Gufeng He

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 organic light emitting diodes (OLED) for diplays and lighting

In this contribution, we discuss several research results which have contributed to the vision of a broad application of organic light emitting diodes in displays and lighting. We discuss the factors which determine the efficiency of OLEDs. First, we briefly discuss work on the controlled molecular doping of organic semiconductors, having the same advantageous influence on the device properties than in inorganic semiconductor devices, in particular in reducing the operating voltage. By comparison with a simple theory, we show that the voltages achieved with doped OLEDs are already very close to the thermodynamic limit. We then show, with the example of red phosphorescent OLEDs, how many properties of the OLED are improved by doping.

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.

54.3: Distinguished Paper: White Stacked OLED with 35 lm/W and 100,000 Hours Lifetime at 1000 cd/m2 for Display and Lighting Applications

The three critical parameters to determine the commercial success of organic light-emitting diodes (OLEDs), both in display and lighting applications, are: power efficiency, lifetime, and price competitiveness. PIN technology is widely considered as the preferred way to maximum power efficiency and lifetime. Here we report a high efficiency and long lifetime white light-emitting diode, which has been realized by stacking a blue fluorescent emission unit together with green and red phosphorescent emission units. Novaled proprietary materials have been used in transport layers of each emission unit, which significantly improves the power efficiency and stability. The power efficiency at 1,000 cd/m2 is 35 lm/W with CIE color coordinates of (0.43, 0.44) and a color rendering index (CRI) of 90. An extrapolated lifetime at an initial luminance of 1000 cd/m2 is above 100,000 hours, which fulfils the specifications for most applications. The emission color can also be easily tuned towards the equal energy white for display applications by selecting emitting materials and varying the transport layer cavities.

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: 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.

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.