Organic electroluminescent device with light-transmissive optical compensation layer

An organic electroluminescent device, a flat panel display, and a portable electronic device using the same are disclosed. The organic electroluminescent device comprises a substrate, a transparent anode disposed on the substrate, a transparent cathode disposed opposite the transparent anode, and an organic light emitting layer interposed between the transparent anode and the transparent cathode. The organic electroluminescent device further comprises a first light transmissive optical compensation layer interposed between the transparent anode and the substrate, wherein the first light transmissive optical compensation layer is substantially made of a transition metal oxide.

BACKGROUND

The present invention relates to an organic electroluminescent device and, more particularly, to an organic electroluminescent device (OELD) having an optical compensation layer disposed on the transparent anode or the transparent cathode, a flat panel display and a portable electronic device using the same.

Organic electroluminescent devices can be fabricated without a backlight module as compared to liquid crystal displays thus simplifying the manufacturing process thereof. They have been rapidly developed and used in a variety of electronic devices, especially portable electronic devices such as mobile phones, game machines, video cameras, digital image reproduction apparatuses, DVD players, a personal digital assistants, or laptop computers. One of the main development issues of organic electroluminescent devices is to improve brightness, luminescence efficiency to reduce power consumption and extend product life.

U.S. Pat. No. 5,714,838 to Haight et al. discloses a top emission type organic electroluminescent device. A Calcium film or a Calcium alloy film is interposed between a transparent electrode (ZnS, GaN, ITO) and a light emitting layer in order to prevent diffusion of the compounds of the transparent electrode into the organic light emitting layer. However, the Ca film or the Ca alloy may reduce the luminescence efficiency of the organic electroluminescent device.

U.S. Pat. No. 6,831,407 to Cok discloses an organic light emitting diode. A topographical feature is located within the light emitting area to disrupt the waveguiding, whereby the light emitting efficiency of the light emitting area is improved. However, the process of the organic light emitting diode becomes relatively complex.

Therefore, there is a need to provide an organic electroluminescent device capable of improving the luminescence efficiency and simplifying the manufacturing process.

SUMMARY

An object of the present invention is to provide an organic electroluminescent device using at least one optical compensation layer to produce construction interference for improving luminescence efficiency and improve color shift at the viewing angle.

Another object of the present invention is to provide an organic electroluminescent device with improve the luminescence efficiency. The organic electroluminescent device includes an optical compensation layer, single or multiple a transition metal oxides, formed on a transparent anode and/or a transparent cathode by evaporation without a complex manufacturing process.

An organic electroluminescent device is provided. An embodiment of the organic electroluminescent device comprises a substrate, a transparent anode disposed on the substrate, a transparent cathode disposed opposite the transparent anode, and an organic light emitting layer interposed between the transparent anode and the transparent cathode. The organic electroluminescent device further comprises a first light transmissive optical compensation layer interposed between the transparent anode and the substrate, wherein the first light transmissive optical compensation layer is substantially made of a transition metal oxide.

The organic electroluminescent device may further comprise a second light transmissive optical compensation layer disposed on the transparent cathode, wherein the second light transmissive optical compensation layer is substantially made of a transition metal oxide.

A flat panel display and a portable electronic device using the same are also disclosed.

DETAILED DESCRIPTION

FIG. 1illustrates a first embodiment of the organic electroluminescent device10. The organic electroluminescent device10includes a substrate100, a transparent anode104and a transparent cathode108disposed opposite the transparent anode104. The substrate100may comprises a glass material, quartz, or a plastic material. The organic electroluminescent device10further comprises an organic light emitting layer106interposed between and directly contacting the transparent anode104and the transparent cathode108. The organic electroluminescent device10further includes a first light transmissive optical compensation layer102and a second light transmissive optical compensation layer110disposed on the transparent cathode108. The first light transmissive optical compensation layer102is interposed between the substrate100and the transparent anode104. The first light transmissive optical compensation layer102may comprise a transition metal oxide such as TiO2, WO3, Ta2O3, V2O5, ZnO, ZrO, CeO2, Nb2O5, Gd2O3, Cr2O3, NiO, Bi2O3, SmO, Nd2O5, or the combinations thereof. The thickness of the first light transmissive optical compensation layer102is substantially less than about 10,000 Å, and preferably ranges from about 500 Å to about 1000 Å. The first light transmissive optical compensation layer102may have a complex index of refraction N=n−ik, where n is an index of refraction substantially less than or equal to about 3.5, k is an extinction coefficient substantially less than or equal to about 0.2 at a wavelength of about 380 nm to about 780 nm and i is an imaginary number. The thickness, material, or optical property of the second light transmissive optical compensation layer110is substantially identically as that of the first light transmissive optical compensation layer102.

The manufacturing process of the organic electroluminescent device10is described in the following. The first light transmissive optical compensation layer102, the transparent anode104, the organic light emitting layer106, the transparent cathode108, and the second light transmissive optical compensation layer110are sequentially formed on the substrate100. Note that both the first and the second light transmissive optical compensation layers102, and110are preferably formed by E-beam deposition, thermal evaporation, molecular beam epitaxy, vapor phase epitaxy, or metal organic chemical vapor deposition.

In some embodiments of the present invention, the first light transmissive optical compensation layer102disposed on the substrate100includes a bottom optical compensation layer102aand a top optical compensation layer102bas shown inFIG. 4. Alternately, the first light transmissive optical compensation layer102is a single layer as shown inFIG. 5. The first light transmissive optical compensation layer102of the present invention is not limited to one or two layers, it may have more than two layers. Moreover, the thickness of the top optical compensation layer102band the thickness of the bottom optical compensation layer102ranges from about 500 Å to about 1,000 Å, respectively, preferably ranges from about 700 Å to about 900 Å. The second light transmissive optical compensation layer110may also be a single layer, a double layer, or multiple layers.

The transparent anode104may comprise a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The thickness of the transparent anode104ranges from about 700 Å to about 800 Å. The transparent cathode108may comprise a transparent conductive material such as about 700 Å to about 800 Å of indium tin oxide (ITO) or indium zinc oxide (IZO) or about 50 Å of aluminum.

The organic light emitting layer106may comprise Tris (8-hydroxyquinoline) aluminum III (Alq3). When a forward bias voltage generated by a DC power supply is applied to the organic electroluminescent device10, electrons and holes are injected into the organic light emitting layer106through the transparent cathode108and the transparent anode104respectively. Therefore, the chemical compounds of the organic light emitting layer106are excited by energy thereby producing fluorescence or phosphorescence and radiating toward the emission direction A (the direction of an arrow as shown inFIG. 1) passing through the transparent anode104, the first light transmissive optical compensation layer102and substrate100. On the other hand, fluorescence or phosphorescence generated from the organic light emitting layer106also radiates toward emission direction B (the direction of an arrow as shown inFIG. 1) passing through the transparent cathode108and the second light transmissive optical compensation layer110. That is, one embodiment of the present invention is a double emission organic electroluminescent device capable of top emission (direction A) and bottom emission (direction B).

Next,FIG. 2shows a cross section of an organic electroluminescent device20with an optical compensation layer according to a second embodiment of the present invention. The organic electroluminescent device20includes a first light transmissive optical compensation layer102, a transparent anode104, an organic light emitting layer106and a transparent cathode108sequentially formed on a substrate100. The device20is substantially similar to the organic electroluminescent device10of a first embodiment except for the lack of the second light transmissive optical compensation layer110mentioned in a first embodiment.

FIG. 3shows a cross section of an organic electroluminescent device30with an optical compensation layer according to a third embodiment of the present invention. The organic electroluminescent device30includes a transparent anode104, an organic light emitting layer106, a transparent cathode108and a second light transmissive optical compensation layer110sequentially formed on a substrate100. The device30is substantially similar to the organic electroluminescent device10of a first embodiment except for the lack of the first light transmissive optical compensation layer102mentioned in a first embodiment.

FIG. 6shows a cross section of an organic electroluminescent device40with an optical compensation layer according to a fourth embodiment of the present invention. The organic electroluminescent device40includes a first light transmissive optical compensation layer102, a transparent anode104, an organic light emitting layer106, a transparent cathode108and a second light transmissive optical compensation layer110sequentially formed on a substrate100. The device40is substantially similar to the organic electroluminescent device10of a first embodiment except for the addition of a high molecular conductive layer105, serving as a hole injection layer, between the transparent anode104and the organic light emitting layer106. The high molecular conductive layer105may comprise a mixture composed of polystyrene dioxythiophene (PEDT) or polysterene sulphonate (PSS). The organic light emitting layer106may comprise poly(p-phenylene vinylene) (PPV).

FIG. 7shows a cross section of an organic electroluminescent device50with an optical compensation layer according to a fifth embodiment of the present invention. The organic electroluminescent device50includes a first light transmissive optical compensation layer102, a transparent anode104, an organic light emitting layer106, a transparent cathode108and a second light transmissive optical compensation layer110sequentially formed on a substrate100. The device50is substantially similar to the organic electroluminescent device10mentioned in a first embodiment except for adding a hole transport layer103bof naphtha-phenyl benzidine (NPB) and an electron transport layer107bof Alq3.

FIG. 8shows a cross section of an organic electroluminescent device60with an optical compensation layer according to a sixth embodiment of the present invention. The organic electroluminescent device60includes a first light transmissive optical compensation layer102, a transparent anode104, an organic light emitting layer106, a transparent cathode108, a second light transmissive optical compensation layer110sequentially formed on a substrate100. The device60is substantially similar to the organic electroluminescent device50except for the addition of a hole injection layer103aof copper phthalocyanine (CuPc) and an electron injection layer107aof LiF film.

At least one optical compensation layer is disposed on the transparent anode104and/or the transparent cathode108next to the light-out side of the organic electroluminescent device thus the luminescence efficiency thereof can be improved and the color shift at the viewing angle of the organic electroluminescent device can be improved.

FIG. 9shows an embodiment flat panel display. The flat panel display includes an organic electroluminescent device200according to of the present invention and a peripheral element202such as an outer frame and an external circuit.

The portable electronic devices are described herein below.FIG. 10ashows a mobile phone with the organic electroluminescent device of the present invention. The mobile phone includes a main body301, a housing302, a display area303of the organic electroluminescent device, an operation key306, an external connecting port307and an antenna308.

FIG. 10bshows a digital camera with the organic electroluminescent device of the present invention. The digital camera includes a main body401, a display area402of the organic electroluminescent device, an image receiving portion403, an operation key404, an external connection port405, and a shutter406.

FIG. 10cshows a personal digital assistant (PDA) with the organic electroluminescent device of the present invention. The PDA includes a main body501, a display area502of the organic electroluminescent device, a power switch503, an operation connection portion504and an infrared port505.

FIG. 10dshows a laptop computer with the organic electroluminescent device of the present invention. The laptop computer includes a main body601, a housing602, a display area603of organic electroluminescent device, operation key604, an external connection portion605, and a pointing mouse606.

FIG. 10eshows a DVD player with the organic electroluminescent device of the present invention. The DVD player includes an image reproduction apparatus including a recording medium (more specifically, a DVD reproduction apparatus), which includes a main body701, casing702, a display area703of the organic electroluminescent device a recording medium (DVD or the like) reading portion705, an operation key706, and a speaker portion707.

FIG. 10fshows a video camera with the organic electroluminescent device of the present invention. The video camera includes a main body801, a display area802of the organic electroluminescent device, a sound input portion803, an operation key804, a battery805and an image receiving portion806.