Patent Description:
OLED is a light emitting device in which an organic solid state semiconductor is used as a light emitting material. It will have wide future application due to its advantages of simple process, low cost, low power consumption, high luminance, and a wide range of operation temperature. Currently there is a need for increasing the light extracting efficiency of OLED.

Document <CIT> provides structured LED and OLED devices and component structures with improved efficiency and reduced defects. The improved performance of these devices is enabled by the use of micro- or nano- structured features that reduce lattice strain and improve p-doping in inorganic LEDs, and facilitate carrier injection and recombination of OLEDs. The structures can also confine current flow and provide internal light guiding to enhance efficiency and thereby improve device performance.

Document <CIT> provides an optoelectronic device that has at least one charge carrier injecting or transporting layer that includes inorganic nanoparticles having a bimodal particle size distribution and dispersed in an organic matrix. Light extraction from wet-coated OLED devices may be improved by optimizing the charge injection or transport layers to direct more light into a supporting substrate, thus maximizing the final light extraction efficiency.

Document "<NPL>" investigated insertion of a thin film of Al<NUM>O<NUM> at the interface of electrodes and organic layers. Insertion of a thin film of Al<NUM>O<NUM> at the interface of the ITO anode and the diamine derivative layers, as well as at the interface of the <NUM>-hydroxyquinoline aluminum and the Mg:Ag cathode in the electroluminescent diode has been examined. The insertion of an Al<NUM>O<NUM> layer with a proper thickness was observed to enhance the emission efficiency of the device.

Document <CIT> relates to an organic light-emitting device (OLED) comprising at least: a first electrode; a second electrode; an organic light emissive layer arranged between said first electrode and said second electrode; and an organic charge transport layer arranged between said first electrode and said emissive layer, the charge transport layer is patterned or provided with a periodic surface structure on a surface of the charge transport layer facing the emissive layer, an alignment layer which allows for charge transport to the emissive layer is provided between said charge transport layer and said emissive layer, which alignment layer promotes alignment of the optical dipoles of molecules of said light emissive layer towards a common preferred direction of the molecular axes.

Document <CIT> provides a manufacturing method capable of forming a structure for disturbing a reflection angle of a reflective electrode for improving extraction efficiency of light with high precision and productivity. An organic El element is formed by sandwiching a functional organic layer formed of a plurality of layers including a light emitting layer between a translucent electrode formed of a translucent conductive material and a reflective electrode having a structure for disturbing the reflection angle. The method includes a process for forming an uneven part on a hole transport layer which is at least one layer of the functional organic layer.

It is objects of embodiments of the present application to alleviate or eliminate one or more of the above problems. In particular, embodiments of the present application provide an OLED, a method for fabricating the same, and a display device comprising the OLED, which can efficiently increase the light extracting efficiency of OLED.

In a first aspect, it is provided an OLED, comprising: a substrate, a cathode, a light extracting layer, an organic light emitting layer, a hole transporting layer, a hole injecting layer and a reflective anode. A surface of the light extracting layer has a periodic structure. The substrate comprises a n-type TFT, the cathode, the light extracting layer, the organic light emitting layer, the hole transporting layer, the hole injecting layer and the reflective anode are arranged on the substrate in sequence from bottom to top, the cathode comprises ITO, the cathode is directly connected with a drain of the n-type TFT, and the light extracting layer is made from an undoped electron transporting material.

In an exemplary embodiment of the OLED, the light extracting layer is arranged close to a light exit side in the OLED.

According to the present embodiment, the surface of the light extracting layer has a periodic structure, thus increasing the light extracting efficiency of OLED.

In an exemplary embodiment of the OLED, the periodic structure comprises one-dimensional prisms which have a triangular or curved cross section, or periodic patterns which are arranged in a matrix.

In an exemplary embodiment of the OLED, the undoped electron transporting material comprises a polymer.

In an exemplary embodiment of the OLED, the OLED further comprises an electrode modifying layer which is arranged between the cathode and the light extracting layer.

In an exemplary embodiment of the OLED, the electrode modifying layer is made from Al<NUM>O<NUM> or ZnO, and has a thickness of about <NUM>-<NUM>.

In an exemplary embodiment of the OLED, the OLEED further comprises an n-doped electron transporting layer which is arranged between the light extracting layer and the electrode modifying layer.

In a second aspect, embodiments of the present application provide a display device, which comprises the OLED as described in any of the above embodiments.

In a third aspect, embodiments of the present application provides a method for fabricating an OLED, comprising: providing a substrate, and forming a cathode, a light extracting layer, an organic light emitting layer, a hole transporting layer, a hole injecting layer and a reflective anode on the substrate. A surface of the light extracting layer has a periodic structure, the substrate comprises a n-type TFT. The cathode, the light extracting layer, the organic light emitting layer, the hole transporting layer, the hole injecting layer and the reflective anode are arranged on the substrate in sequence from bottom to top, the cathode comprises ITO, the cathode is directly connected with a drain of the n-type TFT, and the light extracting layer is made from an undoped electron transporting material.

In an exemplary embodiment of the method, the method further comprising: forming an electrode modifying layer between the cathode and the light extracting layer.

In an exemplary embodiment of the method, the method further comprises forming an n-doped electron transporting layer between the light extracting layer and the electrode modifying layer. According to the present embodiment, the OLED is an inverted OLED. The OLED comprises a cathode which is arranged at the bottom and made from ITO. The cathode thus is directly connected with a drain of an n-type TFT, and this facilitates integration of the cathode and TFT to increase stability of the display device. The ITO cathode has a relatively high work function. There a relatively large electron injecting barrier between the ITO cathode and the electron transporting material, which makes it difficult for electrons to inject. The above mentioned electrode modifying layer helps to decrease the injecting barrier for electrons, so that this problem is solved.

Specific embodiments of the present disclosure will be further described hereinafter with reference to the drawings and embodiments. The following embodiments are only used for explaining more clearly the technical solution of the present disclosure rather than limiting the protection scope of the present disclosure.

Reference numerals: <NUM>, <NUM> substrate; <NUM> first electrode; <NUM> first carrier transporting layer; <NUM> organic light emitting layer; <NUM> second carrier transporting layer; <NUM> second carrier injecting layer; <NUM> second electrode; <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> light extracting layer; <NUM>, <NUM>, <NUM> electrode modifying layer; <NUM> cathode; <NUM> electron transporting layer; <NUM> organic light emitting layer; <NUM> hole transporting layer; <NUM> hole injecting layer; <NUM> anode; <NUM>, <NUM>, <NUM> n-doped electron transporting layer; <NUM>, <NUM> imprinting body.

In an embodiment of the present application, an OLED is provided. In the embodiment shown in <FIG>, the OLED comprises a first electrode <NUM>, a first carrier transporting layer <NUM>, an organic light emitting layer <NUM>, a second carrier transporting layer <NUM>, and a second electrode <NUM> on a substrate <NUM>. The OLED further comprises a light extracting layer <NUM> between the first electrode <NUM> and the first carrier transporting layer <NUM>. The light extracting layer <NUM> is made from a first carrier transporting material.

In the embodiment shown in <FIG>, the OLED is a bottom emitting type. Accordingly, the substrate <NUM> is made from a transparent material, so that the light generated by the organic light emitting layer <NUM> can pass through the substrate <NUM>. The light extracting layer <NUM> is arranged at the light exit side of OLED, thus increasing light extracting efficiency.

Optionally, the OLED comprises a second carrier injecting layer <NUM> between the second carrier transporting layer <NUM> and the second electrode <NUM>.

In an embodiment not forming part of the claimed invention, the OLED can also be a top emitting type. For example, in the embodiment shown in <FIG>, the OLED comprises the first electrode <NUM>, the first carrier transporting layer <NUM>, the organic light emitting layer <NUM>, the second carrier transporting layer <NUM>, and the second electrode <NUM> on the substrate <NUM>. The OLED further comprises a light extracting layer <NUM> between the second electrode <NUM> and the second carrier transporting layer <NUM>. In case the OLED comprises the second carrier injecting layer <NUM> which is arranged at a side of the second carrier transporting layer <NUM> away from the substrate <NUM>, the light extracting layer <NUM> is arranged between the second electrode <NUM> and the second carrier injecting layer <NUM>. The light extracting layer <NUM> is made from a second carrier transporting material.

In the embodiment shown in <FIG>, the OLED is a top emitting type. The light extracting layer <NUM> is arranged at the light exit side of OLED, thus increasing light extracting efficiency.

As shown in <FIG>, by forming the light extracting layer at the light exit side of OLED from a corresponding carrier transporting material, it is possible to efficiently increase the light extracting efficiency of OLED. Since the light extracting layer is made from the corresponding carrier transporting material, the process for forming the light extracting layer is compatible with the existing process for fabricating OLED, especially with the process for forming the corresponding carrier transporting layer, so that it is easy to fabricate and the cost can be efficiently controlled.

As an example, the light extracting layer <NUM>, <NUM> is made from a polymer carrier transporting material. In this case, the polymer material applied on the electrode by spin coating, and is patterned by nano-imprinting to form the periodic structure. The light extracting layer made from the polymer material is relatively dense, and isolates the organic light emitting layer from the environment. This prevents environmental factors like moisture from destroying the organic material in the organic light emitting layer, thus increasing the lifetime of OLED.

A surface of the light extracting layer <NUM>, <NUM> has a periodic structure. The periodic structure comprises one-dimensional prisms which have a triangular or curved cross section. Optionally, the periodic structure comprises periodic patterns which are arranged in a matrix. The light extracting layer which has the periodic structure in the surface facilitates increasing the light extracting efficiency of OLED. Besides, these one-dimensional prisms and periodic patterns which are arranged in a matrix are easy to fabricate. However, the present application is not limited in this regard. For example, the surface of the light extracting layer may have a quasi-periodic structure or a non-periodic structure, as long as the structure can increase the light extracting efficiency of OLED.

The light extracting layer <NUM>, <NUM> is made from any known carrier transporting material. In the embodiment shown in <FIG>, the light extracting layer <NUM> is made from a same material as the first carrier transporting layer <NUM>. In the embodiment shown in <FIG>, the light extracting layer <NUM> is made from a same material as the second carrier transporting layer <NUM> or the second carrier injecting layer <NUM>. For example, in case the first electrode <NUM> is a cathode made from ITO, the light extracting layer <NUM> is made from any known electron transporting material, e.g., poly(<NUM>,<NUM>-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS).

As shown in <FIG>, the OLED further comprises an electrode modifying layer <NUM> between the first electrode <NUM> and the light extracting layer <NUM>. The electrode modifying layer <NUM> decreases the interface barrier between the first electrode <NUM> and the organic material of the organic light emitting layer <NUM>, so that the first carriers are injected efficiently, which increases the performance of OLED. In case the first electrode <NUM> is a cathode, the electrode modifying layer <NUM> is made from Al<NUM>O<NUM> or ZnO. The electrode modifying layer <NUM> has a thickness about <NUM>-<NUM>.

Similarly, in the embodiment shown in <FIG>, the OLED comprises an electrode modifying layer <NUM> between the light extracting layer <NUM> and the second electrode <NUM>. The electrode modifying layer <NUM> facilitates injecting the second carriers from the second electrode <NUM>.

In the embodiments shown in <FIG>, the first carriers are electrons, and the second carriers are holes. Accordingly, the first electrode <NUM> is a cathode, the first carrier transporting layer <NUM> is an electron transporting layer, the second carrier transporting layer <NUM> is a hole transporting layer, the second carrier injecting layer <NUM> is a hole injecting layer, and the second electrode <NUM> is an anode.

In the embodiment shown in <FIG>, the OLED has an inverted configuration, the substrate <NUM> is transparent substrate, and light is output from the first electrode <NUM> (namely, from the substrate <NUM>). As an example, the second electrode <NUM> is made from a reflective material, e.g., a reflective metal layer, so as to further increase the light extracting efficiency of OLED. As an example, in case the first electrode <NUM> is a cathode, the first electrode <NUM> is made from ITO.

OLEDs in embodiments of the present application will be described hereinafter with reference to <FIG>, <FIG>. In particular, these OLEDs are inverted OLEDs (IOLED).

<FIG> shows an inverted OLED according to an embodiment of the present application. As shown, the OLED comprises a cathode <NUM>, an electron transporting layer <NUM>, an organic light emitting layer <NUM>, a hole transporting layer <NUM>, and an anode <NUM>, which are arranged on a substrate <NUM> in this order. Optionally, the OLED further comprises a hole injecting layer <NUM> between the hole transporting layer <NUM> and the anode <NUM>. The electron transporting layer <NUM> is generally made from an undoped electron transporting material, but the present application is not limited in this regard. The OLED further comprises a light extracting layer <NUM> which is arranged at the light exit side and an electrode modifying layer <NUM> which is arranged on the cathode <NUM>. The light extracting layer <NUM> and the electrode modifying layer <NUM> shown in <FIG> are similar to the light extracting layer <NUM> and the electrode modifying layer <NUM> shown in <FIG>, which are not repeated here for simplicity.

As shown in <FIG>, for example, the OLED further comprises an n-doped electron transporting layer <NUM>, which is arranged at a side of the electron transporting layer <NUM> facing the cathode <NUM>. The n-doped electron transporting layer is made from an electron transporting material doped with an n-type dopant. For example, the n-type dopant is Ce or Li. The n-doped electron transporting layer <NUM> decreases the injecting barrier for electrons, which increases the efficiency for injecting electrons, and further increases the performance of OLED.

It is noted that OLED further comprises other functional layers such as an electron blocking layer, a hole blocking layer. These functional layers are known for the ordinary skilled person in the art, and thus are not repeated here for simplicity.

As compared with a conventional non-inverted OLED, the inverted OLED can be integrated with the n-type TFT more easily. Currently, a TFT with an IGZO (indium gallium zinc oxide) active layer provides a better match with the inverted OLED. In the inverted OLED, in case ITO is used the transparent cathode, OLED is directly connected with the drain of n-type TFT, and this facilitates integration of the cathode and TFT to increase stability of the display device. In this case, the substrate <NUM> in <FIG> is an n-type TFT. However, since ITO has a relatively high work function, so that electrons are subject to a relatively high injecting barrier, the efficiency for injecting electrons is low, and the performance of OLED is affected. According to the present embodiment, the electrode modifying layer <NUM> is formed on the cathode <NUM>, injecting barrier for electrons are efficiently decreased, so that the above problem about integration the inverted OLED and the n-type TFT is solved.

The electrode modifying layer <NUM> comprises Al<NUM>O<NUM> or ZnO, so as to efficiently decrease the surface work function of the cathode <NUM> for increasing electron injecting capability. The electrode modifying layer <NUM> generally has a thickness about <NUM>-<NUM>, e.g., <NUM> or <NUM>. The electrode modifying layer <NUM> becomes an insulating layer when it is too thick, and this is disadvantageous for the electrical performance of inverted OLED. In case the electrode modifying layer <NUM> comprises Al<NUM>O<NUM> or ZnO, the electrode modifying layer <NUM> is formed as follow. A suspension comprising Al<NUM>O<NUM> or ZnO in an organic solvent is spin coated, and the OLED is annealed to form a dense Al<NUM>O<NUM> or ZnO film. The dense electrode modifying layer <NUM> isolates the organic light emitting layer <NUM> from the environment. This prevents environmental factors like moisture from destroying the organic material in the organic light emitting layer, which is favorable for the lifetime of inverted OLED.

Similar with the embodiment of <FIG>, for example, the inverted OLED further comprises the light extracting layer <NUM> which is arranged between the cathode <NUM> and the electron transporting layer <NUM>. Optionally, as shown in <FIG>, the light extracting layer <NUM> is arranged between the electrode modifying layer <NUM> and the n-doped electron transporting layer <NUM>.

The light extracting layer <NUM> is arranged at the light exit side of the inverted OLED, thus increasing light extracting efficiency. The light extracting layer <NUM> is made from an electron transporting material, thus efficiently increasing the light extracting efficiency of inverted OLED, without adversely affecting injecting and transporting of electrons. As an example, the light extracting layer <NUM> is made from a polymer carrier transporting material, so that it is applied on the cathode <NUM> by spin coating and is nano-imprinted to form a periodic structure. As an example, a surface of the light extracting layer <NUM> has a periodic structure which comprises one-dimensional prisms which have a triangular or curved cross section, or periodic patterns which are arranged in a matrix. This facilitates increasing the light extracting efficiency of inverted OLED.

<FIG> shows an inverted OLED in another embodiment of the present application. As shown, the inverted OLED comprises the cathode <NUM>, the electrode modifying layer <NUM>, the n-doped electron transporting layer <NUM>, a light extracting layer <NUM>, the electron transporting layer <NUM>, the organic light emitting layer <NUM>, the hole transporting layer <NUM>, the hole injecting layer <NUM>, and the anode <NUM>, which are arranged on the substrate <NUM> in this order. As compared with the embodiment of <FIG>, in the embodiment shown in <FIG>, the light extracting layer <NUM> is arranged between the n-doped electron transporting layer <NUM> and the electron transporting layer <NUM>.

<FIG> shows an inverted OLED in yet another embodiment of the present application, which is according to the claimed invention. As shown, the inverted OLED comprises the cathode <NUM>, the electrode modifying layer <NUM>, the n-doped electron transporting layer <NUM>, a light extracting layer <NUM>, the organic light emitting layer <NUM>, the hole transporting layer <NUM>, the hole injecting layer <NUM>, and the anode <NUM>, which are arranged on the substrate <NUM> in this order. As compared with the embodiment of <FIG>, the inverted OLED of <FIG> does not comprise an individual electron transporting layer. The light extracting layer <NUM> is arranged between the n-doped electron transporting layer <NUM> and the organic light emitting layer <NUM>. According to the invention, the light extracting layer <NUM> is made from an undoped electron transporting material. In the present embodiment, the light extracting layer <NUM> not only improves the light extracting efficiency, but also acts as an electron transporting layer in the inverted OLED.

Among the foregoing embodiments described with reference to <FIG>, <FIG>, the embodiment corresponding to <FIG> falls into the scope of the claimed invention, whereas the embodiments corresponding to <FIG>, <FIG> do not form part of the claimed invention.

<FIG> show different embodiments of a light extracting layer of the present application.

As shown by the cross-sectional view in <FIG>, after the electrode modifying layer <NUM> is formed on the cathode <NUM>, a film of polymer carrier transporting material is formed on the electrode modifying layer <NUM> by spin coating. As an example, the film has a thickness about <NUM>-<NUM>, e.g., <NUM>. Then, the film of polymer carrier transporting material is nano-imprinted by an imprinting body <NUM>, and a pattern of the imprinting body <NUM> is transferred to the film of polymer carrier transporting material, thus forming a light extracting layer <NUM>. As shown in <FIG>, the light extracting layer <NUM> comprises one-dimensional prisms which have a triangular cross section.

As shown by the cross-sectional view of <FIG>, after the electrode modifying layer <NUM> is formed on the cathode <NUM>, a film of polymer carrier transporting material is formed on the electrode modifying layer <NUM> by spin coating. Then, the film of polymer carrier transporting material is nano-imprinted by an imprinting body <NUM>, and a pattern of the imprinting body <NUM> is transferred to the film of polymer carrier transporting material, thus forming a light extracting layer <NUM>. As shown in <FIG>, the light extracting layer <NUM> comprises one-dimensional prisms which have a curved (wave shaped) cross section.

In the embodiments shown in <FIG>, the surface of the light extracting layer <NUM>, <NUM> has a periodic structure comprising one-dimensional prisms which have a triangular or curved cross section. However, the present application is not limited in this regard. The light extracting layer may comprise periodic patterns which are arranged in a matrix. Besides, it is possible for the surface of the light extracting layer to have a quasi-periodic structure or non-periodic structure, as long as this structure increases the light extracting efficiency of OLED.

The imprinting body <NUM>, <NUM> is fabricated by forming a specific pattern on an imprinting substrate (not shown) via electron beam deposition, laser direct writing, chemical synthesis, self-assembling, or the like. The specific pattern is complementary with the pattern which is desired to be formed on the surface of the light extracting layer.

It is noted that the light extracting layer <NUM>, <NUM> shown in <FIG> is applicable to the light extracting layer <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in OLED shown in <FIG>, <FIG>. For sake of simplicity, the surface morphology of the light extracting layer <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is not shown in <FIG>, <FIG>.

Furthermore, in case the above light extracting layer is formed in OLED, functional layers in OLED, e.g., the electron transporting layer, the organic light emitting layer, the hole transporting layer, the hole injecting layer, and the anode, are formed on the light extracting layer in this order and conform to the surface morphology of the light extracting layer. Namely, each functional layer formed on the light extracting layer also has a same periodic structure as the light extracting layer, which further increases the light extracting efficiency of OLED. According to an embodiment of the present application, a display device is provided, which comprises the OLED as described above. The display device can be any product or component with a display function like a mobile phone, tablet computer, TV, monitor, notebook computer, digital photo frame, and navigator. As known for the ordinary skilled person in the art, apart from the OLED, the display device further comprises other components like a driving circuit. These components are known in the art, and thus are not repeated here for simplicity.

According to an embodiment of the present application, a method for fabricating an OLED is provided. As shown in <FIG>, the method comprises steps of:.

As an example, patterning the first carrier transporting material comprises: nano-imprinting the first carrier transporting material by means of a nano-imprinting body.

As an example, forming the first carrier transporting material on the first electrode comprises: spin coating a polymer carrier transporting material on the first electrode to a thickness about <NUM>-<NUM>.

As an example, after forming the first electrode and prior to forming the light extracting layer, the method further comprise: spin coating on the first electrode a suspension which comprises an electrode modifying material in an organic solvent; and annealing the OLED on which the suspension has been spin coated to form an electrode modifying layer.

As an example, the electrode modifying layer comprises Al<NUM>O<NUM> or ZnO.

The first electrode is a cathode, the first carrier transporting layer is an electron transporting layer, the second carrier transporting layer is a hole transporting layer, and the second electrode is an anode; and the method comprises forming the second electrode from a reflective material.

As an example, forming the first electrode on the substrate comprise: depositing ITO on the substrate; and performing ultraviolet and ozone treatment on ITO to form the first electrode.

In an exemplary embodiment, the method comprises the following steps.

The cathode <NUM>, which is made from ITO, is formed on the substrate <NUM>. An ultraviolet and ozone treatment is performed on the surface of the cathode <NUM>. In a non-inverted OLED, it is generally not required to perform ultraviolet and ozone treatment on the ITO cathode. However, in the inverted OLED, after deposition of ITO, ultraviolet and ozone treatment is generally performed on ITO to decrease the work function of cathode.

A layer of oxide precursor suspension is spin coated on the cathode <NUM> for modifying the surface of ITO. For example, the oxide is Al<NUM>O<NUM> or ZnO, which acts to decrease the work function of ITO to increase electron injecting capability. Then, the OLED on which the oxide precursor suspension has been spin coated is annealed, to form a dense oxide film, i.e., the electrode modifying layer <NUM>. Optionally, prior to annealing, the oxide precursor suspension is subject to drying treatment. As an example, the electrode modifying layer <NUM> has a thickness about <NUM>-<NUM>, e.g., <NUM> or <NUM>.

A film of polymer electron transporting material is spin coated on the electrode modifying layer <NUM>. As an example, the film has a thickness about <NUM>-<NUM>, e.g., <NUM>. The film is nano-imprinted by an imprinting body which is prepared in advance, to form a periodic structure, thus forming the light extracting layer <NUM>.

The structure resulting from the previous step is transferred to a vacuum deposition chamber. The n-doped electron transporting layer <NUM>, the (undoped) electron transporting layer <NUM>, the organic light emitting layer <NUM>, the hole transporting layer <NUM>, the hole injecting layer <NUM>, and reflective the anode <NUM> are deposited in this order on the light extracting layer <NUM> with the periodic structure.

From the above steps, the inverted OLED with an improved light extracting efficiency shown in <FIG> is obtained.

The process for fabricating the inverted OLED shown in <FIG> has been described above. On basis of the disclosure of the present application, the ordinary skilled person in the art will know the process for fabricating OLEDs shown in <FIG> and <FIG>, which are not repeated here for simplicity.

According to embodiments of the present application, the light extracting layer is formed between the first electrode and the organic light emitting layer in the OLED from a first carrier transporting material. This increases the light extracting efficiency of OLED. The light extracting layer further acts as the first carrier transporting layer, thus simplifying the structure of OLED , so that it is easy to fabricate and the cost can be efficiently controlled.

Claim 1:
An OLED, comprising:
a substrate (<NUM>), and
a cathode (<NUM>), a light extracting layer (<NUM>), an organic light emitting layer (<NUM>), a hole transporting layer (<NUM>), a hole injecting layer (<NUM>) and a reflective anode (<NUM>),
wherein a surface of the light extracting layer (<NUM>) has a periodic structure,
characterized in that, the substrate (<NUM>) comprises a n-type TFT, wherein the cathode (<NUM>), the light extracting layer (<NUM>), the organic light emitting layer (<NUM>), the hole transporting layer (<NUM>), the hole injecting layer (<NUM>) and the reflective anode (<NUM>) are arranged on the substrate (<NUM>) in sequence from bottom to top, the cathode (<NUM>) comprises ITO, the cathode (<NUM>) is directly connected with a drain of the n-type TFT, and the light extracting layer (<NUM>) is made from an undoped electron transporting material.