“For the first time an OLED not only is able to achieve a light yield of over 60 lm/W, but also at the same time meet the international Energy Star SSL Standard with regard to colour requirements,” said BASF.
Sheet-form OLED emitters are touted as a possible replacement for fluorescent office and retail lighting – once efficiency, colour rendering, and lifetime are high enough. Fluorescent lighting varies in efficiency from 50 to 100 lm/W.
To meet Energy Star, BASF has used a combination of red, green and blue emitters.
“The OLEDs contain phosphorescent metal complexes as emitter materials and customised complementary materials, which ensure optimum constancy of the colour temperatures,” said BASF. “That means the diodes are very colour-stable even when there are variations in luminous intensity.”
Lifetime is still an issue, particularly with the blue emitter – in 2003 BASF developed a class of phosphorescent blue emitters based on an iridium complex.
“Our aim is to develop stable blue phosphorescence emitters. Whilst the colour coordinates and efficiencies of the new blue OLEDs are already outstanding, the service life still presents many challenges,” said Dr Elmar Kessenich, project manager at BASF. “If we manage to produce deep-blue stable emitters, that will open up the way for us to make white OLED light tiles with a light yield of more than 100 lm/W.”
BASF and Osram are conducting research together within the framework of the OLEDs for Applications on the Lighting Market (OPAL) project, which also includes Philips.
“The challenge now lies with process engineers to apply these high efficiencies economically to large active areas,” said Dr Karsten Heuser, OPAL coordinator and director OLED lighting technology at Osram.
OPAL is sponsored by the German Federal Ministry for Education and Research.