Enhanced electroluminescence and reduced efficiency roll-off in electrophosphorescent devices using a very high electron mobility material as emitter host and electron transporter

Abstract

We demonstrate markedly improved electroluminescence (EL) intensity and reduced external quantum efficiency (EQE) roll-off of a device which presents two emitting layers of fac-tris-(2-phenylpyridine) iridium [Ir(ppy) 3 ] in 4,4-bis(9-carbazolyl)-2,2-biphenyl (CBP) and 1,3-bis[2-(2,2-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene (Bpy-OXD); 4,7-diphenyl-1,10-phenanthroline/Bpy-OXD layers were used as hole blocking and electron transport layers. The device exhibits a maximum EQE of 15.5% (corresponding to an efficiency of 56.8 cd A −1) at a luminance of 600 cd m −2 , which is twice the value (8.2%) of the reference diode using Ir(ppy) 3 doped CBP as a single emitting layer; the device still maintained a 6.5% efficiency at a luminance of 70 450 cd m −2. The mechanism of this marked improvement in EL intensity and decrease in the EQE roll-off was also explored in detail.

Trap-free space-charge-limited electron transport in amorphous tin(IV) phthalocyanine dichloride thin film

“…It is generally considered that metal electrodes have a significant effect on charge injection [24,25]. To investigate the bulk properties of organic films, it is necessary to realize the Ohmic contact at the organic/metal electrode interface [26][27][28].…”

Monte Carlo study of efficiency roll-off of phosphorescent organic light-emitting diodes: Evidence for dominant role of triplet-polaron quenching

“…The beneficial effects of steps 1 and 2 have already been implemented by using thin exciton blocking layers (e.g., in Ref. 27) at the HTL/EML interface.…”

Reduced efficiency roll-off in phosphorescent OLEDs with a stack emitting layer facilitating triplet exciton diffusion

“…9,10 To suppress triplet exciton quenching, on one hand, the charge carrier in device should be as balanced as possible to minimize polaron accumulation at the interface. [11][12][13] On the other hand, the local triplet exciton density should be decreased by extending exciton formation zone or by shortening triplet exciton lifetime. The introduction of double EMLs [14][15][16][17][18][19] can broaden the exciton formation zone.…”