Organic light-emitting diodes (OLEDs) with high power efficiency are desirable for lighting applications. A prerequisite for high power efficiency is the achievement of low driving voltages, which can be done via charge carrier doping of the transport layers in PIN organic light-emitting diodes (PIN- OLEDs). We have looked at how to combine low voltage with high current efficiency and long lifetime and have therefore investigated different ways of changing the charge carrier balance in PIN-OLEDs. The carrier supply to the emitting layer was adjusted by electron and hole-blocking layers to allow for an undisturbed exciton formation and radiative decay while keeping the total voltage low. In further investigations, we developed highly efficient and stable white PIN bottom emission OLED devices using novel evaporation processable outcoupling enhancement materials inside the PIN OLED stack. In white bottom emission OLEDs the use of this outcoupling enhancement material in combination with a standard micro-lens arrays (MLA) outcoupling film can yield an efficiency enhancement of up to 1.8.
By combining the well-balanced stack with the internal outcoupling approach we achieved a power efficiency of 51.9 lm/W. With additional flat external outcoupling, the power efficiency has been further increased to 60 lm/W. The color coordinates are 0.470/0.429 with color rendering index (CRI) of 87. The 50% lifetime of the OLED could be estimated to 90,000 h.
Molecular redox dopants are tested concerning their application to organic thin-film transistors (OTFT). Here we report
on the feasibility of solution processing of molecular-doped transport layers, showing high air-stability of solutions and
layers. We apply capacitance spectroscopy to investigate the interface of intrinsic and electrically doped layers. We also
show that there is virtually no dopant migration in real devices, even when high electric fields up to 300 kV/cm2 are
applied for 1000 h. We report on p- and n-type on OTFTs with silver contacts. The application of injection layers based
on redox dopants improves the measured field-effect mobility by about 2 orders of magnitude.
Organic light-emitting devices (OLEDs) containing highly efficient phosphorescent emitters and highly conductive
doped organic transport layers were studied. Saturated red devices with luminous efficiency of 15 cd/A operate at <4 V;
hence, they have a record power efficiency of 12 lm/W at 1,000 cd/m2.
Additionally, two high-efficiency red OLEDs were serially connected and vertically stacked to create a stacked OLED
having a luminous and power efficiency (at 1,000 cd/m2) of 28 cd/A and 12 lm/W, respectively. The electrical
connection between the two OLEDs is enabled by molecular p- and n-type doped organic transport layers.
The single emissive layer red OLED has a projected lifetime (time to half initial luminance) of ~150,000 hrs from an
initial brightness of 500 cd/m2. The stacked device shows very similar lifetime characteristics when driven at similar
currents, which results in significantly prolonged lifetime of ~260,000 hrs at an initial luminance of 500 cd/m2.
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.