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13 Aug 2001

Volume 79, Issue 7, pp. 895-1063

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High-efficiency yellow double-doped organic light-emitting devices based on phosphor-sensitized fluorescence

Brian W. D’Andrade, Marc A. Baldo, Chihaya Adachi, Jason Brooks, Mark E. Thompson, and Stephen R. Forrest

Appl. Phys. Lett. 79, 1045 (2001); http://dx.doi.org/10.1063/1.1388159 (3 pages) | Cited 93 times

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We demonstrate high-efficiency yellow organic light-emitting devices (OLEDs) employing [2-methyl-6-[2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2) as a fluorescent lumophore, with a green electrophospho- rescent sensitizer, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] co-doped into a 4,4′-N,N′dicarbazole-biphenyl host. The devices exhibit peak external fluorescent quantum and power efficiencies of 9%±1% (25 cd/A) and 17±2 lm/W at 0.01 mA/cm2, respectively. At 10 mA/cm2, the efficiencies are 4.1%±0.5% (11 cd/A) and 3.1±0.3 lm/W. We show that this exceptionally high performance for a fluorescent dye is due to the ∼100% efficient transfer of both singlet and triplet excited states in the doubly doped host to the fluorescent material using Ir(ppy)3 as a sensitizing agent. These results suggest that 100% internal quantum efficiency fluorescent OLEDs employing this sensitization process are within reach. © 2001 American Institute of Physics.
Show PACS
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
71.35.-y Excitons and related phenomena
85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds
78.60.Fi Electroluminescence

High-efficiency red electroluminescence from a narrow recombination zone confined by an organic double heterostructure

Z. Y. Xie, L. S. Hung, and S. T. Lee

Appl. Phys. Lett. 79, 1048 (2001); http://dx.doi.org/10.1063/1.1390479 (3 pages) | Cited 88 times

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Red light-emitting diodes (LEDs) with both a conventional bilayer structure and a double heterostructure (DH) have been investigated. In these LEDs, N,N′-bis-(1-naphthl)-diphenyl-1, 1′-biphenyl-4,4′-diamine (NPB), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and tris(8-quinolinolato) aluminum (Alq3) were used as hole-transporting, hole-blocking, and electron-transporting layers, respectively. The bilayer and DH LEDs had a configuration of ITO/NPB/Alq3:red dopant/Alq3/MgAg and ITO/NPB/Alq3:red dopant/BCP/Alq3/MgAg, respectively. Three kinds of red fluorescent dyes—nile red, DCJTB, and DCM—were used as dopants. Compared with the bilayer structures, the luminance efficiencies of the DH LEDs were found to increase as much as 100%. We attribute the efficiency enhancement to the formation of a narrow recombination zone, in which both charge carriers and excitons were confined. High charge concentrations in the emissive layer resulted in efficient collision capture in the electron–hole recombination process. Exciton confinement led to improved energy transfer. The two factors were simultaneously operating and consequently benefitted from efficiency enhancement. © 2001 American Institute of Physics.
Show PACS
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.Gg Exciton-mediated interactions

Fatigue-free lead zirconate titanate-based capacitors for nonvolatile memories

S. R. Shannigrahi and Hyun M. Jang

Appl. Phys. Lett. 79, 1051 (2001); http://dx.doi.org/10.1063/1.1392970 (3 pages) | Cited 37 times

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The development of lead zirconate titanate (PZT)-based capacitors has been a long time goal of ferroelectric random access memories (FRAM). However, PZT-based perovskites with common platinum (Pt) electrodes have suffered from a significant reduction of the remanent polarization (Pr) after a certain number of read/write cycles (electrical fatigue). We now report the development of fatigue-free lanthanum-modified PZT capacitors using common Pt electrodes. The capacitors fabricated at 580 °C by applying a PZT seed layer exhibited fatigue-free behavior up to 6.5×1010 switching cycles, a quite stable charge retention profile with time, and comparatively high Pr values, all of which assure their suitability for practical FRAM applications. © 2001 American Institute of Physics.
Show PACS
84.32.Tt Capacitors
85.50.Gk Non-volatile ferroelectric memories
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
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