Exciton Blocking Materials Research Articles

A design strategy of exciton blocking materials using simulations and the analysis of device properties

A hole transporting type exciton blocking layer (hEBL) is one of the important device architecture components in phosphorescence organic light emitting diodes (PhOLEDs).

Isomer engineering of universal electron transport materials for suppressed exciton quenching in organic light-emitting diodes

A regioisomer of 2,7-bis(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9′-spirobi[fluorene] (m-SBFTrz), 3,6-bis(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9′-spirobi[fluorene] (p-SBFTrz) was developed as a high triplet energy electron transport material by engineering the substitution position of diphenyltriazine to the spirobifluorene core. The p-SBFTrz showed great potential as an electron transport and exciton blocking materials in various devices such as thermally activated delayed fluorescence organic light-emitting diodes (OLEDs) and phosphorescence OLEDs due to increased triplet energy. A large improvement of the external quantum efficiency was achieved using the p-SBFTrz instead of m-SBFTrz by completely suppressing exciton quenching.

Energy level management of CN substituted terdibenzofuran exciton blocking materials by controlling interconnect position of dibenzofuran and CN substitution positions

Three CN modified terdibenzofuran compounds, [2,2':8′,2″-terdibenzo[b,d]furan]-8,8″-dicarbonitrile (2CN2TDBF), [2,4':6′,2″-terdibenzo[b,d]furan]-8,8″-dicarbonitrile (2CN4TDBF), and [4,2':8′,4″-terdibenzo[b,d]furan]-6,6″-dicarbonitrile (4CN2TDBF), were synthesized as exciton blocking materials of blue phosphorescent organic light-emitting diodes (PhOLEDs) to understand the effect of interconnect position between dibenzofuran units and CN substitution positions in the dibenzofuran. Both the interconnect position and CN substitution position affected the lowest unoccupied molecular orbital (LUMO) of the exciton blocking materials. The LUMO stabilization effect was significantly noted in the 4CN2TDBF exciton blocking material, while it was marginal in the 2CN4TDBF exciton blocking material. The LUMO of 2CN2TDBF was in between that of 4CN2TDBF and that of 2CN4TDBF. Therefore, the LUMO level management of the CN modified terdibenzofuran compounds was effectively accomplished by engineering the interconnect position of dibenzofuran and CN modification position.

5,9-Dioxa-13b-Oxophosphanaphtho[3,2,1-de]anthracenes Prepared by Tandem Phospha-Friedel–Crafts Reaction as Hole-/Exciton-Blocking Materials for OLEDs

We report a short synthesis of phosphorus-fused triarylphosphine oxides, 5,9-dioxa-13b-oxophosphanaphtho[3,2,1-de]anthracenes (DOPNAs), based on a tandem phospha-Friedel–Crafts reaction. Phosphorescence, UV–visible absorption, and photoelectron yield spectroscopy of vacuum-deposited thin films revealed that the triplet energies, optical band gaps, and ionization potentials of these materials were sufficiently large for them to be utilized in organic light-emitting diodes (OLEDs). Therefore, we fabricated a set of phosphorescent OLEDs based on the above phosphine oxides, confirming that the utilization of these compounds as hole-/exciton-blocking materials significantly improved OLED efficiencies and lifetimes.

High triplet energy electron transport type exciton blocking materials for stable blue phosphorescent organic light-emitting diodes

High triplet energy electron transport materials with dibenzothiophene and dibenzofuran cores modified with a diphenyltriazine unit were investigated as electron transport type exciton blocking materials for stable blue phosphorescent organic light-emitting diodes. The two exciton blocking materials showed high triplet energy above 2.80 eV and enhanced quantum efficiency of the blue phosphorescent devices by more than 40% while maintaining stability of the pristine blue devices without the high triplet energy exciton blocking layer.

Arylsilanes and siloxanes as optoelectronic materials for organic light-emitting diodes (OLEDs)

Arylsilanes and siloxanes have been extensively studied as components of OLEDs. In this review, we summarize the recent advances in the utilization of arylsilanes and siloxanes as fluorophore emitters, hosts for phosphor emitters, hole and exciton blocking materials, and as electron and hole transporting materials.

Silicon‐Based Material with Spiro‐Annulated Fluorene/Triphenylamine as Host and Exciton‐Blocking Layer for Blue Electrophosphorescent Devices

A novel silicon-based compound, 10-phenyl-2'-(triphenylsilyl)-10H-spiro[acridine-9,9'-fluorene] (SSTF), with spiro structure has been designed, synthesized, and characterized. Its thermal, electronic absorption, and photoluminescence properties were studied. Its energy levels make it suitable as a host material or exciton-blocking material in blue phosphorescent organic light-emitting diodes (PhOLEDs). Accordingly, blue-emitting devices with iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C(2)']picolinate (FIrpic) as phosphorescent dopant have been fabricated and show high efficiency with low roll-off. In particular, 44.0 cd A(-1) (41.3 lm W(-1)) at 100 cd m(-2) and 41.9 cd A(-1) (32.9 lm W(-1)) at 1000 cd m(-2) were achieved when SSTF was used as host material; 28.1 lm W(-1) at 100 cd m(-2) and 20.6 lm W(-1) at 1000 cd m(-2) were achieved when SSTF was used as exciton-blocking layer. All of the results are superior to those of the reference devices and show the potential applicability and versatility of SSTF in blue PhOLEDs.

A phenanthroline derivative as exciton blocking material for organic solar cells

Abstract Functionalization of phenanthroline in the 4,7-positions with pyridine groups is reported. The new material, 2,9-dimethyl-4,7-di(pyridin-4-yl)-1,10-phenanthroline (DMPP), shows lower HOMO and LUMO levels than those of bathophenanthroline (BPhen). DMPP-based zinc phthalocyanine (ZnPc):C 60 flat-heterojunction solar cells exhibit a 3.5% power efficiency which is higher than that of those devices with BPhen as the exciton blocking material.

Durene-decorated CBP derivatives as phosphorescent hosts and exciton-blocking materials for efficient blue OLEDs

Two novel durene-containing molecules, 1,4-bis-[4-(9-carbazolyl)-phenyl]-durene (CPD) and 1,4-bis-{4-[9-(3,6-(di-tert-butyl)carbazoyl)]-phenyl}-durene (t-BuCPD), which are derived from 4,4′-bis(9-carbazolyl)biphenyl (CBP) by inserting durene in its biphenyl core, are designed and synthesized for use as host materials for blue phosphors in organic light-emitting diodes (OLEDs). Inserting durene in biphenyl causes a right-angle torsion between the durene and the adjacent phenyl groups due to the strong steric hindrance effect of the durene group, confining the effective π-conjugation on only one carbazole and one phenyl and increasing the triplet energies of CPD and t-BuCPD to over 3.0 eV. These durene-decorated molecules show higher thermal stabilities than many other CBP derivatives. Blue phosphorescent OLEDs were fabricated using CPD and t-BuCPD as triplet hosts and traditional iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as a dopant and excellent performances were achieved. In particular, peak efficiencies of 26.2 cd A−1 and 14.8 lm W−1 were realized when CPD was used as both a host and exciton-blocking material. This is the first report using durene to tune the triplet energy levels of phosphorescent host materials.

4-Hydroxy-8-methyl-1,5-naphthyridine aluminium chelate: a morphologically stable and efficient exciton-blocking material for organic photovoltaics with prolonged lifetime

A stable exciton-blocking layer (EBL) with rigid ball-like 4-hydroxy-8-methyl-1,5-naphthyridine aluminium chelate (AlmND3) has been newly developed for organic photovoltaics (OPVs) based on a double-heterostructure of pentacene/C60/EBL. Unlike the common EBL materials, such as tris-(8-hydroxyquinoline)aluminium (Alq3) and bathocuproine (BCP), AlmND3 exhibits a relatively high electron mobility (∼10−4 cm2 V−1 s−1 at the electric field of 6.4 × 105 V cm−1) and a wide band gap energy (∼3.3 eV) in addition to a high glass transition temperature (Tg ∼ 194 °C). Having such EBL between active region (pentacene/C60) and the metal cathode, pristine device performances were comparable with those of BCP-based OPV due to its high mobility and wide band gap energy. Moreover, due to its significantly higher Tg than that of BCP, an extended lifetime performance was observed for AlmND3-based OPV, compared with the BCP-based OPV aged at the elevated temperature of 75 °C.

A high triplet energy phosphine oxide derivative as a host and exciton blocking material for blue phosphorescent organic light-emitting diodes

We have designed and synthesized a blue phosphorescent host material based on a phosphine oxide moiety. 2-(diphenylphosphine oxide)-9,9′-spirobifluorene ( SPPO1) was compared with N, N′-dicarbazolyl-3,5-benzene (mCP) as a blue host material in blue phosphorescent organic light-emitting diodes (PHOLEDs). The SPPO1 was effective as a host for blue PHOLEDs and the SPPO1 based blue PHOLEDs showed much higher quantum efficiency than common mCP based blue PHOLEDs. A high quantum efficiency of 16.3% and a current efficiency of 31.4 cd/A were obtained in the blue PHOLED with iridium(III) bis(4,6-(di-fluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) as a blue phosphorescent dopant. In addition, SPPO1 was also effective as an exciton blocking material for the blue PHOLED.

The use of sublimable chlorotricarbonyl bis(phenylimino)acenaphthene rhenium(I) complexes as photosensitizers in bulk-heterojunction photovoltaic devices

A series of sublimable substituted chlorotricarbonyl bis(phenylimino)acenaphthene rhenium(I) complexes was synthesized and used in the fabrication of photovoltaic devices. The hole and electron carrier mobilities of these complexes are in the order of 10 −3 to 10 −4 cm 2 V −1 s −1. Heterojunction devices with CuPc/complex/C 60 (CuPc = copper phthalocyanine) as the active layer and bulk heterojunction devices with complex:C 60 as the active layer were fabricated. The rhenium complexes function as photosensitizer in the devices, and exhibit optical absorption in the region between 500 and 550 nm within which other components in the device do not absorb. Other devices with hole transport materials, exciton blocking materials, and different active layer thickness were also fabricated. Variation of substitution groups in the ligand did not show significant difference in device performance. The best power conversion efficiency of the devices was measured to be 1.29% under illumination of AM1.5 simulated solar light.

Silane- and triazine-containing hole and exciton blocking material for high-efficiency phosphorescent organic light emitting diodes

One of the important factors for high efficiency phosphorescent organic light-emitting devices is to confine triplet excitons within the emitting layer. We synthesized and characterized a new hole blocking material containing silane and triazine moieties, 2,4-diphenyl-6-(4′-triphenylsilanyl-biphenyl-4-yl)-1,3,5-triazine (DTBT). Electrophosphorescent devices fabricated using the material as the hole-blocking layer and N,N′-dicarbazolyl-4,4′-biphenyl (CBP) doped with fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] as the emitting layer showed a maximum external quantum efficiency (ηext) of 17.5% with a maximum power efficiency (ηp) of 47.8 lm W−1, which are much higher than those of devices using bathcuproine (BCP) (ηext = 14.5%, ηp = 40.0 lm W−1) and 4-biphenyloxolate aluminium(III) bis(2-methyl-8-quinolinato)-4-phenylphenolate (BAlq) (ηext = 8.1%, ηp = 14.2 lm W−1) as hole-blocking layers.

High operational stability of electrophosphorescent devices

Electrophosphorescent devices with fac-tris(2-phenylpyridine)iridium as the green emitting dopant have been fabricated with a variety of hole and exciton blocking materials. A device with aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) demonstrates an efficiency of 19 cd/A with a projected operational lifetime of 10 000 h, operated at an initial brightness of 500 cd/m2; or 50 000 h normalized to 100 cd/m2. An orange-red electrophosphorescent device with iridium(III) bis(2-phenylquinolyl-N,C2′)acetylacetonate as the dopant emitter and BAlq as the hole blocker demonstrates a maximum efficiency of 17.6 cd/A with a projected operational lifetime of 5000 h at an initial brightness of 300 cd/m2; or 15 000 h normalized to 100 cd/m2. The average voltage increase for both devices is <0.3 mV/h. The device operational lifetime is found to be inversely proportional to the initial brightness, typical of fluorescent organic light emitting devices.