Electroluminescence efficiency

The composition of the copolymer determines its electroluminescence efficiency. Optimal efficiency (0.3%) was achieved in system 34 when the feed ratio of monomer 4 to monomer 34 was 9 1. This represents a 30-fold improvement in luminescence efficiency relative to PPV in the same device configuration (AlALOj/polymer/Al) 58, 62. Copolymer 33 has found uses as waveguides and... 

P.K.H. Ho, M. Granstrom, R.H. Friend, and N.C. Greenham, Ultrathin self-assembled layers at the ITO interface to control charge injection and electroluminescence efficiency in polymer light-emitting diodes, Adv. Mater., 10 769-774, 1998. 

Fig. 15. The electroluminescent efficiency versus number of monolayers or substituted phthalocyanine for the device shown in Fig, 14...

The /3-diketonate [Nd(dbm)3bath] (see figs. 41 and 117) has a photoluminescence quantum efficiency of 0.33% in dmso-7r, solution at a 1 mM concentration. It has been introduced as the active 20-nm thick layer into an OLED having an ITO electrode with a sheet resistance of 40 il cm-2, TPD as hole transporting layer with a thickness of 40 nm, and bathocuproine (BCP) (40 nm) as the electron injection and transporting layer (see fig. 117). The electroluminescence spectrum is identical to the photoluminescence emission the luminescence intensity at 1.07 pm versus current density curve deviates from linearity from approximately 10 mA cm-2 on, due to triplet-triplet annihilation. Near-IR electroluminescent efficiency <2el has been determined by comparison with [Eu(dbm)3bath] for which the total photoluminescence quantum yield in dmso-tig at a concentration of 1 mM is Dpi, = 6% upon ligand excitation, while its external electroluminescence efficiency is 0.14% (3.2 cdm-2 at 1 mAcm-2) ... 

A single-layer OLED with [Er(acac)3phen] doped into a 80-nm thick film of PVK (see fig. 117) prepared by spin-coating and deposited on an ITO electrode, and with a 100-nm lithium-doped (0.1%) aluminum cathode has also been tested and shows an onset voltage of about 12 V for electroluminescence (Sun et al., 2000). [Er(dbm)3bath] has a photoluminescence quantum yield of 0.007% in dmso-7fl at 1 mM concentration the OLED based on this compound and similar to the one described above for Ndm has a NIR external electroluminescence efficiency of 1 x 10-6 (Kawamura et al., 2001). 

TAZ) shown in Figure 11.5, is often added between the layer of luminescent material and the electron-transport layer or the metallic electrode, to balance the charge injection and transport rates. Then the recombination of electrons and holes is confined to the emitting layer and consequently a high electroluminescent efficiency can be obtained. Some hole-injection materials are shown in Figure 11.6. 

Figure 4.14. Top (not to scale) An Au-LB film-GaP structure. The semiconductor-organic film interface is common to all four devices. Bottom A plot of the electroluminescent efficiency versus the number of monolayers of substituted phthalocyanine (see reference 55).

Nuese C. J., Tietjen J. J., Gannon J. J., Gossenberger H. F. Optimization of electroluminescent efficiencies for vapor-grown GaAsP diodes J. Electrochem Soc. Solid State Science 116, 248 (1969). 

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