CN102969454A - High-contrast organic light-emitting device (OLED) with band-pass filter film and top-emitted green ray - Google Patents

Abstract

The invention belongs to the field of organic electroluminescence, and in particular relates to a high-contrast top-emitting green light organic electroluminescence device combined with a filter film. It consists of a substrate, a metal anode, an organic functional layer, a metal cathode and a band-pass filter film. The organic functional layer sequentially comprises a hole injection layer, a hole transport layer, an electron blocking layer, a green light emitting layer, an electron transport layer and an electron injection layer. The introduction of the filter film can weaken the influence of ambient light on the contrast of the display device, thereby realizing a high-contrast organic electroluminescent device. The high-contrast organic electroluminescent device of the present invention overcomes the shortcomings of complicated device structure and difficult process brought about by the previous top-emitting device in order to achieve high contrast. At the same time, this invention improves the contrast. Efficiency has little effect. The top emission organic electroluminescent device prepared by the invention has the advantages of high contrast, low efficiency loss, simple process and low cost.

Description

A high-contrast top-emitting green organic electroluminescent device with a bandpass filter

technical field

The invention belongs to the field of organic electroluminescence, in particular to a high-contrast top-emitting green light organic electroluminescence device with a band-pass filter film.

Background technique

The traditional organic electroluminescent device (OLED) is a bottom-emitting device that grows on a glass substrate and uses ITO as an anode to emit light from one side of the substrate. However, when the device is used to actively drive the organic electroluminescent display, the pixel drive circuit of the display device and the display light-emitting area compete with each other, which directly affects the aperture ratio of the display device. For the top-emitting organic electroluminescent device (TEOLED, the light is emitted from the side of the top electrode, and the pixel drive circuit can be fabricated under the organic light-emitting device, which solves the problem of competition between the device pixel drive circuit and the display light-emitting area. The aperture ratio of the display device has been improved, and the aperture ratio can reach 100% in theory. In addition, the silicon-based OLED microdisplay must also adopt a top emission structure. The bottom electrode of a traditional top emission organic electroluminescent device is a metal electrode with high reflectivity Such as Ag, Al, etc. The introduction of these electrodes greatly reduces the contrast of organic electroluminescent display devices, especially for the display under strong outdoor ambient light, which brings serious problems.

Based on the above reasons, the development of high-contrast top-emitting organic electroluminescent devices has become a research hotspot in recent years. Traditional organic electroluminescent devices use transparent substrates such as ITO, and metal electrodes such as Mg and Ag with high reflectivity. The electrodes can emit internally generated light to the glass substrate, thereby increasing the luminosity of light emission. However, this high-reflectivity electrode will also reflect the ambient light entering the device, resulting in a decrease in the contrast of the device. For practical organic electroluminescent devices, such as organic microdisplay devices, it is required that the content displayed by the device can be easily seen by the observer under ambient light ranging from very dark to sunlight brightness. Therefore, it is very important to prepare organic electroluminescent devices with high contrast. One way to reduce ambient light emission is to use polarizers, especially circular polarizers. This polarizer is usually placed on the outer surface of the light transmissive substrate. But the introduction of the polarizer greatly reduces the brightness and efficiency of the device itself. This has an adverse effect on improving the lifetime of the device.

For bottom-emitting organic electroluminescent devices, the improvement of contrast mainly focuses on the bottom electrode with low reflectivity and high conductivity. Liang-sun Hung et al. (Liang-sun Hung, Joseph Madathil, Adv. Mater. 2001, 13, 23.) from the Department of Physics and Materials Science, City University of Hong Kong proposed to grow between the high reflectivity electrode and the electron transport layer of the device A layer of anti-reflection layer for ambient light, this functional layer has optical absorption and conductive properties. Liang-sun Hung's group prepared an organic electroluminescent device based on Alq ₃ , and used 90nm thick zinc oxide as the ambient light anti-reflection layer, which greatly weakened the high reflectivity of the metal electrode. The reflectivity of the composite bottom electrode at the wavelength of 410nm-690nm is lower than 10%, which greatly increases the contrast of the device. However, from the perspective of the photoelectric characteristics of the device, the brightness of the device is reduced by as much as 50%, and the efficiency of the device is also reduced. From this point of view, although the contrast of the device is increased, the performance of the device is greatly sacrificed. In 2006, Professor STLee of the University of Hong Kong et al. (KCLau, WFXie, HYSun, CSLee, and STLee, Appl.Phys.Letts, 2006, 88, 083507.) proposed to use an alloy of Sm and Ag as the bottom electrode, and its reflectivity varies in wavelength The reflectivity in the range of 400nm to 700nm is lower than 20%, while the reflectivity of Mg and Ag alloy electrodes is maintained at 90%. The reflectivity of the device can reach 390:1 under the ambient light of 140 lux under the driving voltage of 10V, which is 8 times higher than that of the traditional device. However, the electroluminescent efficiency of the device (corresponding to a current of 100mA/cm ² ) decreased from 3.36 to 2.56cd/A.

In top-emitting organic electroluminescent devices, Yang CJ et al. A high-contrast top-emitting organic electroluminescent device was realized by using the modulated reflective metal layer Mo as the reflective electrode combined with TeO ₂ /LiF bilayer as the anti-reflective coating (AR). In 2010, Shufen Chen et al. (Shufen Chen, Jun Xie, Yang Yang, Chunyan Chen and Wei Huang, J.Phys.D: Appl.Phys.2010, 43, 365101.) used Ni/ZnS/CuPc/Ni as contrast enhancement layer, ZnS is used as the anti-reflection layer, and the high contrast ratio of the device is 139.4:1 and 462.3:1 under 140lx ambient light, 300 and 1000cd/m ² on-state brightness, respectively. But the complexity of the process (optical calculations, growth of high-temperature materials, etc.) limits cost and yield.

Contents of the invention

The object of the invention is to provide a green top-emitting organic electroluminescent device with high contrast and low efficiency loss with a band-pass filter film.

The present invention adopts the method of adding a band-pass filter film outside the top-emitting organic electroluminescence, which overcomes the disadvantage of using the bottom electrode with low reflectivity at the expense of the efficiency of the device, and the production rate introduced by the complicated device preparation process Reduce the drawbacks, thereby preparing a high-contrast monochromatic top-emitting organic electroluminescent device. By selecting a suitable organic electroluminescent material and a filter film with a suitable transmittance range, a top-emitting green light device with high contrast and low efficiency loss is realized.

The device with the structure described in the present invention consists of a substrate, a metal anode, an organic functional layer, a metal cathode and a band-pass filter film in sequence, and the organic functional layer is sequentially composed of a hole transport layer, an electron blocking layer, a green light-emitting layer and a electron transport layer.

In the present invention, a band-pass filter film with a thickness of 1-2mm is covered on the metal cathode, and the band-pass wavelength range of the band-pass filter film corresponds to the light-emitting wavelength range of the green light-emitting layer. light absorption. The performance of the organic electroluminescence device itself is not affected, and there is no damage to the organic layer.

The luminescence peak of the green light-emitting layer is located at 500nm-540nm, so it is required that the center wavelength of the above-mentioned bandpass filter film is 500nm-540nm, and have good transmittance (>80%) in the range of center wavelength ±20nm.

In order to optimize the luminous efficiency and driving voltage of the above device, a hole injection layer is added between the metal anode and the hole transport layer. In order to optimize the luminous efficiency and driving voltage of the above devices, an electron injection layer is added between the electron transport layer and the metal cathode.

The high-contrast top-emitting organic electroluminescent device proposed by the present invention overcomes the complicated device preparation process and low yield caused by the need to prepare low-reflection electrodes in the past, and also overcomes the need to use low-reflectivity bottom electrodes to achieve high contrast at the expense of efficiency. disadvantages of top-emitting devices. The top-emitting white light organic electroluminescent device prepared by the invention has the advantages of high brightness, high efficiency and weak angle effect. By selecting a suitable organic electroluminescent material and a filter film with a suitable transmittance range, a top-emitting green light device with high contrast and low efficiency loss is realized.

Description of drawings

Figure 1: Schematic diagram of the structure of a top-emitting organic electroluminescent device combined with a filter film;

Figure 2: Bandpass characteristics of the bandpass filter film;

Figure 3: Comparison of sunlight spectrum changes after introducing band-pass filter film;

Fig. 4: The comparison curve of the luminescence spectra of the high-contrast top-emitting organic electroluminescent device prepared in Example 1 and the organic electroluminescent device without a band-pass filter film;

Figure 5: Current efficiency-current density curves of the high-contrast top-emitting organic electroluminescent device prepared in Example 1 and the organic electroluminescent device without a band-pass filter film;

Figure 6: Contrast curves of the high-contrast top-emitting organic electroluminescent device prepared in Example 1 and the organic electroluminescent device without a band-pass filter film under different on-state brightness;

As shown in Figure 1, wherein 1 is a substrate, which can be materials such as glass or silicon with an insulating layer, the present invention preferably has a silicon substrate with an insulating layer; 2 is a metal anode, which can be Ag or Al, the present invention Al is preferred; 3 is the hole injection layer, which can be MoO ₃ , H ₂ PC, F4-TCNQ or ZnPC doped TAPC or m-MTDATA, and the present invention preferably MoO ₃ doped m-MTDATA (the doping concentration is 15wt %); 4 is the hole transport layer, which can be TAPC or m-MTDATA; 5 is the electron blocking layer, which can be Ir(ppz) ₃ ; 6 is the green light emitting layer, which can be green phosphorescent Ir(ppy) ₃ or Ir(ppy) ₂ acac is incorporated into the bipolar matrix CBP to form a green light-emitting unit. In the present invention, Ir(ppy) _{3 is} preferably incorporated into the bipolar matrix CBP to produce green (doping concentration is 8wt%); 7 is Electron transport layer, the present invention uses BPhen; 8 is an electron injection layer, Liq, LiF or CsF can be used, and LiF is preferred in the present invention; 9 is a metal cathode, and the present invention adopts a composite cathode of Al (1nm)/Ag (180-300nm) ; 10 is a band-pass filter film; 11 is a DC drive power supply.

Detailed ways

The abbreviations, full names and molecular structural formulas of the organic materials involved in this manual are as follows:

Example 1:

The structure is Si/SiO ₂ /Al/m-MTDATA:MoO ₃ /m-MTDATA/Ir(ppz) ₃ /CBP:Ir(ppy) ₃ /BPhen/LiF/Al/Ag/bandpass filter film Top-emitting green organic electroluminescent device, the preparation of the device is carried out in a multi-source organic molecular vapor deposition system, and the detailed preparation process is as follows:

[1] The silicon substrate covered with silicon dioxide with a thickness of 340 nm was scrubbed repeatedly with acetone and ethanol cotton balls in sequence, then ultrasonicated with acetone, ethanol, and deionized water in sequence, and then dried.

[2] Place the treated substrate in the metal evaporation system. The vacuum chamber of the system contains 4 metal evaporation sources and every two evaporation sources share a set of control systems, which can simultaneously carry out the deposition of two metal materials. Evaporation, in order to ensure the uniformity of evaporation and facilitate the evaporation of metal materials, the substrate is 25cm away from the evaporation source, which can rotate and revolve to ensure the uniformity of the metal film. The metal materials used are placed in different evaporation sources, and then vacuumed to 4 ×10 ^-4 Pa.

[3] Maintaining the above vacuum conditions unchanged, a metal anode Al was grown on a silicon substrate with a thickness of 80nm and an evaporation rate of 1nm/s.

[4] Transfer the silicon substrate with grown metal Al anode to a multi-source organic molecule vapor deposition system in a nitrogen atmosphere. The vacuum chamber of the system contains 12 organic sources. There is a metal isolation cover, and the substrate is 25cm away from the evaporation source. It can rotate and revolve to ensure the uniformity of the metal film. The metal materials used are placed in different evaporation sources. Every three evaporation sources share a set of temperature control system, and then the vacuum to 4×10 ^-4 Pa.

[5] Keeping the above vacuum constant, sequentially vapor-deposit MoO ₃ doped m-MTDATA, m-MTDATA, Ir(ppz) ₃ , Ir(ppy) ₃ doped CBP, BPhen, LiF on the above Al anode, They are respectively used as hole injection layer, hole transport layer, electron blocking layer, green light emitting layer, electron transport layer, and electron injection layer, with thicknesses of 28, 10, 10, 20, 48, and 1 nm, respectively. The evaporation rates of M-MTDATA, Ir(ppz) ₃ , CBP, and BPhen are 0.1-0.2nm/s, and the evaporation rates of Ir(ppy) ₃ , LiF, and MoO ₃ are 0.01nm/s.

[6] After evaporating the organic functional layer, the substrate was transferred to the metal evaporation system in a nitrogen atmosphere again, and the above vacuum conditions were kept unchanged, and Al and Ag were sequentially evaporated on LiF as the metal cathode. The thickness is 1nm, the evaporation rate is 0.1-0.2nm/s, the thickness of the Ag layer is 20nm, and the evaporation rate is 0.5nm/s.

[7] After vapor-depositing the metal cathode, cover a layer of filter film on the above-mentioned Al/Ag composite cathode. The comparative device was not covered with a filter film.

The bandpass filter film is purchased from evaporated coating inc company in Maryland, USA, the model is ECI#1020, the center wavelength is 500nm, the transmittance at 480nm~520nm is >90%, the peak transmittance is 100%, and the passband fluctuates Less than 0.05%, the overall thickness is 1mm.

The above substrates, organic materials, and P-type dopant _MoO3 were all purchased from Changchun Hanhe Technology Co., Ltd. The thickness and growth rate of the material growth were monitored by the MATEX-400 film thickness controller made in the United States. The prepared device photoelectric The performance is tested with PR655 brightness spectrometer and Keithley2400 voltage and current source at room temperature and atmospheric environment. The efficiency-current density, spectrum, and contrast characteristics of the device are shown in Figure 4, Figure 5 and Figure 6.

It can be seen from Figure 2 that the central wavelength of the bandpass filter film is 500nm, and its transmittance is >90% in the wavelength range of 500nm±20nm, and has a small bandpass fluctuation.

It can be seen from Figure 3 that curve 1 is the normalized spectral intensity of sunlight without a filter film, and sunlight emits light of various wavelengths in the visible light range (380nm-780nm). Curve 2 is the sunlight spectrum after passing through the filter film. It can be seen that the visible light corresponding to the wavelength range of 380nm-470nm and 530nm-780nm is basically absorbed by the filter film. The shape of the spectral line of the light in the bandpass range (480nm ~ 520nm) basically does not change. The filter film has good bandpass characteristics.

It can be seen from Fig. 4 that curve 1 is the emission spectrum of a top-emitting organic electroluminescent device without a filter film, and curve 2 is the emission spectrum of a top-emitting organic electroluminescent device covered with a filter film. From the comparison between the two, after adding the filter film, the spectral change of the device is weak, and only the luminescence at 520nm to 600nm is weakened. It can be seen from this point that the phosphorescent material Ir(ppy)3 (peak wavelength 512nm, half maximum width ~ 30nm) we have chosen has very little light loss after passing through the band-pass filter film (pass band 480nm-520nm).

It can be seen from Fig. 5 that curve 1 is the current efficiency of the device without a filter film. Curve 2 is the current efficiency of the device after adding the filter film. It can be seen that the introduction of the filter film has little effect on the photoelectric performance of the device. The maximum current efficiency of the device without the filter film is 46.1cd/A, while the maximum current efficiency of the device with the filter film only decreases to 43.5cd/A. The introduction of the filter film has little effect on the photoelectric characteristics of the device.

It can be seen from FIG. 6 that curve 1 is the contrast characteristic of the device without the filter film, and curve 2 is the contrast characteristic of the device covered with the filter film. The ambient light is 140 lux, and the introduction of the filter film significantly increases the contrast of the top-emitting organic electroluminescent device. The contrast ratios of the device with the brightness of 500cd/m ² , 1000cd/m ² , and 2000cd/m ² without filter film and covered with filter film are 28:1 and 195:1, 51:1 and 388:1 respectively , 108:1 and 775:1.

The above descriptions are only preferred embodiments of the present invention, and should not be used to limit the implementation scope of the present invention. Generally, all equivalent changes and improvements made according to the application scope of the present invention should still fall within the scope of the present invention.

Claims (7)

1. high-contrast top transmitting green light organic electroluminescence device with bandpass filters, formed by substrate (1), metal anode (2), organic function layer and metallic cathode (9) successively, formed by hole transmission layer (4), electronic barrier layer (5), green luminescence layer (6) and electron transfer layer (7) successively in the organic function layer; It is characterized in that: covering a layer thickness at metallic cathode is the bandpass filters (10) of 1～2mm, and the logical wave-length coverage of the band of bandpass filters (10) is corresponding with the emission wavelength scope of green luminescence layer (6), to the light absorption of its all band in the surround lighting.

2. a kind of high-contrast top transmitting green light organic electroluminescence device with bandpass filters as claimed in claim 1 is characterized in that: substrate (1) is glass or with the silicon of insulating barrier; Metal anode (2) is Ag or Al; Hole transmission layer (4) is TAPC or m-MTDATA; Electronic barrier layer (5) is Ir (ppz) ₃Green luminescence layer (6) is Ir (ppy) ₃Or Ir (ppy) ₂Acac mixes the green luminescence unit that consists of among the CBP; Electron transfer layer (7) is BPhen; Metallic cathode (9) is the composite cathode of Al/Ag.

3. a kind of high-contrast top transmitting green light organic electroluminescence device with bandpass filters as claimed in claim 2, it is characterized in that: the centre wavelength of bandpass filters is 500nm～540nm, has the transmitance greater than 80% in centre wavelength ± 20nm scope.

4. a kind of high-contrast top transmitting green light organic electroluminescence device with bandpass filters claimed in claim 1 is characterized in that: increase hole injection layer (3) between metal anode (2) and hole transmission layer (4).

5. a kind of high-contrast top transmitting green light organic electroluminescence device with bandpass filters as claimed in claim 4, it is characterized in that: the material of hole injection layer (3) is MoO ₃, H ₂TAPC or m-MTDATA that PC, F4-TCNQ or ZnPC mix.

6. a kind of high-contrast top transmitting green light organic electroluminescence device with bandpass filters as claimed in claim 1 is characterized in that: increase electron injecting layer (8) between electron transfer layer (7) and metallic cathode (9).

7. a kind of high-contrast top transmitting green light organic electroluminescence device with bandpass filters as claimed in claim 6, it is characterized in that: the material of electron injecting layer (8) is Liq, LiF or CsF.

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