Simultaneous Achievement of High Efficiency and Long Lifetime in Deep Blue Phosphorescent Organic Light‐Emitting Diodes

Abstract

phosphorescent emitters and stable high triplet energy hosts. [7][8][9][10][11][12] The only lifetime results of the deep blue PhOLEDs was described in the work by Li et al., which tested the lifetime of the deep blue Pt emitters. [10] However, the high efficiency and good lifetime could not be simultaneously achieved in the deep blue PhOLEDs because high triplet energy hosts could not be properly chosen. For example, the deep blue device in Li's work with a y coordinate of 0.18 showed only 800 h lifetime at 100 cd m -2 and low external quantum efficiency of 3.2%. Even the sky blue device with y coordinate of 0.21 exhibited only 9.8% EQE although the lifetime at 100 cd m -2 was about 17 000 h. [10] In order to realize high efficiency and long lifetime at the same time, a stable high triplet energy host as well as a stable deep blue emitter is essential. In general, high triplet energy hosts for deep blue PhOLEDs were either single bipolar hosts such as 3,6-bis(diphenylphosphoryl)-9-phenyl-9H-carbazole, 9-(3-(9H-carbazole-9-yl)phenyl)-3-(dibromophenylphosphoryl)-9H-carbazole or single unipolar hosts such as diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide). [13][14][15][16][17] However, their chemical instability was an issue for application in the lifetime study of the deep blue PhOLEDs. In order to overcome the challenging stability issues of the singlet hosts, mixed hosts of p-type host and n-type host were developed, but lifetime results were not described. [18][19][20][21] Recently, we demonstrated an exciplex host and an electroplex host for extended lifetime in sky blue PhOLEDs. [22,23] Although those two hosts were effective to elongate the lifetime of the sky blue PhOLEDs, intrinsic low triplet energy of each host comprising the exciplex and electroplex hosts limited the application of them in the deep blue PhOLEDs. Therefore, it is necessary to design a high triplet energy host system for deep blue PhOLEDs.In order to develop the high triplet energy host, we focused on the weakly bound exciplex host because the emission energy of the strongly bound exciplex host is largely decreased by strong binding of the p-type and n-type host. The weak binding of the p-type and n-type hosts is advantageous to secure high emission energy for efficient energy transfer to the deep blueemitting phosphorescent emitter. In this work, we developed a high emission energy exciplex host for application in high efficiency and long lifetime deep blue PhOLEDs. Two n-type High triplet energy exciplex hosts are developed using new electron transport type hosts with triphenylsilyl blocking groups to obtain high solid state triplet energy and exciplex triplet energy. Two triphenyltriazine derived hosts, 2-phenyl-4,6-bis(4-(triphenylsilyl)phenyl)-1,3,5-triazine (pSiTrz) and 2-phenyl-4,6-bis(3-(triphenylsilyl)phenyl)-1,3,5-triazine (mSiTrz), are synthesized as the high triplet energy hosts with electron transport properties. The two hosts show high triplet energy over 2.90 eV both in solution and solid film, and afford high triplet e...

Triplet Exciton Upconverting Blue Exciplex Host for Deep Blue Phosphors

“…The LUMO was deepened by the LUMO governing diphenyltriazine unit. The HOMO-LUMO gap was 3.26 eV and it was much smaller than that of the 2-phenyl-4,6-bis(3-(triphenylsilyl) phenyl)-1,3,5-triazine (mSiTrz) [4] host which was reported as a pure n-type host for blue phosphors. The weakly electron rich cyanocarbazole made the HOMO shallow, which decreased the HOMO-LUMO gap of the mSiTrzCzCN host.…”

Novel Positive Polaron Stabilizing n-Type Host for High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light-Emitting Diodes

“…At this time, since the 4 position of the core is more reactive than the 2 position, the next intermediate can be synthesized by controlling the molar ratio of the reactant. 27 Then, the prepared dioxaborolane tetraphenylsilyl 28 was attached to the 2 position by the Suzuki coupling reaction. In the case of the mSiBTPCz, the tetraphenylsilyl unit was substituted at the 4 position of the BTP core prior to the carbazole substitution at the 2 position based on the high reactivity at the 4 position.…”

Bicarbazole-triazine hybrid type mixed host materials for blue phosphorescent OLEDs with enhanced efficiency and lifetime

“…8–11 For instance, the combination of dibenzofurans, carbazole, triphenyl-silyl, and 1,3,5-triazine groups was supposed to be one of the representative strategies to realize blue phosphorescent host materials with high BDEs and high triplet (T 1 ) energy levels. 12–17 The local electron distribution density of the molecules was tuned by adequately adjusting the substitutional positions, enabling the compensation of weak bonds of the molecules by supplying electrons to the bond site properly and making the blue host materials stable under electrical excitation. In addition, their photophysical and charge transport characteristics were appropriately modified using the strategies, opening a room to enhance the efficiency and operational lifetime of blue PhOLEDs.…”