Intermediate connecting layer of serial white LED and preparation method thereof

Abstract

This invention discloses an intermediate connecting layer for a series-connected white LED and its fabrication method, belonging to the field of semiconductor optoelectronic device technology. The intermediate connecting layer is a three-layer composite structure consisting of a lithium fluoride insulating barrier layer, an aluminum electron transport layer, and a 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer stacked sequentially. By precisely controlling the thickness of each layer, both carrier balance control and light extraction efficiency optimization are achieved. Using the aforementioned intermediate connecting layer and its fabrication method, the series-connected white LED employing this intermediate connecting layer achieves an external quantum efficiency of 21.9% and a peak luminance of 31307 cd / m². 2 100cd / m 2 T 50 With a lifespan of up to 35,671 hours, excellent color stability, and no need for intermediate interconnecting layer patterning, it is suitable for display and lighting applications and can accelerate the commercialization of quantum dot LEDs.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device technology, and in particular to an intermediate connecting layer for a series-connected white LED and its preparation method. Background Technology

[0002] Quantum dot (QD)-based light-emitting diodes (QLEDs), with their unique advantages such as narrow half-width at half-maximum (WHM), continuously tunable emission spectra, and solution processability, have become the most promising next-generation display and lighting technology after organic light-emitting diodes (OLEDs). Currently, the external quantum efficiency (EQE) of red and green QLEDs has exceeded 20%, but the large-scale commercialization of QLEDs still faces two major bottlenecks: First, the micropatterning technology for high-resolution pixel arrays is not mature, and existing processes such as inkjet printing and micro-transfer printing are difficult to achieve precise side-by-side arrangement of red, green, and blue quantum dot layers; second, the stability of blue QLEDs is much lower than that of red and green devices, and the chemical instability of the wide bandgap blue quantum dots themselves makes it difficult for their working life to meet practical requirements.

[0003] White QLEDs with integrated color filters are a mainstream alternative to avoid the patterning problem. However, traditional single-emitting-layer white QLEDs are limited by the Foster resonance energy transfer (FRET) effect between red, green, and blue quantum dots, resulting in severe exciton quenching and making it difficult to further improve efficiency. A series structure, by vertically stacking multiple light-emitting units, can achieve a combination of efficiency and brightness. Simultaneously, using a stable blue fluorescent OLED instead of an unstable blue QLED can fundamentally solve the device lifetime problem. However, the core of the series structure lies in the high-performance interlayer (ICL). In existing technologies, schemes using indium tin oxide (ITO) as the intermediate electrode require additional electrode patterning, significantly increasing process complexity and cost. Other organic / inorganic composite interlayers generally suffer from insufficient charge generation capacity, unbalanced carrier injection, and high optical loss, making it difficult to simultaneously achieve high efficiency, lifetime, and color stability in hybrid series white LEDs. Currently, there is no mature solution that does not require patterning and has an EQE exceeding 20%. Summary of the Invention

[0004] The purpose of this invention is to provide an intermediate connecting layer for a series-connected white LED and a method for preparing the same, in order to solve the above-mentioned problems.

[0005] This invention provides an intermediate connecting layer for a series-connected white LED, used to connect the bottom light-emitting unit and the top light-emitting unit to form a quantum dot / organic hybrid series-connected white LED. The intermediate connecting layer is a three-layer composite structure consisting of a lithium fluoride (LiF) insulating barrier layer, an aluminum (Al) electron transport layer, and a 1,4,5,8,9,11-hexaazatriphenylhexanitrile (HATCN) charge generation layer stacked sequentially. The thickness of the lithium fluoride insulating barrier layer is 1 nm; the thickness of the aluminum electron transport layer is 2 nm; and the thickness of the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer is 10 nm to 40 nm.

[0006] Preferably, the thickness of the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge-generating layer is 30 nm.

[0007] Preferably, the bottom light-emitting unit is a yellow quantum dot light-emitting diode (Y-QLED), and the top light-emitting unit is a blue organic light-emitting diode (B-OLED). The lithium fluoride insulating barrier layer of the intermediate connecting layer is in contact with the zinc magnesium oxide (ZnMgO) electron transport layer of the yellow quantum dot light-emitting diode, and the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge-generating layer of the intermediate connecting layer is in contact with the N,N'-bis(naphthyl-1-yl)-N,N'-bis(phenyl)-benzidine (NPB) hole transport layer of the blue organic light-emitting diode. The three together constitute a quantum dot / organic hybrid series white LED.

[0008] Preferably, the light-emitting layer of the yellow quantum dot light-emitting diode is a mixed layer of red quantum dots and green quantum dots with a mass ratio of 1:9; the light-emitting layer of the blue organic light-emitting diode is a mixed layer of 2-methyl-9,10-bis(naphthyl-2-yl)anthracene (MADN):4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DSA-ph), wherein the doping concentration of 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl is 6%.

[0009] Preferably, the thicknesses of each functional layer of the quantum dot / organic hybrid tandem white LED are as follows: indium tin oxide (ITO) anode 110 nm, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) hole injection layer 45 nm, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] (TFB) hole transport layer 40 nm, and red quantum dot:green quantum dot hybrid light-emitting layer 20 nm. The structure includes: a zinc-magnesium oxide electron transport layer (55 nm), an N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine hole transport layer (60 nm), a 2-methyl-9,10-bis(naphth-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl luminescent layer (25 nm), a 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) electron transport layer (50 nm), a lithium fluoride electron injection layer (1 nm), and an aluminum cathode (100 nm).

[0010] Preferably, the intermediate connecting layer is a patternless continuous thin film, wherein the aluminum electron transport layer serves as an internal charge transport layer and does not serve as a pixel electrode; the pixel partitioning of the quantum dot / organic hybrid tandem white LED is achieved through a patterned indium tin oxide anode and a top aluminum cathode.

[0011] A method for fabricating an intermediate interconnect layer in a series-connected white LED, as described above, includes the following steps: On the surface of the electron transport layer of the bottom light-emitting unit, at a base vacuum of 4 × 10⁻⁶... -4 In a high-vacuum evaporation chamber, a lithium fluoride insulating barrier layer, an aluminum electron transport layer, and a 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer are sequentially deposited using thermal evaporation to form the three-layer composite intermediate connecting layer. The deposition rate of the lithium fluoride insulating barrier layer is 0.1 nm / s, the deposition rate of the aluminum electron transport layer is 0.2 nm / s, and the deposition rate of the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer is 1 nm / s.

[0012] Preferably, in the intermediate connecting layer, a 2nm aluminum electron transport layer is used to reduce the electron transport barrier from 1,4,5,8,9,11-hexaazatriphenylhexanitrile to zinc magnesium oxide, and a 1nm lithium fluoride insulating barrier layer is used to suppress excessive electron injection into the bottom yellow quantum dot light-emitting diode.

[0013] Preferably, the method also includes a method for preparing a quantum dot / organic hybrid tandem white LED, specifically comprising the following steps: S1. Fabrication of bottom yellow quantum dot light-emitting diode unit: The pre-cleaned indium tin oxide glass substrate is treated with oxygen plasma, spin-coated with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate solution and annealed; in a nitrogen glove box, a poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] layer, a red quantum dot:green quantum dot mixed layer and a zinc magnesium oxide layer are spin-coated sequentially, and each layer is annealed after spin-coating; S2. An intermediate connection layer is prepared on the surface of the zinc-magnesium oxide electron transport layer obtained in step S1. S3. On the surface of the intermediate connecting layer, the functional layers of the top blue organic light-emitting diode and the aluminum cathode are sequentially deposited by thermal evaporation to obtain the quantum dot / organic hybrid series white LED.

[0014] Preferably, in step S1, the oxygen plasma treatment time is 12 min; the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate solution is spin-coated at 3000 rpm for 40 s and annealed in air at 130°C for 30 min; the poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] layer is spin-coated at 4000 rpm for 40 s and annealed at 100°C for 15 min using an 8 mg / mL chlorobenzene solution; the red quantum dot:green quantum dot mixed layer is spin-coated at 1500 rpm for 40 s and annealed at 100°C for 5 min using a 10 mg / mL octane mixed solution at a mass ratio of 1:9; the zinc magnesium oxide layer is spin-coated at 20 mg / mL nanoparticle ethanol solution for 40 s and annealed at 100°C for 10 min. Preferably, in step S3, the thermal evaporation process has a base vacuum of 4×10⁻⁶. -4 The deposition was carried out in the chamber of Pa, and the specific parameters of each layer were as follows: N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine layer deposition rate 1 nm / s, thickness 60 nm; 2-methyl-9,10-bis(naphth-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl light-emitting layer deposition rate 1 nm / s, thickness 25 nm, doping concentration 6%; 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene layer deposition rate 1 nm / s, thickness 50 nm; lithium fluoride electron injection layer deposition rate 0.1 nm / s, thickness 1 nm; aluminum cathode deposition rate 2 nm / s, thickness 100 nm.

[0015] Therefore, the present invention employs the above-mentioned intermediate connecting layer of a series-connected white LED and its preparation method, which has the following beneficial effects: (1) Precise balance of carrier injection was achieved by precisely controlling the thickness of each layer: the 1nm ultrathin lithium fluoride insulating layer effectively suppressed the problem of excessive electron injection that is common in quantum dot light-emitting diodes by utilizing its electron blocking effect, and improved the external quantum efficiency of the bottom yellow QLED to more than 18%; the 2nm ultrathin aluminum electron transport layer significantly reduced the electron transport barrier between HATCN and zinc magnesium oxide, ensuring efficient charge transport; the energy levels of HATCN and N,N'-bis(naphthyl-1-yl)-N,N'-bis(phenyl)-benzidine are highly matched, which can efficiently generate electron-hole pairs at the interface and provide a stable carrier supply for the upper and lower light-emitting units.

[0016] (2) By adjusting the thickness of the HATCN layer, the light extraction efficiency was significantly improved. The optimal thickness of 30 nm effectively suppressed the optical losses of the waveguide mode and the surface plasmon polariton mode, while also taking into account the charge generation capability, achieving the best balance between optical gain and electrical performance. The quantum dot / organic hybrid tandem white LED fabricated using this intermediate connecting layer has an external quantum efficiency of up to 21.9%, which is almost equal to the sum of the efficiencies of the two sub-devices, and a peak brightness of 31307 cd / m². 2 Of particular note is the device's performance at 100 cd / m². 2 T at brightness 50 With a lifespan of up to 35,671 hours, it meets the lifespan requirements for commercial applications.

[0017] (3) The quantum dot / organic hybrid tandem white LED prepared using this intermediate connecting layer has excellent color stability and wide color gamut characteristics, and its brightness is increased from 0 to 31307 cd / m². 2 At that time, the CIE color coordinates only shifted from (0.42, 0.35) to (0.30, 0.37), which is suitable for displaying commonly used 500-5000 cd / m² colors. 2 The color coordinate shift is less than 0.03 within the brightness range, and the color gamut covers 113.7% of NTSC and 118.3% of DCI-P3. Meanwhile, the intermediate connecting layer is a patternless continuous thin film, which does not require additional patterning processes. Pixel partitioning can be achieved through patterned ITO anodes and top aluminum cathodes, which greatly simplifies the manufacturing process and lays a solid foundation for the commercial application of QLED in the display and lighting fields.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1This is a diagram illustrating the device structure and working mechanism of a series-connected white LED in the intermediate connecting layer and its fabrication method of the present invention; wherein, a is a schematic diagram of the overall device structure; b is the device band structure; c is a schematic diagram of the charge generation mechanism of the intermediate connecting layer; d is the current density and voltage curves of single-electron devices with different aluminum thicknesses; e is the optical transmittance curves of thin films with different aluminum thicknesses. Figure 2 This diagram illustrates the influence of key parameters of the intermediate interconnect layer on device performance in a series-connected white LED and its fabrication method according to the present invention. Specifically, a represents the current density, luminance, and efficiency curves of yellow quantum dot LEDs with different lithium fluoride thicknesses; b represents the external quantum efficiency (EQE) versus current density (J) characteristic curve; c represents the current density and voltage curves of single-electron devices with different lithium fluoride thicknesses; d represents the effect of HATCN thickness on the light extraction efficiency of the bottom yellow quantum dot LED; e represents the effect of HATCN thickness on the light extraction efficiency of the top blue organic light-emitting diode; f represents the effect of HATCN thickness on the overall light extraction efficiency of the series-connected device; g represents the effect of HATCN thickness on the overall light extraction efficiency of the series-connected device; h represents the current density and voltage curves of devices with only the intermediate interconnect layer and different HATCN thicknesses; and i represents the current density and voltage curves of series-connected devices with different HATCN thicknesses. Figure 3 This image shows the performance characterization of a quantum dot organic hybrid tandem white LED in the intermediate connecting layer and its fabrication method of a tandem white LED according to the present invention. In the image, a is the electroluminescence spectrum of the device; b is the electroluminescence emission photograph under different driving voltages; c is the CIE color coordinate variation curve under different brightness levels; d is a comparison of the voltage-brightness curves of the tandem device and its sub-devices; e is the brightness-current density curve of the tandem device; f is the external quantum efficiency-brightness curve of the tandem device; g is the statistical distribution of external quantum efficiency of devices from different batches; h is the device lifetime test curve; and i is a comparison of the electroluminescence spectra before and after the lifetime test. Figure 4This diagram shows the optimized parameters of the luminescent layer of the intermediate connecting layer in a series-connected white LED of the present invention and its fabrication method. Specifically, a represents the electroluminescence spectrum of a yellow quantum dot LED with a quantum dot ratio of 1:6; b represents the electroluminescence spectrum of a yellow quantum dot LED with a quantum dot ratio of 1:9; c represents the electroluminescence spectrum of a yellow quantum dot LED with a quantum dot ratio of 1:12; d represents the current density luminance curves of yellow quantum dot LEDs with different quantum dot ratios; e represents the external quantum efficiency luminance curves of yellow quantum dot LEDs with different quantum dot ratios; f represents the CIE color coordinates of the yellow quantum dot LED as a function of voltage at the optimal quantum dot ratio; g represents the current density luminance curves of blue organic light-emitting diodes with different 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl doping concentrations; and h represents the external quantum efficiency luminance curves of blue organic light-emitting diodes with different 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl doping concentrations. Detailed Implementation

[0020] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0022] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0023] Example 1 This embodiment provides a quantum dot organic hybrid tandem white LED, the overall structure of which is as follows: Figure 1 As shown in 'a', the band structure is as follows: Figure 1 As shown in b, the charge generation mechanism of the intermediate connecting layer is as follows: Figure 1As shown in c in the diagram. The device, from bottom to top, consists of a glass substrate, an indium tin oxide anode, a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole injection layer, a poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] hole transport layer, a red quantum dot / green quantum dot mixed light-emitting layer, a zinc magnesium oxide electron transport layer, a lithium fluoride insulating barrier layer, an aluminum electron transport layer, and 1,4,5,8... The structure consists of a 9,11-hexaazatriphenylhexanitrile charge generation layer, an N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine hole transport layer, a 2-methyl-9,10-bis(naphth-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl light-emitting layer, a 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene electron transport layer, a lithium fluoride electron injection layer, and an aluminum cathode.

[0024] The thicknesses of each functional layer are as follows: indium tin oxide anode 110 nm, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole injection layer 45 nm, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] hole transport layer 40 nm, red quantum dot / green quantum dot mixed light-emitting layer 20 nm, zinc magnesium oxide electron transport layer 55 nm, lithium fluoride insulating barrier layer 1 nm, aluminum electron transport layer 2 nm, 1,4,5,8, The structure consists of a 30 nm charge generation layer of 9,11-hexaazatriphenylhexanitrile, a 60 nm hole transport layer of N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine, a 25 nm light-emitting layer of 2-methyl-9,10-bis(naphth-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl, a 50 nm electron transport layer of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, a 1 nm lithium fluoride electron injection layer, and a 100 nm aluminum cathode.

[0025] The mass ratio of red quantum dots to green quantum dots is 1:9. The doping concentration of 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl in the 2-methyl-9,10-bis(naphthyl-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl luminescent layer is 6%.

[0026] The intermediate connecting layer is a patternless continuous thin film, in which the aluminum electron transport layer serves only as an internal charge transport layer and does not function as a pixel electrode. The pixel partitioning of the quantum dot organic hybrid tandem white LED is achieved through a patterned indium tin oxide anode and a top aluminum cathode.

[0027] Preparation steps: Fabrication of the bottom yellow quantum dot light-emitting diode unit: A pre-cleaned indium tin oxide glass substrate was subjected to oxygen plasma treatment for 12 minutes; a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate solution was spin-coated at 3000 rpm for 40 seconds, followed by annealing in air at 130°C for 30 minutes to form a hole injection layer; the substrate was then transferred to a nitrogen glove box and spin-coated with a poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)]chlorobenzene solution at a concentration of 8 mg / mL at 400 rpm. A hole transport layer was formed by spin-coating a mixed solution of red and green quantum dots in octane with a concentration of 10 mg / mL (mass ratio of red to green quantum dots 1:9) at 1500 rpm for 40 seconds and annealing at 100°C for 5 minutes. A mixed luminescent layer was formed by spin-coating a zinc magnesium oxide nanoparticle ethanol solution with a concentration of 20 mg / mL at 2000 rpm for 40 seconds and thermally annealing at 100°C for 10 minutes.

[0028] Intermediate connecting layer fabrication: The substrate of the prepared yellow quantum dot light-emitting diode unit was transferred to a high-vacuum evaporation chamber with a base vacuum of 4 x 10⁻⁴ Pa. The following layers were deposited by thermal evaporation in sequence: lithium fluoride insulating barrier layer, deposition rate 0.1 nm / s, thickness 1 nm; aluminum electron transport layer, deposition rate 0.2 nm / s, thickness 2 nm; 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer, deposition rate 1 nm / s, thickness 30 nm.

[0029] Fabrication of the top blue organic light-emitting diode (OLED) unit: Further thermal evaporation deposition of the following layers continues on the surface of the intermediate connecting layer: N,N'-bis(naphthyl-1-yl)-N,N'-bis(phenyl)-benzidine layer, deposition rate 1 nm / s, thickness 60 nm; 2-methyl-9,10-bis(naphthyl-2-yl)anthracene and 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl co-deposition layer, deposition rate 1 nm / s, thickness 25 nm, wherein the doping concentration of 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl is 6%; 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene layer, deposition rate 1 nm / s, thickness 50 nm; lithium fluoride electron injection layer, deposition rate 0.1 nm / s, thickness 1 nm; aluminum cathode, deposition rate 2 nm / s, thickness 100 nm.

[0030] Performance verification methods and results: This embodiment uses the following standard method for performance verification: Film thickness measurement: Thin films prepared by solution method were measured using a step meter, and vapor-deposited layers were monitored using an in-situ quartz crystal microbalance; Transmittance measurement: Measured using a spectrophotometer; Electroluminescence spectrum and efficiency characteristics: recorded using a commercial LED testing system; Lifetime testing: An 8-channel lifetime testing system was used, conducted under constant current drive, room temperature (20±2 degrees Celsius), and ambient air conditions. The devices were tested after being encapsulated with a glass cover. T 50 Defined as brightness decaying to 50% of its initial value.

[0031] The performance of the prepared quantum dot organic hybrid tandem white LED is as follows: The electroluminescence spectrum contains three characteristic peaks located at 461 nm, 534 nm, and 625 nm, respectively, which are the superposition of the light emitted by the yellow quantum dot LED at the bottom and the blue organic light-emitting diode at the top. Figure 3 As shown in 'a'; It maintains bright and uniform white electroluminescent emission across the entire driving voltage range of 8 to 14 volts, see example... Figure 3 As shown in b; The turn-on voltage is 5.6 volts, consistent with the sum of the turn-on voltages of the bottom yellow quantum dot LED (2.1 volts) and the top blue organic light-emitting diode (3.1 volts), demonstrating that the two sub-devices are effectively connected in series in the stacked structure. Figure 3 As shown in d; The external quantum efficiency can reach up to 21.9%, almost equal to the sum of the efficiencies of the bottom yellow quantum dot LED (18.1%) and the top blue organic light-emitting diode (4.8%). Current efficiency and power efficiency show similar trends to the external quantum efficiency. Figure 3 As shown in f; Peak brightness reached 31,307 candela per square meter, such as Figure 3 As shown in e; Lifetime performance: At an initial luminance of 6312 candela per square meter, T 50 The lifetime is 31.05 hours; analysis of multi-brightness stability data yields an acceleration factor of approximately 1.7, extrapolated to a T value of 100 candela per square meter. 50 With a lifespan of up to 35,671 hours; tests showed that the top blue organic light-emitting diode (OLED) was the lifespan-limiting unit, while the bottom yellow quantum dot OLED exhibited excellent stability, such as... Figure 3 As shown in h; Color stability: When the brightness increases from 0 to 31307 candela per square meter, the CIE color coordinates shift only from (0.42, 0.35) to (0.30, 0.37); within the commonly used brightness range of 500 to 5000 candela per square meter, the CIE color coordinate shift is less than 0.03. Figure 3 As shown in c; Color gamut performance: Covers 113.7% of NTSC, 118.3% of DCI-P3, and 84.9% of Rec.2020; Reproducibility: Eight devices from different batches were fabricated, with an average external quantum efficiency of 21.2%, which is highly consistent with the sum of the average efficiencies of the bottom yellow quantum dot LED (17%) and the top blue organic light-emitting diode (4.4%). Figure 3 As shown in g; Spectral stability: The change in the electroluminescence spectrum of the device before and after lifetime testing is negligible, such as... Figure 3 As shown in i in the diagram.

[0032] The core performance parameters of the bottom yellow quantum dot light-emitting diode, the top blue organic light-emitting diode, and the quantum dot-organic hybrid tandem white LED prepared in this embodiment are compared as follows: Table 1 Comparison of core performance parameters of each component

[0033] Example 2 Compared with Example 1, the difference is that the thickness of the aluminum electron transport layer in the intermediate connecting layer is 1 nanometer and 3 nanometers, respectively.

[0034] Control methods and verification methods: The electron transport function of the aluminum electron transport layer was verified using a single-electronic device. The single-electronic device structure consisted of a glass substrate, an indium tin oxide anode, a zinc magnesium oxide layer, a lithium fluoride insulating barrier layer, an aluminum electron transport layer, and an aluminum cathode. Single-electronic devices with different aluminum thicknesses were prepared using the same process as in Example 1, and their current density and voltage characteristics were tested. Simultaneously, the optical transmittance of films with different aluminum thicknesses was measured using a spectrophotometer.

[0035] Performance test results: Test results are as follows Figure 1 As shown in d and e, the device with the aluminum electron transport layer exhibits significantly higher current than the device without it, demonstrating that aluminum effectively lowers the electron transport barrier from 1,4,5,8,9,11-hexaazatriphenylhexanitrile to zinc magnesium oxide. As the aluminum thickness increases from 1 nm to 3 nm, electron transport performance improves, but the film's optical transmittance gradually decreases. Considering both electrical and optical performance, 2 nm is determined to be the optimal thickness for the aluminum electron transport layer.

[0036] Example 3 Compared with Example 1, the difference is that the thickness of the lithium fluoride insulating barrier layer in the intermediate connecting layer is 0 nanometers and 2 nanometers, respectively.

[0037] Control methods and verification methods: Yellow quantum dot light-emitting diode devices with different lithium fluoride thicknesses were fabricated, and their current density, brightness, external quantum efficiency, current efficiency, and power efficiency were tested. At the same time, a single-electron device was fabricated to verify the electron blocking effect of lithium fluoride. The single-electron device structure consisted of a glass substrate, an indium tin oxide anode, a zinc magnesium oxide layer, a red quantum dot-green quantum dot mixed layer, a zinc magnesium oxide layer, a lithium fluoride insulating barrier layer, and an aluminum cathode.

[0038] Performance test results: Test results are as follows Figure 2 As shown in a and c, the device current density and brightness gradually decrease with increasing lithium fluoride thickness. This is because the insulating properties of lithium fluoride require electrons to tunnel through the layer for transmission. When the lithium fluoride thickness is 1 nm, the external quantum efficiency of the device reaches its maximum value of approximately 18%, and the current efficiency and power efficiency are also optimal. When the thickness increases to 2 nm, excessive electron blocking disrupts the charge injection balance, and the device performance degrades. Single-electron device test results further confirm the electron blocking effect of lithium fluoride; at the same voltage, the device current density decreases significantly with increasing lithium fluoride thickness.

[0039] Example 4 Compared with Example 1, the difference is that the thickness of the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer in the intermediate connecting layer is 10 nm, 20 nm and 40 nm, respectively.

[0040] Control methods and verification methods: Devices with only intermediate connecting layers and different charge generation layer thicknesses were fabricated to verify their charge generation capabilities. The structure of the devices with only intermediate connecting layers consisted of a glass substrate, an indium tin oxide anode, a zinc magnesium oxide layer, a lithium fluoride insulating barrier layer, an aluminum electron transport layer, a 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer, an N,N'-bis(naphthyl-1-yl)-N,N'-bis(phenyl)-benzidine layer, a molybdenum trioxide layer, and an aluminum cathode. Corresponding tandem devices were also fabricated, and their light extraction efficiency and electrical performance were tested.

[0041] Performance test results: Test results are as follows Figure 2As shown in di, the light extraction efficiency of the bottom yellow quantum dot LED significantly improves with increasing thickness from 10 nm to 40 nm, mainly due to the effective suppression of optical losses in the waveguide mode and surface plasmon polariton mode. The light extraction efficiency of the top blue organic light-emitting diode also slightly improves due to the reduction in substrate mode losses. However, increasing thickness leads to a decrease in charge generation capability. When the thickness exceeds 30 nm, the charge generation performance deteriorates significantly, decreasing by 43% at 40 nm compared to 30 nm. Considering both optical gain and electrical loss, 30 nm is determined to be the optimal thickness for the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer.

[0042] Example 5 Compared with Example 1, the difference is that the mass ratio of red quantum dots to green quantum dots in the bottom yellow quantum dot light-emitting diode is 1:6 and 1:12, respectively.

[0043] Control methods and verification methods: Yellow quantum dot light-emitting diode devices with different quantum dot ratios were fabricated, and their electroluminescence spectra, current densities, brightness, and external quantum efficiency were tested. The influence of the Foster resonance energy transfer effect on the emission spectrum was analyzed.

[0044] Performance test results: Test results are as follows Figure 4 As shown in Figure af, when the ratio is 1:6, due to the Foster resonance energy transfer effect, excitons preferentially recombine on the red quantum dots, resulting in a predominantly red emission spectrum. At a ratio of 1:9, the contribution of green emission is significantly enhanced, achieving stable yellow emission and optimal device performance. When the ratio decreases to 1:12, although green emission further enhances, excessive Foster resonance energy transfer leads to a decrease in charge recombination efficiency, degrading device performance. The variation in emission intensity with the quantum dot ratio can be attributed to the interaction between energy transfer and charge recombination efficiency; a 1:9 ratio optimally balances these effects. At the optimal ratio of 1:9, the yellow quantum dot LED maintains stable yellow emission within a driving voltage range of 2-8 volts.

[0045] Example 6 Compared with Example 1, the difference is that the doping concentration of 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl in the top blue organic light-emitting diode is 4% and 8%, respectively.

[0046] Control methods and verification methods: Blue organic light-emitting diode devices with different doping concentrations were fabricated, and their current density, brightness, and external quantum efficiency were tested.

[0047] Performance test results: Test results are as follows Figure 4The values ​​of g and h are shown in the figure. The external quantum efficiency of the device reaches a maximum of 4.84% when the doping concentration is 6%, and deviations from this concentration lead to performance degradation. Considering that only 25% of excitons in fluorescent organic light-emitting diodes are spin-allowed radiative recombination, this efficiency value is reasonable. At doping concentrations below 6%, the electroluminescence spectrum of the blue organic light-emitting diode shows only a slight redshift, and the color purity remains good.

[0048] Comparative Example 1 Compared with Example 1, the difference is that the intermediate connection layer is replaced with a 100-nanometer indium tin oxide layer, and additional photolithography and etching processes are required to pattern the indium tin oxide intermediate electrode.

[0049] Performance comparison with Example 1: Process complexity: The preparation process adds 3 steps, increasing production costs by approximately 30%; External quantum efficiency: only 16.2% at most, a 26% decrease compared to Example 1; Lifespan: 100 candela per square meter at T 50 The lifespan is approximately 18,200 hours, a 49% reduction compared to Example 1; Color stability: When the brightness is increased from 0 to 31307 candela per square meter, the CIE color coordinate offset is 0.21, which is 1.75 times that of Example 1.

[0050] Comparative Example 2 Compared with Example 1, the difference is that the intermediate connecting layer only contains a 30 nm 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer, and does not have a lithium fluoride insulating barrier layer and an aluminum electron transport layer.

[0051] Performance comparison with Example 1: External quantum efficiency: only 12.7% at most, a 42% reduction compared to Example 1; Peak brightness: only 15,600 candela per square meter, a 50% reduction compared to Example 1; Lifespan: 100 candela per square meter at T 50 The lifespan is approximately 9800 hours, a 73% reduction compared to Example 1; Charge balance: The device suffers from severe electron over-injection, resulting in an excessively high proportion of yellow emission at low brightness and extremely poor color stability.

[0052] Therefore, this invention employs the aforementioned intermediate connecting layer of a series-connected white LED and its fabrication method, achieving precise balance of carrier injection through precise control of the thickness of each layer: the 1nm ultrathin lithium fluoride insulating layer utilizes its electron blocking effect to effectively suppress the problem of excessive electron injection commonly found in quantum dot light-emitting diodes, increasing the external quantum efficiency of the bottom yellow QLED to over 18%; the 2nm ultrathin aluminum electron transport layer significantly reduces the electron transport barrier between HATCN and zinc magnesium oxide, ensuring efficient charge transport; the energy levels of HATCN and N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine are highly matched, enabling efficient generation of electron-hole pairs at the interface, providing a stable carrier supply for the upper and lower light-emitting units.

[0053] By adjusting the thickness of the HATCN layer, a significant improvement in light extraction efficiency was achieved. The optimal thickness of 30 nm effectively suppresses optical losses in both waveguide and surface plasmon polariton modes, while also maintaining charge generation capability, thus achieving the best balance between optical gain and electrical performance. A quantum dot / organic hybrid tandem white LED fabricated using this intermediate connecting layer achieves an external quantum efficiency of 21.9%, almost equal to the sum of the efficiencies of the two sub-devices, and a peak luminance of 31307 cd / m². 2 Of particular note is the device's performance at 100 cd / m². 2 T at brightness 50 With a lifespan of up to 35,671 hours, it meets the lifespan requirements for commercial applications.

[0054] The quantum dot / organic hybrid tandem white LED fabricated using this intermediate connecting layer exhibits excellent color stability and wide color gamut characteristics, with brightness increased from 0 to 31307 cd / m². 2 At that time, the CIE color coordinates only shifted from (0.42, 0.35) to (0.30, 0.37), which is suitable for displaying commonly used 500-5000 cd / m² colors. 2 The color coordinate shift is less than 0.03 within the brightness range, and the color gamut covers 113.7% of NTSC and 118.3% of DCI-P3. Meanwhile, the intermediate connecting layer is a patternless continuous thin film, which does not require additional patterning processes. Pixel partitioning can be achieved through patterned ITO anodes and top aluminum cathodes, which greatly simplifies the manufacturing process and lays a solid foundation for the commercial application of QLED in the display and lighting fields.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An intermediate connecting layer for connecting bottom light-emitting units and top light-emitting units to form a quantum dot / organic hybrid series white LED, characterized in that, The intermediate connecting layer is a three-layer composite structure consisting of a lithium fluoride insulating barrier layer, an aluminum electron transport layer, and a 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer stacked sequentially; the thickness of the lithium fluoride insulating barrier layer is 1 nm; the thickness of the aluminum electron transport layer is 2 nm; and the thickness of the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer is 10 nm to 40 nm.

2. The intermediate connection layer of a series-connected white LED according to claim 1, characterized in that, The bottom light-emitting unit is a yellow quantum dot light-emitting diode, and the top light-emitting unit is a blue organic light-emitting diode. The lithium fluoride insulating barrier layer of the intermediate connecting layer is in contact with the zinc magnesium oxide electron transport layer of the yellow quantum dot light-emitting diode, and the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge-generating layer of the intermediate connecting layer is in contact with the N,N'-bis(naphthyl-1-yl)-N,N'-bis(phenyl)-benzidine hole transport layer of the blue organic light-emitting diode. The three together constitute a quantum dot / organic hybrid series white LED.

3. The intermediate connection layer of a series-connected white LED according to claim 2, characterized in that, The light-emitting layer of the yellow quantum dot LED is a mixed layer of red quantum dots and green quantum dots with a mass ratio of 1:9; the light-emitting layer of the blue organic light-emitting diode is a mixed layer of 2-methyl-9,10-bis(naphthyl-2-yl)anthracene and 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl, wherein the doping concentration of 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl is 6%.

4. The intermediate connecting layer of a series-connected white LED according to claim 3, characterized in that, The thicknesses of each functional layer in the quantum dot / organic hybrid tandem white LED are as follows: indium tin oxide anode 110nm, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole injection layer 45nm, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] hole transport layer 40nm, red quantum dot:green quantum dot hybrid light-emitting layer 20nm, zinc magnesium oxide electron transport layer... The light-emitting layer consists of a 55nm core, a 60nm hole transport layer of N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine, a 25nm luminescent layer of 2-methyl-9,10-bis(naphth-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl, a 50nm electron transport layer of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, a 1nm lithium fluoride electron injection layer, and a 100nm aluminum cathode.

5. The intermediate connecting layer of a series-connected white LED according to claim 3, characterized in that, The intermediate connecting layer is a patternless continuous thin film, in which the aluminum electron transport layer serves as the internal charge transport layer.

6. A method for preparing an intermediate connecting layer of a series-connected white LED as described in any one of claims 1-5, characterized in that, Includes the following steps: On the surface of the electron transport layer of the bottom light-emitting unit, at a background vacuum of 4×10⁻⁶... -4 In a high-vacuum evaporation chamber, a lithium fluoride insulating barrier layer, an aluminum electron transport layer, and a 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer are sequentially deposited using thermal evaporation to form the three-layer composite intermediate connecting layer. The deposition rate of the lithium fluoride insulating barrier layer is 0.1 nm / s, the deposition rate of the aluminum electron transport layer is 0.2 nm / s, and the deposition rate of the 1,4,5,8,9,11-hexaazatriphenylhexanitrile charge generation layer is 1 nm / s.

7. The method for preparing the intermediate connecting layer of a series-connected white LED according to claim 6, characterized in that, It also includes a method for preparing quantum dot / organic hybrid tandem white LEDs, specifically comprising the following steps: S1. Fabrication of bottom yellow quantum dot light-emitting diode unit: The pre-cleaned indium tin oxide glass substrate is treated with oxygen plasma, spin-coated with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate solution and annealed; in a nitrogen glove box, a poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] layer, a red quantum dot:green quantum dot mixed layer and a zinc magnesium oxide layer are spin-coated sequentially, and each layer is annealed after spin-coating; S2. An intermediate connection layer is prepared on the surface of the zinc-magnesium oxide electron transport layer obtained in step S1. S3. On the surface of the intermediate connecting layer, the functional layers of the top blue organic light-emitting diode and the aluminum cathode are sequentially deposited by thermal evaporation to obtain the quantum dot / organic hybrid series white LED.

8. The method for preparing the intermediate connecting layer of a series-connected white LED according to claim 7, characterized in that, In step S1, the oxygen plasma treatment time is 12 min; the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate solution is spin-coated at 3000 rpm for 40 s and annealed in air at 130℃ for 30 min; the poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)] layer is spin-coated at 4000 rpm for 40 s and annealed at 100℃ for 15 min using an 8 mg / mL chlorobenzene solution. Red quantum dots: The green quantum dot mixed layer was prepared by spin-coating with a 10 mg / mL octane solution at a mass ratio of 1:9 at 1500 rpm for 40 s and annealing at 100℃ for 5 min; the zinc magnesium oxide layer was prepared by spin-coating with a 20 mg / mL nanoparticle ethanol solution at 2000 rpm for 40 s and annealing at 100℃ for 10 min.

9. A method for preparing an intermediate connecting layer of a series-connected white LED according to claim 7, characterized in that, In step S3, the thermal evaporation process has a base vacuum of 4×10⁻⁶. -4 The deposition was carried out in the chamber of Pa, and the specific parameters of each layer were as follows: N,N'-bis(naphth-1-yl)-N,N'-bis(phenyl)-benzidine layer deposition rate 1 nm / s, thickness 60 nm; 2-methyl-9,10-bis(naphth-2-yl)anthracene:4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl light-emitting layer deposition rate 1 nm / s, thickness 25 nm, doping concentration 6%; 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene layer deposition rate 1 nm / s, thickness 50 nm; lithium fluoride electron injection layer deposition rate 0.1 nm / s, thickness 1 nm; aluminum cathode deposition rate 2 nm / s, thickness 100 nm.

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