Organic electroluminescent element and organic electroluminescent display

An organic EL element including an anode and a cathode opposing to each other, and at least a luminescent layer, positioned therebetween, including an aromatic amine derivative designated by a general formula &lsqb;1&rsqb; and a dibenzo-&lcub;&lsqb;f,f′&rsqb;-4,4′,7,7′-tetraphenyl&rcub;-diindeno-&lsqb;1,2,3-cd:1′,2′,3′-lm&rsqb; perylene derivative designated by a general formula &lsqb;2&rsqb;. The organic EL element has the excellent luminescent efficiency, brightness and chromaticity. 1

PREFERRED EMBODIMENTS OF THE INVENTION Now, the present invention is more specifically described with reference to accompanying drawings. Embodiment 1 As shown in FIG. 2 , an organic EL element of the present Embodiment includes a transparent anode 12 made of ITO (indium-tin oxide), a hole injecting layer. 13 , a hole transporting layer 14 , a luminescent layer 15 , an electron transporting layer 16 and a cathode 17 sequentially stacked on a glass substrate 11 . The hole injecting layer 13 has an excellent resistance to higher temperature for improving the thermal stability of the organic EL element. The luminescent layer 15 includes an aromatic amine derivative designated by a general formula &lsqb;1&rsqb; and a dibenzo-&lcub;&lsqb;f,f′&rsqb;-4,4′,7,7′-tetraphenyl&rcub;-diindeno-&lsqb;1,2,3-cd:1′,2′,3′-lm&rsqb; perylene derivative designated by a general formula &lsqb;2&rsqb; mixed with each other. The doping amount of the perylene derivative is controlled by a vapor deposition rate, and is preferably between 1 and 10% with respect to the aromatic amine derivative for suppressing the concentration quenching of pigment itself. The luminescent layer 15 may be formed by stacked two layers each containing the above perylene derivative having the different doping amounts. The compound designated by the general formula &lsqb;1&rsqb; can be synthesized in accordance with a known process, for example, by reacting an anthracene derivative or an anthraquinone derivative with a substituted or non-substituted amine derivative under existence of potassium carbonate, sodium carbonate, potassium hydroxide or sodium hydroxide in a solvent such as benzene, toluene and xylene. A catalyst employable therefor includes copper powder, cuprous chloride, tin, stannous chloride and pyridine. The compound designated by the general formula &lsqb;2&rsqb; can be synthesized in accordance with a known process, for example, by reacting a benzo&lsqb;k&rsqb;fluoran derivative under existence of aluminum chloride/sodium chloride, cobalt fluoride or thallium trifluoroacetate. The use of the organic metal complex designated by the general formula &lsqb;3&rsqb; having a higher ionization potential in the electron transporting layer 16 increases the ionization potential of the electron transporting layer larger than that of the luminescent layer. As a result, the hole blocking ability of the electron transporting layer 16 is improved for preventing the leakage of the hole into the electron transporting layer, thereby further elevating the recombination yield between the hole and the electron in the luminescent layer. The electron transporting material designated by the general formula &lsqb;3&rsqb; can also be synthesized in accordance with a known process, for example, by reacting a gallium compound with a compound having a part specified in a bracket of the general formula &lsqb;3&rsqb; and a ligand residue of “L”. That is, alkyl gallium, gallium alkoxide, gallium halogenide, gallium nitride or gallium oxide is reacted with a compound having, as the ligands in the brackets of the general formula &lsqb;3&rsqb;, two ligands of a quinoline residue such as 8-hydroxyquinoline and 2-methyl-8-hydroxyquinoline and one ligand (for the “L” ligand) of a halogen atom, substituted or non-substituted alkoxy group, aryloxy group or alkyl group in a solvent such as methanol, ethanol-benzene, toluene and tetrahydrofuran. 
 EXAMPLE 1 In an organic EL element of Example 1, an aromatic amine derivative designated by a compound &lsqb;1&rsqb; shown below was doped with dibenzotetraphenyl-peryfurantene designated by a compound &lsqb;2&rsqb; shown below in a vapor deposition rate of 2.5% to prepare a luminescent layer. An electron transporting layer was prepared by using a gallium metal complex designated by a compound &lsqb;3&rsqb; shown below. As a result, red light emission could be obtained having a current efficiency of 6 cd/A or more (up to 1,000 cd/m 2 ) and a maximum brightness of 38,000 cd/m 2 each of which was at the practical level. The chromaticity stability of the organic EL element was excellent, and the change of the color shade due to the applied voltage was small. 9 A graph of FIG. 3 shows the relations between the applied voltage (V, abscissa) and the coordinates of “X” and “Y” of the CIE chromaticity (ordinate) of the organic EL element of the Example 1 and of the conventional organic EL element. As shown therein, the change of the color shade in the chromaticity “X” was suppressed when the applied voltage was increased, compared with the conventional EL element. As shown in a graph of FIG. 4 in which the abscissa indicates the driving time (Hr) and the ordinate indicates the relative brightness, the life characteristic of the organic EL element of the Example 1 at the constant current driving of 5 mA/cm 2 was improved. The organic EL element of the Example 1 maintained 90% or more of the initial brightness even after the lapse of 3,000 hours. Further, dark spots (non-emitting section) were seldom observed. 
 COMPARATIVE EXAMPLE 1 Procedures similar to those used in the Example 1 were conducted except that the aromatic amine derivative of the compound &lsqb;1&rsqb; was added with the red light emitting material at 1% in weight to prepare a luminescent layer (refer to JP-A-10(1998)-72581). Similar results to those of Example 1 were obtained; that is, the maximum emitting efficiency of 41 m/W and the maximum brightness of 38,000 cd/m 2 . However, the life time of the organic EL element of Comparative Example 1 was short. The stable emission at 3 mA/cm 2 continued for only about 1000 hours, and the practical use thereof seemed difficult. 
 COMPARATIVE EXAMPLE 2 Procedures similar to the procedures used in Example 1 were conducted except that the compound &lsqb;2&rsqb; was used alone as luminescent layer (refer to JP-A-10(1998)-330295). Similar results to those of Example 1 were obtained, that is, red light emission having brightness of 1,250 cd/m 2 was obtained by applying a direct voltage of 15 V. In addition, another luminescent layer was prepared by doping 4,4′-bis&lsqb;N-phenyl-N-(1″-naphtyl)amino&rsqb;biphenyl with the compound &lsqb;2&rsqb; at 5% in weight. In the organic EL element using the luminescent layer, red light emission having brightness of 2,650 cd/m 2 was obtained by applying a direct voltage of 15 V. However, the brightness of these organic EL elements was much lower than that of Example 1, and the practical use thereof seemed difficult. 
 COMPARATIVE EXAMPLE 3 Procedures similar to the procedures used in Example 1 were conducted except that the compound &lsqb;4&rsqb; was added with the compound &lsqb;2&rsqb; at 8% in weight to prepare a luminescent layer (refer to JP-A-11(1999)-233261). Red light emission having brightness of about 52 cd/m 2 was obtained by applying a voltage of 9.7 V. However, the brightness of the organic EL element after the stable and successive operation at the constant current for 2,700 hours was reduced as low as to 30 cd/m 2 . The brightness of the organic EL element was much lower than that of Example 1 and the period of life was short. Accordingly, the practical use thereof seemed difficult. 
 COMPARATIVE EXAMPLE 4 Procedures similar to the procedures used in Example 1 were conducted except that the gallium metal complex designated by the compound &lsqb;3&rsqb; was used as an electron injecting layer (refer to JP-A-10(1998)-88121 in which the gallium metal complex &lsqb;3&rsqb; is used as a luminescent layer or an electron injecting layer). Bluish green light emission having brightness of 15,000 cd/m 2 and a luminescent efficiency of 2.351 m/W was obtained by applying a direct voltage of 8 V. The brightness and the luminescent efficiency were insufficient, and the brightness, the luminescent efficiency, the period of life and the chromaticity stability could be improved by using the metal complex of the general formula &lsqb;3&rsqb; as the electron transporting layer of the red EL element. 
 COMPARATIVE EXAMPLE 5 Procedures similar to the procedures used in Example 1 were conducted except that a gallium metal complex &lsqb;tris-(2-methyl-8-quinolinolate) gallium&rsqb; and a perylene derivative were used as an electron injecting layer and a luminescent layer, respectively (refer to Japanese Patent No.2828821). Yellow light emission having brightness of 850 cd/m 2 was obtained by applying a direct voltage of 8 V. The period of life of light emission was 4 days. The brightness thereof was much lower than that of Example 1, and the period of life was quite short. 
 EXAMPLE 2 Procedures similar to the procedures used in Example 1 were conducted except that the tris-(8-quinolinolate) aluminum designated by the general formula &lsqb;4&rsqb; was used as an electron transporting layer to fabricate an organic EL element. When a direct voltage was applied between a cathode and an anode of the EL element, red light emission could be obtained having a current efficiency of 6 cd/A or more (up to 1,000 cd/m 2 ) and a maximum brightness of 38,000 cd/m 2 . 
 EXAMPLE 3 Procedures similar to the procedures used in Example 1 were conducted except that the perylene derivative designated by the compound &lsqb;5&rsqb; was used, as a luminescent layer, in place of the aromatic amine derivative designated by the compound &lsqb;1&rsqb;. When a direct voltage was applied between a cathode and an anode of the EL element, red light emission could be obtained having a current efficiency of 5 cd/A or more (up to 1,000 cd/m 2 ) and a maximum brightness of 33,000 cd/m 2 . Since the above embodiments are described only for examples, the present invention is not limited to the above embodiments and various modifications or alternations can be easily made therefrom by those skilled in the art without departing from the scope of the present invention.