Deep blue exciplex tandem OLEDs using n- and p-doped planar heterojunction as a charge generation layer

Abstract

The tandem organic light-emitting diodes (OLEDs) have the advantages of small current density, high current efficiency (CE), and long lifetime. We have developed the conventional and inverted tandem OLEDs using n- and p-doped planar heterojunction as a charge generation layer (CGL). The CGL consists of the bathophenanthroline:Cs2CO3 and N,N’-di-[(1-naphthalenyl)-N,N’-diphenyl]-1,1′-biphenyl)-4,4′-diamine:MoO3 bilayer structure to connect the deep blue- and deep red-emitting units. The turn-on voltage, luminescence, CE, and external quantum efficiencies of the conventional tandem OLED are 7.2 V, 5083 cd m−2, 8.45 cd A−1, and 13.94%, respectively, and the color rendering ability remains stable at a high current density of 60 mA cm−2. Moreover, the efficiency roll-off of the inverted tandem OLED is optimized to 5.5% at a luminance of 1000 cd m−2. Furthermore, a large-area (50 × 50 mm2) parallel OLEDs with a tunable red-emitting area are fabricated. The development of the OLEDs provides a new direction for the application of OLEDs in plant growth.