Soo-Kang Kim

Exceedingly efficient deep-blue electroluminescence from new anthracenes obtained using rational molecular design

9,10-Bis(3′,5′-diphenylphenyl)anthracene [MAM], 9-(3′,5′-diphenylphenyl)-10-(3‴,5‴-diphenylbiphenyl-4″-yl)anthracene [MAT], and 9,10-bis(3″,5″-diphenylbiphenyl-4′-yl)anthracene [TAT] were newly synthesized through boration and Suzuki aryl–aryl coupling reactions. We have demonstrated that the EL performance of blue-light emitters can be optimized and improved by varying the chemical structures of the side groups. In the thin film state, the three materials exhibit PLmax values in the range of 439–445 nm. MAM, MAT, and TAT all have high Tg values above 120 °C; TAT has the highest Tg value, above 150 °C. This is twice as high as that of DPVBi (64 °C) and is much higher than that of MADN (120 °C) as well. It also exhibits excellent color coordinates (0.156, 0.088), which are very close to the NTSC blue standard, and an external quantum efficiency of 7.18%, twice that of MADN, which are the best reported results for deep-blue OLED emitters.

New deep-blue emitting materials based on fully substituted ethylene derivatives

New blue fluorescent compounds containing tetra-substituted ethylene moieties have been designed and synthesized. These materials, 1,2-di(4′-tert-butylphenyl)-1,2-bis(4′-(anthracene-9-yl)phenyl)ethene [BPBAPE, 1A], 1,2-diphenyl-1,2-bis(4′-(anthracene-9-yl)phenyl)ethene [PBAPE, 1B], 9,10-bis(4-(1,2,2-tris(4-tert-butylphenyl)vinyl)phenyl)anthracene [BTBPPA, 2A], and 9,10-bis(4-(1,2,2-triphenylvinyl)phenyl)anthracene [BTPPA, 2B], were synthesized through Suzuki and McMurry reactions. By fabricating multilayered non-doped OLED devices using these new blue materials, we achieved luminance efficiencies of 4.00 lm W−1 (10.33 cd A−1 at 8.1 V) for BPBAPE [1A] and 1.82 lm W−1 (3.93 cd A−1 at 6.8 V) for BTPPA [2B] at 10 mA cm−2. The maxima in the electroluminescence spectra of ITO/2-TNATA (60 nm)/NPB (15 nm)/BPBAPE [1A] and BTPPA [2B] (30 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (200 nm) devices were found to be 475 and 452 nm respectively. The BPBAPE [1A] and BTPPA [2B] devices exhibited sky blue emission (0.195, 0.303) and deep blue emission (0.159, 0.135) at 10 mA cm−2 respectively.

Dual efficiency enhancement by delayed fluorescence and dipole orientation in high-efficiency fluorescent organic light-emitting diodes

To explain the origin of extremely high efficiencies of deep-blue fluorescent organic light-emitting diodes(OLEDs) with anisotropic-shapedanthracene derivatives, the enhancements of singlet-exciton generation efficiency and outcoupling efficiency were investigated by transient electroluminescence measurement and variable angle spectroscopic ellipsometry, respectively. Both the delayed fluorescence from singlet excitons generated via triplet-triplet annihilation and the outcoupling enhancement by dipole orientation of emitters were found to contribute to the high external quantum efficiencies of the devices. This dual efficiency enhancement is important for understanding and further improving high-performance fluorescent OLEDs.

The Origin of the Improved Efficiency and Stability of Triphenylamine-Substituted Anthracene Derivatives for OLEDs: A Theoretical Investigation†

Herein, we describe the molecular electronic structure, optical, and charge-transport properties of anthracene derivatives computationally using density functional theory to understand the factors responsible for the improved efficiency and stability of organic light-emitting diodes (OLEDs) with triphenylamine (TPA)-substituted anthracene derivatives. The high performance of OLEDs with TPA-substituted anthracene is revealed to derive from three original features in comparison with aryl-substituted anthracene derivatives: 1) the HOMO and LUMO are localized separately on TPA and anthracene moieties, respectively, which leads to better stability of the OLEDs due to the more stable cation of TPA under a hole majority-carrier environment; 2) the more balanceable hole and electron transport together with the easier hole injection leads to a larger rate of hole-electron recombination, which corresponds to the higher electroluminescence efficiency; and 3) the increasing reorganization energy for both hole and electron transport and the higher HOMO energy level provide a stable potential well for hole trapping, and then trapped holes induce a built-in electric field to prompt the balance of charge-carrier injection.

Synthesis and Hole-Transporting Properties of Phenyl-Carbazyl Derivatives

We synthesized new hole-transporting material, 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole(P-Cvz-2), 9,9′-diphenyl-6-(9-phenyl-9H-carbazol-3-yl)-9H,9′H-3,3′-bicarbazole(P-Cvz-3), 6-(9,9′-diphenyl-9H,9′H-3,3′-bicarbazol-6-yl)-9,9′-diphenyl-9H,9′H-3,3′-bicarbazole(P-Cvz-4A) and 9-phenyl-6-(9-phenyl-9H-3,9′-bicarbazol-6-yl)-9H-3,9′-bicarbazole(P-Cvz-4B). EL luminance efficiencies of P-Cvz-2, P-Cvz-3, P-Cvz-4A and P-Cvz-4B devices were found to be 5.24, 5.64, 4.86 and 4.94 cd/A at 50 mA/cm2, respectively, when synthesized materials are using as a HTL material. The luminance efficiency of P-Cvz-3 is 20% higher than that of NPB, a commercialized HTL material used as a reference in this study.

New Zn Complex Derivatives for Red OLEDs Host Materials

New two metal complexes, di-(Phenyl dipyrrylmethene)zinc (Zn(PPM)2) and di-(Pentafluorophenyl dipyrrylmethene)zinc (Zn(PFPPM)2) as a host material instead of Alq3 were synthesized. To evaluate electroluminescent properties, multi-layered organic light-emitting devices were fabricated by using 4-(dicyanomethylene)-2-tert-buthyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as a dopant and Alq3 as an electron transporting layer. Alq3 and Zn(PPM)2 host EL devices exhibited DCJTB emission peak at around 617 nm due to energy transfer from Alq3 and Zn(PPM)2 to DCJTB. However Zn(PFPPM)2 host device shows no DCJTB emission peak because Zn(PFPPM)2 device emit EL light of 563 and 700 nm. The Zn(PPM)2 device showed same luminance efficiency as Alq3 device, but showed better power efficiency of 1.2 times than Alq3 device.

New Fluoranthene Derivatives in Electroluminescence

7,8,10-triphenylfluoranthene [TPF], 7,10-diphenyl-8-(1-naphthyl) fluoranthene[DPNF], 7,10-diphenyl-8-(9-phenanthrenyl)fluoranthene[DPPF] were synthesized by using the Knoevenagel condensation and Diels–Alder addition. PL maximum values of TPF, DPNF and DPPF are 458 nm, 460 nm and 461 nm, respectively. TPF showed sky-blue CIE value of (0.192, 0.269) and 3.27cd/A at 10 mA/cm2. DPNF also showed sky-blue CIE value of (0.189, 0.262) and 3.24 cd/A at 10 mA/cm2. DPPF showed much better operating voltage, luminance and power efficiency of 3.96 cd/A and 2.11 lm/W although it had worse C.I.E. value than TPF.

P‐182: New Deep‐Blue EML Materials Based on Fully Substituted Ethylene and Anthracene Derivatives

New blue fluorescent compounds containing tetra-substituted ethylene moieties have been designed and synthesized. By fabricating multilayered non-doped OLED devices using these new blue materials, we achieved luminance efficiencies of 4.00 lm/W (10.33 cd/A at 8.1 V) for BPBAPE[CB-104] and 1.82 lm/W (3.93 cd/A at 6.8 V) for BTPPA [CB-105B] at 10 mA/cm2. The BPBAPE [CB-104] and BTPPA [CB-105B] devices exhibited sky blue emission (0.195, 0.303) and deep blue emission (0.159, 0.135) at 10mA/cm2 respectively. We also synthesized new kinds of blue materials such as CB-201, 202, and 203. CB-203 device showed 3.11cd/A of current efficiency and (0.148, 0.088) CIE value.

New Blue and Bluish Green Electroluminescent Properties of Fully Substituted Ethylene Moieties

We synthesized 1,1,2,2-tetrakis(4′-tert-butylbiphenyl)ethene[TBBPE] and 1,2-di(4′-tert-butyl-phenyl)-1,2-bis(4′-tert-butyl-biphenyl) ethene [BPBBPE]. TBBPE and BPBBPE film showed PL maximum value of 489 nm and 511 nm due to longer conjugation length of TBBPE. In EL device, TBBPE device showed slightly better I-V curve than BPBBPEs because there is lower energy barrier between Alq3 and TBBPEs LUMO levels. We observed luminance efficiency of 1.87 cd/A with blue color as (0.177, 0.249) CIE value in BPBBPE emitting system and 4.44 cd/A with (0.240, 0.435) CIE value in TBBPE device.

Synthesis and Luminescent Properties of Poly(alkylated indenopyrazine) and Its Copolymer Containing an Alkylated Spirofluorene Moiety

We have synthesized new alkylated indenopyrazine homopolymer and its copolymer having an alkylated spirofluorene moiety. Poly(6,6,12,12-(Tetra-2-ethylhexyl)-6,12-Dihydrodiindeno[1,2-b:1,2-e]pyrazine-2,8-diyl) [PEHIP] and Poly(6,6,12,12-(tetra-2-ethylhexyl)-6,12-dihydrodiindeno[1,2-b:1,2-e]pyrazine-co-2′,3′,6′,7′-tertrakis-octyloxy-9-spirofluorene) [PEHIPSF] were polymerized by using Yamamoto reaction. PEHIP and PEHIPSF showed the PL maximum values of 470 nm and 454 nm in PL spectra. The PEHIPSF was fabricated into an EL device and it exhibited the EL maximum value of 463 nm.