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Cesium azide (CsN3) is employed as a novel n-dopant because of its air stability and low deposition temperature. CsN3 is easily co-deposited with the electron transporting materials in an organic molecular beam deposition chamber so that it works well as an n-dopant in the electron transport layer because its evaporation temperature is similar to that of common organic materials. The driving voltage of the p-i-n device with the CsN3-doped n-type layer and a MoO3-doped p-type layer is greatly reduced, and this device exhibits a very high power efficiency (57 lm W−1). Additionally, an n-doping mechanism study reveals that CsN3 was decomposed into Cs and N2 during the evaporation. The charge injection mechanism was investigated using transient electroluminescence and capacitance–voltage measurements. A very highly efficient tandem organic light-emitting diodes (OLED; 84 cd A−1) is also created using an n–p junction that is composed of the CsN3-doped n-type organic layer/MoO3 p-type inorganic layer as the interconnecting unit. This work demonstrates that an air-stable and low-temperature-evaporable inorganic n-dopant can very effectively enhance the device performance in p-i-n and tandem OLEDs, as well as simplify the material handling for the vacuum deposition process.

Although significant progress has been made in the development of vacuum-deposited small-molecule organic light-emitting diodes (OLEDs), one of the most desired research goals is still to produce flexible displays by low-cost solution processing. The development of solution-processed OLEDs based on small molecules could potentially be a good approach but no intensive studies on this topic have been conducted so far. To fabricate high-performance devices based on solution-processed small molecules, the underlying nature of the produced films and devices must be elucidated. Here, the distinctive characteristics of solution-processed small-molecule films and devices compared to their vacuum-deposited counterparts are reported. Solution-processed blue OLEDs show a very high luminous efficiency (of about 8.9 cd A–1) despite their simplified structure. A better hole-blocking and electron-transporting layer is essential for achieving high-efficiency solution-processed devices because the solution-processed emitting layer gives the devices a better hole-transporting capability and more electron traps than the vacuum-deposited layer. It is found that the lower density of the solution-processed films (compared to the vacuum-deposited films) can be a major cause for the short lifetimes observed for the corresponding devices.

A new blue light-emitting fluorene derivative 2,7-di[8-(7,10-diphenylfluoranthenyl)]-9,9-dimethylfluorene (DFDF) with good thermal stability at 420 °C has been synthesized and characterized. An organic light-emitting device (OLED) with the structure of ITO/NPB (70 nm)/DFDF (30 nm)/TPBI (20 nm)/LiF (0.5 nm)/Al (100 nm) has been investigated, where DFDF serves as a nondoped host emitter. Such a device possesses high current and power efficiencies of 3.8 cd/A and 2.6 lm/W, respectively, and stable bright blue-light emission at λ = 474 nm with Commission Internationale de L’Eclairage coordinates of (0.16, 0.23) over a wide range of operating voltages. The present results verify that DFDF is a promising candidate for a fluorescent blue-light-emitting OLED.

In this paper, we describe a new approach for fabrication of high efficient polymeric light-emitting diodes (PLEDs). In the device configuration of ITO/HTL/EBL/EML/BaF2:Ca:Al (ITO: indium tin oxide, HTL: hole transport layer, EBL: electron blocking layer, EML: emitting layer), EBL contains cross-linkable moieties in order to make the layer which is insoluble to layering of an additional emitting polymer. The devices with EBL exhibit strong blue emissions and higher efficiency values than those in devices without EBL. The synthesis, characterization, device fabrication, and electroluminescence (EL) properties of devices will be presented.

In this paper, we describe a simple method for fabrication of high efficiency multilayered polymeric light-emitting diodes (PLEDs). In the device configuration of ITO/HIL/BL/EML/BaF 2 :Ca:Al (ITO: indium tin oxide, BL: blocking layer, HIL: hole injection layer as PEDOT:PSS, EML: emitting layer as poly(alkylfluorene) derivative), poiy(9-vinyl carbazole) (PVK) was selected as an BL because it has a hole transporting property and a relatively higher band gap, especially a lower LUMO level than the emitting polymer and higher HOMO level than PEDOT:PSS. As a result, the PVK layer could effectively block the electrons from metal cathode and confine them in the emitting polymer layer. In addition, it could properly control the amount of holes from ITO anode by partial blocking. The charge balance was achieved and the device with a PVK. layer exhibits a higher brightness and luminance efficiency than those in devices without PVK. Also, the thickness of PVK was easily controlled by solvents for emitting polymer and the device with a thicker PVK layer shows better performance.

N doped organic light-emitting diodes were developed by using Li 3 N as a n type dopant in electron transport layer. Driving voltage was greatly lowered by using Li 3 N doped electron transport layer and combination of MoO 3 doped hole transport layer with Li 3 N doped electron transport layer gave high quantum efficiency of 15% and low driving voltage of 4 V at 1000 cd/m 2 in green phosphorescent organic light-emitting diodes. Decomposition of Li 3 N during evaporation into Li and N 2 was found to be responsible for n doping effect of Li 3 N.

It is a great challenge to develop solution-processed, polymeric hole-injection layers (HILs) that perform better than small molecular layers for realizing high-performance small-molecule organic light-emitting diodes (SM-OLEDs). We have greatly improved the injection efficiency and the current efficiency of SM-OLEDs by introducing conducting polymer compositions composed of polyaniline doped with polystyrene sulfonate and perfluorinated ionomer (PFI) as the HIL. During single spin-coating of conducting polymer compositions, the PFI layer was self-organized at the surface and greatly increased the film work function. It enhanced hole-injection efficiency and current efficiency by introducing a nearly ohmic contact and improving electron blocking. Our results demonstrate that solution-processed polyaniline HILs with tunable work functions are good candidates for reducing process costs and improving OLED performance.

This article reports the fabrication of 10-μm-level stripe patterns on an organic layer using microthermal evaporation. During this process, an organic layer is coated on a glass substrate with a bridge-type microheater array, and then selectively evaporated and deposited to form a fine pattern onto another glass substrate, separated by a micron-scale gap from the microheater array. Using a unique numerical model for microthermal evaporation, thickness profiles of the pattern were calculated and matched to experimental data. Furthermore, high optical qualities of the transferred luminescent pattern layer were confirmed using microphotoluminescence spectroscopy. This microthermal evaporation method confirms the feasibility of fabricating fine organic patterns with scalability to larger sizes.

We report efficient tandem white organic light-emitting diodes (WOLEDs) by using bathocuproine:Cs2CO3∕MoO3 as an effective interconnecting layer. We utilized two primary colors of sky blue and orange fluorescent emitters to obtain efficient white electroluminescence. Although single WOLEDs using two adjacent emitting layers showed a maximum current efficiency of 7.96cd∕A with Commission Internationale d’Eclairage (CIE) coordinates of (0.28, 0.34), the tandem WOLED device made by stacking two single color OLEDs in series demonstrated doubled maximum current efficiency of 17.14cd∕A with CIE coordinates of (0.28, 0.41). The stacking of different single color OLEDs in series instead of double stacking of WOLEDs can be useful to achieve highly efficient WOLEDs because it can reduce the number of layers of the devices.

We have developed a high performance fluorescent host material, 6-anthracene-9-yl-2,3-di-p-tolyl benzo[b]thiophene (ATB), for blue organic light-emitting diodes. ATB formed a stable amorphous solid state film with a high glass transition temperature (Tg=116°C). The multilayer devices fabricated using ATB as a blue host material showed higher power efficiency (6.4lm∕W at 1000cd∕m2) than the conventional device using 2-tert-butyl-9,10-di(2-naphthyl)anthracene (TBADN) (4.3lm∕W at 1000cd∕m2). The half lifetime of the ATB device (6480h at 1000cd∕m2) was also enhanced compared to the TBADN device (5341h at 1000cd∕m2).

The authors report the effect of thermal treatment of hole-transporting interlayers between a polymeric hole injection layer and an emitting layer (EML) on the luminous efficiency and the lifetime performance in blue polymer light-emitting diodes. As the thermal annealing temperature of the interlayer increased, the hole mobility of the interlayer tended to decrease, which results in reducing the hole current injected into the EML in the devices. Hence, the device luminous efficiency decreased due to lower electron-hole balance. Nevertheless, the device lifetime increased, which can be attributed to the formation of the thicker interlayer and the better defined interlayer/EML interface.