Abstract:Articles you may be interested inDistinguishing triplet energy transfer and trap-assisted recombination in multi-color organic light-emitting diode with an ultrathin phosphorescent emissive layer
“…Oxadiazoles typically exhibit electron transporting characteristics which can be used as the host for phosphorescent OLEDs [ 28 – 31 ]. In our previous study, we demonstrated an efficient blue phosphorescent OLED consisting of iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato- N ,C2′]picolinate (FIrpic) doped into 2-phenyl-5-(2′,4′,6′-trimethyl-[1,1′-biphenyl]-4-yl)-1,3,4-oxadiazole (OXD) possessing good electron transporting characteristics and a wide bandgap [ 32 ]. In this paper, we investigate the carrier injection and transport characteristics in the EML of such an OLED.…”
In this paper, we investigate the carrier injection and transport characteristics in iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) doped phosphorescent organic light-emitting devices (OLEDs) with oxadiazole (OXD) as the bipolar host material of the emitting layer (EML). When doping Firpic inside the OXD, the driving voltage of OLEDs greatly decreases because FIrpic dopants facilitate electron injection and electron transport from the electron-transporting layer (ETL) into the EML. With increasing dopant concentration, the recombination zone shifts toward the anode side, analyzed with electroluminescence (EL) spectra. Besides, EL redshifts were also observed with increasing driving voltage, which means the electron mobility is more sensitive to the electric field than the hole mobility. To further investigate carrier injection and transport characteristics, FIrpic was intentionally undoped at different positions inside the EML. When FIrpic was undoped close to the ETL, driving voltage increased significantly which proves the dopant-assisted-electron-injection characteristic in this OLED. When the undoped layer is near the electron blocking layer, the driving voltage is only slightly increased, but the current efficiency is greatly reduced because the main recombination zone was undoped. However, non-negligible FIrpic emission is still observed which means the recombination zone penetrates inside the EML due to certain hole-transporting characteristics of the OXD.
“…Oxadiazoles typically exhibit electron transporting characteristics which can be used as the host for phosphorescent OLEDs [ 28 – 31 ]. In our previous study, we demonstrated an efficient blue phosphorescent OLED consisting of iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato- N ,C2′]picolinate (FIrpic) doped into 2-phenyl-5-(2′,4′,6′-trimethyl-[1,1′-biphenyl]-4-yl)-1,3,4-oxadiazole (OXD) possessing good electron transporting characteristics and a wide bandgap [ 32 ]. In this paper, we investigate the carrier injection and transport characteristics in the EML of such an OLED.…”
In this paper, we investigate the carrier injection and transport characteristics in iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic) doped phosphorescent organic light-emitting devices (OLEDs) with oxadiazole (OXD) as the bipolar host material of the emitting layer (EML). When doping Firpic inside the OXD, the driving voltage of OLEDs greatly decreases because FIrpic dopants facilitate electron injection and electron transport from the electron-transporting layer (ETL) into the EML. With increasing dopant concentration, the recombination zone shifts toward the anode side, analyzed with electroluminescence (EL) spectra. Besides, EL redshifts were also observed with increasing driving voltage, which means the electron mobility is more sensitive to the electric field than the hole mobility. To further investigate carrier injection and transport characteristics, FIrpic was intentionally undoped at different positions inside the EML. When FIrpic was undoped close to the ETL, driving voltage increased significantly which proves the dopant-assisted-electron-injection characteristic in this OLED. When the undoped layer is near the electron blocking layer, the driving voltage is only slightly increased, but the current efficiency is greatly reduced because the main recombination zone was undoped. However, non-negligible FIrpic emission is still observed which means the recombination zone penetrates inside the EML due to certain hole-transporting characteristics of the OXD.
“…For 2CbzTAZ, electron mobility also exhibited a more increased slope than that of holes 23 . Therefore, with increasing voltage, the recombination zone in the EML shifts toward the anode side and the emission spectrum becomes redshift because of the microcavity effect inside the device 24,36 .Figure 5EL spectra at different driving voltages for BPOLEDs with different hosts: ( a ) mCP, ( c ) TAZ, ( e ) mCP:TAZ, and ( g ) 2CbzTAZ. ( b ), ( d ), ( f ), and ( h ) are zoomed-in spectra at short wavelength region (380–460 nm) of ( a ), ( c ), ( e ), and ( g ), respectively.…”
In this study, we demonstrated a blue phosphorescent organic light-emitting diode (BPOLED) based on a host with two carbazole and one trizole (2CbzTAZ) moiety, 9,9′-(2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-1,3-phenylene)bis(9H-carbazole), that exhibits bipolar transport characteristics. Compared with the devices with a carbazole host (N,N’-dicarbazolyl-3,5-benzene, (mCP)), triazole host (3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole, (TAZ)), or a physical mixture of mCP:TAZ, which exhibit hole, electron, and bipolar transport characteristics, respectively, the BPOLED with the bipolar 2CbzTAZ host exhibited the lowest driving voltage (6.55 V at 10 mA/cm
2
), the highest efficiencies (maximum current efficiency of 52.25 cd/A and external quantum efficiency of 23.89%), and the lowest efficiency roll-off, when doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as blue phosphor. From analyses of light leakage of the emission spectra of electroluminescence, transient electroluminescence, and partially doped OLEDs, it was found that the recombination zone was well confined inside the emitting layer and the recombination rate was most efficient in a 2CbzTAZ-based OLED. For the other cases using mCP, TAZ, and mCP:TAZ as hosts, electrons and holes transported with different routes that resulted in carrier accumulation on different organic molecules and lowered the recombination rate.
“…Organic light-emitting device (OLED) is advantageous to use as one of the most promising lighting technologies for the next generation due to its low cost, light weight, self-emission, wide view-angle [1,2]. Hence, its output efficiency and lifetime are critical factors for mass production [3]. Currently, the most efforts and reports focused on pursuing the high efficiency OLED, especially on blue OLED.…”
Two novel bipolar carbzol-triazole derivatives was synthesized by conjugating hole transporting moiety carbazole (Cbz) with electron transporting moiety triazole (TAZ) to achieve the bipolar molecules, which were employed as the hosts of emitting layer doped with blue emitter FIrpic inside blue phosphorescence OLEDs with high current efficiency of 50 and 50.6 cd/A, and EQE of 20% and 21.6%.
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