Two-dimensional π-conjugated molecules based-on 2,6,9,10-tetra(prop-1-yn-1-yl)anthracene and their application to solution-processed photovoltaic cells

Novel two-dimensional π-conjugated molecules, i.e., 5′,5″′-((9,10-bis((4-hexylphenyl)ethynyl)anthracene-2,6-diyl)bis(ethyne-2,1-diyl))bis(5-hexyl-2,2′-bithiophene) (2,6-HBT) and 5′,5″′-((2,6-bis((4-hexylphenyl)ethynyl)anthracene-9,10-diyl)bis(ethyne-2,1-diyl))bis(5-hexyl-2,2′-bithiophene) (9,10-THB) were successfully synthesized and utilized as highly soluble p-type organic semiconductors for organic thin film transistors (TFTs) and solar cells. From the TFTs, the high hole mobility of the pristine film of 9,10-THB was measured to be 0.07 cm² V⁻¹ s⁻¹ (I_on/off = 10⁶–10⁷), which is mainly attributed to slip-stacked charge-transport behavior in J-aggregation-induced crystallites. Further, a solution-processed solar cell made of 9,10-THB and PC₆₁BM exhibited very promising and reproducible power conversion efficiencies of 3.30% and 2.53% with composition 1:1 and 1:2 w/w ratio, respectively.     

Stable and efficient blue fluorescent organic light-emitting diode by blade coating with or without electron-transport layer

Multi-layer small-molecule blue fluorescent organic light-emitting diode (OLED) is fabricated by blade coating. The emission layer is based on a mixed host of 1-(7-(9,9′-bianthracen-10-yl)-9,9-dioctyl-9H-fluoren-2-yl)pyrene (PT-404) and electron-transport material 2,7-Bis(diphenylphosphoryl)-9,9′ -spirobifluorene (SPPO13), and the blue guest emitter is 4-4′-(1E,1′E)-2,2′-(naphthalene-2,6-diyl)bis(ethane-2,1-diyl)bis(N,N-bis(4-hexyl- Phenyl) aniline) (Blue D). A hole-transport layer of Poly-(9, 9-dioctylfluorenyl-2, 7-diyl)-co-(4, 4-(N-(4-sec-butylphenyl)) diphenylamine) (TFB) is added on top of PEDOT: PSS anode. The electrons are blocked away from TFB by a layer of pure host emission layer of PT-404 between TFB and the mixed –host emission layer. For the device with the electron transport layer of Tris(8-hydroxyquinolinato)aluminum (Alq₃) blade-coated over the emission layer the efficiency and lifetime at initial brightness of 500 cd m⁻² are 7.5 cd A⁻¹ and 150 h for Alq₃/CsF/Al cathode. When the Alq₃/CsF/Al is replaced by simply CsF/Al over the mixed-host emission layer the efficiency and lifetime are 6.4 cd A⁻¹ and 300 h (2 times longer than that of the Alq₃/CsF/Al cathode). The lifetime depends on the electron-hole balance tuned by the mixed-host blending ratio as well as the electron injection from the cathode. This work shows good stability is possible for all-solution-processed blue OLED.     

All-solution-processed blue small molecular organic light-emitting diodes with multilayer device structure

All-solution-processed multilayer blue small molecular organic light-emitting diodes are fabricated by blade coating method. Fluorescent blue host,1-(7-(9,9′-bianthracen-10-yl)- 9,9-dioctyl-9H-fluoren-2-yl)pyrene, and blue dopant, 4,4′-(1E,1′E)-2,2′-(naphthalene-2,6-diyl)bis(ethene-2,1-diyl)bis(N,N-bis(4-hexylphenyl)aniline), are used to achieve good solubility and pinhole-free thin film by solution process. The multilayer device structure with hole/electron transport layer is achieved by blade coating method without the dissolution problem between layers. The efficiency of the all-solution-processed device is 4.8 cd/A at 1200 cd/m², close to that by thermal deposition in high vacuum chamber. The device performance is optimized with the annealing temperature of TPBi layer at 50 °C.     

Fully solution-processed and multilayer blue organic light-emitting diodes based on efficient small molecule emissive layer and intergrated interlayer optimization

Efficient and fully solution-processed blue organic light-emitting diodes (OLEDs) based on fluorescent small-molecule and methanol/water soluble conjugated polymer as electron-injection material are reported. The emitting layer is 3,6-bis(9,9,9′,9′-tetrakis (6-(9H-carbazol-9-yl)hexyl)-9H,9′H-[2,2′-bifluoren]-7-yl)dib-nzo[b, d]thiophene 5, 5-dioxide (OCSoC) with a blue-fluorescent small-molecule, and a methanol/water soluble polymer poly[(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)] (PFN) acted as electron-injection layer (EIL). All the organic layers are spin-coated from solution. The multilayer device structure with emitting layer/electron-injection layer is achieved by solution-processed method without the dissolution problem between layers. The performances of the devices show that the maximum luminous efficiency of the multilayer device is increased about 43%, compared to the single-layer device. PFN acting as the EIL material plays a key role in the improvement of the device performance when used in solution-processed small-molecule OLEDs.     

Efficient solution-processed blue phosphorescent organic light-emitting diodes with halogen-free solvent to optimize the emissive layer morphology

Efficient solution-processed blue phosphorescent organic light-emitting diodes (OLEDs) featuring with halogen-free solvent processing are fabricated in this study. The organic molecule 3,6-bis(diphenylphosphoryl)-9-(4′-(diphenylphosphoryl) phenyl)-carbazole (TPCz) that possesses good solubility in halogen-free polar solvents is selected to serve as the host of blue phosphorescent iridium(III) [bis(4,6-difluorophenyl)-pyridinato-N,C²]-picolinate (FIrpic) dopant. The morphology of the TPCz:FIrpic emissive layer prepared with different polar solvents including chlorobenzene (CB), n-butanol (ButA) and isopropanol (IPA) and the effect on their electroluminescent performance have been investigated in detail. It is found that the more polar halogen-free solvent IPA restrains the FIrpic aggregation and renders a more densely packed emissive layer as compared to the CB-processed counterpart, which results in the enhanced electroluminescent performance. The luminous efficiency and power efficiency of the blue phosphorescent OLEDs prepared with CB are merely 5.7 cd/A and 3.3 lm/W, respectively. When using more polar halogen-free solvent IPA, the efficiencies are enhanced to 22.3 cd/A and 15.6 lm/W, about 2.9 and 3.7-time increment, respectively. This work provides an approach to fabricate efficient solution-processed phosphorescent OLEDs with environmental-friendly solvents, which is highly required in large-scale solution-processed manufacturing.     

Thermally cross-linkable host materials for enabling solution-processed multilayer stacks in organic light-emitting devices

A thermally cross-linkable host material, i.e., two vinylbenzyl ether groups containing a carbazole derivative (DV-CBP), was developed for solution-processed multilayer organic light-emitting devices (OLEDs). DV-CBP was thermally cross-linked at styrene end-groups through curing at approximately 180 °C in the absence of a polymerization initiator. This cross-linking reaction rendered the emissive layer insoluble and enabled the subsequent solution deposition of an upper electron-transporting layer. Furthermore, photoluminescence quantum efficiencies of the emissive layer were maintained at greater than 75% throughout the cross-linking reaction. A solution-processed small-molecule electron-transporting layer on top of the cross-linked emissive layer led to lower driving voltages and higher efficiencies in the OLEDs compared to those of a device with a vacuum-deposited Ca electrode on the emissive layer.     

Great improvement of operation-lifetime for all-solution OLEDs with mixed hosts by blade coating

We investigated some effective device designs and fabrication methods for long operation-lifetime all-solution-processed Phosphorescent OLEDs (PhOLEDs) and fluorescent OLEDs with mixed-hosts system and thin Poly [(9, 9-dioctylfluorenyl-2, 7-diyl)-co-(4, 4′-(N-(4-sec-butylphenyl) diphenylamine)] (TFB). The all-solution-processed green PhOLEDs had high current efficiency (30.3 cd/A) and long operation-lifetime. The best half-lifetime of green PhOLEDs with thin HTL, MH-hosts EML and optimized deposition was 310 h at an initial luminance 1000 cd/m², 250 h at an initial luminance 500 cd/m² for green PhOLEDs with thin HTL, and MH-hosts EML, and the lifetime of triple layer PhOLEDs device was only 0.5 h for the same materials. The red PhOLEDs exhibited a high current efficiency (10.93 cd/A) and half-lifetime with 157.9 h at an initial luminance 500 cd/m². For the blue fluorescent OLEDs, the thin polymer TFB, mixed-hosts EML, double EMLs and optimization deposition yield a high current efficiency (5.68 cd/A) and long operation-lifetime with 117.7 h at an initial luminance 500 cd/m². Single host fluorescent device had half-lifetime of 73.5 h only at an initial luminance 100 cd/m². Finally, by doping red emitter Rubrene into stable blue device, we achieved soft yellow OLEDs with high efficiency (10.87 cd/A) and 8 fold improvement operation-lifetime (1200 h). We believe that such all-solution-processed OLEDs which showed greatly improved operational lifetimes would be suitable for the indoor supportive lighting with natural colors.     

A high thermal stability terpyridine derivative as the electron transporter for long-lived green phosphorescent OLED

A new terpyridine-based compound of 2,2′,7,7′-tetra([2,2':6′,2″-terpyridin]-4′-yl)-9,9′-spirobi[fluorene] (4oTPSF) was designed and synthesized as the electron transporter in organic light-emitting diodes (OLEDs). 4oTPSF exhibited excellent thermal stability with high glass transition temperature (T_g) of 250 °C and melting temperature (T_m) of 460 °C during the thermal measurement. The excellent thermal stability is attributed to the molecular structure, that the steric effect of rigid twisted spirobiflourene and the connected terpyridine (TPY) resulted in a decrease of the intermolecular π-stacking interaction. The studies on electrical characteristics of electron-only devices revealed that 4oTPSF showed high electron-transporting capability, as good as the conventional electron-transporting material (ETM) 1,3,5-tris(N-phenylbenzimid-azol-2-yl-benzene (TPBi). A series of green phosphorescent OLEDs (PhOLEDs) based on bis(2-phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir(ppy)₂tmd) or tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy)₃) as emitter and 4oTPSF as ETM displayed a turn-on voltage of 2.23 V and a maximum power efficiency of 97.8 l m/W and a half-life (T₅₀) of 101, 5680 and 319 390 h at an initial luminance of 10 000, 1000 and 100 cd/m², respectively. The lifetime of 4oTPSF-based device was twice more than the lifetime of TPBi-based device.     

Tuning electron injection/transporting properties of 9,10-diphenylanthracene based electron transporters via optimizing the number of peripheral pyridine for highly efficient fluorescent OLEDs

By incorporating different number of pyridine rings to the periphery of the 9,10-diphenylanthracene (DPA) core, four new pyridine-containing DPA derivatives, 3-(4-(10-phenylanthracen-9-yl)phenyl)pyridine (AnPy), 9,10-bis(4-(pyridin-3-yl)phenyl)anthracene (AnDPy), 3,3'-((2-(pyridin-3-yl)anthracene-9,10-diyl)bis(4,1-phenylene))dipyridine (AnTPy), 3,3'-(9,10-bis(4-(pyridin-3-yl)phenyl)anthracene-2,6-diyl)dipyridine (AnFPy) were designed and synthesized as electron transporters. Their photophysical properties, energy levels and electron mobilities can be readily regulated through tuning the quantity of the pyridine ring. Through optimizing electron injection/transporting properties, AnTPy exhibits not only a suitable lowest unoccupied molecular orbital (LUMO) energy level for electron injection into light-emitting layer (EML), but also a relatively high electron mobility of around 10⁻³ cm² V⁻¹ s⁻¹, which is about two orders of magnitude higher than that of the widely used material Alq₃. As expected, the blue fluorescent OLEDs with AnPy, AnTPy and AnFPy as an electron-transporting layer (ETL) exhibited superior performance compared to that using Alq₃, remarkably lowering the driving voltages and improving efficiencies. In particular, the device with AnTPy as an ETL showed a maximum current efficiency of 14.4 cd A⁻¹, a maximum power efficiency of 12.1 lm W⁻¹, a maximum external quantum efficiency (EQE) of 8.15% and low efficiency roll-off even at an illumination-relevant luminance of 10,000 cd m⁻². These results clearly demonstrated that tuning electron injection/transporting properties by optimizing the number of peripheral electron-withdrawing groups was an efficient strategy to achieve high-performance ETMs.     

Solution-processed planar white light-emitting diodes based on cadmium-free Cu-In-Zn-S/ZnS quantum dots and polymer

Bright white light-emitting diodes (WLEDs) were fabricated by using a simple solution-processed technique, in which the yellow cadmium-free Cu-In-Zn-S/ZnS core/shell quantum dots (QDs) blending with poly [(9, 9-dioctylfluorenyl-2, 7-diyl)-co-(4, 4′-(N-(p-butylphenyl)) diphenylamine)] (TFB) was used as emissive layers. The color of the electroluminescence (EL) from the device could be tuned from blue-green to white by varying the thermal annealing temperatures, and white EL emission could be obtained under the annealing temperature of 95 °C. A high color rendering index (CRI) of 90 and the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.32) were achieved in the WLEDs annealed at 95 °C, respectively. The WLEDs exhibited a low turn-on voltage of 2.5 V and a maximum luminance of 1500 cd/m², which were maintained at 0.1 cd/A over a wide range of luminance from 100 to 1300 cd/m². This work may open up a new way to realize white light in the planar WLEDs based on the cadmium-free QDs.     

Synthesis and device properties of mCP analogues based on fused-ring carbazole moiety

Novel mCP analogues consisting of blue phosphorescent host materials with fused-ring, 1,3-bis(5H-benzofuro[3,2-c]carbazol-5-yl)benzene (BFCz) and 1,3-bis(5H-benzo[4,5]thieno[3,2-c]carbazol-5-yl)benzene (BTCz) were designed and synthesized using benzofurocarbazole and benzothienocarbazole donor moieties. BFCz and BTCz exhibit high glass transition temperatures of 147 and 157 °C, respectively, and high triplet bandgaps of 2.94 and 2.93 eV, respectively. To explore the electroluminescence properties of these materials, multilayer blue phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated in the following device structure: indium–tin-oxide (ITO)/PEDOT:PSS/4,4’-cyclohexylidene bis[N,N-bis(4-methylphenyl)aniline] (TAPC)/1,3-bis(N-carbazolyl) benzene (mCP)/host:FIrpic/diphenylphosphine oxide-4-(triphenylsilyl)phenyl (TSPO1)/LiF)/Al. The PHOLEDs with BTCz exhibited efficient blue emission with luminous and quantum efficiencies of 30.9 cd/A and 15.5% at 1000 cd/m², respectively.     

Development of a new class of hole-transporting and emitting vinyl polymers and their application in organic electroluminescent devices

A new class of hole-transporting vinyl polymers, poly{4-vinyl-4^′-[bis(4^′-tert-butylbiphenyl-4-yl)amino]biphenyl} (PVBAB) and poly{4-vinyl-4^′-[N,N-bis(9,9-dimethylfluoren-2-yl)amino]biphenyl} (PVFAB), and a new emitting vinyl polymer, poly(2-{4-[4-vinylphenyl(4-methylphenyl)amino]phenyl}-5-dimesitylborylthiophene) (PVPhAMB-1T), were designed and synthesized. These new vinyl polymers form smooth amorphous films with high glass-transition temperatures of ca. 200 °C. PVBAB and PVFAB possess electron-donating properties, and PVPhAMB-1T possesses bipolar character with both electron-donating and accepting properties, exhibiting strong fluorescence in solution and as films. Organic electroluminescent devices using PVBAB or PVFAB as a hole-transport layer and N,N^′-dimethylquinacridone-doped tris(8-quinolinolato)aluminum as an emitting layer were thermally stable and exhibited very high performance. The use of PVPhAMB-1T as an emitting material also permitted the fabrication of a high-performance, green-emitting organic EL device.     

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.     

Tetrasubstituted adamantane derivatives with arylamine groups: Solution-processable hole-transporting and host materials with high triplet energy and good thermal stability for organic light-emitting devices

Four new host/hole-transporting materials, namely 4,4′,4″,4‴-(adamantane-1,3,5,7-tetrayl)tetrakis(N,N-diphenylaniline) (4TPA-Ad, 1),4,4′,4″,4‴-(adamantane-1,3,5,7-tetrayl)tetrakis(N,N-di-p-tolylaniline) (4MTPA-Ad, 2), 1,3,5,7-tetrakis(4-(9H-carbazol-9-yl)phenyl)adamantane (4Cz-Ad, 3) and 1,3,5,7-tetrakis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)adamantane (4tBuCz-Ad, 4), were designed and synthesized by incorporating four electron-donating arylamine units into the rigid adamantane skeleton via a simple C–N coupling reaction. Their thermal, photophysical and electrochemical properties were investigated. The molecular design endows the materials with high triplet energies of ∼3.0 eV, good solution processability, high thermal stability and appropriate HOMO levels. Two types of electroluminescent devices using 1–4 as hole-transporting or host materials were fabricated. The device based on 2 as solution-processed hole-transporting material and tris(quinolin-8-yloxy)aluminum as an emitter revealed a maximum current efficiency of 4.2 cd A⁻¹, which was comparable with the TAPC-based control device. The sky-blue device employing 2 as solution-processed host material and 4,6-(difluorophenyl)pyridine-N,C^2′)picolinate (FIrpic) as an emitter showed a maximum current efficiency of 16.6 cd A⁻¹ with Commission Internationale de I’Eclairage (CIE) coordinates of (0.16, 0.32).     

(2,2′-Binaphthyl-6,6′-diyl)bis(diphenylphosphine oxide) as a potentially simple and efficient electron-transport layer for stable organic light-emitting diodes

The synthesis of organic electron-transport materials (ETMs) for organic light-emitting diodes (OLEDs) has been intensely pursued. Herein we report an organic phosphinyl compound (2,2′-Binaphthyl-6,6′-diyl)bis(diphenylphosphine oxide) (BiNa-BiDPO) with concise synthesis and purification. BiNa-BiDPO is thermally stable up to ca. 415 °C and exhibits distinct glass transition with a T_g of 112 °C after being cooled from the melt. Upon further heating, no crystallization or melting is observed. Ultraviolet photoemission spectroscopy studies reveal that E_HOMO ≈ −6.12 eV for the new compound. Consequently, the LUMO level was roughly estimated as −2.77 eV based on the onset of the film absorption spectrum. BiNa-BiDPO possesses a higher electron mobility of 1.6–8.4 × 10⁻⁵ cm² V⁻¹ s⁻¹ at E = 2–5 × 10⁵ V cm⁻¹, relative to a common ETM 1,3,5-tris(N-phenylbenzimidazolyl)benzene (TPBi), thus providing better OLED efficiency with lower working voltage. Moreover the OLED devices involving BiNa-BiDPO as the electron-transport layer showed a half life-time of 172 h at an initial luminance of ca. 1000 cd m⁻², driven at a constant current density, in contrast with the TPBi device with a shortened t_1/2 of 93 h. Further device engineering as well as molecular design may provide enhanced device durability.     

Design of high triplet energy electron transporting material for exciplex-type host: Efficient blue and white phosphorescent OLEDs based on solution processing

A high triplet energy electron transporting material 1,3,5-tris(diphenylphosphoryl)benzene (TPO) was successfully designed and synthesized to form an efficient exciplex with the commonly used hole transporting molecule tris(4-carbazoyl-9-ylphenyl)amine (TCTA). The singlet-triplet energy difference in this exciplex was only 0.03 eV, which leads to the successive triplet up-conversion and delayed fluorescence. In addition, due to the high triplet energies of TPO and TCTA, the energy leakage from exciplex-state to the constituting molecule was eliminated. By employing this exciplex as host, solution-processed white phosphorescent OLEDs have been realized with a low turn-on voltage of 3 V and a high power efficiency of 20.5 lm W⁻¹. These results indicate that the well-designed exciplex can be used as efficient host material for low-cost solution-processed OLEDs.     

Green Ir(III) complexes with multifunctional ancillary ligands for highly efficient solution-processed phosphorescence organic light-emitting diodes with high current efficiency

Two new highly efficient green emitting heteroleptic Ir(III) complexes, namely, bis[5-(2-ethylhexyl)-8-(trifluoromethyl)benzo[c][1,5]naphthyridin-6(5H)-one]iridium-4-((3,5-di(9H-carbazol-9-yl)benzyl)oxy)picolinate (Ir-HT) and bis[5-(2-ethylhexyl)-8-(trifluoromethyl) benzo[c][1,5]naphthayridin-6(5H)-one]iridium-4-((4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzyl) oxy)picolinate (Ir-ET) were designed and synthesized for solution-processed phosphorescence organic light-emitting diodes (PHOLEDs). These new Ir(III) complexes are based on amide-bridged trifluoromethyl (-CF₃) substituted phenylpyridine unit as main ligand and 1,3-bis(N-carbazolyl)benzene (mCP) unit and 1,3,4-oxadiazole (OXD) unit functionalized picolinate (pic) as an ancillary ligand. These multifunctional groups were attached into the 4-position of pic ancillary ligands via ether linkage. Interestingly, the solution-processed PHOLED device using Ir-HT as a dopant exhibited a maximum external quantum efficiency (EQE_max) of 20.92% and a maximum current efficiency (CE_max) of 64.04 cd A⁻¹. Whereas PHOLED device using Ir-ET displayed a EQE_max of 20.68% and a CE_max of 65.02 cd A⁻¹. This is one of best CE with high EQE for green Ir(III) complexes via solution-processed PHOLEDs using multifunctional ancillary ligands so far.     

Indenocarbazole based bipolar host materials for highly efficient yellow phosphorescent organic light emitting diodes

We report bipolar host materials with robust indenocarbazole and biphenyl moiety as hole-electron-transporting unit for phosphorescent yellow organic light-emitting diodes (OLEDs). New host materials demonstrated an excellent morphological stability with high glass transition temperature of 207 °C. Simultaneously, it also revealed appropriate triplet energy of about 2.6 eV for ideal triplet energy transfer to yellow phosphorescent dopant. A phosphorescent yellow OLED with new host ICBP1 (and ICBP2) and conventional yellow dopant iridium(III)bis(4-(4-t-butylphenyl)thieno[3,2-c]pyridinato-N,C2′)acetylacetonate (Ir(tptpy)₂acac) shows a low driving voltage of 3.4 (and 3.6 V) at 1000 cd/m², and maximum external quantum efficiency as high as 26.4%. Such efficient performance of phosphorescent yellow OLEDs is attributed to a good charge balance and high electron transport properties of host materials.     

Molecular orientation of a new anthracene derivative for highly-efficient blue fluorescence OLEDs

A new anthracene derivative of 9,10-bis(2,5-dimethyl-4-(naphthalen-2-yl)phenyl)-2,3-diphenylanthracene (BDNPA) was designed and synthesized as a non-doped blue emitter in organic light emitting diodes (OLEDs). BDNPA has highly rigid structure and thermal stability with decomposition temperature (corresponding to 5% weight loss) of 490 °C, because p-naphthyl xylene groups in 9,10-positions were highly twisted to anthracene core due to steric hindrance of xylene groups, and because the 2,3-diphenyl groups were also twisted about 45–49° to anthracene. OLEDs with BDNPA non-doped emitter showed high efficiency of 5.21 cd/A due to the carrier mobility with well-aligned π-stacking structure toward out-of-plane by the face-on orientation by grazing incidence X-ray diffraction.     

Highly efficient solution-processed small-molecule white organic light-emitting diodes

Solution-processed small-molecule white organic light-emitting diodes (WOLEDs) were fabricated with a co-host of hole-transporter 4,4′,4″-Tris(carbazol-9-yl)triphenylamine (TCTA) and electron-transporter 2,7-Bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13). By doping 15 wt% FIrpic or F₃Irpic and 0.5 wt% Ir(MDQ)₂(acac) in to the TCTA/SPPO13 host, highly efficient white OLEDs have been achieved which exhibit nearly identical emission spectra at different luminance. The F₃Irpic and Ir(MDQ)₂(acac)-based WOLED shows maximum efficiencies of 40.9 cd/A, 36.7 lm/W and 16.9%, and even high efficiencies of 30.1 cd/A and 12.3% at the practical luminance of 1000 cd/m², which are among the highest efficiencies of the solution-processed small-molecule WOLEDs. These results demonstrate a convenient way to realize solution-processed WOLEDs with high efficiency and high spectral stability through full small-molecule materials system.