was gradually enhanced, and the electric field distribution became nearly linear： the voltage drops in two light units gradually became the same. Meanwhile, the carrier injection ability decreased as another carrier injection barrier increased. The simulation re- sults agree with the experimental data. The obtained results can provide us with a deep understanding of the work mechanism of TMOs-based tandem OLEDs.     

CMOS-compatible organic light-emitting diodes

We report a new method for the integration of light-emitting devices on a silicon substrate. As an active layer, we use unsubstituted PPV or PPV-based organic macromolecules with a p⁺-silicon anode and a cathode made from aluminum or titanium. The polymer is deposited by spin-coating the precursor, followed by a thermal conversion step to form the macromolecules. All process steps, including the possibility of dry etching of the active layer and the upper electrode, are typical for MOS technology. Spectrum analysis, current-voltage, and intensity measurements have been carried out for device characterization. These organic light-emitting diodes allow the monolithic integration of microelectronic circuits and light-emitting devices on one silicon chip applying only typical MOS process steps     

Highly efficient solution-processable europium-complex based organic light-emitting diodes

The development of solution-processable europium-complex based organic light-emitting diodes (OLED) has been limited by their low efficiency. In this paper, we show that it is possible to produce a highly efficient, solution-processable, europium-complex based OLED with an external quantum efficiency of 4.3% at a brightness of 100 Cd/m² using off-the-shelf materials and without any specific optical design for improved light extraction. This is achieved by optimizing the device structure and the host matrix used. To our knowledge, this is the highest efficiency reported for solution-processable europium-complex based OLED devices, and the efficiency roll-off has been reduced compared with other reported europium-complex based devices. Our approach should be applicable to a wide range of solution-processable lanthanide complexes.     

Efficiency analysis of organic light-emitting diodes based on optical simulation

In spite of huge progress in improving the internal quantum efficiency of organic light-emitting diodes (OLEDs), these devices still suffer from poor light out-coupling. Loss mechanisms are for example waveguiding in the organic layers and the substrate as well as the excitation of surface plasmons at metallic electrodes. Their relative strength and the mutual dependence on the OLED structure have been studied both experimentally and by numerical simulation. Here, we consider the impact of the radiative quantum efficiency of the emitter material on predictions of light extraction from OLEDs. Competing processes resulting in non-radiative recombination of charge carriers usually reduce the emitter quantum efficiency in a real device. We show that optical simulation leads to erroneous conclusions when neglecting these competing processes. Furthermore, we demonstrate a method, which allows determining both the radiative quantum efficiency and the charge recombination factor via simulation based analysis of experimental data. This analysis of device efficiency is applied on a set of red-emitting electrophosphorescent devices.     

Effect of bulk and planar heterojunctions based charge generation layers on the performance of tandem organic light-emitting diodes

Tandem organic light-emitting diodes (OLEDs) were fabricated using organic planar and bulk heterojunctions based charge generation layers (CGLs), which were composed of cobalt phthalocyanine (CoPc) and fullerene (C₆₀). The electroluminescent (EL) characteristics of these two kinds of devices were systematically studied. The results showed that, compared to the corresponding devices with planar heterojunction (PHJ) based CGL, the tandem OLEDs with bulk heterojunction (BHJ) based CGL exhibited a dramatic improvement of performance. By investigating the electrical characteristics of CGLs, it was found that more hetero-interfaces introduced in the BHJ blend were beneficial for generating more interfacial dipoles and charge carriers, and the optimized charge transport pathways were favorable to promote both electron and hole mobilities. As a result, the improved charge carrier balance led to the efficiency enhancement of device performance. The results demonstrated the advantageous effect of BHJ blend film for the rational design of CGLs on the realization of high OLEDs performance.     

Fluoropolymer-assisted graphene electrode for organic light-emitting diodes

Organic light-emitting diodes (OLEDs) were fabricated on a graphene electrode, with synthesized graphene being transferred and simultaneously doped with supporting polymers. Poly[methyl methacrylate] (PMMA) and fluoropolymer (CYTOP) layers were used as the supporting polymers. The sheet resistance of CYTOP-assisted graphene (CYTOP-G) with 4 layers of graphene is 200 Ω/sq., which is lower than that of PMMA-assisted graphene (PMMA-G, 330 Ω/sq.) The transmittance value of PMMA-G and CYTOP-G with 4 graphene layers is higher than 85%. CYTOP-G is shown to exhibit a higher tolerance to UV–O₃ treatment and thermal annealing than PMMA-G. Work function of CYTOP-G is 4.7 eV, which is higher than that of PMMA-G (4.3 eV). X-ray photoemission and Raman spectroscopy data indicate that CYTOP-G has numerous C-F bonds on the surface exhibiting p-type semiconductor properties, owing to the high electronegativity of fluorine. The turn-on voltage of an OLED based on CYTOP-G with 4 graphene layers is 4.2 V, which is lower than that of indium tin oxide (ITO)-based one (4.5 eV). Furthermore, the luminance ratio of graphene-based OLEDs to ITO-based OLEDs was calculated to be 104% for CYTOP-G, and 97% for PMMA-G. According to the ultraviolet photoemission spectra, the hole injection barrier in CYTOP-G is lower by about 0.5 eV than the hole injection barrier in PMMA-G. These results are very encouraging to the prospect of replacing ITO electrodes with graphene ones in OLED applications.     

High-performance thin-film encapsulation for organic light-emitting diodes

Organic light-emitting diodes degrade rapidly by means of local cathode oxidation when exposed to the ambient atmosphere, resulting in visible non-emissive areas called black spots. High performance inorganic based encapsulations are required to protect the OLED. We have applied a hybrid thin-film encapsulation stack consisting of two inorganic barrier layers of silicon nitride deposited at low temperature with an organic layer in between. The resulting water permeation mechanism into the OLED is solely by means of lateral pinhole-to-pinhole transport. With the application of CaO nanoparticles in the organic layer the lateral water transport rate is reduced and we show that black spot formation in 8 cm² OLEDs is delayed by 6000 h at accelerated climate conditions of 60°C/90% relative humidity. This is estimated to correspond to 20 years at ambient conditions.     

Efficient nondoped blue organic light-emitting diodes based on phenanthroimidazole-substituted anthracene derivatives

A series of new blue materials based on highly fluorescent di(aryl)anthracene and electron-transporting phenanthroimidazole functional cores: 2-(4-(anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (ACPI), 2-(4-(10-(naphthalen-1-yl)anthracen-9-yl)phenyl)-1-p-henyl-1H-phenanthro[9,10-d]imidazole (1-NaCPI), 2-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (2-NaCPI) were designed and synthesized. These materials exhibit good film-forming and thermal properties as well as strong blue emission in the solid state. To explore the electroluminescence properties of these materials, three layer, two layer and single layer organic light-emitting devices were fabricated. With respect to the three layer device 4 using ACPI as the emitting layer, its maximum current efficiency reaches 4.36 cd A⁻¹ with Commission Internationale del’Eclairage (CIE) coordinates of (0.156, 0.155). In the single layer device 10 based on ACPI, maximum current efficiency reaches 1.59 cd A⁻¹ with Commission Internationale del’Eclairage (CIE) coordinates of (0.169, 0.177). Interestingly, both device 4 and 10 has low turn on voltage and negligible efficiency roll off at high current densities.     

Efficient blue organic light-emitting diodes based on triphenylimidazole substituted anthracene derivatives

A series of new blue emissive materials based on the conjugates of highly fluorescent diaryl anthracene and electron-transporting triphenylimidazole moieties: 2-(4-(anthracen-9-yl)phenyl)-1,4,5-triphenyl-1H-imidazole (ACBI), 2-(4-(10-(naphthalen-1-yl)anthracen-9-yl)phenyl)-1,4,5-triphenyl-1H-imidazole (1-NaCBI), 2-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-1,4,5-triphenyl-1H-imidazole (2-NaCBI) were designed and synthesized successfully. These materials exhibit good film-forming properties and excellent thermal stabilities. Meanwhile, the decreased π-conjugation in these compounds compared with phenanthroimidazole derivatives leads to obvious hypsochromic shift. To explore the electroluminescence properties of these materials, typical three-layer organic light-emitting devices were fabricated. With respect to the three layer device 2 using 1-NaCBI as the emitting layer, its maximum current efficiency reaches 3.06 cd A⁻¹ with Commission Internationale del’Eclairage (CIE) coordinates of (0.149, 0.092). More interestingly, sky blue doped device 5 based on 1-NaCBI achieved a maximum current efficiency of 15.53 cd A⁻¹ and a maximum external quantum efficiency of 8.15%, high EQE has been proved to be induced by the up-conversion of a triplet excited state.     

A red tandem organic light-emitting diode based on organic photovoltaic-type charge generation layer

In this paper, a significant enhancement in current efficiency of a red tandem organic light-emitting diode (OLED), which is based on an organic photovoltaic-type charge generation layer (CGL) of fullerene carbon 60/copper (Ⅱ) phthalocyanine, is introduced. The CGL can absorb a part of photons, radiated from emission zone, then form excitons, which are dissociated into free charges. It induces in lower driven voltage and better efficiency of tandem OLED. Compared with single emitter-unit OLED and tandem OLED with bulk heterojunction CGL, the luminous efficiency boosts remarkably with increasing current density and shows rather slower roll-off. Our results demonstrate that the organic photovoltaic heterojunction, consists of two matched n- and p-type organic semiconductors, is a promising CGL for tandem OLEDs with high efficiency.     

Phthalonitrile based charge transfer type host for yellow phosphorescent organic light-emitting diodes

An phthalonitrile based 3,3''-di(9H-carbazol-9-yl)-[1,1':2′,1''-terphenyl]-4′,5′-dicarbonitrile (IPNCz) was explored as a charge transfer type host of a yellow emitting bis(4-phenyl-thieno[3,2-c]pyridinato-C2,N)(acetylacetonato)iridium(III) (PO-01) dopant. The phthalonitrile unit was an electron deficient unit and 9-phenylcarbazole was an electron rich unit of the IPNCz host. The phthalonitrile unit combined with the phenylcarbazole unit allowed strong charge transfer character by the donor-acceptor structure, delivering good thermal stability, bipolar carrier transport and proper triplet energy. Therefore, the IPNCz host assisted low driving voltage and high quantum efficiency close to 25% in the yellow phosphorescent device.     

高亮度微腔有机电致发光器件

为了实现有机电致发光器件(OLED)发射光谱的窄化和高亮度,真空热蒸镀具有不同微腔结构的OLED(MOLED):玻璃衬底/分布式布拉格反射器(DBR)(1～4对的SiO2/Ta2O5层)/ITO/空穴传输层(HTL,α-NPD)/发光层(EML,Alq3:Rubrene或Alq3:Coumarin6)/电子传输层(ERL,Alq3)LiF/Mg/Ag,其中沉积DBR结构采用电子束沉积法。实验表明:该MOLED的发射光谱半波长宽度(FWHM)随DBR层数的增加而减小至最小值10nm;并且在2层DBR时,掺杂Rubrene器件得到更大的电流效率,约20cd/A,最大亮度为2.6×105cd/m2。研究发现,蓝光MOLED能够对自发光产生吸收现象,降低了出光效率。     

Thermal properties of organic light-emitting diodes

Thermal management is important for the efficient operation of organic light-emitting diodes (OLED, or PHOLED) at high brightness, with the device operating temperature influencing both lifetime and performance. We apply a transmission-matrix approach to analytically model the effects of thermal conduction, convection and radiation on OLED temperature. The model predictions match experiment without requiring the use of fitting parameters. This allows for the simulation of the thermal response of various device architectures, materials combinations and environmental factors under a variety of operating conditions. Using these simulations, we find that 87% of the heat is dissipated through the air space adjacent to the glass package cap. Furthermore, an air gap between the device cathode and cap provides a significant thermal impedance. Minimizing the thickness of the internal air gap can lead to nearly room temperature operation, even at very high brightness.     

Organic semiconductor heterojunction as charge generation layer in tandem organic light-emitting diodes for high power efficiency

High-performance tandem organic light-emitting diodes (OLEDs) employing a buffer-modified C₆₀/pentacene organic semiconductor heterojunction (OHJ) as a charge generation layer (CGL) are demonstrated. The unique cooperation of charge generation, transport, and extraction processes occurred in the OHJ-based CGL remarkably reduces the operational voltage. As a result, an approximately twofold enhancement in power efficiency (21.9 lm W^?1 VS 10.1 lm W^?1) can be achieved that has previously been suggested to be difficult for tandem OLEDs. When the pentacene is replaced by zinc phthalocyanine (ZnPc), copper phthalocyanine (CuPc), or phthalocyanine (H₂Pc), a similar power efficiency improvement can be also achieved. The novel design concept of the buffer-modified OHJ-based CGL is superior to that of the conventional CGLs. The investigations on the operational mechanism are performed, from which it is found that the mobile charge carriers firstly are needed to be accumulated at both sides of the heterojunction interface and then transport along the two organic semiconductors in terms of their good carrier transport characteristics under an external electrical field, and finally inject into the corresponding electroluminescent (EL) units by the interfacial layers.     

Soft fabric-based flexible organic light-emitting diodes

We reported the first organic light-emitting diodes (OLEDs) on actual soft fabrics that can be used for a wearable display. Polyurethane (PU) and poly(vinyl alcohol) (PVA) layers, which only degrade slightly the flex stiffness of bare fabrics due to their ductile characteristics, were used as planarization layers via a simple fabrication process involving lamination and spin-coating. Therefore, many of the mechanical characteristics of the bare fabric substrates were retained in the planarized fabric substrates. Non-inverted top-emitting OLEDs, designed by considering the optical microcavity effects, were fabricated on a planarized surface by thermal evaporation. The fabricated OLEDs on soft fabrics showed a high current efficiency of around 8 cd/A, reliability during a 1000 cycle bending test with a bending radius of 5 mm, and clear green emission up to an emission angle of 70°. Consequently, we developed high-performance OLEDs on very similar to real fabric via a simple universalized fabrication method.     

High triplet energy exciton blocking materials based on triphenylamine core for organic light-emitting diodes

A series of novel high triplet energy materials have been designed and synthesized from the simple starting compounds through a simple one-step Friedel–Crafts reaction by using triphenylamine and methoxy, fluoro substituted diphenylmethanoles and triphenylmethanol as the starting materials. The synthesized compounds exhibit the ionization potentials in an interval of 5.4–5.7 eV in the solid state, the wide bang-gaps of 3.6 eV and the high triplet energies of about 3.0 eV. The photophysical properties have been confirmed by DFT. The introduction of a material with the lowest ionization potential as the high triplet energy exciton blocking thin layer of the green organic light-emitting diode doubled the quantum efficiency of the device. The best fabricated green device exhibited the maximum current, power, and external quantum efficiencies of 80.1 Cd A⁻¹ and 31.4 Lm W⁻¹, 23.2%, respectively. The triplet-triplet annihilation and triplet-polaron quenching effects for the devices without and with exciton blocking layer have been analyzed.     

High-performance green phosphorescent top-emitting organic light-emitting diodes based on FDTD optical simulation

We have successfully applied finite-difference time-domain (FDTD) method in top-emitting organic light-emitting diodes (TOLEDs) for structure optimization, demonstrating good agreement with experimental data. A mixed host with both hole transport and electron transport materials is employed for the green phosphorescent emitter to avoid charge accumulation and broaden the recombination zone. The resulting TOLEDs exhibit ultra-high efficiencies, low current efficiency roll-off, and a highly saturated color, as well as hardly detectable spectrum shift with viewing angles. In particular, a current efficiency of 127.0 cd/A at a luminance of 1000 cd/m² is obtained, and maintains to 116.3 cd/A at 10,000 cd/m².     

High efficiency ITO-free flexible white organic light-emitting diodes based on multi-cavity technology

The technology of white organic light-emitting diodes (WOLEDs) is attracting growing interest due to their potential application in indoor lighting. Nevertheless the simultaneous achievement of high luminous efficacy (LE), high color rendering index (CRI), very low manufacturing costs and compatibility with flexible thin substrates is still a great challenge. Indeed, very high efficiency devices show usually low values of CRI, not suitable for lighting applications, and use expensive indium tin oxide (ITO) electrodes which are not compatible with low cost and/or flexible products. Here we show a novel low cost ITO-free WOLED structure based on a multi-cavity architecture with increased photonic mode density and still broad white emission spectrum, which allows for simultaneous optimization of all device characteristics. Without using out-coupling optics or high refractive index substrates, CRI of 85 and LE as high as 33 lm W⁻¹ and 14 lm W⁻¹ have been demonstrated on ITO-free glass and flexible substrates, respectively.     

A highly efficient tris-cyclometalated iridium complex based on phenylphthalazine derivative for organic light-emitting diodes

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 20 h. 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 2948 cd/m² at a current density of 115.6 mA/cm² and a maximum external quantum efficiency of 20.2% at 0.18 mA/cm².