The influence of the organic layer thickness on short-circuit photocurrent spectra and efficiency is investigated in heterojunction photovoltaic cells with the electron donor materials poly͑p-phenylenevinylene͒ ͑PPV͒ and Cu-phthalocyanine ͑CuPc͒, respectively, together with C 60 as electron acceptor material. The main process of photocurrent generation after light absorption, exciton generation, and exciton diffusion in the bulk of the absorbing material is given by the exciton dissociation at the donor-acceptor interface. We determined a strong dependence of the optimum layer thickness of the absorbing material on the exciton diffusion length by systematically varying the layer thickness of the electron donor material. Additionally, a significant photocurrent contribution occurred due to light absorption and exciton generation in the C 60 layer with a subsequent hole transfer to PPV, respectively, CuPc at the dissociation interface. Using a simple rate equation for the exciton density we estimated the exciton diffusion lengths from the measured photocurrent spectra yielding ͑12Ϯ3͒ nm in PPV and ͑68Ϯ20͒ nm in CuPc. By systematically varying the layer thickness of the C 60 layer we were able to investigate an optical interference effect due to a superposition of the incident with backreflected light from the Al electrode. Therefore both the layer thickness of the donor and of the acceptor layer significantly influence not only the photocurrent spectra but also the efficiencies of these heterolayer devices. With optimized donor and acceptor layer thicknesses power conversion efficiencies of about 0.5% under white light illumination were obtained.

The optical outcoupling of top-emitting organic light-emitting diodes ͑OLEDs͒ can be improved by a thin dielectric capping layer on top of the transparent cathode. We investigate the emission properties of a set of top-emitting OLEDs with the same device structure, but different organic capping layer thicknesses to understand the capping layer effect. We demonstrate that the distribution pattern of the emitted light from top-emitting OLEDs depends strongly on the capping layer thickness, showing not only a maximum current efficiency enhancement by a factor of 1.38 ͑up to 78 cd/ A in forward direction at 1000 cd/ m 2 ͒, but also a quantum efficiency improvement by 35%. This leads to a device efficiency of up to 17.8% and 69 lm/ W at a brightness of 1000 cd/ m 2 . We show that this efficiency enhancement is not due to the redistribution of emitted light, but mainly due to the improvement of outcoupling efficiency by changing the optical structure of the devices with the organic capping layer. The maximum outcoupling efficiency is achieved at a capping layer thickness where the top contact stack ͑cathode+ capping layer͒ shows low absorption and high reflection.

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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.

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