Franz P. Wenzl

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We report on the efficiency behavior of light-emitting electrochemical cells (LECs) fabricated from a methyl-substituted ladder-type poly(p-phenylene) (mLPPP) that was blended with a crown ether based solid state electrolyte. Unlike organic light-emitting diodes (oLEDs) utilizing mLPPP as an active layer, the LECs suffer from a loss of efficiency at(More)
With increasing power loss of electrical components, thermal performance of an assembled device becomes one of the most important quality factors in electronic packaging. Due to the rapid advances in semiconductor technology, particularly in the regime of high-power components, the temperature dependence of the long-term reliability is a critical parameter(More)
  • S. Tasch, J. Gao, +5 authors K. Müllenc
  • 1999
Blue and green light-emitting electrochemical cells (LECs) based on a ladder-type poly(paraphenylene) (m-LPPP) are described. These LECs are characterized by an extremely low onset for light emission (between 2.2 and 2.7 V in reverse direction for blue emission) yielding an external quantum efficiency of approximately 0.3% and a brightness of about 250(More)
For a systematic approach to improve the reliability and the white light quality of phosphor converted light-emitting diodes (LEDs) it is imperative to gain a better understanding of the individual parameters that affect color temperature constancy and maintenance. By means of a combined optical and thermal simulation procedure, in this contribution we give(More)
We show that with an appropriate combination of two optical simulation techniques-classical ray-tracing and the finite difference time domain method-an optical device containing multiple diffractive and refractive optical elements can be accurately simulated in an iterative simulation approach. We compare the simulation results with experimental(More)
In this study the applicability of an interface procedure for combined ray-tracing and finite difference time domain (FDTD) simulations of optical systems which contain two diffractive gratings is discussed. The simulation of suchlike systems requires multiple FDTD↔RT steps. In order to minimize the error due to the loss of the phase information in an(More)
Based on optical ray-tracing simulations we discuss the effect of the extinction coefficient and the quantum efficiency of the phosphors on the color temperature and the angular homogeneity of the white light emitted from phosphor converted light-emitting diodes. The individual absorption profiles of the blue LED light and the related radiative loss(More)
We present an iterative optical and thermal simulation procedure which enables the determination of the temperature distribution in the phosphor layer of a phosphor converted LED with good accuracy. Using the simulation both the highest phosphor temperatures, which are mostly relevant to material degradation as well as the temperatures of those phosphor(More)
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