Simultaneous Realization of High EQE of 30%, Low Drive Voltage, and Low Efficiency Roll‐Off at High Brightness in Blue Phosphorescent OLEDs

Abstract

86 wileyonlinelibrary.com COMMUNICATION challenge. For example, Lee and Lee [ 14 ] reported an iridium(III) bis [(4,6-difl uorophenyl)-pyridinate-N,C2 ′ ]picolinate (FIrpic)-based blue OLED with an EQE of 30% at 100 cd m −2 using a pyrido [2,3-b]indole derivative as a host material. However, the driving voltages at 100 cd m −2 are very high (over 4.5 V) compared with those of low-drive-voltage green devices. [ 15,16 ] Shin et al. [ 17a ] reported a FIrpic-based OLED with an EQE of 29.5% using an exciplex-forming co-host system. However, the driving voltages at 1000 cd m −2 are relatively high at around 5.0 V. Very recently, Lee et al. [ 17b ] further reduced the driving voltage of this exciplex system by changing the electron-transport layer (ETL) from B3PyMPM to PO-T2T. Therefore, reducing the drive voltage at high brightness is a critical issue in blue OLEDs.Recently, Lee et al. [ 18 ] reported a low-driving-voltage blue device using a mixed-host system consisting of two host materials: 2-(diphenylphosphoryl)spirofl uorene (SPPO1) as an n-type host material and 4,4,4-tris( N -carbazolyl)triphenylamine (TCTA) as a p-type host material. The mixed-host device showed two times higher EQE than a single-host device with SPPO1 at the high-luminance region over 1000 cd m −2 . The mixed-host device also realized a low driving voltage of 3.9 V at 1000 cd m −2 . Therefore, the use of a mixed-host system represents a promising method to realize a low drive voltage and high EQE at high brightness.In this study, we realized a high EQE of 30%, a low drive voltage, and a low effi ciency roll-off at the high-brightness region (>1000 cd m −2 ) in blue OLEDs using a mixed-host system. We used two types of host materials: TCTA as a p-type host material and 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy) as an n-type host material. Consequently, the mixed-host device gave a high-performance blue OLED with a driving voltage of 3.25 V, an EQE of 32.6%, and a power efficiency of 77.6 lm W −1 at 1000 cd m −2 without any enhancement in light outcoupling. We also developed a white OLED based on this blue device and iridium(III) bis-(2-phenylquinoly-N , C 2 ′ ) dipivaloylmethane [PQ 2 Ir(dpm)] as an orange emitter. The white OLED achieved a driving voltage of 3.35 V and an EQE of 24.4% at 1000 cd m −2 .Very recently, we have reported a blue OLED with a driving voltage of 3.0 V and an EQE of 30% at 100 cd m −2 . [ 19 ] We used a carrier-and exciton-confi ning structure along with a double emission layer (DEML) strategy using high-triplet-energy ( E T ) materials. All the neighboring materials, the hole-transport layer (HTL), host materials, and ETL have higher values of E T than a blue phosphorescent emitter, fac -tris(mesityl-2-phenyl-1H-imidazole)iridium(III) [ fac -Ir(mpim) 3 ]. [ 20 ] Thereby, the quenching of the triplet excitons of fac -Ir(mpim) 3 in the EML White organic light-emitting devices (OLEDs) are expected to be used in next-generation general lighting and large display applications. [1][2][3][4][5] Phosphorescent OLE...

Unlocking the Potential of Pyrimidine Conjugate Emitters to Realize High‐Performance Organic Light‐Emitting Devices

“…These OLEDs also exhibited an η p of over 110 lm W −1 (84.9 cd A −1 , η ext = 25.1%) while maintaining extremely low voltages of 2.2 V at 1 cd m −2 and 3.0 V at 1000 cd m −2 , and an η p,1000 of 78.3 lm W –1 (75.5 cd A –1 , η ext = 22.3%). These performances clearly exceed those of previous TADF devices and are comparable to those of their state‐of‐the‐art phosphorescent counterparts …”

Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers

“…For the EML, we chose tris (4‐carbazoyl‐9‐ylphenyl)amine (TCTA) and TPBi as the co‐host to avoid space charge buildup to tune the recombination zone by adjusting the ratio of hole and electron dominant hosts and minimizing exciton quenching by adjacent transport layers . For the emitter, we chose bis (2‐phenylquinoline)(2,2,6,6‐tetramethylheptane‐3,5‐dionate)iridium(III) (PQ 2 Ir(dpm)) due to its high solubility in organic solvent and high quantum yield . The devices were fully optimized to ensure that the comparison is made on devices with optimized efficiencies.…”

“…However, compared to thermal‐evaporated OLEDs with internal quantum efficiencies close to 100%, achieving high efficiencies is still one of the challenges to overcome in solution processed OLEDs. A multilayer structure for exciton confinement and charge blocking is still an ideal architecture for OLEDs to achieve high external quantum efficiencies (EQEs).…”

Recent Progress in High‐Efficiency Blue‐Light‐Emitting Materials for Organic Light‐Emitting Diodes

“…The fac ‐Ir(mpim) 3 emitter also showed a shallow HOMO of –5.2 eV and short excited state lifetime of 1.50 µs. The fac ‐Ir(mpim) 3 blue dopant performed similarly to the Ir(dbi) 3 emitter and host engineering in PhOLEDs demonstrated a high EQE of 33.2% and low driving voltage of 3.4 V at 1000 cd m −2 . This is one of the best EQE of blue PhOLEDs, although the lifetime was not determined.…”