White organic light emitting device and method for producing the same

Abstract

The present invention relates to a white organic light emitting device (WOLED), comprising an electroluminescent material (ELM) and a Bragg converter arranged adjacent to the ELM. In addition, the present invention also relates to a method for generating white light using the WOLED, the use of the WOLED for generating white light and a method for producing the WOLED.

Description

Technical Field

[0001] The present invention relates to a white organic light emitting device (WOLED), comprising an electroluminescent medium (ELM) and a Bragg converter arranged adjacent to the ELM. In addition, the present invention also relates to a method for generating white light using the WOLED, the use of the WOLED for generating white light and a method for producing the WOLED. Background Art

[0002] Over the past three decades, light emitting diodes (LEDs) have been used for a large number of optoelectronic applications and constitute one of the main trends in modern research. Due to their significant impact on energy saving, LEDs have been established as versatile and efficient general lighting systems. In particular, the light emission in organic light emitting devices (OLEDs) relies on the electroluminescence of organic or organometallic molecules, which are much less expensive compared to their inorganic counterparts. In addition to the low manufacturing cost of OLEDs, their ease of integration in large surfaces and flexible substrates makes them particularly attractive as glare-free lamps, but also for integration with complex lighting design architectures.

[0003] One of the key requirements for general lighting devices is to emit high-intensity and high-quality white light that is color-stable at any given power input. In general, the methods for manufacturing white-light-emitting organic light-emitting devices (WOLEDs) can be divided into three main designs: 1) WOLEDs based on a single-emission layer (s-EML) structure, in which white light is generated by near-molecular energy transfer (NET) between a host material (single molecule or polymer) and multiple dopant emitters (e.g., blue-green-red). or Dexter). While these structures offer manufacturing flexibility (vacuum deposition or solution methods), especially for WOLED research, precise control of dopant concentration is one of the main challenges. 2) Multi-emission layer WOLEDs can achieve stable electroluminescence and high device yield. Here, white light is generated by mixing red-green-blue (RGB) light from multiple EMLs or stripe structures stacked vertically. However, their manufacturing is complex and their active regions are thick, usually resulting in high operating currents. In addition, electronic drive circuits are required to control the color combination from multiple color layers. 3) Incorporation of multiple cavity modes in a thick active medium consisting of a single emitter (sometimes doped) with a broadband emission spectrum. Cavity mode resonant Purcell located at the RGB wavelengths enhances the emission of RGB. The advantage of these photonic multi-resonance structures is that they can be designed to utilize any class of EMLs discussed previously. The main challenge here is the increased cavity length, typically thicker than 380nm, which introduces additional lossy waveguide modes and hinders efficient electron-hole recombination (efficiency roll-off) in OLEDs.

[0004] U.S. Patent Application Publication No. 2008 / 0137008 teaches a device having three stacked layers, wherein each layer has a plurality of pixels, one third of which are emissive active for a selected color, but where the three layers are properly aligned, the colored pixels of one layer are vertically aligned with the inactive pixels of the other layers. The layers can be independently addressed to provide a color temperature of about 5500K to about 6500K or about 2800K to about 5500K.

[0005] US Patent Application Publication No. 2012 / 0153320 teaches a light emitting device in which alternating strips of two or three differently colored electroluminescent OLEDs are constructed for a microcavity effect so that the device can have enhanced light output. Summary of the invention

[0006] Unexpectedly, it was found that white light can be produced from a top-emitting OLED (TOLED) comprising a single light-emitting layer (s-EML) coupled to a photonic Bragg mode of a dielectric distributed Bragg reflector (DBR). It was also found that Bragg modes with resonances at the main white light colors, red-green-blue (RGB), can modify the spectrum of the s-EML and produce broadband white light emission.

[0007] Advantages of the present invention include that the structure of white light emitting OLEDs is simplified, and WOLEDs can be easily and cost-effectively manufactured on an industrial scale.

[0008] A first aspect of the present invention is a white organic light emitting device (WOLED). According to the present invention, it comprises an electroluminescent medium (ELM) and a Bragg converter arranged next to the ELM. The WOLED can be used to generate white light.

[0009] The second aspect of the present invention is a method for producing the WOLED. According to the present invention, the method comprises the following steps:

[0010] a. sequentially depositing an anode layer and a hole injection layer through a patterned shadow mask,

[0011] b. sequentially depositing a light emitting layer, a hole blocking layer, an electron injection layer, and a cathode layer through a patterned shadow mask, and

[0012] c. Sputtering the Bragg converter layer directly onto the cathode surface through a patterned shadow mask.

[0013] A third aspect of the invention is a method of producing white light using a WOLED as described herein.

[0014] A fourth aspect of the invention is the use of a WOLED as described herein for producing white light.

[0015] The objects of the invention are achieved by means of a device, a process, a method and a use which are characterized in the independent claims. The dependent claims disclose preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic illustration of the principle of a WOLED according to the present invention.

[0017] Figure 2 The simulated reflectivity of WORLD and the experimentally measured emission spectrum of WORLD are shown.

[0018] Figure 3 Shown are the experimentally measured emission spectra of an OLED as well as the experimentally measured emission spectra of two different WOLEDs.

[0019] Figure 4 is a schematic illustration of a WOLED according to the present invention. DETAILED DESCRIPTION

[0020] In one embodiment, the present invention aims to develop a new type of white organic light emitting device (WOLED) based on a single electroluminescent layer producing monochromatic light and a Bragg converter that converts the monochromatic electroluminescence into polychromatic outgoing electroluminescence. In certain applications where OLED-based devices are used for lighting, white light is required.

[0021] In one embodiment of the present invention, it was unexpectedly found that white light can be produced from a top-emitting OLED (TOLED) consisting of a sub-100 nm thick blue single emitting layer (s-EML) coupled to a photonic Bragg mode of a dielectric distributed Bragg reflector (DBR). The Bragg mode is a mode located outside the stop band of the DBR, and its wavelength is defined by the length of the DBR in the direction of the periodic layer structure. It was also found that the Bragg modes with resonance at the main white light colors red-green-blue (RGB), although located outside the DBR photonic band, can modify the optical transition density of states and produce broadband white light emission.

[0022] In one embodiment of the WOLED according to the present invention, the DBR stopband does not act as a conventional cavity mirror, but suppresses UV radiation while enhancing the outcoupling of the red-shifted emission. In addition, by depositing the DBR on top of the OLED, protection of the organic layers can be achieved, thereby extending the service life of the final product.

[0023] The expression "Bragg converter" as used herein refers to a periodic structure that converts light emitted by an OLED into light of a different color. In one embodiment, the Bragg converter converts light from an OLED into a different color by blocking part of the radiation through its stop band and outcoupling the desired wavelength of the selected color through Bragg modes. In one embodiment of the present invention, the Bragg converter refers to a distributed Bragg reflector (DBR) for blocking part of the radiation (e.g., ultraviolet radiation) through its stop band and outcoupling the desired wavelength of the selected color through Bragg modes. In one embodiment, the Bragg converter includes alternating layers of high refractive index material and low refractive index material. In a specific embodiment of the present invention, the Bragg converter includes a transparent layer of two materials with alternating high and low refractive indices, and supports multiple transparent Bragg modes in the visible spectrum (400nm-700nm).

[0024] In one embodiment of the invention, the desired exit light from the WOLED comprising a Bragg converter is polychromatic light. In another embodiment of the invention, the desired exit light from the WOLED comprising a Bragg converter is white light.

[0025] The expression "white light" as used herein refers to light having a color temperature in the range of 2700K to 6500K.

[0026] In one embodiment of the present invention, a WOLED comprises an organic light emitting device (OLED) and a Bragg converter arranged next to the OLED.

[0027] In one embodiment, the WOLED comprises an organic light emitting device (OLED) comprising an electroluminescent medium (ELM); and a Bragg converter comprising a pair of alternating layers of a high refractive index material and a low refractive index material, and which is arranged adjacent to the OLED, wherein the ELM comprises a single organic light emitting layer (EML), and the Bragg converter converts light from the OLED into a desired wavelength of a different color by blocking part of the radiation through its stop band and outcoupling the selected color through the Bragg mode.

[0028] Figure 1 A schematic diagram of a WOLED according to the present invention is shown. The WOLED according to the present invention comprises an electroluminescence providing medium (electroluminescent medium, ELM). In one embodiment of the present invention, the ELM is sandwiched between an anode and a cathode. The WOLED further comprises a Bragg converter arranged on the cathode side of the device. Optionally, the WOLED according to the present invention can be arranged on a suitable optically flat solid substrate.

[0029] In one embodiment of the present invention, the ELM comprises an organic light emitting layer (EML). In another embodiment of the present invention, the ELM comprises an EML, a hole injection layer, a hole blocking layer and an electron injection layer. In one embodiment of the present invention, the light emitting layer and the hole blocking layer together form a double-layer organic stack.

[0030] Relative to the direction of electroluminescence (e.g. Figure 1 and Figure 4 In one embodiment of the present invention, the Bragg converter is arranged on the top side, that is, on the light exit surface of the OLED. In one embodiment of the present invention, the Bragg converter is arranged next to the OLED. In a specific embodiment of the present invention, the Bragg converter is in contact with the OLED.

[0031] In one embodiment of the present invention, the OLED comprises a double layer organic stack comprising at least two layers of organic components. In a specific embodiment of the present invention, the organic layers are a hole blocking layer (HBL) and an emitting layer (EML). In one embodiment of the present invention, the emitting layer (EML) is free of dopants and other additives.

[0032] In one embodiment of the present invention, an OLED comprises a cathode, an electron injection layer, a double-layer organic stack, a hole injection layer and an anode.

[0033] In one embodiment of the present invention, an OLED comprises a cathode, an electron injection layer, a hole blocking layer, a light emitting layer, a hole injection layer and an anode.

[0034] In one embodiment of the present invention, the electroluminescent medium (ELM) comprises an electron injection layer, a bilayer organic stack and a hole injection layer.

[0035] The colors of the OLED and WOLED according to the present invention are defined as coordinate pairs according to the CIE 1931 XYZ color space defined by the International Commission on Illumination (CIE).

[0036] In one embodiment of the invention, the double-layer organic stack comprises an emitting layer and a hole blocking layer. In a specific embodiment of the invention, the double-layer organic stack comprises an oligofluorene as the emitting layer and a phenanthroline as the hole blocking layer. In a very specific embodiment of the invention, the double-layer organic stack comprises a layer of 2,7-bis[9,9-di(4-methylphenyl)-fluorene-2-yl]-9,9-di(4-methylphenyl)fluorene (TDAF) as the active organic layer and the hole blocking layer comprises 4,7-diphenyl-1,10-phenanthroline (BPhen).

[0037] In one embodiment of the present invention, the bi-layer organic stack is substantially free of dopants and other additives.

[0038] In one embodiment of the present invention, the thickness of the light emitting layer is 1 nm to 100 nm, 10 nm to 90 nm, 20 nm to 80 nm, 30 nm to 70 nm, 40 nm to 60 nm, or 45 nm to 55 nm.

[0039] In one embodiment of the present invention, the thickness of the light emitting layer is less than 100 nm, less than 90 nm, less than 80 nm, less than 70 nm, less than 60 nm, or less than 55 nm.

[0040] In one embodiment of the present invention, the thickness of the light emitting layer is greater than 1 nm, greater than 10 nm, greater than 20 nm, greater than 30 nm, greater than 40 nm, or greater than 45 nm.

[0041] In one embodiment of the present invention, the thickness of the hole blocking layer is 1 nm to 70 nm, 1 nm to 60 nm, 2 nm to 50 nm, 5 nm to 40 nm, 10 nm to 30 nm, or 15 nm to 25 nm.

[0042] In one embodiment of the present invention, the thickness of the hole blocking layer is less than 70 nm, less than 60 nm, less than 50 nm, less than 40 nm, less than 30 nm, or less than 25 nm.

[0043] In one embodiment of the present invention, the thickness of the hole blocking layer is greater than 1 nm, greater than 2 nm, greater than 5 nm, greater than 10 nm, or greater than 15 nm.

[0044] In one embodiment of the present invention, the thickness of the light emitting layer is 50 nm and the thickness of the hole blocking layer is 20 nm.

[0045] In one embodiment of the present invention, the TOLED comprising TDAF and BPhen emits blue light with coordinates (0.19, 0.15) according to 1931 CIE (International Commission on Illumination), with a peak emission at 442 nm.

[0046] In one embodiment of the invention, the EML emits a broad range of light, with part of the emission being in the ultraviolet and blue wavelengths.

[0047] In addition to the double-layer organic stack, the ELM also comprises an anode and a cathode, in which the double-layer organic stack is sandwiched. The anode and the cathode are selected from any suitable conductive material.

[0048] The ELM may be composed of any suitable combination of materials that emit light when an electric current is applied. It will be apparent to those skilled in the art that the choice of materials for the ELM will depend on the color temperature of the light that the WOLED is required to emit.

[0049] In one embodiment of the present invention, the thickness of the cathode is 0.1 nm to 70 nm, 1 nm to 60 nm, 2 nm to 50 nm, 5 nm to 40 nm, 10 nm to 30 nm, or 10 nm to 20 nm.

[0050] In one embodiment of the invention, the thickness of the cathode is less than 70 nm, less than 60 nm, less than 50 nm, less than 40 nm, less than 30 nm, or less than 20 nm.

[0051] In one embodiment of the present invention, the thickness of the cathode is greater than 0.1 nm, greater than 1 nm, greater than 2 nm, greater than 5 nm, or greater than 10 nm.

[0052] In one embodiment of the present invention, the thickness of the anode is from 10 nm to 130 nm, from 20 nm to 120 nm, from 30 nm to 110 nm, from 40 nm to 100 nm, from 50 nm to 90 nm, or from 60 nm to 80 nm.

[0053] In one embodiment of the invention, the thickness of the anode is less than 130 nm, less than 120 nm, less than 110 nm, less than 100 nm, less than 90 nm, or less than 80 nm.

[0054] In one embodiment of the present invention, the thickness of the anode is greater than 10 nm, greater than 20 nm, greater than 30 nm, greater than 40 nm, greater than 50 nm, or greater than 60 nm.

[0055] In one embodiment of the present invention, the material of the cathode is aluminum and the thickness of the cathode is 10 nm. In one embodiment of the present invention, the material of the anode is aluminum and the thickness of the anode is 70 nm.

[0056] It will be readily understood by those skilled in the art that the metal anode will also act as a reflector to reflect the light emitted by the ELM to the surface of the OLED or WOLED. In one embodiment of the present invention, the OLED comprises a reflective layer arranged on one side of the ELM. In one embodiment of the present invention, the Bragg converter is arranged on the side of the ELM opposite to the reflective material. In another embodiment of the present invention, the anode comprises a reflective material.

[0057] In one embodiment of the present invention, the WOLED comprises a hole injection layer sandwiched between the anode and the bilayer organic stack. In a specific embodiment of the present invention, the hole injection layer comprises MoO3 (molybdenum trioxide) and has a thickness of about 5 nm.

[0058] In one embodiment of the present invention, the thickness of the hole injection layer is 0.1 nm to 70 nm, 1 nm to 60 nm, 2 nm to 50 nm, 5 nm to 40 nm, 10 nm to 30 nm, or 15 nm to 25 nm.

[0059] In one embodiment of the present invention, the thickness of the hole injection layer is less than 70 nm, less than 60 nm, less than 50 nm, less than 40 nm, less than 30 nm, or less than 25 nm.

[0060] In one embodiment of the present invention, the thickness of the hole injection layer is greater than 1 nm, greater than 2 nm, greater than 5 nm, greater than 10 nm, or greater than 15 nm.

[0061] In one embodiment of the invention, the WOLED comprises an electron injection layer sandwiched between the cathode and the bilayer organic stack. In a specific embodiment of the invention, the electron injection layer comprises LiF (lithium fluoride) and has a thickness of about 0.5 nm.

[0062] In one embodiment of the present invention, the thickness of the hole injection layer is 0.1 nm to 7 nm, 0.2 nm to 6 nm, 0.3 nm to 5 nm, 0.4 nm to 4 nm, 0.3 nm to 3 nm, or 0.2 nm to 2 nm.

[0063] In one embodiment of the present invention, the thickness of the hole injection layer is less than 7 nm, less than 5 nm, less than 4 nm, less than 3 nm, less than 2 nm, or less than 1 nm.

[0064] In one embodiment of the present invention, the thickness of the hole injection layer is greater than 0.1 nm, greater than 0.2 nm, greater than 0.3 nm, greater than 0.4 nm, or greater than 0.45 nm.

[0065] In one embodiment of the present invention, the total thickness of the ELM including the double-layer organic stack, the anode, the cathode, the electron injection layer and the hole injection layer is about 160 nm.

[0066] In one embodiment of the present invention, the total thickness of the ELM comprising a double-layer organic stack, an anode, a cathode, an electron injection layer and a hole injection layer is 50 to 500 nm, 75 nm to 450 nm, 100 nm to 350 nm, 125 nm to 250 nm, 130 nm to 200 nm, or 140 nm to 190 nm.

[0067] In one embodiment of the present invention, the total thickness of the ELM comprising a double-layer organic stack, an anode, a cathode, an electron injection layer and a hole injection layer is less than 500 nm, less than 450 nm, less than 350 nm, less than 250 nm, less than 200 nm, or less than 190 nm.

[0068] In one embodiment of the present invention, the total thickness of the ELM comprising a double-layer organic stack, an anode, a cathode, an electron injection layer and a hole injection layer is greater than 50 nm, greater than 75 nm, greater than 100 nm, greater than 125 nm, greater than 130 nm, or greater than 140 nm.

[0069] In one embodiment of the present invention, the WOLED comprises a substrate. The substrate can be any material that is chemically compatible with the adjacent layers, optically flat and strong enough to support the layers. Depending on the specific application, the substrate can be flexible or non-flexible, transparent, translucent or opaque, compatible with silicon technology, and can have integrated circuits. In a specific embodiment of the present invention, the substrate can also be used as a reflector. Non-limiting examples of materials that can be used as substrates are metals, plastics, semiconductors, and dielectrics, such as glass, quartz or sapphire. Non-limiting examples of suitable substrates are metal-coated glass or silicon.

[0070] As used herein, the term "glass" refers to any material that has or can have glass characteristics. This includes, but is not limited to, materials such as soda-lime glass, soda-lime-silica glass, fused quartz, fused silica glass, vitreous silica glass, sodium borosilicate glass, Pyrex glass, lead oxide glass, crystal glass, lead glass, aluminosilicate glass, germanium oxide glass, sapphire glass, and mixtures thereof.

[0071] In one embodiment of the invention, a substrate is attached to the side of the OLED opposite to the Bragg converter.

[0072] In one embodiment of the invention, the Bragg converter comprises alternating pairs of high and low refractive index materials. The choice of materials used depends on the exact nature of the conversion of the desired wavelength. The layers of high refractive index material and low refractive index material can be arranged in any order; with high refractive index layers arranged above low refractive index layers, or with low refractive index layers arranged above high refractive index layers.

[0073] Figure 2 The calculated refractive index of the WOLED and the emission spectrum of the WOLED are shown.

[0074] As used herein, the term "low refractive index material" refers to a material having a refractive index of 1.65 or less for visible light wavelengths, and the term "high refractive index material" refers to a material having a refractive index of 1.7 or more for visible light wavelengths.

[0075] In one embodiment of the invention, the Bragg converter comprises alternating layers of a dielectric compound selected from transparent oxides of silicon, tantalum, titanium or hafnium. Non-limiting examples of suitable oxides include silicon oxides such as silica (silicon dioxide, SiO2), tantalum oxides such as tantalum pentoxide (Ta2O5), titanium oxides such as titanium dioxide (TiO2) and hafnium oxides such as hafnium dioxide (HfO2).

[0076] In one embodiment of the present invention, the thickness of each layer of low refractive index material is 1 nm to 100 nm, 10 nm to 90 nm, 20 nm to 80 nm, 30 nm to 70 nm, 35 nm to 65 nm, or 40 nm to 60 nm.

[0077] In one embodiment of the present invention, the thickness of each layer of low refractive index material is less than 100 nm, less than 90 nm, less than 80 nm, less than 70 nm, less than 65 nm, or less than 60 nm.

[0078] In one embodiment of the present invention, the thickness of each layer of low refractive index material is greater than 1 nm, greater than 10 nm, greater than 20 nm, greater than 30 nm, greater than 35 nm, or greater than 40 nm.

[0079] In one embodiment of the invention, the thickness of a single layer of low refractive index material is about 42 nm. In another embodiment of the invention, the thickness of a single layer of low refractive index material is about 53 nm.

[0080] In one embodiment of the present invention, the low refractive index material is selected from the group consisting of silicon transparent oxides. In a specific embodiment of the present invention, the low refractive index material is silica (SiO2).

[0081] In one embodiment of the present invention, the thickness of a single layer of high refractive index material is from 10 nm to 200 nm, from 40 nm to 150 nm, from 50 nm to 130 nm, from 60 nm to 120 nm, from 70 nm to 110 nm, or from 80 nm to 100 nm.

[0082] In one embodiment of the present invention, the thickness of a single layer of high refractive index material is less than 70 nm, less than 60 nm, less than 50 nm, less than 40 nm, less than 30 nm, or less than 25 nm.

[0083] In one embodiment of the present invention, the thickness of a single layer of high refractive index material is greater than 1 nm, greater than 2 nm, greater than 5 nm, greater than 10 nm, or greater than 15 nm.

[0084] In one embodiment of the present invention, the thickness of the individual layers of high refractive index material is 41 nm each, and in another embodiment of the present invention, the thickness of the individual layers of high refractive index material is 42 nm each.

[0085] In one embodiment of the invention, the high refractive index material is selected from the group comprising transparent oxides of tantalum, titanium and hafnium. In a specific embodiment of the invention, the high refractive index material is selected from the group comprising transparent oxides of tantalum. In a very specific embodiment of the invention, the high refractive index material is tantalum pentoxide (Ta2O5).

[0086] In one embodiment of the present invention, the thickness of a pair of high and low refractive index layers is 30 nm to 300 nm, 45 nm to 275 nm, 50 nm to 260 nm, 60 nm to 200 nm, 70 nm to 180 nm, or 80 nm to 110 nm.

[0087] In one embodiment of the present invention, the thickness of a pair of high and low refractive index layers is less than 300 nm, less than 200 nm, less than 160 nm, less than 100 nm, less than 120 nm, or less than 100 nm.

[0088] In one embodiment of the present invention, the thickness of a pair of high and low refractive index layers is greater than 10 nm, greater than 35 nm, greater than 50 nm, greater than 60 nm, greater than 70 nm, or greater than 80 nm.

[0089] In one embodiment of the present invention, the thickness of the pair of high and low refractive index layers is 83 nm. In another embodiment of the present invention, the thickness of the pair of high and low refractive index layers is 96 nm.

[0090] In one embodiment of the present invention, the Bragg converter comprises at least one, at least two, at least three, at least four, or at least five layers each comprising a high refractive index layer and a low refractive index layer, arranged one above the other. In a specific embodiment of the present invention, the Bragg converter comprises at least six layers each comprising a high refractive index layer and a low refractive index layer, arranged one above the other.

[0091] In one embodiment of the present invention, the total thickness of the Bragg converter is 20 nm to 2000 nm, 30 nm to 1000 nm, 40 nm to 800 nm, 50 nm to 700 nm, 400 nm to 650 nm, or 500 nm to 600 nm.

[0092] In one embodiment of the present invention, the total thickness of the Bragg converter is less than 2000 nm, less than 1000 nm, less than 800 nm, less than 700 nm, less than 650 nm, or less than 600 nm.

[0093] In one embodiment of the present invention, the total thickness of the Bragg converter is greater than 20 nm, greater than 100 nm, greater than 200 nm, greater than 300 nm, greater than 400 nm, or greater than 500 nm.

[0094] In one embodiment of the invention, the total thickness of the Bragg converter is about 498 nm. In another embodiment of the invention, the total thickness of the Bragg converter is about 576 nm. The choice of thickness used depends on the exact nature of the conversion of the desired wavelength.

[0095] It will be understood by those skilled in the art that the color of the light emitted by the WOLED will depend on the color emitted by the OLED and the structure of the Bragg converter. As a non-limiting example, the applicant proposes that in one embodiment of the present invention, a WOLED comprising a blue OLED according to the present disclosure that emits light having 1931 CIE coordinates (0.19, 0.15) encapsulated with a Bragg converter consisting of six layers (each comprising a high refractive index layer and a low refractive index layer, disposed one above the other) with a total thickness of 498 nm, uniformly emits white light having 1931 CIE coordinates (0.32, 0.36). As another non-limiting example, the applicant proposes that in one embodiment of the present invention, a WOLED comprising a blue OLED according to the present disclosure that emits light having 1931 CIE coordinates (0.19, 0.15) encapsulated with a Bragg converter consisting of six layers (each comprising a high refractive index layer and a low refractive index layer, disposed one above the other) with a total thickness of 576 nm, uniformly emits white light having 1931 CIE coordinates (0.36, 0.35).

[0096] Figure 3 Shown are the experimentally measured emission spectra of an OLED as well as the experimentally measured emission spectra from two different WOLEDs. Figure 3 A shows the emission spectrum of a WOLED containing a Bragg converter with a total thickness of 498 nm, and Figure 3 B shows the emission spectrum of a WOLED comprising a Bragg converter with a total thickness of 576 nm. In both cases, the WOLED comprises an OLED emitting blue light with 1931 CIE coordinates (0.19, 0.15).

[0097] In one embodiment of the present invention, the WOLED comprises an OLED and a Bragg converter.In a further embodiment, the WOLED comprises an OLED, a Bragg converter and a substrate.

[0098] In one embodiment of the present invention, the WOLED comprises an OLED and a Bragg converter, wherein the OLED comprises an aluminum anode, a MoO3 hole injection layer, an oligofluorene light-emitting layer, a BPhen (4,7-diphenyl-1,10-phenanthroline) hole blocking layer, a LiF electron injection layer and an aluminum cathode.

[0099] In one embodiment of the present invention, the WOLED comprises an OLED and a Bragg converter, wherein the OLED comprises an aluminum anode, a MoO3 hole injection layer, a TDAF (2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene) light-emitting layer, a BPhen (4,7-diphenyl-1,10-phenanthroline) hole blocking layer, a LiF electron injection layer and an aluminum cathode.

[0100] In one embodiment of the present invention, the WOLED comprises an aluminum anode, a MoO3 hole injector, a TDAF (2,7-bis[9,9-di(4-methylphenyl)-fluorene-2-yl]-9,9-di(4-methylphenyl)fluorene) light-emitting layer, a BPhen (4,7-diphenyl-1,10-phenanthroline) hole blocking layer, a LiF electron injection layer, an aluminum cathode and a Bragg converter, wherein the Bragg converter comprises a 2,7-bis[9,9-di(4-methylphenyl)-fluorene-2-yl]-9,9-di(4-methylphenyl)fluorene) light-emitting layer, a BPhen (4,7-diphenyl-1,10-phenanthroline) hole blocking layer, a LiF electron injection layer, an aluminum cathode and a Bragg converter. Figure 4 Alternating layers of SiO2 and Ta2O5 are shown.

[0101] In one embodiment of the present invention, the WOLED comprises an aluminum anode, a MoO3 hole injector, a TDAF (2,7-bis[9,9-di(4-methylphenyl)-fluorene-2-yl]-9,9-di(4-methylphenyl)fluorene) light-emitting layer, a BPhen (4,7-diphenyl-1,10-phenanthroline) hole blocking layer, a LiF electron injection layer, an aluminum cathode and a Bragg converter, wherein the Bragg converter comprises a substrate arranged according to Figure 4 Alternating layers of SiO2 and Ta2O5 are shown.

[0102] Figure 4 is a schematic illustration of a WOLED according to the present invention.

[0103] In one embodiment of the present invention, the WOLED according to the present invention has a thickness of 150 nm to 1350 nm, 250 nm to 1250 nm, 350 nm to 1150 nm, 450 nm to 1050 nm, 550 nm to 950 nm, or 650 nm to 850 nm.

[0104] In one embodiment of the present invention, the thickness of a WOLED according to the present invention is less than 1350 nm, less than 1250 nm, less than 1150 nm, less than 1050 nm, less than 950 nm, or less than 850 nm.

[0105] In one embodiment of the present invention, the WOLED according to the present invention has a thickness greater than 150 nm, greater than 250 nm, greater than 350 nm, greater than 450 nm, greater than 550 nm, or greater than 650 nm.

[0106] In one specific embodiment of the present invention, the total thickness of the WOLED comprising the light emitting layer, cathode, anode, hole injection layer, electron injection layer and Bragg converter is about 750 nm.

[0107] As will be appreciated by those skilled in the art, WOLEDs according to the present invention may be manufactured in one of many different ways. Non-limiting examples of techniques for manufacturing WOLEDs according to the present invention are vacuum deposition and spin coating.

[0108] In one embodiment of the invention, a WOLED can be constructed by applying a mask to a suitable substrate or surface, followed by vacuum deposition of materials for the anode and hole injection layers in sequence. After deposition, the vacuum is broken, the mask is removed, and a second mask is added perpendicular to the direction of the first mask. Finally, the organic bilayer, electron injection layer, and cathode layer are added to complete the OLED. Once the deposition chamber is vented to atmospheric conditions and the mask layer has been removed, the Bragg converter can be added by vacuum sputtering to complete the WOLED.

[0109] In one embodiment of the present invention, the OLED device can be replaced with an inorganic LED as a colored inorganic semiconductor, which, when combined with a Bragg converter, produces an output light of a color different from the color of the LED. For example, colored inorganic semiconductors suitable for inclusion in the device include, but are not limited to, InGaN / GaN, ZnS, GaP:N, AllnGaP, GaAsP, GaAsP:N, InGaP, AlGaAs, and GaAs.

[0110] The WOLED of the present invention provides the additional advantage that the dielectric DBR used provides effective encapsulation of the OLED, blocking the diffusion of moisture and oxygen into the OLED, thereby significantly extending the lifetime of the device. This means that there is no need to encapsulate the device, for example by epoxy resin.

[0111] One embodiment of the present invention is a method of generating white light using the WOLED according to the present invention by applying power to the WOLED.

[0112] In one embodiment of the present invention, a WOLED is used to generate white light.

[0113] Example

[0114] The present invention is described below with the aid of examples. The examples are given for illustrative purposes only and they do not limit the scope of the present invention.

[0115] Example 1: Method for producing WOLED

[0116] OLED fabrication was achieved by using a standard vacuum evaporator (Edwards E306) with multiple deposition sources. The deposition base pressure was about 10 -6 mbar and the deposition rate is The OLED was deposited on a quartz substrate with a thickness of 1 mm. The OLED was patterned into a square by using a shadow mask in direct contact with the substrate. The bottom Al anode and the MoO3 hole injection layer were first deposited, and the reactor was vented to ambient atmosphere to change the mask. The top part of the OLED consisting of TDAF, Bphen, LiF and Al was deposited and then vented to atmospheric conditions before removing the mask. The Bragg converter was sputtered directly on the OLED.

[0117] Example 2: Characterization

[0118] A combination of ellipsometry (JAWoollam M2000) and profilometry (Bruker DektakXT) was used to determine film thickness and obtain optical constants. All devices were electrically characterized using a Keithley source meter unit (2602B). An absolutely calibrated 2D CCD camera (Pixis 400) connected to a spectrometer (Acton SpectrPro 2500) was used to measure the forward spectral radiation for increased current. With an angular aperture of ±15 degrees and a magnification of 2.5, the pixels on the spectrometer slit were imaged directly. The angle-dependent electroluminescence of the device was obtained by using an objective lens (10x, 0.3NA) to collect emission and using a goniometer to rotate the WOLED (OLED) on the optical axis. The rear focal plane objective image was then focused to the 200μm spectrometer entrance slit. A vacuum microchamber that allows the device to be rotated was developed internally. All measurements were performed at 8x10 -2 mbar base pressure. To determine the external quantum efficiency (EQE), the known angle-resolved EL and forward spectral radiation are parameterized to correct the measured photon number. The EQE is then the ratio of emitted photons to injected electrons.

[0119] Measurements have shown that an OLED having a thickness of about 160 nm produced according to the method disclosed in Example 1, before encapsulation with a Bragg converter, emits light having 1931 CIE coordinates (0.19, 0.15).

[0120] The blue OLED was encapsulated using a Bragg converter to produce a WOLED with a total thickness of 498 nm, producing white light emitting with 1931 CIE coordinates (0.32, 0.36), while a WOLED with a total thickness of 576 nm produced white light emitting with 1931 CIE coordinates (0.36, 0.35).

Claims

1. A white organic light emitting device (WOLED), comprising a. an organic light emitting device (OLED) comprising an electroluminescent medium (ELM), and b. a Bragg converter disposed adjacent to the OLED, the Bragg converter comprising alternating layers of a high refractive index material and a low refractive index material disposed in pairs, The ELM comprises a single organic light-emitting layer (EML) which emits light whose luminescent portion is located in the ultraviolet and blue wavelength range, and the Bragg converter converts the light from the OLED into different colors by suppressing UV radiation through its stop band and enhancing the outcoupling of red-shifted emission through Bragg modes.

2. The WOLED according to claim 1, characterized in that The ELM includes a reflective layer disposed on one side of the EML.

3. The WOLED according to claim 2, characterized in that The Bragg converter is arranged on a side of the ELM opposite to the reflective layer.

4. The WOLED according to any one of claims 1 to 3, characterized in that The light emitting portion of the OLED includes an anode, an electron injection layer, a light emitting layer, a hole blocking layer, a hole injection layer and a cathode.

5. The WOLED according to any one of claims 1 to 3, characterized in that The Bragg converter comprises a transparent oxide of a dielectric material.

6. The WOLED according to claim 5, wherein: The Bragg converter contains an oxide of silicon or tantalum.

7. The WOLED according to claim 2, characterized in that The WOLED is arranged on a substrate disposed below a reflective layer.

8. The WOLED according to claim 7, characterized in that The substrate is any optically flat solid material onto which a reflective layer can be deposited.

9. The WOLED according to claim 7 or 8, characterized in that: The substrate is attached to the side of the OLED opposite to the Bragg converter.

10. The WOLED according to any one of claims 1 to 3, comprising an aluminum anode, a MoO3 hole injection layer, a TDAF (2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene) light-emitting layer, a BPhen (4,7-diphenyl-1,10-phenanthroline) hole blocking layer, a LiF electron injection layer, an aluminum cathode and a Bragg converter comprising alternating layers of SiO2 and Ta2O5.

11. The WOLED according to claim 5, characterized in that The Bragg converter includes oxides of silicon, tantalum, titanium, hafnium, or mixtures thereof.

12. The WOLED according to claim 6, wherein: The Bragg converter includes silicon dioxide and tantalum pentoxide.

13. A method for producing a WOLED as claimed in any one of claims 1 to 12, the method comprising the following steps: a. sequentially depositing an anode layer and a hole injection layer through a patterned shadow mask, b. sequentially depositing a light-emitting layer, a hole blocking layer, an electron injection layer, and a cathode layer through a patterned shadow mask, and c. Sputtering the Bragg converter layer directly onto the surface of the cathode through a patterned shadow mask.

14. A method for producing white light using a device comprising a WOLED as claimed in any one of claims 1 to 12.

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