Abstract:
An organic electroluminescent device. The device has an organic electroluminescent light recovery layer consisting of dielectric material and nanoscale metal particles or organic material and nanoscale metal particles. The membrane of the organic electroluminescent light recovery layer cross couples with surface plasmon resonance and recovers light trapped in the device, enhancing the light emission efficiency of the organic electroluminescent device.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 092101786 filed in TAIWAN, R.O.C. on Jan. 28, 2003, which is(are) herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic electroluminescent device, and more particularly to an organic electroluminescent device solving low external quantum efficiency problems of surface plasmon resonance. 
     2. Description of the Related Art 
     Organic electroluminescent devices are also known as organic light emitting diodes (OLED). The OLED luminescent principle applies a voltage to organic molecular material or polymer material, and the device luminesces. Due to OLED&#39;s self emission characteristics, it can form a dot matrix type display with light weight, slim profile, high contrast, low power consumption, high resolution, fast response time, no need for backlighting, and full viewing angle. Possible display parameters range from 4 mm microdisplay to 100 inch outdoor billboards, making it a preferred type of flat panel display (FPD). If the OLED luminescent efficiency is over 100 Lm/W, it can replace conventional lighting. 
     In organic electroluminescence, electrons are propelled from a cathode layer and holes from an anode layer, and the applied electric field induces a potential difference, such that the electrons and holes move and centralize in a thin film layer, resulting in recombination. The energy of this recombination excites the luminescent layer moleculars to higher energy levels and unstable excited states, and when the energy is released, they return to lower energy levels and stable ground states. OLED luminescent efficiency depends on the internal and external quantum efficiency of the device. Internal quantum efficiency is the internal efficiency of converting electricity to light. After exciting the organic moleculars, a quarter of the excited electrons assume a single-state asymmetric spin configuration, releasing energy in the form of fluorescence. The other three-quarters assume triple-state symmetric spin configuration, and release energy in the form of phosphorescence. The triple state excited electrons also release energy in the form of phosphorescence in organometallic compounds. Therefore, OLED internal quantum efficiency depends on the excitation mechanism, and on the fluorescence or phosphorescence of luminescent material chosen. 
     OLED external quantum efficiency is the ratio of luminescent output from device to the luminescent from the organic layer. In a typical OLED, not all light from the organic layer can pass through the device, with more than 40% of OLED light lost to surface plasmon resonance. In addition, the organic material and the glass substrate have a higher refraction index than air, so some light is limited in the device due to total reflection, some scattering outward from the device side. Around 80% of light is dissipated in the device, making conventional OLED external quantum efficiency below 20%. In the unused device light can be recovered, the OLED external quantum efficiency improves. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an OLED comprising a nanostructured organic electroluminescent recovery layer, with dielectric material and nanoscale metal particles. The surface plasmon resonance of OLED device is cross-coupled to the surface plasmon resonance of nanostructured film. Trapped device light is thus recovered, increasing external quantum efficiency and luminescent efficiency. 
     To achieve the above-mentioned object, the present invention provides an OLED with nanostructured organic electroluminescent recovery layer, having at least one layer formed with dielectric material and nanoscale metal particles, or with organic material and nanoscale metal particles. 
     The OLED with the nanostructured organic electroluminescent recovery layer of the present invention comprises at least a substrate with a first electrode formed thereon, an organic luminescent layer on the first electrode, a second electrode on the organic luminescent layer and at least one nanostructured organic electroluminescent recovery layer. The organic luminescent layer is between the first electrode and the second electrode. The nanostructured organic electroluminescent recovery layer is between the substrate and the first electrode, the first electrode and the organic luminescent layer, the organic luminescent layer and the second electrode, or on the second electrode. 
     If a second nanostructured organic electroluminescent recovery layer is present, it is disposed between the organic luminescent layer and the second electrode or on the second electrode. 
     The OLED with the nanostructured organic electroluminescent recovery layer of the present invention is substrate side emitting, top emitting (the second electrode side) or two-side emitting. 
     The present invention&#39;s nanostructured organic electroluminescent recovery layer for the OLED is formed with dielectric material and nanoscale metal particles, or organic material and nanoscale metal particles. The dielectric or organic material and the nanoscale metal particles are formed at the same time using the same or different methods, and the nanoscale metal particles are doped into the dielectric or organic material. The dielectric material comprises silicon oxide, aluminum oxide, magnesium oxide, silicon nitride, aluminum nitride or magnesium fluoride. The organic material is molecular or polymer. The nanoscale metal particles comprise Au, Ag, Ge, Se, Sn, Sb, te, Ga or combinations thereof. 
     The substrate of the present invention is transparent or opaque glass or plastic. The plastic substrate is polyethyleneterephthalate, polyester, polycarbonate, polyimide, Arton, polyacrylate or polystyrene. 
     The OLED organic luminescent layer of the present invention comprises molecular organic luminescent material and polymer organic luminescent material. The organic luminescent layer is formed with a single organic luminescent layer or stacked organic luminescent layers, and the organic luminescent layer is fluorescent or phosphorescent luminescent material. 
     The first electrode and the second electrode are transparent, metal, or complex. The transparent electrode comprises ITO, IZO, AZO or ZnO, the metal electrode Li, Mg, Ca, Al, Ag, In, Au, Ni, Pt, or alloys thereof, and the complex electrode Li, Mg, Ca, Al, Ag, In, Au, Ni, Pt, ITO, IZO, AZO or ZnO. 
     According to OLED of the present invention, the nanostructured organic electroluminescent recovery layer is formed with nanoscale metal particles, wherein the surface plasmon resonance of OLED device is cross-coupled to the surface plasmon resonance of nanostructured film. Trapped light is thus recovered. A nanostructured organic electroluminescent recovery layer on the device thereby improves the OLED luminescent efficiency. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, reference is made to a detailed description to be read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross-section showing the OLED according to the first embodiment of the present invention; 
         FIG. 2  is a cross-section showing the OLED according to the second embodiment of the present invention; 
         FIG. 3  is a cross-section showing the OLED according to the third embodiment of the present invention; 
         FIG. 4  is a cross-section showing the OLED according to the fourth embodiment of the present invention; and 
         FIGS. 5–8  illustrate a cross-sectional view of the OLED according to the fifth embodiment of the present invention. 
     
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
     
         
         
           
               10 ,  20 ,  30 ,  40  and  50  OLED 
               110 ,  210 ,  310 ,  410  and  510  substrate 
               120 ,  220 ,  320  and  420  nanostrctured organic electroluminescent recovery layer 
               121 ,  221 ,  321 ,  421 ,  521  and  561  dielectric material 
               122 ,  222 ,  322 ,  422 ,  522  and  562  nanoscale metal particles 
               130 ,  230 ,  330 ,  430  and  530  first electrode 
               140 ,  240 ,  340 ,  440  and  540  organic luminescent layer 
               150 ,  250 ,  350 ,  450  and  550  second electrode 
               520  first nanostrctured organic electroluminescent recovery layer 
               560  second nanostrctured organic electroluminescent recovery layer. 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to understand the above and other objects, characteristics and advantages, six preferred embodiments of the present invention are now detailed described with reference to the attached figures. 
     The embodiments are designed to accommodate a wide range of possible device structures, enabling broader application of the inventive benefits. 
     The OLED of the present invention comprises at least a substrate, a first electrode, an organic luminescent layer, a second electrode, and a nanostructured organic electroluminescent recovery layer between the substrate and the first electrode (in the first embodiment), the first electrode and the organic luminescent layer (in the second embodiment), the organic luminescent layer and the second electrode (in the third embodiment), or on the second electrode (in the fourth embodiment). 
     First Embodiment 
     First, a substrate  110  is provided as  FIG. 1 , transparent or opaque, formed with glass or plastic (flexible) material. 
     Nanostructured organic electroluminescent recovery layer  120  is formed with dielectric or organic material  121  and nanoscale metal particles  122  on the substrate  121 . The dielectric or organic material  121  and the nanoscale metal particles  122  are formed at the same time using the same or different methods. The nanoscale metal particles  122  are doped into the dielectric or organic material  121 . The dielectric material for the nanostructured organic electroluminescent recovery layer is silicon oxide, aluminum oxide, magnesium oxide, silicon nitride, aluminum nitride or magnesium fluoride, and is formed by sputtering or plasmon enhanced chemical vapor deposition. The organic material for the nanostructured organic electroluminescent recovery layer is molecular or polymer organic material, formed by thermal evaporation, spin coating, ink jet, or screen printing. The nanoscale metal particles comprise Au, Ag, Al, Ge, Se, Sn, Sb, te, Ga or combinations thereof, formed by sputtering, electron beam evaporation, thermal evaporation, chemical vapor deposition, spin coating, ink jet, or screen printing. The ratio of the nanoscale metal particles doped in the dielectric or organic material to the combinations thereof is from 0.001 to 70 wt %. The ratio is determined by different deposition rate (power) between the dielectric material and the nanoscale metal particles or by different mixing ratio between the organic material and the nanoscale metal particles. 
     A first electrode  130  is formed on the nanostructured organic electroluminescent recovery layer  120 , between the substrate  110  and the first electrode  130 . The first electrode is transparent, metal, or complex. 
     An organic luminescent layer  140  is formed on the first electrode  130 , of molecular or polymer organic luminescent material. The organic luminescent layer  140  may comprise a single organic luminescent layer or stacked organic luminescent layers, so as the organic luminescent layer  240 ,  340 ,  440 , and  540  below. If the organic luminescent layer is molecular organic luminescent material, it can be formed by vacuum evaporation. If the organic luminescent layer is polymer organic luminescent material, it can be formed by spin coating, ink jet, or screen printing. 
     Finally, a second electrode  150  is formed on the organic luminescent layer  140 . The second electrode  150  is transparent, metal, or complex. The first electrode  130  and the second electrode  150  are formed by sputtering, electron beam evaporation, thermal evaporation, chemical vapor deposition or spray pyrolysis. 
     The OLED  10  of this embodiment is substrate side emitting, top emitting (the second electrode side) or two-side emitting. 
     Second Embodiment 
     The nanostructured organic electroluminescent recovery layer  220  of this embodiment differs only from the previous embodiment in that the nanostructured organic electroluminescent recovery layer  220  is between the first electrode  230  and the organic luminescent layer  240 . 
     Third Embodiment 
     The nanostructured organic electroluminescent recovery layer  320  of this embodiment differs only from the previous embodiments in that the nanostructured organic electroluminescent recovery layer  320  is between the organic luminescent layer  340  and the second electrode  350 . 
     Fourth Embodiment 
     The nanostructured organic electroluminescent recovery layer  420  of this embodiment differs only from the previous embodiments in that the nanostructured organic electroluminescent recovery layer  420  is on the second electrode  450 . 
     Fifth Embodiment 
     Referring to  FIGS. 5–8 , the nanostructure organic electroluminescent recovery layer  520  of this embodiment is the same as the first embodiment, with the OLED  50  further comprising a second nanostructured organic electroluminescent recovery layer  560  on the second electrode  550 . 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.