Jan Birnstock

Screen-printed passive matrix displays based on light-emitting polymers

Due to their outstanding properties, e.g., good contrast, wide viewing angle, low power consumption, and self-emission organic light-emitting (OLE) displays on the basis of conjugated polymers are on the verge of commercialization. Two major disadvantages of the current processing technique for the polymers—spin coating—are the material waste and the difficulties involved in patterning multichrome or even full-color displays. Therefore, we investigated the screen-printing technique for the production of OLE displays. In this letter, we present performance data and images of screen-printed OLE diodes. They are already comparable to spin-coated ones. We observed luminance of 10u200a000 cd/m2 at 8 V and peak efficiencies exceeding 10 cd/A for green diodes. These data indicate that printed organic displays have the potential to replace “classical” spin-coated devices.

Screen-printed passive matrix displays and multicolor devices

Due to their outstanding properties organic light-emitting displays based on conjugated polymers are on the verge of commercialization. Two major disadvantages of the current processing technique for polymers, spin-coating of polymer solutions, are the material waste and the difficulties involved in patterning the polymers. Therefore we investigate the screen-printing for the production of polymer displays. Here we present performance data of screen-printed light-emitting diodes of different colors. In the production process of these diodes we printed two layers successively one over the other. Furthermore, we show images of printed multichrome demonstrators and passive matrix displays. Our data indicate that the screen-printing technique has the potential to replace the classical spin-coat process. We observe luminance of 10,000 cd/m2 at 8 V and peak efficiencies exceeding 10 cd/A for green diodes and half lifetime of 170 hours at 80 degree(s)C and 100 cd/m2 for red diodes which corresponds to about 7,000 hours at room temperature. These values of printed devices are comparable to those of spin-coated ones.

Impact of the metal cathode on the performance of polymer light-emitting diodes

An appropriate choice of the cathode material and the process of cathode deposition is a key issue in the development of polymer light emitting devices. In this paper, we report on the impact of low work function metals on the luminescence efficiency of thin films of polyfluorene type polymers. Photoluminescence as well as electroluminescence experiments are presented, and in both cases, a strong correlation between the metal layer thickness and the luminescence efficiency is demonstrated. By means of time-of-flight secondary ion mass spectroscopy (TOF-SIMS), the distribution of the metal contamination within the polymer layers is determined. The results strongly suggest that impurity quenching of excitons by metal atoms inside the polymer layer takes place and strongly affects luminescence and device efficiency.

42.4: Passive Matrix Displays Based on the New Red Emitting Dopant RedATDB

We present investigations on a new red emitting dye RedATDB. Doping small concentrations of RedATDB in an Alq3 host leads to red OLEDs (x=0.650, y=0.346) with good efficiency values (4.3 cd/A; 2.1 lm/W @ 100 cd/m2). To test our material for display applications, we produced monochrome red passive matrix displays (32 × 100 pixels). With appropriate display measurement equipment we investigate the pixel resolved electrical (I-V) and optical (luminance) characteristics. Homogenous pixel performance data in terms of luminance and driving voltage has been observed.