BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematically cross-sectional diagram illustrating an inverted organic light emitting structure in accordance with a preferred embodiment of the present invention.
FIG. 1B is a schematically cross-sectional diagram illustrating an organic light emitting structure in accordance with a preferred embodiment of the present invention.
FIG. 2A and FIG. 2B are diagrams illustrating the relation of luminance and current density vs. voltage for the devices with or without an electron-injection layer in accordance with the present invention.
FIG. 3 is a diagram illustrating the structures in FIGS. 2A and 2B with different degraded luminance in accordance with the present invention.
FIG. 4 is a diagram illustrating the structures in FIGS. 2A and 2B with different raised voltages in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, a “layer” of a given material includes a region of that material whose thickness is small compared to both its length and width. Examples of layers include sheets, foils, films, laminations, coatings, and so forth. As used herein a layer need not be planar, but can be bent, folded or otherwise contoured, for example, to at least partially envelop another component. As used herein a layer can also include multiple sub-layers. A layer can also consist of a collection of discrete portions.
Shown in FIG. 1A, an inverted organic light emitting diode 10 includes a substrate 102, a cathode 104, an electron-transport layer 106, a hole-transport layer 108 and an anode 200. In one embodiment, the substrate 102 may be a glass substrate, a plastic substrate or a flexible substrate. Next, the cathode 104 on the substrate 102 may be transparent, opaque, reflective single layer of composition, such as indium tin oxide (ITO), indium zinc oxide (IZO), Au, Ag, Pt, Ni, Cr, Mo, Cu, Al, Ca or the combination thereof. The anode 200 may be also transparent, opaque, reflective single layer of composition, such as Au, Pt, Li, Mg, Ca, Al or Ag, or ITO, IZO, LiF/Au, Be/Al or Mg/Al.
Next, the electron-transport layer 106 may be capable of transporting electron, such as n-type dopants in an organic material to form an n-type doped layer. On the other hand, the hole-transport layer 108 may be capable of transporting holes, such as p-type dopants in another organic material to form a p-type doped layer. Alternatively, the electron-transport layer 106 may be made of electron-injection, electron-transport, hole-blocking or emitting material or composition, such as Alq3 (tris-(8-hydroxyquinoline aluminum), fluorescence material, or phosphorescence material. The hole-transport layer 108 may be made of hole-injection, hole-transport, or electron-blocking material or composition. According to the spirit of the present invention, alkaline-earth metal material, such as Be, Ma, Ca, Sr, Ba, Ra, is added between the cathode 104 and the electron-transport layer 106, whose low work function may enhance the stability of a device under operation. In a preferred embodiment, an electron-injection layer 202 is formed between the cathode 104 and the electron-transport layer 106 of n-type doped layer. Accordingly, the electron-transport layer 106 and the hole-transport layer 108 are combined to form an active layer for injecting, transporting electron/hole, or emitting or combination of aforementioned function.
Shown in FIG. 1B, an organic light emitting diode 15 includes a substrate 152, an anode 250, a hole-transport layer 158, an electron-transport layer 156 and a cathode 154. A hole-injection layer 252 is positioned between the electron-transport layer 156 and the cathode 154. The layers in the organic light emitting diode 15 are similar to the ones of the inverted organic light emitting diode 10 in FIG. 1A and not illustrated herein. Accordingly, the hole-injection layer 252 may be applied to various organic light emitting diodes.
Referred to FIG. 2A and FIG. 2B, FIG. 2A illustrates the relation of voltage versus luminance and current intensity for the device of ITO/Cs2CO3:Bphen/Alq3/NPB/WO3/Al, and FIG. 2B illustrates the relation of voltage versus luminance and current intensity for the device of ITO/Mg/Cs2CO3:Bphen/Alq3/NPB/WO3/Al, in which Bphen is 4,7-diphenyl-1,10-phenanthroline, and NPB is N,N′-di(naphthalene-1-yl)-N, N′-diphthalbenzidine. With the comparison of FIG. 2A and FIG. 2B, the luminance an electricity of the device is not influenced in the existence of the electron-injection layer 202. Referred to FIG. 3, the addition of the electron-injection layer 202 may reduce the degraded luminance of the device. Referred to FIG. 4, the addition of the electron-injection layer 202 may enhance the stability of the device in operation.
Accordingly, an organic light emitting structure includes a substrate; a cathode and an anode corresponding each other on the substrate; a hole-transport layer between the cathode and the anode; an electron-transport layer between the hole-transport layer and the cathode; and an electron-injection layer between the cathode and the electron-transport layer. The electron-injection layer includes an alkaline-earth metal material.
Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.
Patent Application
20080042556
