CN102931355B - OLED device - Google Patents

Abstract

The present invention relates to an OLED device. The OLED device comprises a substrate, a transparent anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and a cathode, wherein the transparent anode is arranged on the substrate, the hole injection layer is arranged on the transparent anode, the hole transport layer is arranged on the hole injection layer, the light emitting layer is arranged on the hole transport layer, the electron transport layer is arranged on the light emitting layer, the electron injection layer is arranged on the electron transport layer, and the cathode is arranged on the electron injection layer. The invention has the advantages of effectively avoiding the accumulation of current carriers at the interface, balancing the recombination of the current carriers, limiting the light-emitting layer on the light-emitting layer, and leading the phosphorescent material to exert the optimal effect, thereby meeting the use requirement of an OLED device adopting the phosphorescent material. The invention is particularly suitable for OLEDs.

Description

OLED device

technical field

The invention relates to an OLED device.

Background technique

Kodak Corporation of the United States first proposed the "sandwich" organic electroluminescent device structure in the patent US4769292 in 1987, which attracted global attention; two years later, Kodak Corporation of the United States still introduced the hole transport layer for the first time in the patent US4885211. The key point of OLED device design is revealed, and the OLED research boom has been opened since then. Because OLED has many advantages such as self-illumination, full solid state, wide viewing angle, and fast response, it is considered to have great application prospects in flat panel displays, and is even considered to be a new generation of flat panel displays after liquid crystal (LCD) and plasma (PDP). products and technologies. In order to avoid the luminescence quenching of the device due to the deflection of the luminescent center to the electrode, a carrier injection layer and a transport layer were introduced on the basis of the simple "sandwich" device structure, and gradually formed the more common multi-layer OLED device structure. As shown in accompanying drawing 1, substrate 1, the ITO transparent anode 2 placed on the substrate, the hole injection layer (HIL) 3 placed on the ITO transparent anode, the hole transport layer (HTL) placed on the hole injection layer ) 4, the light emitting layer (EML) 5 placed on the hole transport layer, the electron transport layer (ETL) 6 placed on the light emitting layer, the electron injection layer (EIL) 7 placed on the electron transport layer and the electron Cathode 8 on the injection layer. In order to improve the efficiency of the device, the light-emitting layer usually adopts a host/guest doping system.

However, in order for OLED to have an advantage in the flat panel display market, the driving voltage and luminous efficiency of OLED still need to be further improved. The most effective way to improve the luminous efficiency of OLEDs is to directly research and develop efficient phosphorescent electroluminescent devices.

According to spin statistics, the probability ratio of holes and electrons combining to form singlet and triplet excitons is 1:3, that is, 25% of the excited molecules will form a singlet state, while 75% of the excited molecules will form a triplet state. Due to the restriction of the selection rule, the transition from the triplet state to the ground state of the fluorescent luminescent material is prohibited, and only rely on the singlet state transition to emit light, so the quantum efficiency can only reach 25% at the highest; while the phosphorescent luminescent material has a strong spin-orbit The coupling effect makes the selection rule to be lifted to a certain extent, and the probability of optical radiation transition from the triplet excited state T1 to the ground state S0 increases, and the singlet and triplet state can be used to emit light at the same time. Theoretically, the quantum efficiency can reach 100%, which is 4 times that of fluorescent luminescent materials. It can be seen that if an efficient phosphorescent material is introduced into an OLED device and the device structure is rationally designed, the efficiency of the device can be greatly improved.

However, due to the relatively long radiation lifetime of triplet phosphorescence, the triplet excitons can easily migrate to the carrier transport layer and cause the material of the transport layer to emit light; in addition, to obtain a high-efficiency, low-voltage driven phosphorescent OLED must be matched with an excellent performance Carrier injection and transport layers, all of which put forward higher requirements for the structural design of high-efficiency phosphorescent OLED devices, and current OLED devices do not yet have a structure that supports high-efficiency phosphorescent light-emitting materials.

Contents of the invention

The problem solved by the invention is to propose a high-efficiency OLED device that can support phosphorescent materials.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: an OLED device comprising a substrate, a transparent anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode, and the transparent anode is provided with On the substrate, the hole injection layer is disposed on the transparent anode, the hole transport layer is disposed on the hole injection layer, the light emitting layer is disposed on the hole transport layer, the electron transport layer is disposed on the light emitting layer, and the electron injection layer is disposed on the On the electron transport layer, the cathode is arranged on the electron injection layer, characterized in that the hole transport layer is a multi-layer structure including 2-4 hole transport layers.

Specifically, the hole transport layer is three layers, including a first hole transport layer, a second hole transport layer and a third hole transport layer, and the second hole transport layer is arranged on the first hole transport layer. layer, the third hole transport layer is disposed on the second hole transport layer.

Specifically, the thickness of the first hole transport layer is greater than that of the second hole transport layer, and the thickness of the second hole transport layer is greater than that of the third hole transport layer.

Specifically, the thickness of the hole transport layer is not greater than 60 nm.

The beneficial effect of the present invention is that the accumulation of carriers at the interface is effectively avoided, the recombination of carriers is balanced, and the light-emitting layer is limited to the light-emitting layer, so that the phosphorescent material exerts the best effect, and the device efficiency is improved. The method is effectively improved, thereby satisfying the use of OLED devices using phosphorescent luminescent materials.

Description of drawings

FIG. 1 is a schematic structural view of an existing OLED device;

Fig. 2 is a schematic structural view of the OLED device of the present invention.

Detailed ways

Below in conjunction with accompanying drawing and embodiment, describe technical scheme of the present invention in detail:

As shown in Figure 1, the current OLED device includes a substrate 1, a transparent anode 2, a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, an electron injection layer 7 and a cathode 8, wherein the transparent The anode 2 is arranged on the substrate 1, the hole injection layer 3 is arranged on the transparent anode 2, the hole transport layer 4 is arranged on the hole injection layer 3, the light emitting layer 5 is arranged on the hole transport layer 4, the electron transport layer 6 It is disposed on the light emitting layer 5 , the electron injection layer 7 is disposed on the electron transport layer 6 , and the cathode 8 is disposed on the electron injection layer 7 .

The main technical solution adopted by the present invention to overcome the prior art is to improve the structure of the hole transport layer 4 by improving the original single-layer hole transport layer into a multi-layer hole transport layer stacking method. , improving the hole transport layer to 2-4 layers can effectively avoid the accumulation of carriers at the interface and balance the recombination of carriers, thereby confining the light-emitting layer to the light-emitting layer, so that the phosphorescent light-emitting material can exert the best effect. At the same time, in order to reduce the driving voltage and improve the efficiency of OLED devices, a P-type doped hole injection structure is adopted. The multi-layer hole transport layer needs to have a large number of "free holes" formed by carrying the P-type doped injection structure and prevent injection. A layer in which holes are quenched by P-type dopant guests, a layer that transports injected hole carriers, and a layer that matches the energy level of the light-emitting layer and confines excitons in the light-emitting layer layer.

The light-emitting layer of the present invention is a phosphorescent light-emitting layer, which mainly includes a non-emissive host material and a phosphorescent light-emitting material, and adopts the method of doping the non-emissive host material with the phosphorescent light-emitting material, wherein the electron mobility of the phosphorescent light-emitting material is better than that of the air. Hole mobility can be, but not limited to, red phosphorescent materials, green phosphorescent materials, blue phosphorescent materials, and yellow phosphorescent materials. In order to achieve a relatively ideal luminous effect, the doping concentration of the phosphorescent luminescent material is at least 0-12%.

In the actual production process, in order to cooperate with the new structure that can support high-efficiency phosphorescent materials, other components of the OLED panel can adopt the following methods:

The substrate adopts transparent glass or flexible substrate with good light transmission in the visible light region, such as polyester polymer compound and polyolefin polymer compound, and has certain oxygen and water resistance and good surface smoothness.

The anode has good electrical conductivity, good chemical and morphological stability, high work function, and high transparency in the visible light region, usually using transparent conductive oxides (such as ITO, ZnO, AZO(Al:ZnO) etc.) and metals (Ni, Au, Pt, etc.); further, the anode can be combined with some surface treatment (such as O ₂ plasma or UV-ozone treatment) to improve its work function.

The hole injection layer used requires good energy level matching with the anode and the adjacent hole transport layer, which can be but not limited to CuPc, TNATA, PEDOT. A preferred solution is that the hole injection layer adopts a P-type doping structure, and the hole transport material is doped with an oxidant such as SbCl ₅ , FeCl ₃ , iodine, F4-TCNQ or TBAHA. Of course, any other structure that can improve hole injection, such as a quantum well structure, can also be used.

The light-emitting layer adopts a host-guest doping structure, and the doped guest is a phosphorescent material, and the host material used must have electron mobility and hole mobility, preferably the electron mobility is at least ten times that of the hole mobility. In order to better improve the efficiency of the light-emitting layer.

The new hole transport layer composed of multi-layer hole transport layers requires a hole mobility of at least 10-4cm ² /(V·S) order, and has high thermal stability, and can be vacuum evaporated to form pinhole film; optional hole transport materials are pair-coupled diamine compounds, such as TPD, TAPC, NPB, β-NPB, α-NPD; triphenylamine compounds, such as TDAB, TDAPB, PTDATA, spiro- mTTB; or one of certain triarylamine polymers, carbazoles.

Preferably, the total thickness of the hole transport layer does not exceed 60 nm, and the optimum total thickness of the hole transport layer is 35 nm. The total thickness of the hole transport layer is the sum of the thicknesses of each hole transport layer. The different thicknesses mainly affect the performance of each hole transport layer. It has been proved by experiments that to achieve a better improvement in the light emitting layer Efficiency, preferably the total thickness of the hole transport layer does not exceed 60nm.

The electron transport layer used is required to have high electron mobility, high glass transition temperature and thermal stability, and can form a uniform, non-porous film through thermal evaporation. It is an oxazole derivative, a metal chelate One of quinoline derivatives, oxaline derivatives, diazanthracene derivatives, phenanthroline derivatives, and silicon-containing heterocyclic compounds.

The electron injection layer can be lithium oxide, lithium boron oxide, potassium silicon oxide, cesium carbonate or alkali metal fluoride, such as one of lithium fluoride, potassium fluoride and cesium fluoride.

The cathode can be metal or metal alloy with low work function, which is one of lithium, magnesium, aluminum, magnesium-silver alloy, and lithium-aluminum alloy.

The preparation method of the OLED device described in the present invention is: utilize the method for vacuum evaporation to vapor-deposit each layer in turn, and the alternative scheme is that the evaporation rate of each layer should be controlled at between.

Example:

As shown in Figure 2, the OLED device in this embodiment includes a substrate 1, a transparent anode 2, a hole injection layer 3, a first hole transport layer 41, a second hole transport layer 42, a third hole transport layer 43. The light emitting layer 5, the electron transport layer 6, the electron injection layer 7 and the cathode 8, wherein the transparent anode 2 is arranged on the substrate 1, the hole injection layer 3 is arranged on the transparent anode 2, and the first hole transport layer 41 is arranged on the On the hole injection layer 3, the second hole transport layer 42 is disposed on the first hole transport layer 41, the third hole transport layer 43 is disposed on the second hole transport layer 42, and the light emitting layer 5 is disposed on the third hole transport layer 41. On the hole transport layer 43 , the electron transport layer 6 is disposed on the light emitting layer 5 , the electron injection layer 7 is disposed on the electron transport layer 6 , and the cathode 8 is disposed on the electron injection layer 7 . Wherein the hole mobility of the first hole transport layer, the second hole transport layer, and the third hole transport layer is at least on the order of 10 ^-4 cm ² /(V·S), and the second hole transport layer The hole mobility is better than or equal to that of the first hole transport layer; the hole mobility of the third hole transport layer is lower than or equal to or higher than that of the second hole transport layer. At the same time, the highest occupied molecular orbitals of the first hole transport layer, the second hole transport layer and the third hole transport layer are distributed between the highest occupied molecular orbitals of the hole injection layer and the light emitting layer.

The specific principle of using three hole transport layers is as follows: the first hole transport layer carries a large number of carriers to avoid the accumulation of carriers at the interface; the second hole transport layer quickly transfers carriers; the third hole transport layer The energy levels of the layers are matched, and the excitons of the emission layer are limited to the light-emitting region, so as to achieve the purpose of improving the efficiency of the OLED device, and also have the advantage of further prolonging the life of the OLED device. It has been proved by experiments that the thickness relationship between the three hole transport layers is: the thickness of the first hole transport layer is greater than that of the second hole transport layer, and when the thickness of the second hole transport layer is greater than that of the third hole transport layer, The efficiency of the OLED device can be better improved.

Claims (4)

1. OLED device, comprising substrate, transparent anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer and cathode, described transparent anode is arranged on the substrate, and hole injection layer is arranged on transparent On the anode, the hole transport layer is disposed on the hole injection layer, the light emitting layer is disposed on the hole transport layer, the electron transport layer is disposed on the light emitting layer, the electron injection layer is disposed on the electron transport layer, and the cathode is disposed on the electron injection layer above, it is characterized in that the hole transport layer is a multi-layer structure including 2 to 4 layers of hole transport layers, the light-emitting layer is a phosphorescent light-emitting layer, and the substrate is made of polyester polymer compound or polyolefin A polymer compound, the anode uses a transparent conductive oxide or metal, the hole injection layer adopts a P-type doped structure, the light-emitting layer adopts a host-guest doped structure in which the doped guest is a phosphorescent material, and the phosphorescent light The layer includes a non-emitting host material and a phosphorescent material, and adopts the method of doping the non-emitting host material with the phosphorescent material, wherein the electron mobility of the phosphorescent material is better than the hole mobility, and the doping concentration of the phosphorescent material is greater than 0 is less than or equal to 12%. 2. OLED device according to claim 1, is characterized in that, described hole transport layer is 3 layers, comprises first hole transport layer, second hole transport layer and the 3rd hole transport layer, described The second hole transport layer is disposed on the first hole transport layer, and the third hole transport layer is disposed on the second hole transport layer. 3. The OLED device according to claim 2, wherein the thickness of the first hole transport layer is greater than that of the second hole transport layer, and the thickness of the second hole transport layer is greater than that of the third hole transport layer. 4. The OLED device according to claim 1, wherein the thickness of the hole transport layer is not greater than 60 nm.