Highly efficient deep-blue organic light-emitting diodes with doped transport layers

We demonstrate highly efficient, vapor-deposited blue organic light-emitting diodes (OLEDs) operating at low voltage. For reaching deep-blue color, we used two new fluorophores, 9,10-bis(9,9'-spirobi[9H-fluorene]-2-yl)anthracene (Spiro-Anthracene) from Covion, and 4,4'-bis-(N,N-diphenylamino)-tetraphenyl (4P-TPD) from Syntec-Sensient, sandwiched in between p- and n-type doped wide band-gap transport layers and appropriate blocking layers. These p-i-n OLED devices show high luminance and efficiency at low operating voltages. Both dyes emit deep-blue light at color coordinates of x = 0.15 and y = 0.09 (4P-TPD) and x=0.15 and y=0.18 (Spiro-Anthracene). Optimized devices containing Spiro-Anthracene reach a luminance of 100 and 1000 cd/m(2) already at a voltage of 2.9 and 3.4 V, respectively. At the same time, a deep-blue color with CIE color coordinates of x = 0.14 and y = 0.14 as well as good current efficiencies (3.9 cd/A at 100 cd/m(2)) and quantum efficiencies (3.7% at 100 cd/m(2)) are reached, which shows that the concept of doped transport layers and appropriate fluorescent emitters can be applied successfully to the preparation of blue OLEDs. (C) 2004 Elsevier B.V. All rights reserved.