CN205542905U - Ultraviolet organic light emitting device - Google Patents

Abstract

The utility model discloses an ultraviolet organic light-emitting device. The device comprises a substrate layer, an anode layer, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a reflective metal cathode layer, and the electron injection layer is LiF with a thickness of 1.5nm-6nm; The bottom layer, the anode layer, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the reflective metal cathode layer are sequentially stacked as one. The utility model uses a thick insulating layer as the electron injection layer, and improves the balance of electron-holes in the light-emitting layer by reducing the injection of electrons, so that only a lower current density is required when the same number of electron-hole pairs is reached. , increasing the probability of recombination of electrons and holes in the light-emitting layer, resulting in high-efficiency near-ultraviolet light emission, and improving the luminous efficiency and irradiance of ultraviolet OLED devices.

Description

A kind of ultraviolet organic light-emitting device

technical field

The utility model belongs to the technical field of semiconductor devices, in particular to an ultraviolet organic light-emitting device.

Background technique

Since C.W.Tang et al. invented a high-brightness, low-voltage organic electroluminescent device (OLED) with a double-layer structure in 1987, OLED has been widely favored by people. OLED has excellent characteristics such as rich color performance, ultra-high power efficiency, ultra-thin structure of about 100nm, and mechanical flexibility, so it shines in the fields of new flat panel display and solid-state lighting. After more than 20 years of development, its technology has entered the practical stage. The emission wavelength of ultraviolet OLED is generally in the range of 320nm-400nm, which is also called near-ultraviolet emission. Ultraviolet organic light-emitting devices have the advantages of fast response speed, good mechanical flexibility, ultra-thin and portable, easy to build large-area light-emitting devices, etc., and have incomparable superior performance of traditional SiC, ZnO and other inorganic ultraviolet light-emitting devices. Therefore, UV OLEDs have potential applications in high-density information storage, coating curing, biosensing, and as excitation light sources.

The wavelength of ultraviolet light is shorter than that of visible light, and its energy is greater, which leads to the need for a very wide band gap as an organic material emitting ultraviolet light. Therefore, the energy level of the highest occupied molecular orbital (HOMO) of ultraviolet organic light emitting materials is much higher than that of visible light. For example, the HOMO energy level of CBP, a commonly used ultraviolet organic light-emitting material, is 6.1 eV, the HOMO energy level of OXD-7 is 6.5 eV, and the HOMO energy level of TAZ is 6.6 eV. The HOMO energy level of these organic materials is quite different from the work function of commonly used transparent conductive anodes (such as ITO) (the work function of ITO is generally 4.7eV). Therefore, the potential barrier of holes from the ITO anode to the ultraviolet light-emitting layer is as high as 1.5-2eV. The high hole injection barrier makes it difficult for holes to be injected into the light-emitting layer, resulting in the number of holes in the ultraviolet OLED light-emitting layer often being higher than that of electrons. The number of is very small, which makes the electron-hole balance in the light-emitting layer poor, and the luminous efficiency and irradiance of the device are difficult to improve.

Usually, the method to overcome this high hole injection barrier is to introduce a hole injection layer to increase hole injection, and supplemented with doping to improve hole mobility, but this method of improving hole injection and transport capabilities is very important for UV OLEDs. Still very limited, the effect is not very ideal.

Utility model content

The utility model provides an ultraviolet organic light-emitting device, which effectively improves the luminous efficiency and irradiance of the ultraviolet OLED device by introducing a thick insulating layer as an electron injection layer. The thickness of the electron injection layer in conventional ultraviolet OLED devices is usually 0.5nm-1nm, which is considered to be the optimal size. The utility model breaks through the technical prejudice, uses a thick insulating layer as the electron injection layer, and only needs a lower current density to achieve the same number of electron-hole pairs, which increases the probability of recombination of electrons and holes in the light-emitting layer, resulting in Efficient near-UV light emission. Compared with conventional ultraviolet OLED devices, the external quantum efficiency and irradiance of the utility model are greatly improved. The utility model overcomes the limitation of insufficient carrier balance in the conventional ultraviolet OLED device only relying on improving the hole injection and transport ability, and has simple process and good repeatability, so it has advantages in the construction of high-power ultraviolet OLED device very important practical value.

Technical scheme of the utility model:

1. An ultraviolet organic light-emitting device, comprising a substrate layer, an anode layer, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, a reflective metal cathode layer, and the electron injection layer is 1.5nm in thickness -6nm LiF; substrate layer, anode layer, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and reflective metal cathode layer are sequentially stacked as one.

Description of drawings

Fig. 1 is the structure of the utility model and the schematic diagram of external circuit.

In Figure 1: 1. Substrate layer; 2. Anode layer; 3. Hole injection layer; 4. Hole transport layer; 5. Light emitting layer; 6. Electron transport layer; 7. Electron injection layer; 8. Reflective metal cathode layer; 9. Power supply.

Fig. 2 is a comparison diagram of irradiance between embodiments of the present invention with different electron injection layer thicknesses and conventional ultraviolet OLED devices at different current densities.

Fig. 3 is a comparison diagram of the external quantum efficiency (EQE) of the embodiment of the utility model with different thicknesses of the electron injection layer and the conventional ultraviolet OLED device at different current densities.

Fig. 4 is a comparison diagram of the current density-voltage relationship between embodiments of different electron injection layer thicknesses of the present invention and conventional ultraviolet OLED devices.

In Fig. 2-Fig. 4: the thickness of device 1 is conventional; the thickness of device 2 is 1.5nm; the thickness of device 3 is 2.5nm; the thickness of device 4 is 4nm; the thickness of device 5 is 6nm.

detailed description

Below in conjunction with accompanying drawing and embodiment the content of the utility model is further elaborated.

The substrate is made of glass; the anode is made of ITO indium tin oxide film, and the square resistance is about 10Ω/□; the hole injection layer is made of MoO ₃ with a thickness of 2nm-5nm; the hole transport layer is made of CBP material; the light-emitting layer is made of TAZ material; The transport layer is made of BPhen; the reflective metal cathode layer is made of Al, and its thickness is not less than 100nm; The driving power of the external circuit can be selected as DC 3V-20V. Applying a DC voltage on the device will observe the near-ultraviolet emitting luminous line from the anode side, and obtain a comparison chart of various parameters of the UV OLED device of the present invention through related instruments, such as Figure 2-Figure 4 shows.

in:

CBP means 4,4'-bis(carbazol-9-yl)biphenyl, the thickness is 10nm-40nm.

TAZ means 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole with a thickness of 10nm-40nm.

BPhen means 4,7-diphenyl-1,10-phenanthroline, the thickness is 15nm-110nm.

Conventional ultraviolet OLED device, electron injection layer thickness is 0.5nm-1nm, this device is used as a comparison sample (device 1) of the utility model, and the parameter index comparison diagram shown in Figure 2-Figure 4 is obtained.

It can be seen from Figure 2 that under the same current density, the irradiance of the utility model (device 2 to device 5) is higher than that of the device (device 1) with an electron injection layer of conventional thickness. For example, when the current density is 100mA/cm ² , the irradiance of device 1 is 1.87mW/cm ² , the irradiance of device 2 is 2.28mW/cm ² ; the irradiance of device 3 is 3.74mW/cm ² ; The irradiance of device 4 is 3.29mW/cm ² ; the irradiance of device 5 is 1.93mW/cm ² ; the irradiance of device 2, device 3, device 4 and device 5 is 21.9% higher than that of device 1 , 100%, 75.9%, 3.2%. Therefore, the utility model greatly improves the irradiance and obtains unexpected effects.

It can be seen from Figure 3 that the maximum external quantum efficiency (EQE) of device 1 is 1.07%@2.4mA/cm ² , the maximum EQE of device 2 is 1.3%@2.1mA/cm ² , and the maximum EQE of device 3 is 2.1%@2.5 mA/cm ² , the maximum EQE of device 4 is 1.7%@2.3mA/cm ² , the maximum EQE of device 5 is 1.15%@7.8mA/cm ² , the maximum EQE ratio of device 2, device 3, device 4, and device 5 Device 1 increased by 21.5%, 96.3%, 58.9%, and 7.5%, respectively. At the same time, at the same current density, the EQEs of devices 2 to 5 are higher than those of device 1. Therefore, when the thickness of the electron injection layer LiF is 1.5-6nm, a higher external quantum efficiency can be obtained than that of the conventional thickness (0.5-1nm) electron injection layer, and an unexpected effect is obtained.

It can be seen from Fig. 4 that under the same voltage, the current density of devices 2 to 5 is lower than that of device 1, indicating that the luminous efficiency and irradiance of the utility model are also improved.

Based on the above experimental data, it can be seen that because the utility model breaks through the inertial thinking of conventional technologies, abandons the method of relying on improving hole injection and transmission capabilities, and uses a thick insulating layer as the electron injection layer, all technical indicators have obtained unexpected effect.

Claims (5)

1. An ultraviolet organic light-emitting device, comprising an electron injection layer, characterized in that: the electron injection layer is LiF with a thickness of 1.5nm-6nm. 2. The ultraviolet organic light emitting device according to claim 1, characterized in that: the thickness of the electron injection layer is 1.5nm-2.5nm. 3. The ultraviolet organic light emitting device according to claim 1, characterized in that: the thickness of the electron injection layer is 2.5nm-4nm. 4. The ultraviolet organic light emitting device according to claim 1, characterized in that: the thickness of the electron injection layer is 4nm-6nm. 5. The ultraviolet organic light-emitting device according to any one of claims 1-4, characterized in that: it also comprises a substrate layer, an anode layer, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, a reflection layer The metal cathode layer; the substrate layer, the anode layer, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the reflective metal cathode layer are sequentially stacked into one.