Philipp Wellmann

High‐efficiency p‐i‐n organic light‐emitting diodes with long lifetime

Abstract— High-performance organic light-emitting diodes (OLEDs) are promoting future applications of solid-state lighting and flat-panel displays. We demonstrate here that the performance demands for OLEDs are met by the PIN (p-doped hole-transport layer/intrinsically conductive emission layer/n-doped electron-transport layer) approach. This approach enables high current efficiency, low driving voltage, as well as long OLED lifetimes. Data on very-high-efficiency diodes (power efficiencies exceeding 70 lm/W) incorporating a double-emission layer, comprised of two bipolar layers doped with tris(phenylpyridine)iridium [Ir(ppy)3], into the PIN architecture are shown. Lifetimes of more than 220,000 hours at a brightness of 150 cd/m2 are reported for a red PIN diode. The PIN approach further allows the integration of highly efficient top-emitting diodes on a wide range of substrates. This is an important factor, especially for display applications where the compatibility of PIN OLEDs with various kinds of substrates is a key advantage. The PIN concept is very compatible with different backplanes, including passive-matrix substrates as well as active-matrix substrates on low-temperature polysilicon (LTPS) or, in particular, amorphous silicon (a-Si).

Highly efficient white OLEDs for lighting applications

The use of organic light-emitting diodes (OLEDs) for large area general lighting purposes is gaining increasing interest during the recent years. Especially small molecule based OLEDs have already shown their potential for future applications. For white light emission OLEDs, power efficiencies exceeding that of incandescent bulbs could already be demonstrated, however additional improvements are needed to further mature the technology allowing for commercial applications as general purpose illuminating sources. Ultimately the efficiencies of fluorescent tubes should be reached or even excelled, a goal which could already be achieved in the past for green OLEDs.1 In this publication the authors will present highly efficient white OLEDs based on an intentional doping of the charge carrier transport layers and the usage of different state of the art emission principles. This presentation will compare white PIN-OLEDs based on phosphorescent emitters, fluorescent emitters and stacked OLEDs. It will be demonstrated that the reduction of the operating voltage by the use of intentionally doped transport layers leads to very high power efficiencies for white OLEDs, demonstrating power efficiencies of well above 20 lm/W @ 1000 cd/m2. The color rendering properties of the emitted light is very high and CRIs between 85 and 95 are achieved, therefore the requirements for standard applications in the field of lighting applications could be clearly fulfilled. The color coordinates of the light emission can be tuned within a wide range through the implementation of minor structural changes.

PIN OLEDs — Improved structures and materials to enhance device lifetime

— Currently, three issues are identified that decide upon the commercial success of organic light-emitting diodes (OLEDs), both in display and lighting applications: power efficiency, lifetime, and price competitiveness. PIN OLEDs are widely seen as the preferred way to maximize power efficiency. Here, it is reported that this concept also delivers the world longest lifetimes. For a highly efficient deep-red PIN OLED, a half-lifetime of 25,000 hours for a starting brightness of 10,000 cd/m2 and a minimal voltage increase over lifetime is reported. This value corresponds to more than 1 × 106 hours at 1000 cd/m2 using an exponent of n = 1.7, which was measured by driving the OLEDs at different starting luminances. Because there is no initial luminance drop, these PIN OLEDs also exhibit a very high 80% lifetime (>300,000 hours at 1000 cd/m2). New record lifetime values for blue and green will be reported as well. Additionally, further topics that have impact on the production yield and cost such as the newly developed air-stable organic n-doping material NDN-26 and top-emitting structures will be discussed.

64.4: Novel Materials and Structures for Highly‐Efficient, Temperature‐Stable, and Long‐Living AM OLED Displays

Prerequisite for a wide market penetration of AM OLED displays are price competitiveness and superior performance in comparison with rival flat panel display approaches. In this talk, top emitting Novaled PIN OLED™ architectures will be presented that allow for lifetimes exceeding 100,000 hours at 500 cd/m2. At this brightness, novel OLED materials enable 17,000 hours operating lifetime even at an elevated temperature of 80 °C. For a green top-emitting OLED, a current efficiency of 95 cd/A (1000 cd/m2) at a very low voltage of 2.55 V 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.

30.3: PIN OLEDs — Improved Structures and Materials to Enhance Device Lifetime and Ease Mass Production

Currently, three issues are identified that decide upon the commercial success of organic light emitting diodes (OLEDs), both in display and lighting applications: power efficiency, lifetime, and price competitiveness. PIN OLEDs are widely seen as the preferred way to maximum power efficiency. Here, we report that this concept also delivers the world longest lifetimes. for a highly efficient deep red PIN OLED, a half lifetime of 25,000 hours for a starting brightness of 10,000 cd/m2 and a minimal voltage increase over lifetime is reported. This value corresponds to more than 1 Million hours at 500 cd/m2 assuming a rather low exponent of n = 1.3 only. Since there is no initial luminance drop, these PIN OLEDs also exhibit a very high 80% lifetime (250,000 hours at 500 cd/m2). In the following, new record lifetime values for blue and green will be reported. Additionally, further topics that have impact on the production yield and cost such as newly developed materials and top emitting structures will be discussed.