An inverted top-emitting qled device and a preparation method and application thereof

Abstract

The application discloses an inverted top-emitting QLED device and a preparation method and application thereof. The application provides an inverted top-emitting QLED device, which comprises, from bottom to top, a first electrode, an electron transport layer, a quantum dot light-emitting layer, an interface modification layer, a hole transport layer, a hole injection layer, a seed layer and a second electrode which form a composite electrode. The seed layer can promote the uniform growth of the Ag electrode, and avoids discontinuous film growth. Meanwhile, the seed layer can relieve the energy level mismatch between the functional layer and the Ag electrode and reduce the hole injection barrier as a transition layer between the other functional layer and the Ag electrode.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot light-emitting display, specifically relating to an inverted top-emitting QLED device, its fabrication method, and its application. Background Technology

[0002] Quantum dots (QDs) have attracted widespread attention in the display field due to their advantages such as tunable spectrum, color purity, and high photoluminescence efficiency. Through improvements and optimizations in quantum dot material synthesis methods and device structures, the external quantum efficiency (EQE) of quantum dot light-emitting diodes (QLEDs) has now exceeded 20%. This makes them a promising candidate to become the mainstay of next-generation display technologies.

[0003] The structure of an inverted QLED device generally consists of a bottom cathode, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and a top anode. Depending on the light emission direction, QLED devices can be divided into bottom-emitting (BE) and top-emitting (TE) structures. Compared to the traditional bottom-emitting structure, the top-emitting structure has higher brightness and light extraction efficiency. In the top-emitting structure, the top electrode is extremely thin, allowing light to be emitted directly from the top of the device. To ensure good conductivity even at such a thin thickness, Ag, the metal with the highest conductivity, is often used as the top electrode material. However, using Ag as the top semi-transparent anode in inverted top-emitting QLED devices presents two problems. First, the fabrication of the ultra-thin Ag electrode involves an "island phenomenon," which refers to the discontinuity of the film during growth, leading to a significant decrease in conductivity. Second, the work function of the Ag electrode is relatively shallow (4.2 eV), failing to provide effective hole injection. Therefore, the application of semi-transparent Ag anodes in inverted top-emitting QLED devices requires further improvement and research. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide an inverted top-emitting QLED device. By employing a seed layer / Ag composite electrode, this invention effectively improves the insufficient conductivity of the Ag semi-transparent anode in the inverted top-emitting QLED device, thereby significantly enhancing the device's brightness and efficiency.

[0005] Another object of the present invention is simply to provide a method for fabricating the above-mentioned inverted top-emitting QLED device.

[0006] Another object of the present invention is to provide an application of the above-mentioned inverted top-emitting QLED device.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides an inverted top-emitting QLED device, the structure of which comprises, from bottom to top, the following stacked components: a first electrode, an electron transport layer, a quantum dot light-emitting layer, an interface modification layer, a hole transport layer, a hole injection layer, a seed layer, and a second electrode.

[0009] The seed layer and the second electrode constitute a composite electrode.

[0010] Preferably, the seed layer is made of aluminum.

[0011] Preferably, the thickness of the seed layer is 1–3 nm.

[0012] Preferably, the first electrode is at least one of Ag, Al, Cu, Au, Pt, Ag / ITO, Al / ITO, ITO / Ag / ITO, ITO / Al / ITO, Ag / IZO, Al / IZO, IZO / Ag / IZO, and IZO / Al / IZO.

[0013] Preferably, the thickness of the first electrode is 150–170 nm.

[0014] Preferably, the electron transport layer is at least one of ZnO nanoparticles, ZnMgO nanoparticles, and SnO2 nanoparticles.

[0015] Preferably, the thickness of the electron transport layer is 60–70 nm.

[0016] Preferably, the electron dot emitting layer is at least one of semiconductor nanomaterials such as CdSe, lnP, and ZnSe.

[0017] Preferably, the thickness of the electron dot emitting layer is 25–35 nm.

[0018] Preferably, the interface decoration layer is PEIE.

[0019] Preferably, the thickness of the interface modification layer is 3–8 nm.

[0020] Preferably, the hole transport layer is at least one of TCTA, CBP, NPB, TFB, PF8CZ, and TAPC.

[0021] Preferably, the thickness of the hole transport layer is 35–45 nm.

[0022] Preferably, the hole injection layer is at least one of MoO3, HAT-CN, and PEDOT:PSS.

[0023] Preferably, the thickness of the hole injection layer is 5–10 nm.

[0024] Preferably, the second electrode is Ag.

[0025] Preferably, the thickness of the second electrode is 25–30 nm.

[0026] Preferably, the inverted top-emitting QLED device further includes a substrate located below the first electrode.

[0027] More preferably, the substrate is a glass substrate.

[0028] Secondly, the present invention provides a method for fabricating an inverted top-emitting QLED device, comprising the following steps:

[0029] (1) Fabricate the first electrode on the substrate;

[0030] (2) An electron transport layer is prepared on the surface of the first electrode;

[0031] (3) A quantum dot luminescent layer is prepared on the surface of the electron transport layer;

[0032] (4) Prepare an interface modification layer on the surface of the quantum dot light-emitting layer;

[0033] (5) A hole transport layer and a hole injection layer are sequentially prepared on the surface of the interface modification layer;

[0034] (6) Prepare a seed layer on the surface of the hole injection layer;

[0035] (7) A second electrode is prepared on the surface of the seed layer to obtain the device.

[0036] Preferably, in step (1), the first electrode is prepared by magnetron sputtering.

[0037] Preferably, the electron transport layer in step (2) is prepared by spin coating followed by annealing.

[0038] More preferably, the concentration of the spin-coating solution is 30–40 mg / ml, the solvent is ethanol, the spin-coating speed is 2000–3000 rpm, and the time is 30–50 s.

[0039] More preferably, the annealing temperature is 90–110°C and the time is 20–40 min.

[0040] Preferably, the quantum dot light-emitting layer in step (3) is prepared by spin coating followed by annealing.

[0041] More preferably, the concentration of the spin-coating solution is 15–25 mg / ml, the solvent is n-octane, the spin-coating speed is 2500–3000 rpm, and the time is 30–50 s.

[0042] More preferably, the annealing temperature is 45–55°C and the time is 25–35 min.

[0043] Preferably, the interface modification layer in step (4) is prepared by spin coating followed by annealing.

[0044] More preferably, the spin-coating solution concentration is 4-6 wt%, the solvent is 2-methoxyethanol, the spin-coating speed is 4000-6000 rpm, and the time is 30-50 s.

[0045] More preferably, the annealing temperature is 40–60°C and the time is 20–40 min.

[0046] Preferably, the hole transport layer and the hole injection layer in step (5) are both prepared by thermal evaporation.

[0047] More preferably, the thermal evaporation rate of the hole transport layer is 0.3 to 0.9 Å / s.

[0048] More preferably, the thermal evaporation rate of the hole injection layer is 0.1 to 0.5 Å / s.

[0049] Preferably, the seed layer in step (6) and the second electrode in step (7) are both prepared by thermal evaporation.

[0050] More preferably, the thermal evaporation rate of both the seed layer and the second electrode is 0.1 to 0.5 Å / s.

[0051] Thirdly, the present invention provides an application of the above-mentioned inverted top-emitting QLED device.

[0052] Preferably, the inverted top-emitting QLED device is used in the field of displays.

[0053] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0054] Because the work function of Ag electrodes is shallow, and ultrathin Ag electrodes are prone to film discontinuities during deposition, hole injection is severely hindered in inverted top-emitting QLED devices using pure Ag electrodes as semi-transparent anodes, thus reducing device efficiency. Therefore, to address the poor conductivity of Ag semi-transparent anodes in inverted top-emitting devices, this invention employs a seed layer inserted between the Ag electrode and other functional layers to construct a seed layer / Ag electrode composite electrode structure. First, the seed layer promotes uniform growth of the Ag electrode, avoiding film discontinuities. Second, as a transition layer between other functional layers and the Ag electrode, the seed layer alleviates energy level mismatch between the functional layers and the Ag electrode, reducing the hole injection barrier. The JVL and EQE-J curves of the device demonstrate that the composite electrode device exhibits higher current density, higher brightness, and higher efficiency. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of an inverted top-emitting QLED device according to Embodiment 1 of the present invention.

[0056] Figure 2 These are the current density-voltage-brightness curves of the devices in Embodiment 1 and Comparative Example 1 of the present invention.

[0057] Figure 3 These are the current density-external quantum efficiency curves of the devices in Embodiment 1 and Comparative Example 1 of this invention. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0059] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0060] Example 1

[0061] The fabrication of an inverted top-emitting QLED device includes the following steps:

[0062] Substrate cleaning: Take a Glass / ITO (10 nm) / Ag (150 nm) / ITO (10 nm) substrate, the first electrode being ITO (10 nm) / Ag (150 nm) / ITO (10 nm), and ultrasonically clean it with ultrapure water for 10 min. Then, dry the substrate with nitrogen gas for later use. Substrate surface treatment: Before device fabrication, treat the Glass / ITO (10 nm) / Ag (150 nm) / ITO (10 nm) substrate with UV light for 15 min. Afterward, quickly transfer the substrate to a nitrogen glove box for thin film fabrication.

[0063] Electron transport layer preparation: A ZnMgO nanoparticle solution with a concentration of 35 mg / ml and ethanol as solvent was spin-coated at 2500 rpm for 40 s, followed by a first annealing treatment at 100℃ for 30 min, finally yielding a ZnMgO film with a thickness of 65 nm.

[0064] Quantum dot luminescent layer preparation: The luminescent layer uses CdSe / CdZnSe / ZnSe / ZnSeS / ZnS core-shell structured quantum dots, with n-octane as the solvent and a concentration of 20 mg / ml. Spin coating is performed at 2800 rpm for 40 s, followed by a second annealing treatment at 50℃ for 30 min, resulting in a final film thickness of 30 nm.

[0065] Interface modification layer preparation: PEIE with a concentration of 5 wt% and 2-methoxyethanol as solvent was used for spin coating at 5000 rpm for 40 s, followed by a third annealing treatment at 50℃ for 30 min, resulting in a film thickness of 5 nm.

[0066] Hole transport layer preparation: 40 nm TCTA was thermally vaporized as the hole transport layer, and evaporation rates of 0.3 Å / s, 0.6 Å / s, and 0.9 Å / s were used to vaporize 5 nm, 10 nm, and 25 nm, respectively.

[0067] Hole injection layer preparation: 8 nm MoO3 was thermally vaporized as the hole injection layer with a total rate of 0.1 Å / s.

[0068] Seed layer preparation: 2 nm Al was thermally vaporized as the seed layer, with a total vaporization rate of 0.2 Å / s.

[0069] Ag electrode preparation: The Ag electrode was prepared by thermal evaporation, with a evaporation thickness of 27 nm and a total evaporation rate of 0.2 Å / s.

[0070] Comparative Example 1

[0071] The fabrication method of an inverted top-emitting QLED device is basically the same as that in Example 1, except that the QLED device in Comparative Example 1 does not contain a seed layer. That is, after the MoO3 hole injection layer is prepared, the step of evaporating 2nm Al is skipped, and a 27nm Ag electrode is directly evaporated.

[0072] Device performance comparison

[0073] Figure 1 This is a schematic diagram of the device in Example 1.

[0074] Figure 2 and 3 These are the current density-voltage-brightness curves and external quantum efficiency-current density curves of the devices in Example 1 and Comparative Example 1. The device in Example 1 has a larger current density, as well as higher brightness and efficiency.

[0075] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An inverted top-emitting QLED device, characterized in that, The structure, from bottom to top, includes the following stacked components: a first electrode, an electron transport layer, a quantum dot light-emitting layer, an interface modification layer, a hole transport layer, a hole injection layer, a seed layer, and a second electrode. The seed layer and the second electrode constitute a composite electrode.

2. The inverted top-emitting QLED device according to claim 1, characterized in that, The seed layer is made of aluminum. And / or, the thickness of the seed layer is 1 to 3 nm.

3. The inverted top-emitting QLED device according to claim 1 or 2, characterized in that, The first electrode is at least one of Ag, Al, Cu, Au, Pt, Ag / ITO, Al / ITO, ITO / Ag / ITO, ITO / Al / ITO, Ag / IZO, Al / IZO, IZO / Ag / IZO, and IZO / Al / IZO; And / or, the thickness of the first electrode is 150–170 nm; And / or, the electron transport layer is at least one of ZnO nanoparticles, ZnMgO nanoparticles, and SnO2 nanoparticles; And / or, the thickness of the electron transport layer is 60–70 nm; And / or, the electron dot emitting layer is at least one of semiconductor nanomaterials such as CdSe, lnP, and ZnSe; And / or, the thickness of the electron dot emitting layer is 25–35 nm.

4. The inverted top-emitting QLED device according to claim 1 or 2, characterized in that, The interface modification layer is PEIE; And / or, the thickness of the interface modification layer is 3-8 nm; And / or, the hole transport layer is at least one of TCTA, CBP, NPB, TFB, PF8CZ, and TAPC; And / or, the thickness of the hole transport layer is 35–45 nm; And / or, the hole injection layer is at least one of MoO3, HAT-CN, and PEDOT:PSS; And / or, the thickness of the hole injection layer is 5 to 10 nm.

5. The inverted top-emitting QLED device according to claim 1 or 2, characterized in that, The second electrode is Ag; And / or, the thickness of the second electrode is 25–30 nm; And / or, the inverted top-emitting QLED device further includes a substrate located below the first electrode.

6. A method for fabricating an inverted top-emitting QLED device according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Fabricate the first electrode on the substrate; (2) An electron transport layer is prepared on the surface of the first electrode; (3) A quantum dot luminescent layer is prepared on the surface of the electron transport layer; (4) Prepare an interface modification layer on the surface of the quantum dot light-emitting layer; (5) A hole transport layer and a hole injection layer are sequentially prepared on the surface of the interface modification layer; (6) Prepare a seed layer on the surface of the hole injection layer; (7) A second electrode is prepared on the surface of the seed layer to obtain the device.

7. The preparation method according to claim 6, characterized in that, Step (1) The first electrode is prepared by magnetron sputtering; And / or, the electron transport layer in step (2), the quantum dot light-emitting layer in step (3), and the interface modification layer in step (4) are all prepared by spin coating followed by annealing; And / or, the hole transport layer and hole injection layer in step (5), the seed layer in step (6), and the second electrode in step (7) are all prepared by thermal evaporation.

8. The preparation method according to claim 7, characterized in that, The thermal evaporation rate of the hole transport layer is 0.3–0.9 Å / s; And / or, the thermal evaporation rate of the hole injection layer is 0.1 to 0.5 Å / s; And / or, the thermal evaporation rates of the seed layer and the second electrode are both 0.1 to 0.5 Å / s.

9. The preparation method according to claim 7, characterized in that, The concentration of the solution for spin-coating the electron transport layer in step (2) is 350–40 mg / ml, and the solvent is ethanol; the spin-coating speed is 2000–3000 rpm, and the time is 30–50 s; And / or, the annealing temperature of the electron transport layer in step (2) is 90-110°C and the time is 20-40 min; And / or, in step (3), the concentration of the solution for spin-coating the quantum dot luminescent layer is 15-25 mg / ml, the solvent is n-octane, the spin-coating speed is 2500-3000 rpm, and the time is 30-50 s; And / or, the annealing temperature of the quantum dot light-emitting layer in step (3) is 45-55°C and the time is 25-35 min; And / or, the concentration of the solution for spin-coating the interface modification layer in step (4) is 4-6 wt%, the solvent is 2-methoxyethanol; the spin-coating speed is 4000-6000 rpm, and the time is 30-50 s; And / or, the annealing temperature of the interface modification layer in step (4) is 40-60°C and the time is 20-40 min.

10. The application of the inverted top-emitting QLED device according to any one of claims 1 to 5.

Images