Highly efficient,solution-processed orange–red phosphorescent OLEDs by using new iridium phosphor with thieno[3,2-c]pyridine derivative as cyclometalating ligand

A new orange iridium phosphor of (EtPy)₂Ir(acac) with thieno[3,2-c]pyridine derivative as cyclometalating ligand was designed and synthesized. The combination of thieno[3,2-c]pyridine with rigid fluorene moiety enlarged the π conjugation of ligand, and consequently caused the peak emission of (EtPy)₂Ir(acac) red-shift to 588 nm. By using (EtPy)₂Ir(acac) as the orange phosphor, the fully solution-processed PhOLEDs were fabricated with the following device configuration: ITO/PEDOT:PSS/PVK: PBD: (EtPy)₂Ir(acac)/CsF/Al. With PEDOT:PSS 8000 as the hole-injecting material, the orange device achieved a maximum current efficiency of 13.4 cd A⁻¹, a maximum power efficiency of 5.9 lm W⁻¹ and a maximum external quantum efficiency (EQE) of 11.2% with a CIE coordinate of (0.62, 0.38) that falls into the orange–red region. Moreover, at high luminance of 1000 cd m⁻², the device still remained high current efficiency of 8.7 cd A⁻¹ and EQE of 7.3%. To the best of our knowledge, these efficiencies were among the highest ever reported for solution-processed orange–red PhOLEDs.     

Non-interlayer and color stable WOLEDs with mixed host and incorporating a new orange phosphorescent iridium complex

In this work, we have synthesized a new phosphorescent iridium complex (Bppya)₂Ir(acac), as an orange dopant for organic light-emitting diodes (OLEDs). The device achieved an external quantum efficiency (EQE) of 22.4%, a current efficiency of 49.5 cd A⁻¹ and a power efficiency of 38.9 lm W⁻¹, which are among the highest values for orange OLEDs. Furthermore, color stable and high efficiency phosphorescent white OLED (WOLED) was demonstrated by utilizing a mixed-host in the emissive layers (EMLs) composed of a blue phosphor and the new orange phosphorescent emitter, as well as by avoiding the use of interlayers that commonly exist between different EMLs in WOLEDs. Our WOLED presented decent white emission with maximum efficiencies of 25.3 cd A⁻¹ and 12.6%. Furthermore, the 1931 Commission Internationale de l’Eclairage color coordinates exhibited extremely small variation of (0.3940 ± 0.0102, 0.4323 ± 0.0046) in a wide luminance range from 49 to 38,035 cd m⁻² when driving voltages increased from 4 V to 12 V. The root cause for this excellent color stability is the utilization of the mixed-host to obtain bipolar transport properties in EMLs as well as the eliminating of interlayer between different EMLs, which, on one hand, effectively broaden the exciton recombination zone; on the other hand, reduce the accumulation of triplet excitons at the emissive interface.     

Two novel orange cationic iridium(III) complexes with multifunctional ancillary ligands used for polymer light-emitting diodes

Two novel orange cationic iridium complexes [(npy)₂Ir(o-phen)]PF₆ and [(npy)₂Ir(c-phen)]PF₆ were synthesized. Hnpy: 2-(naphthalen-1-yl)pyridine; o-phen: a 1,10-phenanthroline derivative containing an electron-transporting functional group of 2,5-diphenyl-1,3,4-oxadiazole and a crystallization-resistant tert-butyl functional group; c-phen: a 1,10-phenanthroline derivative containing a hole-transporting functional group of carbazole and a crystallization-resistant 2-ethylhexyl functional group. Both of them are amorphous and possess high thermal stability with 5% weight-reduction temperatures (ΔT_5%) of 386 °C and 383 °C, and glass-transition temperatures (T_g) of 267 °C and 195 °C respectively. They were used as phosphorescent dopants in polymer light-emitting diodes (PLEDs) fabricated by solution-processed technology with configuration of ITO/PEDOT:PSS/PVK:PBD:iridium complex/TPBI/CsF/Al. At the optimal doping concentration of 2.0 wt%, the corresponding PLEDs exhibited the maximum current efficiencies of 9.1 cd A⁻¹ and 10.0 cd A⁻¹, the maximum external quantum efficiencies of 6.5% and 7.1%, and the maximum luminance of 2314 cd m⁻² and 3157 cd m⁻² respectively, with the same CIE coordinates of (0.57, 0.40). The results indicate that cationic iridium complexes are promising candidates for PLED applications when they are designed reasonably.     

High-efficiency deep blue fluorescent emitters based on phenanthro[9,10-d]imidazole substituted carbazole and their applications in organic light emitting diodes

A series of highly efficient deep blue emitters comprising of carbazole and phenanthro[9,10-d]imidazole moieties are designed and synthesized. These compounds present deep blue emission, narrow FWHM, high quantum yields, high thermal and morphological stabilities. Among them, the design strategy of 2:1 ratio of phenanthro[9,10-d]imidazole and carbazole unit affords M2 with more balanced carrier injection and transporting properties. OLEDs using M2 as emitting layer is observed to deliver a truly deep blue CIE of y < 0.06 with a highest external quantum efficiency of 3.02%. By taking the full advantage of these deep blue emitters, they are further served as excellent hosts for fluorescent and phosphorescent dyes. High-performance green phosphorescent device based on M2/Ir(ppy)₃ is attained with a maximum current efficiency of 33.35 cd A⁻¹, a power efficiency of 22.99 lm W⁻¹ and a maximum external quantum efficiency of 9.47%. When doped with an orange fluorescent material, upon careful tuning the doping proportion, the two-emitting-component white OLED is successfully fabricated with a maximum current efficiency of 5.53 cd A⁻¹ and CIE coordinates of (0.313, 0.305). Both the non-doped and doped devices exhibited high operational stability with negligible efficiency roll-off over the broad current density range.     

Ultra high-efficiency multi-photon emission blue phosphorescent OLEDs with external quantum efficiency exceeding 40%

We developed high-efficiency multi-photon emission (MPE) blue phosphorescent OLEDs with external quantum efficiency exceeding 40% at 100 cd m⁻². In these MPE devices, we used a blue phosphorescent emitter, FIrpic and pyridine-containing electron-transporters, B3PyPB and B3PyMPM, B4PyMPM. We also used a well-known electron-transporter, BCP for comparison. We used a combination of TAPC/MoO₃/Al/Liq layers as the charge-generation layer unit. An optimized MPE device showed an extremely high current efficiency of over 90 cd A⁻¹ and a high power efficiency of over 40 lm W⁻¹ at 100 cd m⁻² without any outcoupling enhancement.     

High efficiency blue PhOLEDs using spiro-annulated triphenylamine/fluorene hybrids as host materials with high triplet energy,high HOMO level and high Tg

Two spiro-annulated triphenylamine/fluorene oligomers, namely 4′-(9,9′-spirobifluoren-4-yl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene] (NSF-SF), and 4,4′-di(spiro(triphenylamine-9,9′-fluorene)-2-yl)-spiro(triphenylamine-9,9′-fluorene) (NSF-NSF), are designed and synthesized. Their thermal, electrochemical and photophysical properties were investigated. The introduction of spiro-annulated triphenylamine moieties assurances the high HOMO energy levels of NSF-NSF and NSF-SF at −5.31 eV and −5.33 eV, respectively, which accordingly facilitates the hole injection from nearby hole-transporting layer. Meanwhile, the perpendicular arrangement of the spiro-conformation and the full ortho-linkage effectively prevents the extension of the π-conjugation and consequently guarantees their high triplet energies of 2.83 eV. Phosphorescent organic light-emitting devices (PhOLEDs) with the configurations of ITO/MoO₃/TAPC/EML/TmPyPB/LiF/Al were fabricated by using the two compounds as host materials and bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^2′]iridium(III) picolate (FIrpic) as the dopant. The turn-on voltage of the device B based on NSF-NSF was 2.8 V. Simultaneously, the device exhibited excellent performance with the maximum current efficiency of 41 cd A⁻¹, the maximum power efficiency of 42 lm W⁻¹ and the maximum external quantum efficiency (EQE) of 19.1%. At a high brightness of 1000 cd m⁻², the device remained EQE of 16.2% and the roll-off value of external quantum efficiency is 15%.     

Carbazole-bridged triphenylamine-bipyridine bipolar hosts for high-efficiency low roll-off multi-color PhOLEDs

Three new bipolar molecules composed of carbazole, triarylamine, and bipyridine were synthesized and utilized as host materials in multi-color phosphorescent OLEDs (PhOLEDs). These carbazole-based materials comprise a hole-transport triarylamine at C3 and an electron-transport 2,4′- or 4,4′-bipyridine at N9. The different bipyridine isomers and linking topology of the bipyridine with respect to carbazole N9 not only allows fine-tuning of physical properties but also imparts conformational change which subsequently affects molecular packing and carrier transport properties in the solid state. PhOLEDs were fabricated using green [(ppy)₂Ir(acac)], yellow [(bt)₂Ir(acac)], and red [(mpq)₂Ir(acac)] as doped emitters, which showed low driving voltage, high external quantum efficiency (EQE), and extremely low efficiency roll-off. Among these new bipolar materials, the 2Cz-44Bpy-hosted device doping with 10% (ppy)₂Ir(acac) as green emitting layer showed a high EQE of 22% (79.8 cd A⁻¹) and power efficiency (PE) of 102.5 lm W⁻¹ at a practical brightness of 100 cd m⁻². In addition, the device showed limited efficiency roll-off (21.6% EQE) and low driving voltage (2.8 V) at a practical brightness of 1000 cd m⁻².     

Efficient blue and bluish-green iridium phosphors: Fine-tuning emissions of FIrpic by halogen substitution on pyridine-containing ligands

Three new iridium compounds, 4-F-FIrpic, 4-Cl-FIrpic and 4-Br-FIrpic, were designed and synthesized by introducing the F, Cl and Br atoms to the 4-position of pyridine ring in the frame of sky-blue emitter, FIrpic. Adding F atom stabilizes the HOMO level of FIrpic but keeps the LUMO level of FIrpic almost unchanged, which consequently broadens the HOMO–LUMO gap of FIrpic and finely tunes the emission to 465 nm of 4-F-FIrpic from 470 nm of FIrpic. In contrast, introducing of Cl and Br atoms simultaneously lowers the HOMO and LUMO levels of FIrpic, which brings about the squeeze of HOMO–LUMO gap in FIrpic and makes the emissions of 4-Cl-FIrpic and 4-Br-FIrpic red-shift to 475 and 479 nm, respectively. The phosphorescent organic light-emitting devices using the three iridium compounds as dopants were fabricated with the following configuration: ITO/MoO₃/TAPC/TCTA:dopants/Tm/LiF/Al. The device based on 4-F-FIrpic showed a blue emission with the Commission Internationale de L’Eclairage coordinate of (0.15, 0.28), and revealed rather high efficiencies, with maximum current efficiency of 29 cd A⁻¹, power efficiency of 29 lm W⁻¹ and external quantum efficiency of 14.6%.     

Solution processed single-emissive-layer white organic light-emitting diodes based on fluorene host: Balanced consideration for color quality and electroluminescent efficiency

Cost-effective fabrication of white organic light-emitting diodes (WOLED) is meaningful toward commercial application of environment-friendly solid-state lighting sources. Electroluminescent efficiency and color quality are two opposite performance characteristics facing solution processed WOLEDs requiring balanced consideration. Herein, a recently synthesized molecule of 4,4’-(9,9’-(1,3-phenylene)bis(9H-fluorene-9,9-diyl))bis(N,N-diphenylaniline) (DTPAFB) is introduced as a host material for solution processed all-phosphor WOLEDs, embracing four well-known molecules which are blue iridium (III) bis(2-(4,6-difluorophenyl)pyridinato-N,C²)(picolinate) (FIrpic), green iridium (III) bis[2-(2-pyridinyl-N)phenyl-C](2,4-pentanedionato-O²,O⁴) [Ir(ppy)₂(acac)], and orange iridium (III) bis(2-phenyl-benzothiazole-C²,N)(acetylacetonate) [Ir(bt)₂(acac)] plus a home-made red phosphor of iridium (III) tris(1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine) [Ir(MPCPPZ)₃]. Illumination quality white light with high brightness, high efficiency, suitable correlated color temperature (CCT), high color-rendering index (CRI), and stable electroluminescent (EL) emission is obtained. A stable white emission with a CRI over 70, Commission Internationale de L'Eclairage (CIE) of (0.37, 0.42), and high EL efficiency of 19.6 lm W⁻¹ at high luminance of 2000 cd m⁻² for blue/orange complementary color WOLEDs is demonstrated. The optimized red/green/blue three primary color WOLEDs show improved CRI up to 81, moderate high efficiency of 25.8 cd A⁻¹, 14.4 lm W⁻¹, and EQE of 13.9%. Furthermore, the red/green/blue/orange four primary color WOLEDs show the optional balance between color quality and EL efficiency with high CRI of around 81–83 and medium CCT of 3755–3929 K which is warm and soft to human eyes. At an illumination relevant luminance of 1000 cd m⁻², the total power efficiency reaches 33.6 lm W⁻¹, and still remains 30.2 lm W⁻¹ at 3000 cd m⁻², approaching the efficiency of state-of-the-art fluorescent-tube (40–70 lm W⁻¹), potentially suitable as an environment-friendly solid-state lighting source. This work indicates that developing high performance host materials and highly efficient phosphors and carefully combining them with common phosphors is an effective way toward high performance WOLEDs.     

Ultraefficient Non-Doped Deep Blue Fluorescent OLED: Achieving a High EQE of 10.17% at 1000 cd m−2 with CIEy<0.08

The pursuit for efficient deep blue material is an ever-increasing issue in organic optoelectronics field. It is a long-standing challenge to achieve high external quantum efficiency (EQE) exceed 10% at brightness of 1000 cd m⁻² with a Commission International de L'Eclairage (CIE_y) <0.08 in non-doped organic light-emitting diodes (OLEDs). Herein, this study reports a deep blue luminogen, PPITPh, by bonding phenanthro[9,10-d]imidazole moiety with m-terphenyl group via benzene bridge. The non-doped OLED based on PPITPh exhibits an exceptionally high EQE of 11.83% with a CIE coordinate of (0.15, 0.07). The EQE still maintains 10.17% at the brightness of 1000 cd m⁻², and even at a brightness as high as 10000 cd m⁻², an EQE of 7.5% is still remained, representing the record-high result among non-doped deep-blue OLEDs at 1000 cd m⁻². The unprecedented device performance is attributed to the reversed intersystem crossing process through hot exciton mechanism. Besides, the maximum EQE of orange phosphorescent OLED with PPITPh as host is 32.02%, and remains 31.17% at the brightness of 1000 cd m⁻². Such minimal efficiency roll-off demonstrates that PPITPh is also an excellent phosphorescent host material. The result offers a new design strategy for the enrichment of high-efficiency deep blue luminogen.     

Highly efficient inverted top emitting organic light emitting diodes using a horizontally oriented green phosphorescent emitter

We report a highly efficient phosphorescent green inverted top emitting organic light emitting diode doped with Ir(ppy)₂tmd [bis(2-phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate)] as the horizontally oriented emitter in an exciplex forming co-host system. The device showed a maximum current efficiency of 120.7 cd/A, a maximum external quantum efficiency (EQE) of 27.6% and the power efficiency of 85.9 lm/W at 1,000 cd/m². Moreover the efficiency roll off was small long-lasting to 20,000 cd/m² with EQE’s and current efficiencies of 26.0% and 113.7 cd/A at 10,000 cd/m² and 24.5% and 107.6 cd/A at 20,000 cd/m², respectively. Optical analysis of the efficiencies and emission spectra of the device is also reported.     

Deep blue phosphorescent organic light-emitting diodes with excellent external quantum efficiency

Highly efficient deep blue phosphorescent organic light-emitting diodes (PHOLEDs) using two heteroleptic iridium compounds, (dfpypy)₂Ir(acac) and (dfpypy)₂Ir(dpm), as a dopant and 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)diphenylphosphine oxide as a host material have been developed. The electroluminescent device of (dfpypy)₂Ir(dpm) at the doping level of 3 wt% shows the best performance with external quantum efficiency of 18.5–20.4% at the brightness of 100–1000 cd/m² and the color coordinate of (0.14, 0.18) at 1000 cd/m².     

Organic light-emitting devices with double-block layer

We report on the fabrication of organic light-emitting devices (OLEDs) using double-block layers on the electron transport layer and emitting layer. The current efficiency of the organic light-emitting diode is improved by 43% to 9.16 cd A⁻¹ as compared to the device with a single host of Alq₃ as the electron transport layer. The maximum luminance is over 23 750 cd m⁻² at the bias of 18 V and the current of 338.3 mA cm⁻², which is 33% higher than the single host Alq₃ device without block layer. Using a step-by-step procedure to smooth electron injection and transport, the energy levels introduced by the insertion layers are an effective method of improving the luminance characteristics.     

Novel diarylborane–phenanthroimidazole hybrid bipolar host materials for high-performance red,yellow and green electrophosphorescent devices

In this work, two novel bipolar host materials p-BPPI and m-BPPI containing phenanthroimidazole/dimesitylborane (Mes₂B) with para- and meta-linkage have been designed, synthesized and characterized. The appending Mes₂B moiety improves the thermal stability, electrochemical stability and carrier injection/transport ability of both target compounds. The test results of time-of-flight (TOF) and single-carrier devices show that both the new hosts possess bipolar charge-transporting characteristics. As a result, series of highly efficient green (66.3 cd A⁻¹, 63.1 lm W⁻¹, 18.2%), yellow (55.2 cd A⁻¹, 66.6 lm W⁻¹, 14.5%) and red (20.1 cd A⁻¹, 20.4 lm W⁻¹, 13.5%) PhOLEDs are achieved by using them as the universal host materials. The results indicate that bipolar host p-BPPI and m-BPPI have high potential in fabricating various color OLEDs for displays and lighting applications. Our study further enriches the selection of D and A group for phosphorescent host materials. The relationship between molecular structures and optoelectronic properties is discussed experimentally and theoretically.     

High performance doping-free WOLEDs based on rationally designed asymmetric orange-red Ir(III) emitter with balanced charge mobility

Doping-free organic light-emitting diodes (OLEDs) have attracted continuous attention owing to reduced phase separation, better repeatability, and low cost. Despite demonstrating great potential for white OLEDs (WOLEDs), development of phosphorescent materials capable of achieving high performance with low voltage, high luminance, and low efficiency roll-off simultaneously, still remains a significant challenge. Herein, we design three orange-red Ir(III) phosphors employing functionalized 1,2-diphenylbenzimidazole as main ligands. Clear relationship between structures and electroluminescence (EL)-performances has been established by comprehensively studying their emission properties and intrinsic carrier transporting abilities. Designed phosphor SFIrbiq with spirobifluorene moiety showing negligible intermolecular interactions and balanced carrier transporting ability, not only achieves favorable monochromatic doping-free device but also high-performance doping-free WOLEDs. Optimized WOLED realizes low voltages (2.5 V at 1 cd m⁻², 3.3 V at 100 cd m⁻², and 4.2 V at 1000 cd m⁻²), maximum brightness of 34 505 cd m⁻² and efficiencies of 24.2 cd A⁻¹, 21.7 lm W⁻¹, 10.3%. Such doping-free hybrid WOLED also achieves low efficiency roll-off of 5% for external quantum efficiency (EQE) at 1000 cd m⁻². The device performance can be further improved by employing doping-free all-phosphorescent device structure, achieving maximum efficiencies of 33.3 cd A⁻¹, 32.4 lm W⁻¹, and 16.9%. The results are promising among reported doping-free three-color WOLEDs, paving a feasible way to development of efficient Ir(III) phosphors and doping-free WOLEDs.     

Enhancing the efficiency of simplified red phosphorescent organic light emitting diodes by exciton harvesting

High efficiency red phosphorescent organic light emitting diode (PHOLED) employing co-doped green emitting molecule bis(2-phenylpyridine)(acetylacetonate)iridium(III) [Ir(ppy)₂(acac)] and red emitting molecule bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) [Ir(MDQ)₂(acac)] into 4,4′-bis(carbazol-9-yl)biphenyl (CBP) host in a simplified wide-bandgap platform is demonstrated. The green molecule is shown to function as an exciton harvester that traps carriers to form excitons that are then efficiently transferred to the Ir(MDQ)₂(acac) by triplet-to-triplet Dexter energy transfer, thereby significantly enhancing red emission. In particular, a maximum current efficiency of 37.0 cd/A and external quantum efficiency (EQE) of 24.8% have been achieved without additional out-coupling enhancements. Moreover, a low efficiency roll-off with the EQE remaining as high as 20.8% at a high luminance of 5000 cd/m² is observed.     

Simplified and high-efficiency warm/cold phosphorescent white organic light-emitting diodes based on interfacial exciplex co-host

Possessing the reverse intersystem crossing (RISC) process, exciplex system has vast potential to enhance the efficiency of the white organic light-emitting diodes (WOLEDs). Nevertheless, general structures of the emitting layer always employ triple-doping in a long range (20–30 nm) which is complicated on fabrication progress. In this paper, based on the interfacial exciplex co-host, a flexible and simplified structure design is proposed to realize both warm and cold phosphorescent WOLEDs. In the two devices, with strategically locating the ultrathin orange phosphorescent emitting layers at two sides of the blue phosphorescent emitting layer (2 nm), respectively, multiple energy transfer channels are created to carry out highly efficient exciton utilization. Owing to the different energy transfer mechanisms, different organic emission ratios are obtained in two WOLEDs. The cold WOLEDs exhibited superior maximum external quantum efficiency (EQE), current efficiency (CE) and power efficiency (PE) of 28.37%, 72.17 cd A⁻¹ and 87.17 lm W⁻¹, respectively. Also, the warm WOLEDs showed high values as EQE of 23.80%, CE of 67.70 cd A⁻¹ and PE of 81.10 lm W⁻¹. Furthermore, both the devices presented rather stable color output in the luminance range from 2000 cd m⁻² to 10000 cd m.⁻²     

Highly efficient and stable blue quantum-dot light-emitting diodes based on polyfluorenes with carbazole pendent groups as hole-transporting materials

Highly efficient and stable blue quantum-dot light-emitting diodes (QD-LEDs) have been realized by using poly (9,9-bis(N-(2′-ethylhexyl)-carbazole-3-yl)-2,7-fluorene) (PFCz) as hole-transporting layers (HTLs). Due to the carbazole units as substituents at the 9-position of polyfluorene, PFCz shows higher hole mobility and better electrochemical stability than poly (N-vinlycarbazole) (PVK). As a result, the maximum current efficiency (CE) and external quantum efficiency (EQE) of the blue QD-LEDs increased from 4.32 cd A⁻¹ to 7.9% for PVK HTL to 7.38 cd A⁻¹ and 12.61% for PFCz HTL, respectively. Furthermore, the PFCz-based blue QD-LED exhibited lower turn-on voltage and longer device lifetime than the PVK-based device. The improvement performance of blue QD-LED should be attributed to the conjugated fluorene backbone and the substituents of the carbazole active sites, thus enhancing hole mobility and electrochemical stability. This result demonstrates that polyfluorenes with pendent carbazole groups is a promising hole-transporting materials for improving performance of blue QD-LEDs.     

Alternating current-driven,white field-induced polymer electroluminescent devices with high power efficiency

A solution-processed, all-phosphor, three-color (i.e., blue, green, and red), alternating current-driven white field-induced polymer electroluminescent device (WFIPEL), with low operational voltage, high luminance, high efficiency, high color-rendering index (CRI), and excellent color-stability, was demonstrated. The devices employed poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) [P(VDF–TrFE–CFE)] dielectric modified by single-walled carbon nanotubes (SWNTs) to further improve the dielectric characteristics, as the insulating layer. This significantly lowers the driving voltage of the device. Moreover, hole-generation layer and electron-transporting layer with high conductivity were used to more efficiently form and confine excitons in the emissive layer. The resulting WFIPEL devices show significant improvements in performance as compared to previous reports. Specifically, the devices exhibit a low turn-on voltage of 10 V, a maximum luminance of 7210 cd m⁻², a maximum current efficiency and power efficiency of 33.8 cd A⁻¹ and 10.5 lm W⁻¹, and a CRI of 82. The power efficiency is even 10 times higher than the highest previous report (1 lm W⁻¹).     

High-performance OLEDs based on 4,5-diaza-9,9′-spirobifluorene ligated rhenium(I) complex with enhanced steric hindrance

Highly efficient and emitter concentration insensitive phosphorescent electroluminescent devices based on a novel rhenium(I) [Re(I)] complex, i.e., (4,5-diaza-9,9′-spirobifluorene)Re(CO)₃Br (Re-DSBF), were established. Non-doped device based on Re-DSBF as emitter exhibited outstanding performances with the peak luminance of 8531 cd m⁻² and maximum current efficiency of 16.8 cd A⁻¹, which were the highest reported to date for non-doped phosphorescent electroluminescent devices based on Re(I) emitters. Such excellent performances are closely related to the steric hindrance, large Stokes shift, and short luminescent lifetime of Re-DSBF complex. The luminescent mechanisms of those devices were also investigated.