White Light Emitting Electroluminescence Devices with Organic Oligomers
- PDF / 332,283 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 38 Downloads / 190 Views
INTRODUCTION Organic light emitting diodes based on the PHP oligomer have great potential for application in several optoelectronic devices and for organic light-emitting diodes (OLEDs) to be used in large area displays in particular [1-3]. The intensive, deep blue light emission of PHP can be converted into other visible light due to the fact that its emission spectrum is located on the high energy side of the visible spectrum [4,5]. In a bilayer configuration using PHP and the organic-metal complex Gaq3 as the light-emitting layers, it possible to switch color emission from green to blue depending on the polarity of the applied bias voltage [6]. Recently we have been successful in the realization of multicolor LEDs red, green, blue (RGB) by a new external color conversion technique based on PHP OLEDs [4]. One special goal is to realize efficient white light emission based on OLEDs, which is necessary for many applications such as backlighting of liquid crystal displays and producing full color displays using suitable color filters. There have been several concepts to achieve white light emitting devices based on thermally vacuum deposited organic materials [8-15]; i) using multilayer LEDs consisting of two or more active layer, ii) by spectral filtering of the emission light of a suitable emitter, iii) by superposition of red green and blue LEDs. Recently, we showed how to improve the performance OLEDs by an internal conversion technique using an active layer based on a blend of two conjugated polymers [7]. The white emission in this polymers blend is generated by an excitation energy transfer from the host polymer into lower lying emitting states of the guest polymer [7]. In this article we present the fabrication of efficient white EL devices using a blend of a PHP and an ITSO oligomer as the active layer, which is produced by co-evaporation of the 27 Mat. Res. Soc. Symp. Proc. Vol. 488 ©1998Materials Research Society
Downloaded from https://www.cambridge.org/core. Gothenburg University Library, on 10 Feb 2020 at 15:08:39, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-488-27
oligomers. A pure white EL light emission is obtained by introducing only 4 % ITSO into the PHP oligomer. The combination of two emission spectra, blue light from PHP and orange light from ITSO results in efficient white OLEDs. The EL efficiency of this OLED is 1.25%. The generation of white light in mixed single layer EL is due to an internal color conversion method. The ITSO oligomer, which strongly absorbs in the blue spectral range, is excited when illuminated with the PHP EL emission and subsequently emits PL light at longer wavelengths. A part of the blue PHP emission therefore is absorbed and transformed in the orange spectral range, so that a pure white light emission can be realized, if the concentration ratio of these two oligomers is suitably adjusted. ,
\
PHP
Fig. 1 : Chemical structure of PHP and ITSO oligomers.
-
ITSO EXPERIMENT Fig.1. shows
Data Loading...
