Jan Blochwitz-Nimoth

Low-voltage inverted transparent vacuum deposited organic light-emitting diodes using electrical doping

We demonstrate low-voltage inverted transparent vacuum deposited organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode. The devices comprise an intrinsic 8-tris-hydroxyquinoline aluminum (Alq3) emitting layer sandwiched in between n- and p-doped charge transport layer with appropriate blocking layers. They exhibit low driving voltages (∼4 V for a luminance of ∼100 cd/m2). The devices are about 50% transparent in the Alq3 emission region and emit green light from both sides with a total external current efficiency of about 2.5 cd/A.

High-efficiency electrophosphorescent organic light-emitting diodes with double light-emitting layers

We demonstrate high-efficiency electrophosphorescent organic light-emitting diodes (PHOLEDs) with double light-emitting layers (D–EMLs) by doping both hole and electron transport hosts with fac tris(2-phenylpyridine)iridium [Ir(ppy)3] simultaneously. The D–EMLs PHOLEDs show significantly improved efficiency (peak external quantum efficiency of about 12.6%, corresponding to a current efficiency of 44.3 cd/A) compared to the conventional PHOLEDs with a single EML and either hole or electron transport host doped with Ir(ppy)3. We attribute this improvement mainly to reduced losses of triplet excitons into regions that are not doped by phosphorescent emitter molecules.

Influence of the thickness and doping of the emission layer on the performance of organic light-emitting diodes with PiN structure

We have studied the behavior of various intrinsic emission zones on the characteristics of organic light-emitting diodes with a p-doped hole-transport layer and an n-doped electron-transport layer based on our previous work [J. S. Huang, M. Pfeiffer, A. Werner, J. Blochwitz, K. Leo, and S. Liu, Appl. Phys. Lett. 80, 139 (2002)]. This configuration is referred to as a PiN structure. Because the p- and n-doped regions occupy nearly 80% of the total thickness in our PiN device, the intrinsic region becomes a narrow layer between two doped regions. This intrinsic region includes the region where the radiative recombination occurs. Thus, the nature of this layer plays an important role in determining the actual device performance. Employing 8-tris-hydroxyquinoline aluminum as an emitter, we investigated the influence of the thickness of the emitter layer on the performance of the device. The optimum thickness of the emitter layer is found to be 20 nm. Combining the fluorescence dye doping method, we have optim...

4.4L: Late‐News Paper: Novel OLEDs for Full Color Displays with Highest Power Efficiencies and Long Lifetime

Top emitting PIN-OLEDs that are perfectly suited to full color displays are reported here. For red, green, and blue diodes, power efficiencies at 1000 cd/m2 of 11 lm/W, 70 lm/W, and 8.4 lm/W were achieved. Lifetimes of phosphorescent bottom emitting PIN-OLEDs of 30,000 hours at a brightness of 500 cd/m2 indicate that charge carrier doping allows for very high lifetimes. Even higher stability could be achieved by replacing Cs with the new molecular n-dopant NDN-1. Furthermore, a white bottom emitting OLED (color coordinates (0.35, 0.37), CRI of 95) with a power efficiency of 16.3 lm/W at 1000 cd/m2 is shown.

29.1: Full Color Active Matrix OLED Displays with High Aperture Ratio

For the integration of organic light emitting diodes (OLEDs) on an active matrix backplane, an efficient top-emitting OLED is essential since the TFT-circuitry covers a large space of the pixel aperture. Moreover, for the integration on n-channel transistors used in amorphous silicon technology an inverted (anode on top) OLED setup is necessary. We here present a way to manufacture efficient top emitting inverted OLEDs on active matrix substrates by applying our proprietary technology of intentionally doped charge carrier transport layers. We demonstrate their integration in full color active matrix displays with QVGA and VGA resolution.

17.2: White OLED Structures using Molecularly Doped Charge Transport Layers

White emitter systems are studied in OLED using doped charge transport layers. Mature fluorescent white diodes combining high efficiency with lifetimes exceeding 10,000h at a brightness of 1000 cd/m2 are reported. Stacked devices for applications requiring a high color rendering index perform at a current efficiency of 80 cd/A and power efficiency of 23 lm/W at 1000 cd/m2 with the lifetime exceeding 10,000h at 1000 cd/m2. Efforts towards top-emission white OLED and white OLED for passive matrix applications yield promising results.

30.3: White Fluorescent PIN OLED with High Efficiency and Lifetime for Display Applications

Highly efficient and stable white PIN OLED structures based on Kodaks proprietary emitters and Novaleds proprietary p- and n-type dopants have been developed with a focus on AMOLED display applications. At color coordinates of 0.33/0.36, a current efficiency of 15.1 cd/A at a voltage of 3.0 V was achieved at 1000 cd/m2 brightness. The lifetime of this device is 27,000 hours at a starting luminance of 1000 cd/m2. The spectrum of the devices contains a contribution from four emitters (RGBY) and the emission of the presented OLED structures is therefore ideally suited for use in RGBW AMOLED displays. with variations of the blocking layers, the device efficiency can be increased to 16.8 cd/A, which corresponds to an external quantum efficiency of 7.3%. The results in this paper are based on a joint research effort between Eastman Kodak Company and Novaled.

35.3: High‐Performance Tandem White OLEDs Using a Li‐Free “P‐N” Connector

A nonmetallic connector has been developed for high-efficiency tandem white architecture. Forming the “N” type layer using NDN-26 doped into NET-18 and inserting an organometallic thin layer between the “N” and “P” layers results in a high-performance connector. An efficiency of 33 cd/A has been achieved at 6.7 V, 1000 cd/m2 and 10000K color temperature in a fluorescent based tandem emitter. This >15% EQE device also demonstrates a half-life of ∼80,000 h at 1000 cd/m2.

An overview about the use of electrical doping of charge carrier transport layers in OLEDs and further organic electronic applications

Electrical doping of organic layers is now a well established method for building highly efficient and long living OLEDs. A unique class of OLED devices called PIN-OLEDs based on redox doping technology is emerging as one key technology for OLED applications. These devices exhibit high power efficiency and long life time, which are critical parameters for commercial success. Moreover, PIN OLEDs offer high degree of freedom in choosing layer structures for optimizing the device performance for specific lighting and display applications. For example, optimizing color and power efficiency of OLEDs can be easily achieved without compromising the device operating voltage. It is worth to mention that PIN OLEDS, especially the red emitting PIN OLEDs, exhibit record breaking half life time of more than one million hours with the starting device brightness of 1000 cd/m2. The doping technology also offers benefits to other organic electronic devices such as OTFTs and photovoltaic devices. This paper briefly discusses the improvements made on the OLED device performance such as power efficiency and lifetime using doped transport layers. Few examples of device optimization using doped layers are presented in detail. In addition, a brief discussion on performance of doped transport layers in photovoltaics is also presented.

Highly efficient and low-operating-voltage OLEDs for active and passive matrix displays

The operating voltage of organic light emitting diodes (OLEDs) is important for the power consumption of active or passive matrix displays since it influences both the power consumption of the OLED itself and the power consumption of the driver circuitry. We have shown that very low operating voltages can be achieved in small-molecule OLED by intentional electrical n- and p-type doping. Even more important than the reduction of the voltage is the fact that doping of the charge carrier transport layers improves charge injection, making it basically independent on the actual contact work-functions. Organic light emitting diodes (OLEDs) with electrically doped transport layers show significantly improved properties: For instance, we have achieved a brightness of 100cd/m2 already at a voltage of 2.55V (based on a simple singlet emitter system), well below previous results for undoped small-molecule devices. With phosphorescent emitter dopants, high quantum and power efficiency of OLEDs with doped transport layers can be achieved: operating voltages and current efficiencies of 3.1V and 44cd/A (corresponding to approx. 44lm/Watt at 100cd/m2) are reported here. Inverted and fully transparent devices with parameters comparable to standard bottom-emitting OLED have been demonstrated as well.