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 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.     

Constructing a novel single-layer white organic light-emitting device through a new sky-blue fluorescent bipolar host

A novel device concept was realized for simple single-layer small-molecule white organic light emitting devices. The single organic active layer here is simply comprised of a newly synthesized sky-blue fluorescent bipolar host (TPASO) and a common orange phosphorescent dopant. Suppressed singlet Föster energy transfer induced by a low-concentration doping and spontaneous high- to low-lying triplet energy transfer, respectively, lead to sky-blue fluorescence from TPASO and orange phosphorescence from the dopant. The resulting two-organic-component device exhibits a low turn-on voltage of 2.4 V, maximum current/power efficiencies up to 11.27 ± 0.02 cd A⁻¹ and 14.15 ± 0.03 lm W⁻¹, and a warm-white CIE coordinate of (0.42, 0.45) at 1000 cd m⁻².     

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.     

Highly efficient phosphorescent organic light-emitting diodes using a homoleptic iridium(III) complex as a sky-blue dopant

Homoleptic triscyclometalated iridium(III) complex Ir(dbi)₃ was used as a dopant for sky blue phosphorescent organic light-emitting diodes (PHOLEDs). Its photophysical, thermal, electrochemical properties as well as the device performances were investigated. Ir(dbi)₃ exhibited high quantum yield of 0.52 in solution at room temperature. A maximum current efficiency and external quantum efficiency (EQE) of 61.5 cd A⁻¹ and 23.1% were obtained, which are the highest ever reported for blue homoleptic iridium complexes. High efficiencies of 53.5 cd A⁻¹ and 20.1% EQE were achieved even at the luminance of 1000 cd m⁻².     

Ultra-high general and special color rendering index white organic light-emitting device based on a deep red phosphorescent dye

Ultra-high color rendering index (CRI) white organic light-emitting device (WOLED) was achieved by using a deep red phosphorescent dye Iridium(III)Bis[1-(3,5-dimethylphenyl)-7-methylisoquinoline] (acetylacetone). The WOLED exhibits high luminance of 2529 cd/m² and power efficiency of 7.86 lm/W at 5 V, and shows ultra-high general CRI and R₉ of 96 and 91. The average of all 14 CRIs is up to 95 at 5 V. Besides, the current efficiency roll-off of the WOLED is reduced due to the balance of carrier injection and transportation in emissive layers. The results indicated that the deep red emission is very important for an ultra-high CRI WOLED.     

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.     

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.     

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.     

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.     

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 and superior color-stability white phosphorescent organic light-emitting diodes based on double mixed-host emission layers

We demonstrate high-efficiency and superior color-stability white phosphorescent organic light-emitting diodes based on double blue mixed-host emission layers (EMLs) with different mixed ratios. The key feature of the concept is to introduce double blue mixed-host EMLs with an orange ultrathin layer sandwiched between them. The improved white device without spacer or interlayer achieves superior color-stability and reduced efficiency roll-off, which are consistent with the good ambipolar conductivity of the mixed-host layer. Moreover, peak efficiency of 40.8 lm/W and low turn-on voltage of 2.71 V are realized. The double mixed-host EMLs concept proves to be quite useful in achieving excellent device performance.     

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).     

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     

Doping-free hybrid white organic light-emitting diodes with fluorescent blue,phosphorescent green and red emission layers

Industrialized white organic light-emitting diodes (OLEDs) currently require host-guest doping, a complicated process necessitating precise control of the guest concentration to get high efficiency and stability. Two doping-free, hybrid white OLEDs with fluorescent blue, and phosphorescent green and red emissive layers (EMLs) are reported in this work. An ultra-thin red phosphorescent EML was situated in a blue-emitting electron transport layer (ETL), while the ultra-thin green phosphorescent EML was placed either in the ETL (Device 1), or the hole transport layer (HTL) (Device 2). Device 2 exhibits higher efficiency and more stable spectrum due to the enhanced utilization of excitons by ultra-thin green EML at the exciton generation zone within the HTL. Values of current efficiency (CE), power efficiency (PE), and CRI obtained for the optimized hybrid white OLEDs fabricated through a doping-free process were of 23.2 cd/A, 20.5 lm/W and 82 at 1000 cd/m², respectively.     

High-efficiency host free deep-blue organic light-emitting diode with double carrier regulating layers

A bright high-efficiency host-free deep-blue organic light-emitting diode (OLED) is demonstrated. Without the aid of any carrier regulating layer, the deep-blue OLED shows a power efficiency of 1.7 lm W⁻¹ with CIE coordinates of (0.143, 0.098) at 1000 cd m⁻². The respective power efficiency is increased from 1.7 to 2.1 and 2.2 lm W⁻¹ as a single- and double-carrier regulating layers were incorporated. The respective peak luminance also increases from 5250 to 7620 and 9130 cd m⁻², an increment of 45% and 74%. The marked brightness improvement may be attributed to the incorporated carrier regulating layers that effectively lead carriers to recombine in a wider zone. Moreover, the blue emission can be hypsochromic shifted by varying the incorporation position of the carrier regulating layer and the emissive layer thickness.     

Improved efficiency,stable spectra and low efficiency roll-off achieved simultaneously in white phosphorescent organic light-emitting diodes by strategic exciton management

Despite their merits of high efficiency and environmental friendliness, phosphor based white organic light-emitting diodes (WOLEDs) for commercial applications still face tough challenges of efficiency roll-off and color stability. Herein, we fabricated high-efficiency phosphor WOLEDs with extremely low roll-off and stable white emission by employing mixed spacer layer between the two complementary emissions as well as mixed host in the orange layer. The strategic exciton management in our proposed device structure greatly balanced the transport of charge carriers due to the excellent exciton manipulation of the mixed spacer, and significantly suppressed the exciton quenching owing to the extended exciton recombination region, which significantly minimized the efficiency roll-off of the fabricated WOLEDs. The resulting phosphor WOLED exhibited the maximum current efficiency (CE) and power efficiency (PE) of 47.5 cd A⁻¹ and 44.7 lm W⁻¹, respectively, and the CE still had 43.1 cd A⁻¹ at 5000 cd m⁻², showing a suppressed efficiency roll-off of only 9.2%. Additionally, the device achieved fairly stable spectra over a wide range of luminance with suitable CIE coordinates for indoor lighting and outdoor displays.     

A hybrid white organic light-emitting diode with stable color and reduced efficiency roll-off by using a bipolar charge carrier switch

A hybrid white organic light-emitting diode (WOLED) with an emission layer (EML) structure composed of red phosphorescent EML/green phosphorescent EML/spacer/blue fluorescent EML was demonstrated. This hybrid WOLED shows high efficiency, stable spectral emission and low efficiency roll-off at high luminance. We have attributed the significant improvement to the wide distribution of excitons and the effective control of charge carriers in EMLs by using mixed 4,4′,4″-tri(9-carbazoyl) triphenylamine (TCTA) and bis[2-(2-hydroxyphenyl)-pyridine] beryllium (Bepp₂) as the host of phosphorescent EMLs as well as the spacer. The bipolar mixed TCTA:Bepp_2, which was proved to be a charge carrier switch by regulating the distribution of charge carriers and then the exciton recombination zone, plays an important role in improving the efficiency, stabilizing the spectrum and reducing the efficiency roll-off at high luminous. The hybrid WOLED exhibits a current efficiency of 30.2 cd/A, a power efficiency of 32.0 lm/W and an external quantum efficiency of 13.4% at a luminance of 100 cd/m², and keeps a current efficiency of 30.8 cd/A, a power efficiency of 27.1 lm/W and an external quantum efficiency of 13.7% at a 1000 cd/m². The Commission Internationale de l’Eclairage (CIE) coordinates of (0.43, 0.43) and the color rendering index (CRI) of 89 remain nearly unchanged in the whole range of luminance.     

High efficiency and non-color-changing orange organic light emitting diodes with red and green emitting layers

We report a high performance orange organic light-emitting diode (OLED) where red and green phosphorescent dyes are doped in an exciplex forming co-host as separate red and green emitting layers (EMLs). The OLED shows a maximum external quantum efficiency (EQE) of 22.8%, a low roll-off of efficiency with an EQE of 19.6% at 10,000 cd/m², and good orange color with a CIE coordinate of (0.442, 0.529) and no color change from 1000 to 10,000 cd/m². The exciplex forming co-host system distributes the recombination zone all over the EMLs and reduces the triplet exciton quenching processes.     

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.