High-Efficiency Organic Electrophosphorescent Diodes Using 1,3,5-Triazine Electron Transport Materials

Abstract

This paper reports on novel electron transport materials, 1,3,5-triazine derivatives (TRZ), which have been useful in high-efficiency electrophosphorescent (EP) organic light-emitting diodes (OLEDs). We synthesized four 2,4,6-tris(diarylamino)-1,3,5-triazine derivatives (TRZ1−TRZ4) that had electron-donating substituents and examined their OLED characteristics. Of these, we found that TRZ 2, 3, and 4 function as a host for tris(2-phenylpyridine)iridium (Ir(ppy)3) and, in particular, 2,4,6-tris(carbazolo)-1,3,5-triazine (TRZ2) demonstrated a very high external electroluminescent (EL) quantum efficiency (ηext) of ∼10.2 ± 1.0% and an energy conversion efficiency (ηenergy) of 14.0 ± 2.0 lm/W. Detailed transient photoluminescent (PL) measurement revealed that the triplet energy level of TRZ2 (E T1 = 2.81 eV) is higher than that of conventional 4,4‘-N,N‘-dicarbazol-biphenyl (CBP) (E T1 = 2.56 eV), suggesting that TRZ2 has excellent capabilities in confining Ir(ppy)3 triplet excitons.

High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure

“…5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .The most efficient way to get high recombination efficiency in PHOLEDs is to balance holes and electrons in the emitting layer. 6,8,9,[11][12][13][14] It was reported by He et al that the efficiency of green PHOLEDs could be doubled using a double layer emitting structure.…”

“…6,8,9,[11][12][13][14] It was reported by He et al that the efficiency of green PHOLEDs could be doubled using a double layer emitting structure. 6 The use of an effective hole or exciton blocking layer could also enhance the recombination efficiency of PHOLEDs.…”

“…5 In addition, the performances of PHOLEDs are greatly affected by the charge transport and charge recombination in the light emitting layer ͑EML͒. [6][7][8][9][10] .…”

“…8,11 Other than these, host and dopant materials were found to have a great impact on the recombination efficiency of PHOLEDs. 9,[12][13][14] Another way to get high efficiency in OLED is to confine excitons inside an emitting layer using a multilayer quantum well structure. 15,16 There have been several reports about quantum well structure which can confine holes or excitons within an emitting layer.…”

Enhanced life time and suppressed efficiency roll-off in phosphorescent organic light-emitting diodes with multiple quantum well structures

“…5 An employment of adequate hole and/or exciton blocking layer in PHOLEDs could improve the recombination efficiency in the EML, 6 which are greatly influenced by the recombination efficiency of the hostdopant materials. 7,8 One way to obtain more efficient external quantum efficiency (EQE) is to confine hole-electron charges and excitons inside the EML of PHOLEDs, as a multiple quantum well (MQW) structure to lead an enhanced recombination efficiency between holes and electrons. 9,10 High efficiency in typical OLED structures can be obtained by means of a charge balance inside EML, and moreover, the EL efficiency in case of a QW structure is enhanced by using exciton confinement inside the EML.…”