Deep Blue Phosphorescent Organic Light Research Articles

P‐198: Carboline‐Derived Hosts with Triazine Core for High Efficiency and Long Lifetime in Deep‐Blue Phosphorescent Organic Light‐Emitting Diodes

Two n‐type (electron transport type) hosts derived from carboline and triazine, CblTrz and SiCblTrz, were prepared for high efficiency and long lifetime in deep blue phosphorescent organic light emitting diodes (PhOLEDs). Both materials have diphenyltriazine for acceptor moiety and α‐carboline for donor moiety. In case of SiCblTrz, triphenylsilyl group was attached to the core. The two hosts with high triplet energies of 3.05 eV and 3.02 eV were demonstrated in the mixed hosts with p‐type (hole transport type) mCBP. In addition, device properties of CblTrz and SiCblTrz were measured and EQE of 19.7% and 21.1% in maximum, color coordinate of (0.14, 0.17) and (0.14, 0.16) at 1,000 cd/m2 were obtained, which were suitable for deep blue PhOLEDs. Also, device lifetime values achieved in the deep blue PhOLEDs were 972 h, 1,008 h, respectively.

Triplet energy boosting ternary exciplex host for improved efficiency in deep blue phosphorescent organic light emitting diode

Abstract A high triplet energy exciplex host derived from a ternary mixture of hosts was developed for efficient energy transfer to a deep blue phosphor by suppressing reverse energy transfer. In the thermally activated delayed fluorescent type exciplex host of 4,4′-bis(carbazol-9-yl)-2,2′-dimethylbiphenyl (CDBP) and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), the (oxybis(2,1-phenylene))bis(diphenylphosphine oxide) (DPEPO) was added as a third component to increase the triplet energy of the exciplex host. The addition of DPEPO in the CDBP:PO-T2T exciplex host increased the triplet energy of the exciplex from 2.88 eV to 2.97 eV, and the photoluminescence quantum yield of the deep blue phosphor doped exciplex from 0.77 to 0.86. The triplet energy boosting function of the DPEPO improved the maximum external quantum efficiency of the deep blue phosphorescent organic light-emitting diode from 12.8% to 16.6% at a DPEPO content of 70%.

Synthesis of 3-substituted carbazole derivative as a host material for deep blue phosphorescent organic light-emitting diodes

A high triplet energy material with carbazole and phosphine oxide, phenylbis(9-phenyl-9H-carbazol-3-yl)phosphine oxide (3DCPO), was synthesized as a bipolar host material for deep blue phosphorescent organic light emitting diodes. The 3DCPO host material showed a high triplet energy of 3.01eV, which was high enough for deep blue phosphorescent organic light-emitting diodes. Deep blue phosphorescent organic light-emitting diodes with the 3DCPO host material exhibited high external quantum efficiency of 18.8% at 3% doping concentration.

High external quantum efficiency in deep blue phosphorescent organic light emitting diodes using a simple device structure

Simple high efficiency deep blue phosphorescent organic light-emitting diodes were developed using a mixed host of high triplet energy host materials. A hole transport type host was used both as the hole transport layer and host in the mixed host emitting layer and an electron transport type host was mixed with the hole transport type host in the emitting layer. A three organic layer device structure of the hole transport layer/emitting layer/electron transport layer gave high external quantum efficiency of 26.4% with a color coordinate of (0.14, 0.19).

57.3: Invited Paper: Host and Charge Transport Materials for High Efficiency Deep Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this paper, we describe the development of high efficiency deep blue phosphorescent organic light emitting diodes using high triplet energy host and charge transport materials. The quantum efficiency of deep blue phosphorescent organic light‐emitting diodes could be improved above 20% by using high triplet energy bipolar host materials, hole transport materials and electron transport materials.

Improved power efficiency in deep blue phosphorescent organic light-emitting diodes using an acridine core based hole transport material

A high triplet energy hole transport material with an acridine core was synthesized as the hole transport material for deep blue phosphorescent organic light emitting diodes. The acridine core based hole transport material showed a high triplet energy of 2.89eV for efficient triplet exciton blocking and highest occupied molecular orbital of 5.96eV for efficient hole injection in deep blue phosphorescent organic light-emitting diodes. The acridine core based hole transport material showed low driving voltage than common high triplet energy hole transport material and power efficiency of deep blue phosphorescent organic light-emitting diodes was improved by more than 50%.

Significance of irreversible formation of “electromer” in 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane layer associated with the stability of deep blue phosphorescent organic light emitting diodes

We demonstrate that injection of electrons in 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane (TAPC) layer irreversibly induces defect sites responsible for “electromer” emission. We also show that the defects alter the charge transporting properties of TAPC layer to influence the charge balance of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C2′]tetrakis(1-pyrazolyl)borate (FIr6) based deep blue phosphorescent organic light emitting diodes (PHOLED). The present investigation implies that deep-blue PHOLEDs should be carefully designed for the emission zone to be located far enough from the TAPC layer so as to avoid or minimize the emission from TAPC layer.

Fused indole derivatives as high triplet energy hole transport materials for deep blue phosphorescent organic light-emitting diodes

High triplet energy hole transport materials based on novel fused indole core structure were synthesized and their device performances in deep blue phosphorescent organic light emitting diodes (PHOLEDs) were investigated. The fused indole based hole transport materials showed a high triplet energy over 2.90 eV and high glass transition temperature over 120 °C. The high triplet energy hole transport materials were used in deep blue PHOLEDs and gave a high external quantum efficiency of 24.7% with a color coordinate of (0.137,0.182).

The relationship between the device performance and hole mobility of host materials in mixed host system for deep blue phosphorescent organic light emitting devices

We report on the systematic investigation of the relationship between hole mobility of host materials and device performance to maximize the power efficiency. Three different materials with different hole mobility were used as host materials of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C 2′]tetrakis(1-pyrazolyl)borate (FIr6) based deep blue phosphorescent organic light-emitting device (PHOELD). Host material, tris(4-( N-carbazolyl)phenyl)methylsilane (MCBP), with higher hole mobility (1.1 × 10 −3 cm 2 V −1 s −1), can accommodate more electron current carried by an n-type host, bis(4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl)dimethylsilane (SiTAZ), than the other p-type hosts with lower hole mobility, maintaining the charge balance between hole and electron current. As a result, the optimized device shows high external quantum efficiency (EQE) of 19.0%, high power efficiency of 23.5 lm/W, low efficiency roll off, and deep blue color coordinates of (0.15, 0.23).

Dibenzothiophene derivatives as host materials for high efficiency in deep blue phosphorescent organic light emitting diodes

Various dibenzothiophene derivatives were synthesized as high triplet energy host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) and their device performances were investigated. Dibenzothiophene host materials with a hole transport type carbazole and electron transport type phosphine oxide moieties showed high quantum efficiency and low driving voltage due to balanced charge injection and transport. A high quantum efficiency of 20.2% and only 10% reduction of quantum efficiency at 1000 cd m−2 were demonstrated from the deep blue PHOLEDs with the dibenzothiophene based high triplet energy host materials.

Efficiency and colour optimization of carbazole based deep blue phosphorescent organic light emitting devices

We report highly efficient deep blue phosphorescent organic light emitting devices using a silicon based carbazole host with deep highest occupied molecular orbital level and high triplet energy doped with a phosphorescent dopant, iridium(III)bis(4′,6′,-difluorophenylpyridineato)tetrakis(1-pyrazolyl)borate. The charge transport and emission mechanisms of the light emission layer were investigated by means of current versus voltage measurements, transient photoluminescence and photoemission spectroscopy. By utilizing both energy transfer from host to dopant and direct charge trapping in the dopant material, as well as by optimizing the emission zone, a peak external quantum efficiency of 15%, power efficiency of 19.4 lm W−1 and CIE coordinates of (0.15, 0.23) were achieved.

Adamantane Derivative as Host Material for Efficient Deep-Blue Phosphorescent Organic Light Emitting Diodes

AbstractWe report on a high efficiency deep-blue phosphorescent organic light-emitting diode (POLED) based on new electron-transporting host material. The new electron-transporting host material is an adamantane derivative with high triplet energy and high electron mobility. The deep blue POLED that we have developed utilizes a deep-blue phosphorescent guest material, iridium(III)bis(4’,6’,-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, and exhibits a power efficiency of about 10.2 lm/W at luminance of 100 cd/m2 and maximum external quantum efficiency (EQE) of about 13 %. The power efficiency of our POLED is much higher than that of POLED using p–bis(triphenylsilyly)benzene (UGH2). The maximum EQE of our POLED was also slightly more than that of POLED using UGH2. The obtained difference in power efficiency originates from the new host material having higher electron mobility than that of UGH2.