Black samarium silver cathode raises contrast of organic light-emitter

In the interests of improving the contrast of organic flat-panel displays, researchers at Jilin University (Changchun, China) have created white organic light-emitting devices (WOLEDs) with “black” cathodes of samarium silver (Sm:Ag), rather than the more-usual magnesium:silver (Mg:Ag) cathodes. The efficiency of the Sm:Ag electrodes was comparable to that of their Mg:Ag counterparts, and the contrast of the black cathodes (under 140 lx ambient lighting at a brightness of 1000 cd/m2) was four times better.

Starting with indium tin oxide coated substrates, the researchers deposited organic layers and cathodes without breaking the vacuum environment. So-called delta-doping technology was used for its reproducibility and dopant-free process. White-light emission was obtained by combining blue- and yellow-emitting layers. Optical constants and reflection spectra of the device were taken using variable-angle spectroscopic ellipsometry. In addition to the high contrast, the appearance of the WOLED with a Sm:Ag cathode was insensitive to viewing angles of up to 50°. Contact Wenfa Xie at [email protected].