Patent Application
20080164812
1. Field of the Invention
The invention relates to displaying of images using electroluminescence.
2. Description of the Related Art
Recently, with the development and wide application of electronic products, such as mobile phones, PDAs, and notebook computers, there has been increasing demand for flat display elements which consume less electric power and occupy less space. Among flat panel displays, organic electroluminescent devices are self-emitting, and highly luminous, with wider viewing angle, faster response, and relatively simple fabrication, making them the industry display of choice.
An organic light-emitting diode (OLED) is a light-emitting diode that uses an organic layer as the active layer. In recent years, OLEDs have been gradually employed in flat panel displays. The trend in organic electroluminescent display technology is for higher luminescent efficiency, longer lifetime and full color emission.
Several methods have been employed to achieve full color emission in organic electroluminescent devices, including direct full-color display techniques and indirect full-color display techniques.
In the direct full-color display technique, there is a major tendency to fabricate full color organic electroluminescent devices by a method of RGB emitting layers. The so-called method of RGB emitting layers indicates that red, green and blue color arrays are formed, and then driven by bias voltages to emit red, green and blue, respectively. The individual aging rates of RGB organic electroluminescent materials, however, are different and lead to color deterioration of the organic electroluminescent device after a period of time.
Accordingly, a full-color organic electroluminescent device with a color filter has been developed to solve the problems caused by the above full-color organic electroluminescent devices. In particular, white light emitted from a white organic light emitting diode is converted to RGB by passing through the RGB color filters.
Nevertheless, since the RGB emission spectrum of the white OLED does not precisely correspond to the RGB transmission spectrum of RGB color filters, the spectral FWHM (Full Width Half Maximum) of the filtered RGB luminescence has been enlarged and reduced, such that color saturation (NTSC ratio) of the full-color display employing the white OLED and RGB color filters has been reduced, limiting the color range thereof.
To narrow the spectral FWHM (Full Width Half Maximum) and increase the color saturation (NTSC ratio), an OLED emission element within a microcavity structure has been provided to enhance emission at a specific wavelength as determined by the optical cavity length of the microcavity. Examples of such microcavity devices are disclosed in U.S. Pat. Nos. 5,405,710 and 5,554,911. In this case, use of broad emitting OLED materials, varying the optical length of the cavity for each differently colored sub-pixel, can provide different colored emission.
However, when devices constructed with microcavities are viewed at varying angles, the color of the emission may change. Further, fabrication of the microcavities entails increased process complexity and cost.
Therefore, it is necessary to develop a simple and efficient manufacturing method and structure for a full-color organic electroluminescent device.
Systems for displaying images are provided. An exemplary embodiment of a system comprises an electroluminescent device that comprises: a substrate; a first electrode located on the substrate; electroluminescent layers located on the first electrode; a second electrode located on the electroluminescent layers; and a wavelength narrowing mirror structure located directly on the second electrode, wherein the wavelength narrowing mirror structure comprises a plurality of metal layers, with two adjacent ones of the metal layers being separated by a dielectric layer. Another exemplary embodiment of the system comprises an electroluminescent device, comprising: a substrate; and a wavelength narrowing mirror structure located on the substrate, wherein the wavelength narrowing mirror structure comprises a plurality of metal layers with two adjacent ones of the metal layers being separated by a dielectric layer, the electroluminescent device being operative to emit red, green, and blue (RGB) emissions, wherein the wavelength narrowing mirror structure increases saturation of the RGB emissions.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
a to 2c are cross sections of a wavelength narrowing mirror structure according to embodiments of the invention.
This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
In this regard, systems for displaying images are provided, in which some embodiments employ a wavelength narrowing mirror structure to narrow the spectral FWHM (Full Width Half Maximum) of emitted light, thereby facilitating color saturation (NTSC ratio).
As shown in
Further, the substrate 110 is a transparent substrate since the organic electroluminescent diode 100 is a bottom-emission organic electroluminescent device.
A first electrode 120 is formed on the substrate 110, and can be a transparent electrode, comprising indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), SnO2, In2O3, or combinations thereof, formed by, for example, sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition.
An electroluminescent layer 130 is formed on the electrode 120, comprising at least a light emitting layer, and can further comprise a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer. The electroluminescent layer 130 is organic semiconductor material such as small molecule material, polymer, or organometallic complex, and can be formed by thermal vacuum evaporation, spin coating, dip coating, roll-coating, injection-fill, embossing, stamping, physical vapor deposition, or chemical vapor deposition. The emitting layer can comprise one or multiple light-emitting material and electroluminescent dopants doped into the light-emitting materials and can perform energy transfer or carrier trapping under electron-hole recombination in the emitting layer. The light-emitting material can be fluorescent or phosphorescent.
It should be noted that the electroluminescent layer 130 can comprise a single electroluminescent unit, resulting in an organic electroluminescent diode 100 with red, blue, yellow, or green emission. Further, the electroluminescent layer can comprise a plurality of electroluminescent units, such that a tandem organic electroluminescent diode 100 with white emission can be achieved by mixing different colors.
Next, a second electrode 140, is formed on the electroluminescent layer 130. Suitable material of the electrode 140 can comprise indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), SnO2, In2O3, Al, Cu, Mo, Ti, Pt, Ir, Ni, Cr, Ag, Au or combinations thereof, formed by, for example, sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition. Particularly, the metal materials such as Al, Cu, Mo, Ti, Pt, Ir, Ni, Cr, Ag, Au or combinations thereof are transparent or semitransparent.
Still referring to
Particularly, the metal layers can be formed of the same or different materials. Additionally, the metal layers can be transparent or semitransparent, otherwise the reflection of the mirror can become similar to those formed of thick metal layers, which potentially renders the bandwidth-narrowing function of the mirror useless. Suitable materials are Mg, Ca, Al, Ba, Li, Be, Sr, Ag, Au or combinations thereof. Further, the dielectric layer can be an inorganic or organic compound, such as TeO2, ITO, ZrO, ZnO, ZnSe, ZnS, MgO, Si3N4, SiO2, LiF, MgF2, NaF, CaF2, m-MTDATA, α-NPD, TPD, ADN, Alq3, or combinations thereof. It should be noted that the thickness of the dielectric layer depends on the designed working spectral region of the wavelength narrowing mirror and thickness of other layers within the wavelength narrowing mirror.
The reason that the wavelength narrowing mirror can narrow the spectral width is given in the following. Referring to
According to another embodiment of the invention, as shown in
Next, a wavelength narrowing mirror structure 150 is formed on the substrate 210. It should be noted that wavelength narrowing mirror structure 150 directly contacts the substrate 210 through the metal layer 160. It should be noted that mirror 150 can be provided in various configurations, such as those described previously with respect to
Next, a first electrode 220 is formed on the wavelength narrowing mirror structure 150 and contacts a metal layer thereof. Suitable material of the first electrode 220 can comprise indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), SnO2, In2O3, Mg, Ca, Al, Ba, Li, Be, Sr, Ag, Au or combinations thereof, formed by, for example, sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition. Particularly, the metal materials such as Al, Cu, Mo, Ti, Pt, Ir, Ni, Cr, Ag, Au or combinations thereof is transparent or semitransparent.
An electroluminescent layer 230 is formed on the first electrode 220, wherein the electroluminescent layer 230 comprises at least a light emitting layer, and can further comprise a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer. The electroluminescent layer 230 is organic semiconductor material such as small molecule material, polymer, or organometallic complex, and can be formed by thermal vacuum evaporation, spin coating, dip coating, roll-coating, injection-fill, embossing, stamping, physical vapor deposition, or chemical vapor deposition. The emitting layer can comprise one or multiple light-emitting materials and electroluminescent dopants doped into the light-emitting material and can perform energy transfer or carrier trapping under electron-hole recombination in the emitting layer. The light-emitting material can be fluorescent or phosphorescent. It should be noted that the electroluminescent layer 230 can comprise a single electroluminescent unit, resulting in an organic electroluminescent diode 200 with red, blue, or green emission or combinations thereof. Further, the electroluminescent layer 230 can comprise a plurality of electroluminescent units, thus, a tandem organic electroluminescent diode 200 with white emission can be achieved by mixing different colors.
Next, a second electrode 240 is formed on the electroluminescent layer 230. Suitable material of the electrode 240 can comprise indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), SnO2, In2O3, Al, Cu, Mo, Ti, Pt, Ir, Ni, Cr, Ag, Au or combinations thereof, formed by, for example, sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition.
The following illustrative examples are provided.
A glass substrate with an indium tin oxide (ITO) film of 120 nm in thickness was provided and then washed by a cleaning agent, acetone, and isopropanol with ultrasonic agitation. After drying with nitrogen flow, the ITO film was subjected to UV/ozone treatment. Next, a hole injection layer, hole transport layer, first light-emitting layer, second light-emitting layer, third light-emitting layer, electron transport layer, electron injection layer, aluminum electrode, and a silver electrode were subsequently formed on the ITO film at 10-5 Pa, obtaining the electroluminescent device (1).
For purposes of clarity, the materials and layers formed therefrom are described in the following.
The hole injection layer, with a thickness of 30 nm, consisted of [NOTE=“consisted of” has a very specific legal meaning, please ensure this is accurate] m-MTDATA (4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine). The hole transport layer, with a thickness of 20 nm, consisted of α-NPD (N,N′-di(naphtalene-1-yl)-N,N′-diphenyl-benxidine). The first light-emitting layer (with electron transport characteristic), with a thickness of 7.5 nm, consisted of ADN (Anthracene Dinaphthyl) as host, and Perylene as dopant, wherein the weight ratio between ADN and Perylene was 100:1. The second light-emitting layer (with electron transport characteristic), with a thickness of 5 nm, consisted of Alq3 (tris(8-hydroxyquinoline) aluminum as host, and C545T (10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H, 11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one) as dopant, wherein the weight ratio between Alq3 and C545T was 100:1. The third light-emitting layer (with electron transport characteristic), with a thickness of 7.5 nm, consisted of Alq3 as host, and DCJTB (butyl-6-(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran) as dopant, wherein the weight ratio between Alq3 and DCJTB was 1000:7. The hole transport layer, with a thickness of 40 nm, consisted of Alq3. The electron injection layer, with a thickness of 0.5 nm, consisted of LiF. The aluminum electrode had a thickness of 1 nm. The silver electrode had a thickness of 100 nm.
The emissive structure of the electroluminescent device (1) can be represented as:
ITO 120 nm/m-MTDATA 30 nm/α-NPD 20 nm/ADN:Perylene 100:1 7.5 nm/Alq3:C545T 100:1 5 nm/Alq3:DCJTB 1000:7 7.5 nm/Alq3 40 nm/LiF 0.5 nm/Al 1 nm/Ag 100 nm
The optical properties of electroluminescent device (1), as described in Example 1, were measured by PR650 (purchased from Photo Research Inc.) and Minolta LS110.
A glass substrate with an indium tin oxide (ITO) film of 120 nm in thickness was provided and then washed by a cleaning agent, acetone, and isopropanol with ultrasonic agitation. After drying with nitrogen flow, the ITO film was subjected to UV/ozone treatment. Next, a hole injection layer, hole transport layer, first light-emitting layer, second light-emitting layer, third light-emitting layer, electron transport layer, electron injection layer, aluminum electrode, and a wavelength narrowing mirror structure (comprising a first silver layer, first dielectric layer, second silver layer, second dielectric layer, and third silver layer), were subsequently formed on the ITO film at 10-5 Pa, obtaining the electroluminescent device (2).
For purposes of clarity, the materials and layers formed therefrom are described in the following.
The hole injection layer, with a thickness of 30 nm, consisted of m-MTDATA (4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine). The hole transport layer, with a thickness of 20 nm, consisted of α-NPD (N,N′-di(naphtalene-1-yl)-N,N′-diphenyl-benxidine). The first light-emitting layer (with electron transport characteristic), with a thickness of 7.5 nm, consisted of ADN (Anthracene Dinaphthyl) as host, and Perylene as dopant, wherein the weight ratio between ADN and Perylene was 100:1. The second light-emitting layer (with electron transport characteristic), with a thickness of 5 nm, consisted of Alq3 (tris(8-hydroxyquinoline) aluminum as host, and C545T (10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8i,j)quinolizin-11-one) as dopant, wherein the weight ratio between Alq3 and C545T was 100:1. The third light-emitting layer (with electron transport characteristic), with a thickness of 7.5 nm, consisted of Alq3 as host, and DCJTB (butyl-6-(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran) as dopant, wherein the weight ratio between Alq3 and DCJTB was 1000:7. The hole transport layer, with a thickness of 40 nm, consisted of Alq3. The electron injection layer, with a thickness of 0.5 nm, consisted of LiF. The aluminum electrode had a thickness of 26 nm. The first silver electrode had a thickness of 8 nm. The first dielectric layer consisted of Alq3 with a thickness of 90 nm. The second silver electrode had a thickness of 26 nm. The second dielectric layer consisted of Alq3 with a thickness of 100 nm. The third silver electrode had a thickness of 150 nm.
The emissive structure of the electroluminescent device (2) can be represented as:
ITO 120 nm/m-MTDATA 30 nm/α-NPD 20 nm/AND Perylene 100:1 7.5 nm/Alq3:C545T 100:1 5 nm/Alq3:DCJTB 1000:7 7.5 nm/Alq3 40 nm/LiF 0.5 nm/Al 1 nm/Ag 8 nm/Alq3 90 nm/Ag 26 nm/Alq3 100 nm/Ag 150 nm
The optical properties of electroluminescent device (2), as described in Example 1, were measured by PR650 (purchased from Photo Research Inc.) and Minolta LS110.
Further, referring to
Accordingly, various embodiments of an organic electroluminescent device with wavelength narrowing mirror structure provide simplified structure and fabrication process and exhibit increased color saturation (NTSC ratio), resulting in a system for display images with increased color range.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. 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.
