Transparent quantum dot light-emitting diode and preparation method and application thereof

Abstract

The invention discloses a transparent quantum dot light-emitting diode and a preparation method and application thereof. The transparent quantum dot light-emitting diode comprises an ITO (Indium Tin Oxide) electrode, a hole injection layer, a quantum dot light-emitting layer, an electron transport layer and a zinc oxide-silver nanowire composite electrode which are sequentially stacked, wherein the zinc oxide-silver nanowire composite electrode comprises a zinc oxide film and a silver nanowire layer. The transparent quantum dot light-emitting diode has the advantages of high light transmittance, small driving voltage, high current efficiency, good brightness uniformity, long service life and the like, can be used in the fields of display, illumination, biomedicine and the like, and is simple in preparation method, relatively low in production cost and suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum dot light-emitting devices, and particularly relates to a transparent quantum dot light-emitting diode, a preparation method thereof, and an application thereof. Background Art

[0002] A quantum dot light-emitting diode (QLED) is a new type of light-emitting device, which realizes the light emission of a quantum dot layer through electron excitation, and has the advantages of a wide color gamut, high brightness, fast response, ultra-thin and light, low energy consumption, etc., and has a very broad application prospect. A transparent QLED is a QLED device with a transparent electrode and a transparent quantum dot layer, which can transmit part of the light, so as to achieve the effect of transparent display, and is one of the main directions of the development of a new generation of display technologies. However, the existing transparent QLED devices generally have problems such as low light transmittance, large driving voltage, low current efficiency, poor brightness uniformity, short service life, etc., and it is difficult to meet the increasing actual application requirements.

[0003] Therefore, it is of great significance to develop a transparent QLED device with high light transmittance, small driving voltage, high current efficiency, good brightness uniformity, and long service life. Summary of the Invention

[0004] The purpose of the present invention is to provide a transparent quantum dot light-emitting diode, a preparation method thereof, and an application thereof.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A transparent quantum dot light-emitting diode, which comprises an ITO electrode, a hole injection layer (HIL), a quantum dot light-emitting layer (QDs), an electron transport layer (ZMO), and a zinc oxide-silver nanowire composite electrode (ZnO-AgNWs) stacked in sequence; the zinc oxide-silver nanowire composite electrode comprises a zinc oxide thin film and a silver nanowire layer.

[0007] Preferably, the thickness of the zinc oxide thin film is 1 nm to 20 nm.

[0008] More preferably, the thickness of the zinc oxide thin film is 3 nm to 10 nm.

[0009] Preferably, the length of the silver nanowires (AgNWs) in the silver nanowire layer is 10 μm to 30 μm, and the diameter is 20 nm to 25 nm.

[0010] Preferably, the transmittance of the zinc oxide-silver nanowire composite electrode for light with a wavelength of 550 nm > 85%, and the sheet resistance < 40 Ω / sq.

[0011] Preferably, the hole injection layer comprises PEDOT.

[0012] Preferably, the thickness of the hole injection layer is 45 nm to 55 nm.

[0013] Preferably, the composition of the quantum dot light-emitting layer includes cadmium selenide quantum dots.

[0014] Preferably, the thickness of the quantum dot light-emitting layer is 15 nm to 25 nm.

[0015] Preferably, the composition of the electron transport layer includes magnesium oxide and zinc oxide.

[0016] Preferably, the thickness of the electron transport layer is 40 nm to 50 nm.

[0017] A method for preparing a transparent quantum dot light-emitting diode as described above includes the following steps:

[0018] 1) Using a spin coating method, a hole injection layer, a quantum dot light-emitting layer, and an electron transport layer are sequentially formed on one side of the ITO electrode;

[0019] 2) Using atomic layer deposition, a zinc oxide thin film is deposited on the surface of the electron transport layer, a silver nanowire dispersion is spin-coated on the surface of the zinc oxide thin film, and then annealing is performed to form a zinc oxide-silver nanowire composite electrode, and then encapsulation is carried out to obtain a transparent quantum dot light-emitting diode.

[0020] Preferably, the spin coating in step 2) is carried out under the condition that the spin coating speed is 1500 r / min to 2500 r / min.

[0021] More preferably, the spin coating in step 2) is carried out under the condition that the spin coating speed is 2000 r / min to 2500 r / min.

[0022] Preferably, the mass percentage content of silver nanowires in the silver nanowire dispersion in step 2) is 0.1% to 0.5%.

[0023] Preferably, the solvent in the silver nanowire dispersion in step 2) is ethanol and water.

[0024] Preferably, the mass ratio of ethanol to water is 3:1 to 9.

[0025] Preferably, the annealing in step 2) is carried out under the condition that the temperature is 60 °C to 150 °C.

[0026] More preferably, the annealing in step 2) is carried out under the condition that the temperature is 60 °C to 100 °C.

[0027] Preferably, the annealing time in step 2) is 20 min to 40 min.

[0028] A display device, which includes the above transparent quantum dot light-emitting diode.

[0029] The beneficial effects of the present invention are as follows: The transparent quantum dot light-emitting diode of the present invention has the advantages of high light transmittance, small driving voltage, high current efficiency, good brightness uniformity, long service life, etc. It can be used in the fields of display, lighting, biomedicine, etc. Moreover, its preparation method is simple and the production cost is relatively low, making it suitable for large-scale industrial production and application.

[0030] Specifically:

[0031] 1) The present invention uses a ZnO-AgNWs composite electrode as the cathode of the transparent QLED device. The transmittance of the ZnO-AgNWs composite electrode for light with a wavelength of 550 nm can reach 94% (λ = 550 nm), and the sheet resistance of the ZnO-AgNWs composite electrode < 35 Ω / sq, and the FOM value > 1.25×10 -2 , combining high light transmittance and high conductivity, and having excellent comprehensive performance;

[0032] 2) The present invention uses a ZnO-AgNWs composite electrode as the cathode of the transparent QLED device. The LUMO energy level of the ZnO layer matches that of the electron transport layer (ZMO), reducing the electron injection barrier (ΔE < 0.3 eV). Moreover, the interface passivation effect of the ZnO layer can inhibit the diffusion of Ag + ions (the diffusion of Ag + ions will cause a sharp decline in the service life of the device), and the surface plasmon resonance effect generated by AgNWs can enhance the light extraction efficiency of the transparent QLED device;

[0033] 3) The T 90 lifetime of the transparent QLED device of the present invention > 100 h (@500 cd / m 2 ), with a long service life. Compared with the transparent QLED device using an AgNWs electrode as the cathode, the service life is extended by 239 times;

[0034] 4) The driving voltage of the transparent QLED device of the present invention is as low as 3.0 V (@1 cd / m 2 ), the current efficiency can reach 5.2 cd / A (@1000 cd / m 2 ), and the double-sided brightness uniformity ≥ 97% (i.e., the front and back brightness ratio ≥ 0.97). It has a small driving voltage, high current efficiency, and good brightness uniformity;

[0035] 5) The preparation method of the transparent QLED device of the present invention is simple and the production cost is relatively low, making it suitable for large-scale industrial applications in the fields of display, lighting, biomedicine, etc. Description of the Drawings

[0036] Figure 1For the luminescence lifetime T of the transparent quantum dot light-emitting diodes in Example 3 and the comparative examples 90 Test result diagram.

[0037] Figure 2 Test result diagram of the light transmittance of the transparent quantum dot light-emitting diodes in Examples 1-5.

[0038] Figure 3 For the luminescence lifetime T of the transparent quantum dot light-emitting diodes in Examples 1-5 90 Test result diagram. Specific implementation manners

[0039] The present invention will be further explained and illustrated below in conjunction with specific examples.

[0040] Example 1:

[0041] A transparent quantum dot light-emitting diode (ITO / HIL / QDs / ZMO / ZnO-AgNWs) consists of an ITO electrode, a hole injection layer (HIL), a quantum dot light-emitting layer (QDs), an electron transport layer (ZMO), and a zinc oxide-silver nanowire composite electrode (ZnO-AgNWs); the ITO electrode, the hole injection layer, the quantum dot light-emitting layer, the electron transport layer, and the zinc oxide-silver nanowire composite electrode are stacked in sequence from bottom to top; the hole injection layer is composed of PEDOT with a thickness of 50 nm; the quantum dot light-emitting layer is composed of cadmium selenide quantum dots with a thickness of 20 nm; the electron transport layer is composed of magnesium oxide and zinc oxide, and the molar ratio of magnesium oxide to zinc oxide is 3:17 with a thickness of 45 nm; the zinc oxide-silver nanowire composite electrode consists of a zinc oxide thin film with a thickness of 1 nm and a silver nanowire layer, and the zinc oxide thin film and the silver nanowire layer are stacked from bottom to top (the zinc oxide thin film is in contact with the electron transport layer), and the length of the silver nanowires in the silver nanowire layer is 10 μm - 30 μm, and the diameter is 20 nm - 25 nm.

[0042] The preparation method of the above transparent quantum dot light-emitting diode is as follows:

[0043] 1) The patterned ITO glass electrode was ultrasonically cleaned with deionized water, ethanol, and isopropanol for 15 min each (to remove surface impurities), then irradiated under an ultraviolet lamp for 10 min (to further clean the surface and improve surface hydrophilicity), then transferred to a glove box filled with N2. Next, a PEDOT solution with a mass fraction of 1.3% was spin-coated on one side of the ITO glass electrode at a spin-coating speed of 1500 rpm for 30 s, and then annealed at 200 °C for 30 min to form a 50-nm-thick HIL layer. Then, a cadmium selenide quantum dot dispersion was spin-coated on the surface of the HIL layer at a spin-coating speed of 2500 rpm for 25 s, and then annealed at 60 °C for 10 min to form a 20-nm-thick QDs layer. Next, a magnesium oxide-zinc oxide solution with a mass fraction of 1.5% was spin-coated on the surface of the QDs layer at a spin-coating speed of 2500 rpm for 30 s, and then annealed at 60 °C for 10 min to form a 45-nm-thick ZMO layer;

[0044] 2) Atomic layer deposition (ALD) was used to deposit a 1-nm-thick ZnO thin film on the surface of the ZMO layer. The specific deposition process was as follows: The substrate was placed in an atmospheric pressure chamber, the pressure in the chamber was pumped to 800 Pa, the temperature was adjusted to 100 °C, and after waiting for 450 s, a DEZn pulse cycle was carried out and repeated 2 times. At the same time, it was purged with nitrogen (N2 with a purity of 99.999%) for 15 s, and then an ALD process cycle of ZnO was carried out. The number of pulses of DEZn and H2O per cycle was 0.1, the number of pulses of N2 per cycle was 4 s / cycle, and the growth rate of the ZnO thin film was Next, an ethanol-water dispersion of AgNWs with a mass fraction of 0.5% (mass ratio of ethanol to water is 1:1) was spin-coated on the surface of the ZnO thin film at a spin-coating speed of 2500 rpm for 20 s, and then annealed at 100 °C for 20 min to form a ZnO-AgNWs composite electrode, and then encapsulated with a cover glass to obtain a transparent quantum dot light-emitting diode.

[0045] Example 2:

[0046] A transparent quantum dot light-emitting diode, except that the thickness of the zinc oxide thin film was adjusted from "1 nm" to "3 nm", and the rest was exactly the same as the transparent quantum dot light-emitting diode in Example 1.

[0047] Example 3:

[0048] A transparent quantum dot light-emitting diode, except that the thickness of the zinc oxide thin film was adjusted from "1 nm" to "5 nm", and the rest was exactly the same as the transparent quantum dot light-emitting diode in Example 1.

[0049] Example 4:

[0050] A transparent quantum dot light-emitting diode, except that the thickness of the zinc oxide thin film is adjusted from "1 nm" to "10 nm", is exactly the same as the transparent quantum dot light-emitting diode in Example 1.

[0051] Example 5:

[0052] A transparent quantum dot light-emitting diode, except that the thickness of the zinc oxide thin film is adjusted from "1 nm" to "20 nm", is exactly the same as the transparent quantum dot light-emitting diode in Example 1.

[0053] Comparative example:

[0054] A transparent quantum dot light-emitting diode (ITO / HIL / QDs / ZMO / AgNWs), except that the zinc oxide thin film is not provided (the silver nanowire layer is directly prepared on the surface of the electron transport layer), is exactly the same as the transparent quantum dot light-emitting diode in Example 1.

[0055] Performance test:

[0056] 1) Referring to the preparation method of the transparent quantum dot light-emitting diode in Example 1, first deposit a ZnO thin film with a thickness of 5 nm on one side of a transparent glass plate, and then spin-coat an ethanol-water dispersion of AgNWs. Different ZnO-AgNWs composite electrodes are formed by changing the spin-coating speed (1500 r / min, 2000 r / min, and 2500 r / min) and the annealing temperature (60 °C, 90 °C, 120 °C, and 150 °C). Then, a spectrophotometer is used to measure the transmittance of the ZnO-AgNWs composite electrode for light with a wavelength of 550 nm. The test results are shown in Table 1, and a four-probe resistance tester is used to measure the sheet resistance (Rs) of the ZnO-AgNWs composite electrode. The test results are shown in Table 2. The figure of merit (FOM; calculation formula is as follows: FOM = T 10 / Rs, where T is the transmittance of the ZnO-AgNWs composite electrode for light with a wavelength of 550 nm, and Rs is the sheet resistance of the ZnO-AgNWs composite electrode) is shown in Table 3:

[0057] Table 1 Transmittance of ZnO-AgNWs composite electrodes prepared under different process conditions for light with a wavelength of 550 nm

[0058]

[0059] Table 2 Sheet resistance of ZnO-AgNWs composite electrodes prepared under different process conditions

[0060]

[0061] Table 3 Figure of merit of ZnO-AgNWs composite electrodes prepared under different process conditions

[0062]

[0063] As can be seen from Tables 1 to 3: The performance of the ZnO-AgNWs composite electrode significantly depends on the synergistic effect of the spin-coating speed and the annealing temperature. Under the conditions of a spin-coating speed of 2500 r / min and an annealing temperature of 90 °C, the FOM of the ZnO-AgNWs composite electrode reaches the maximum value (2.03×10 -2 ), showing the optimal comprehensive performance; in contrast, the FOM of the ZnO-AgNWs composite electrodes prepared under other conditions is slightly lower (for example: under the conditions of a spin-coating speed of 2500 r / min and an annealing temperature of 150 °C, the FOM of the ZnO-AgNWs composite electrode drops to 1.63×10 -2 ).

[0064] 2) The performance test data of the transparent quantum dot light-emitting diodes in Example 3 and the comparative examples are shown in the following table (luminescence lifetime T 90 The test results are as Figure 1 shown, where a in the figure is Example 3 and b is the comparative example):

[0065] Table 4 Performance test data of the transparent quantum dot light-emitting diodes in Example 3 and the comparative examples

[0066]

[0067] As can be seen from Table 4: The transparent quantum dot light-emitting diodes in Example 3 and the transparent quantum dot light-emitting diodes in the comparative examples show significantly different electro-optical characteristics under the double-sided light-emitting structure. The top emission brightness of the transparent quantum dot light-emitting diode in Example 3 reaches 14992 cd / m 2 at a driving voltage of 10 V, which is 496.6% higher than the top emission brightness of 2512.8 cd / m 2 of the transparent quantum dot light-emitting diode in the comparative example. Moreover, the current efficiency of the transparent quantum dot light-emitting diode in Example 3 jumps to 2.1 cd / A at a reference brightness of 1000 cd / m 2 (the transparent quantum dot light-emitting diode in the comparative example is 0.3 cd / A), with an increase of 600%. In addition, the front-back brightness ratio of the transparent quantum dot light-emitting diode in Example 3 increases from 0.94 of the transparent quantum dot light-emitting diode in the comparative example to 0.97, approaching the ideal uniformity, indicating a significant improvement in its light extraction ability.

[0068] As Figure 1 can be seen: In contrast, the carrier transport path regularity of the transparent quantum dot light-emitting diode in Example 3 is improved, so that its lifetime (T 2 ) at a brightness of 500 cd / m90 , the time required for the brightness to decay to 90% of the initial value) exceeds 100 h, which is more than 239 times longer than that of the transparent quantum dot light-emitting diode in the comparative example. This magnitude difference reveals the key role of the ZnO thin film in the device stability, and its mechanism of action can be attributed to the inhibition of electrochemical corrosion: the ZnO thin film acts as a physical barrier layer, which can effectively block the diffusion of Ag + ions from the AgNWs layer to the light-emitting functional layer, avoiding the electrochemical degradation caused by the migration of metal ions. This characteristic is crucial for ensuring long-term reliable performance, especially for applications in high-humidity and high-temperature environments. The presence of this functional layer not only enables the transparent quantum dot light-emitting diode in Example 3 to maintain a lower operating voltage at the same brightness but also effectively avoids the influence of the cathode process on its performance.

[0069] 3) The light transmittance test results of the transparent quantum dot light-emitting diodes in Examples 1 to 5 are as Figure 2 shown in the following table:

[0070] Table 5 Light transmittance test results of the transparent quantum dot light-emitting diodes in Examples 1 to 5

[0071]

[0072] It can be seen from Figure 2 and Table 5 that the transparent quantum dot light-emitting diodes in Examples 1 to 5 have high light transmittance.

[0073] 4) The optoelectronic performance test results of the transparent quantum dot light-emitting diodes in Examples 1 to 5 are shown in the following table (the emission lifetime T 90 The test results are as Figure 3 shown, where a to e in the figure correspond to Examples 1 to 5 respectively):

[0074] Table 6 Optoelectronic performance test results of the transparent quantum dot light-emitting diodes in Examples 1 to 5

[0075]

[0076] It can be seen from Table 6 and Figure 3 that:

[0077] The emission lifetimes T 90 of the transparent quantum dot light-emitting diodes in Examples 1 to 5 are 71.1 h, 92.9 h, 105.9 h, 104.8 h, and 66.1 h respectively, showing an obvious non-monotonic change trend. The T 90 of the transparent quantum dot light-emitting diodes in Examples 3 and 4 breaks through 100 h (105.9 h and 104.8 h respectively), which is nearly 50% higher than that of the transparent quantum dot light-emitting diode in Example 1 (71.1 h), while the T of the transparent quantum dot light-emitting diode in Example 590 It decreased to 66.1 h. This phenomenon can be explained by the coupling effect of interface engineering and material degradation mechanism: The process parameters of the transparent quantum dot light-emitting diodes in Example 3 and Example 4 (such as: the thickness of the ZnO thin film, annealing temperature, etc.) are in the optimal window range. At this time, the ALD-ZnO structure can not only effectively passivate the surface defects of the AgNWs layer (inhibit electrochemical corrosion), but also reduce the carrier injection barrier by matching the energy band structure (reduce the accumulation of Joule heat), thereby delaying the non-radiative recombination and ion migration of the quantum dots in the light-emitting layer; The performance decline of the transparent quantum dot light-emitting diode in Example 5 may be due to the process parameters exceeding the threshold, exacerbating the electric field distortion and thermal stress concentration at the interface, and accelerating the irreversible damage at the electrode / light-emitting layer interface. It should be noted that the T of the transparent quantum dot light-emitting diodes in Examples 2 to 4 90 showed a gradient increase with process optimization, indicating that by precisely controlling the thickness of the ZnO thin film (for example: in the range of 5 nm to 10 nm) and the distribution density of AgNWs (optimizing the spin-coating parameters), carrier leakage and Joule heat effect can be systematically suppressed (the power efficiency is increased by more than 30%), and finally a breakthrough extension of the device life is achieved. This result verifies the existence of the "process window critical effect", that is, when the combination of key parameters is within a specific physical threshold, the interface stability and optoelectronic performance of the composite electrode can reach a synergistic optimization state, providing a quantitative regulation basis for the industrial reliability design of transparent QLEDs.

[0078] In summary, the thickness of the ZnO thin film becomes the core variable of device performance by regulating the carrier injection balance, the position of the recombination region, and the light extraction efficiency. The 5-nm-thick ZnO thin film (transparent quantum dot light-emitting diode in Example 3) can achieve the synergistic optimization of carrier balance and light extraction at a low voltage (3.0 V), with a LE of 5.2 cd / A. However, too thin (<3 nm) or too thick (>10 nm) ZnO thin films lead to efficiency degradation due to carrier imbalance or transmission loss respectively. Although the reflection characteristics of the metal cathode generally improve the light extraction efficiency, its effect is restricted by the spatial distribution of the recombination region. This research provides a key theoretical basis for the structural design of quantum dot electroluminescent devices: By precisely controlling the thickness of the electron transport layer and the optical characteristics of the electrode, the triangular constraint of efficiency-brightness-voltage can be broken through.

[0079] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A transparent quantum dot light-emitting diode, characterized in that, The composition includes an ITO electrode, a hole injection layer, a quantum dot light-emitting layer, an electron transport layer, and a zinc oxide-silver nanowire composite electrode that are sequentially stacked; the composition of the zinc oxide-silver nanowire composite electrode includes a zinc oxide thin film and a silver nanowire layer.

2. The transparent quantum dot light-emitting diode according to claim 1, wherein: The thickness of the zinc oxide thin film is 1 nm to 20 nm.

3. The transparent quantum dot light-emitting diode according to claim 1 or 2, characterized in that: The length of the silver nanowires in the silver nanowire layer is 10 μm to 30 μm, and the diameter is 20 nm to 25 nm.

4. The transparent quantum dot light-emitting diode according to claim 1 or 2, characterized in that: The transmittance of the zinc oxide-silver nanowire composite electrode for light with a wavelength of 550 nm > 85%, and the sheet resistance < 40 Ω / sq.

5. The transparent quantum dot light-emitting diode according to claim 1 or 2, characterized in that: The composition of the hole injection layer includes PEDOT; the composition of the quantum dot light-emitting layer includes cadmium selenide quantum dots; the composition of the electron transport layer includes magnesium oxide and zinc oxide.

6. The transparent quantum dot light - emitting diode according to claim 1 or 2, characterized in that: The thickness of the hole injection layer is 45 nm to 55 nm; the thickness of the quantum dot light-emitting layer is 15 nm to 25 nm; the thickness of the electron transport layer is 40 nm to 50 nm.

7. A method for preparing a transparent quantum dot light-emitting diode according to any one of claims 1 to 6, characterized in that, It includes the following steps: 1) Spin-coating method is used to sequentially form a hole injection layer, a quantum dot light-emitting layer, and an electron transport layer on one side of the ITO electrode. 2) Atomic layer deposition method is used to deposit a zinc oxide thin film on the surface of the electron transport layer, then spin-coat a silver nanowire dispersion liquid on the surface of the zinc oxide thin film, then anneal to form a zinc oxide-silver nanowire composite electrode, and then encapsulate to obtain a transparent quantum dot light-emitting diode.

8. The preparation method according to claim 7, characterized in that: The spin-coating in step 2) is carried out under the condition that the spin-coating speed is 1500 r / min to 2500 r / min.

9. The preparation method according to claim 7 or 8, characterized in that: The annealing in step 2) is carried out under the condition that the temperature is 60 °C to 150 °C.

10. A display device, characterized in that, It includes the transparent quantum dot light-emitting diode described in any one of claims 1 to 6.

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