A single-solvent ink-printed, doped light-emitting layer film, electroluminescent device and preparation method thereof

Abstract

The present invention discloses a film, an electroluminescent device and a preparation method thereof for printing a post-doped luminescent layer using a single solute ink. The present invention adopts a single solute ink formula, combined with a growth seed layer and an ink solvent formula to construct a post-doped luminescent layer. The present invention can also achieve the purpose of regulating electroluminescent performance by adjusting inkjet printing parameters to change the degree of mixing of each component in the luminescent layer. The inkjet printing method does not rely on an orthogonal solvent strategy, can save luminescent materials, and is also convenient for the preparation and storage of ink. The preparation method provided by the present invention can avoid the uneven distribution, aggregation, phase separation and the like of different components in the solution caused by the different solubility, polarity and molecular size of the multi-component solutes in the multi-component doping system of the luminescent layer of the conventional inkjet printing doped device. The present invention also provides a preparation method for an electroluminescent device that can achieve white light emission and can be used in display, lighting, optical communication, biomedicine and other fields.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronics, and in particular relates to a post-doped luminescent layer film based on single-solvent ink, an inkjet-printed electroluminescent device and a preparation method thereof. Background Art

[0002] Among solution-processable electroluminescent devices, including organic electroluminescent devices, quantum dot electroluminescent devices, and perovskite electroluminescent devices, the traditional processes such as spin coating and screen printing have the disadvantages of material waste and inability to directly pattern with high precision, and it is difficult to adjust the color in situ after the film is formed once. Inkjet printing technology can effectively solve the above problems. The inkjet printing process has the advantages of high material utilization, direct patterning without a mask, continuous preparation, and no need for a high vacuum environment, which is conducive to the realization of large-area, low-cost electroluminescent devices.

[0003] Conventional solution processing methods for preparing light-emitting thin films usually involve premixing two or more materials in a certain proportion and then directly preparing the doped light-emitting layer. However, this mixed system can easily lead to problems such as uneven solute distribution, aggregation, and phase separation due to the different physical properties of the different components in the solution, such as solubility, viscosity, and polarity. In addition, multi-component solutions or inks have problems such as inconvenient continuous proportion adjustment, complex operation, and unsuitability for long-term storage, which affect the performance of devices prepared continuously over a large area. Therefore, it is necessary to develop a new inkjet printing strategy to provide a practical and effective solution for achieving process simplification, efficient material utilization, in-situ adjustment and repair of light-emitting properties, and improved device performance. Summary of the invention

[0004] In view of the above technical problems, the object of the present invention is to provide a method for preparing an electroluminescent device by post-doping a luminescent layer using inkjet printing of a single solute luminescent ink.

[0005] The present invention realizes the separation and preservation of the host and guest of the doping system by preparing a single solute ink, the host material is prepared in advance to form a growth seed layer, the guest luminescent material is prepared into a single solute ink, and the luminescent ink is partially dissolved and doped to form a luminescent layer after being in situ contacted with the growth seed layer by inkjet printing technology, and combined with the preparation of other functional layers, a solution-processed electroluminescent device that can be directly patterned is finally realized. This process method can solve the quenching effect of commonly used hole injection materials, such as poly (3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS), on the luminescent layer, and provide exciton utilization; in addition, the host material can be pre-grown on the seed layer, which is convenient for screening the host-guest combination with energy level matching to achieve efficient carrier transport performance. The inkjet printing ink only uses a single solute, which is beneficial to improve the stability of the ink, improve the stability and repeatability of the ink, and is beneficial to reduce large-scale manufacturing costs and improve the yield rate.

[0006] The technical solution provided by the present invention is as follows:

[0007] The first aspect of the present invention provides a method for printing a thin film doped with a light-emitting layer using a single-solute ink, comprising the following steps:

[0008] Preparation of hole injection layer:

[0009] preparing a hole injection layer on a substrate;

[0010] Preparation of the growth seed layer: spin coating a solution containing a growth seed layer material on the hole injection layer to obtain the growth seed layer; the growth seed layer material is a single host material, a mixed host material, or a mixed material of a host material and a luminescent sensitizer that provides carrier transport and energy transfer;

[0011] Preparation of inkjet-printed luminescent layer: a single solute is dissolved in a solvent to form an inkjet-printed luminescent ink, which is then deposited onto a growth seed layer through inkjet printing. During inkjet printing, the electroluminescent performance is adjusted by adjusting the inkjet printing parameters. The singlet and triplet energy levels of the growth seed layer material are higher than the energy levels of the inkjet-printed luminescent ink. The growth seed layer and the luminescent ink are partially miscible and doped to form a luminescent layer through energy transfer. The luminescent layer is a new thin layer formed by the growth seed layer after receiving the inkjet-printed single solute ink due to partial miscibility. When complete energy transfer occurs, no luminescence from the growth seed layer can be observed in the electroluminescent spectrum. When incomplete energy transfer occurs, the same ink can be printed multiple times in succession to suppress the luminescence of the main material or luminescent sensitizer in the growth seed layer, or to enhance the luminescence intensity of the solute in the ink after film formation, thereby adjusting the performance of the electroluminescent device.

[0012] Preferably, the substrate is a flat surface, including one of an ITO glass substrate, stainless steel, a flexible substrate polyimide or a silicon wafer.

[0013] Preferably, the growth seed layer material has good film-forming properties and may be incompletely resistant to ink droplets generated by inkjet printing. In addition, the luminescent region and spectral characteristics of the luminescent material can be adjusted by changing the inkjet printing spacing and the number of inkjet printing repetitions; the growth seed layer and the printed region spectrum can also be made complementary and cover the visible light region to achieve a complementary white light device.

[0014] Preferably, the host material is selected from 1,3-di-9-carbazolylbenzene (mCP) and polyvinylcarbazole (PVK), and the triplet energy level of the host material is higher than the triplet energy level of the sensitizer.

[0015] Preferably, the luminescence spectrum of the luminescent photosensitizer and the absorption spectrum of the solute have a certain overlap, and the luminescence peak of the photosensitizer is quenched, disappears or weakened due to energy transfer during the electroluminescence process. The luminescent photosensitizer is selected from bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone.

[0016] Preferably, the solvent in the solution for dissolving the growth seed layer material is selected from one or more mixtures of chlorobenzene, toluene, tetrahydrofuran, dichlorobenzene, dichloromethane, chloroform, and acetonitrile.

[0017] Preferably, the solute of the luminescent ink is selected from 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile, organic boron nitrogen luminescent material, and phosphorescent material.

[0018] Preferably, the solvent of the luminescent ink comprises a mixture of one or more of cyclohexanone, isopropanol, chlorobenzene, toluene, acetonitrile, tetrahydrofuran, o-dichlorobenzene, dodecane, and n-octane. The concentration of the luminescent ink solute is less than 10 mg / ml. More preferably, the solvent of the luminescent ink is a mixed solvent of cyclohexanone and isopropanol in a volume ratio of (70-80):(20-30).

[0019] Preferably, the inkjet printing parameters include parameters such as the number of prints, the inkjet printing spacing, the print pulse waveform, and the substrate heating temperature to adjust the electroluminescent performance. Specifically, changing the number of inkjet printing can adjust the amount of the luminescent object penetrating into the seed layer, and adjust the luminescent brightness and efficiency; the inkjet printing spacing can adjust the in-plane distribution concentration of the luminescent object material, and change the spectrum, brightness, and efficiency; the substrate heating temperature can adjust the solvent evaporation rate and the film morphology; the inkjet printing pulse waveform can adjust parameters such as the inkjet printing droplet state and the coffee ring effect to control the material mixing ratio, the size of the luminescent area, and the uniformity of the ink droplets.

[0020] The second aspect of the present invention provides a light-emitting layer film doped after printing with a single-solvent ink prepared by the method of the first aspect.

[0021] The third aspect of the present invention provides an electroluminescent device with a light-emitting layer doped after printing with a single solute ink, comprising the light-emitting layer film doped after printing with a single solute ink as described in the second aspect, and also comprising a hole blocking layer, an electron transport layer, an electron injection layer and a metal cathode sequentially arranged on the inkjet-printed light-emitting layer, and white light emission can be achieved by regulating the size of the spatial distribution area of ​​the growth seed layer and the single solute light-emitting ink.

[0022] Preferably, the hole blocking layer is selected from [2-((oxy)diphenylphosphino)phenyl]ether, bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum, conjugated molecules containing phosphine oxide groups, and the like.

[0023] The electron transport layer is selected from 1,3,5-tris(3-(3-pyridyl)phenyl)benzene, trihydroxyquinoline aluminum or phenanthroline.

[0024] The electron injection layer is preferably selected from lithium octahydroxyquinoline, lithium fluoride, cesium fluoride or cesium carbonate.

[0025] The metal cathode is preferably selected from aluminum electrode, silver, samarium, copper, ytterbium and the like.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects.

[0027] 1. The present invention provides an inkjet printing process based on a single solute ink for post-doping. The ink is easy to preserve, has a simple preparation process, high precision, and saves materials. It has the characteristics of direct patterning / pixelation and in-situ adjustment or repair of luminescence.

[0028] 2. The post-doping process of inkjet printing a single solute ink provided by the present invention can be applied to the preparation of in-plane complementary color white light devices. Different from the traditional single-layer white light or vertical multi-layer complementary white light device process, this method can conveniently and accurately control the material mixing ratio, the size of the luminous area and the uniformity of the ink droplets by changing the number of inkjet printing, the inkjet printing spacing, the inkjet printing height, the substrate heating temperature, the inkjet printing waveform and other parameters, thereby adjusting the device emission wavelength to achieve white light emission.

[0029] 3. The inkjet-printed electroluminescent device prepared by the present invention has simple process, low cost, high material utilization rate, high ink stability, and easy and precise control of the luminescent area, and is suitable for large-area continuous preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Attached Figure 1 This is a schematic diagram of the post-doping process based on inkjet printing of a single solute ink in the present invention;

[0031] Attached Figure 2 The inkjet printing waveform diagram of Example 1;

[0032] Attached Figure 3 is a comparison diagram of the photoinduced spectra of the luminescent film of Example 1 with and without a seed layer;

[0033] Attached Figure 4 is a device structure diagram of Example 2;

[0034] Attached Figure 5 The normalized electroluminescence spectra of the devices prepared by inkjet printing at different intervals in Example 2;

[0035] Attached Figure 6 The voltage-brightness curve relationship diagram of different devices in Example 2;

[0036] Attached Figure 7 This is a structural diagram of an inkjet-printed narrow-emission light-emitting device using a thermally activated delayed fluorescent material as a sensitizer in Example 3;

[0037] Attached Figure 8 Normalized electroluminescence spectrum of the inkjet-printed narrow emission device of Example 3;

[0038] Attached Fig. 9 This is a device structure diagram of the inkjet-printed white light device of Example 4.

[0039] Attached Fig.10 This is the normalized electroluminescence spectrum of the inkjet-printed white light device of Example 4.

[0040] wherein, a first ITO glass substrate 101; a first hole injection layer 102; a first growth seed layer 103; a single solute inkjet droplet 104; an inkjet head 105; a second ITO glass substrate 201; a second hole injection layer 202; a second growth seed layer 203; a first inkjet printed light-emitting layer 204; a first hole blocking layer 205; a first electron transport layer 206; a first electron injection layer 207; a first cathode 208; a third ITO glass substrate 301; a third ... hole injection layer 302; third growth seed layer 303; second inkjet printed light-emitting layer 304; second hole blocking layer 305; second electron transport layer 306; second electron injection layer 307; second cathode 308; fourth ITO glass substrate 401; fourth hole injection layer 402; fourth growth seed layer 403; third inkjet printed light-emitting layer 404; third hole blocking layer 405; third electron transport layer 406; third electron injection layer 407; third cathode 408. DETAILED DESCRIPTION

[0041] The content of the present invention is further described below in conjunction with specific embodiments, but the content of the present invention is not limited thereto at all.

[0042] The present invention relates to an inkjet printing process based on a single solute ink to realize a post-doped luminescent layer. The problem it solves is to avoid the problems of uneven solute distribution, aggregation, phase separation, etc. that often occur when two or more luminescent materials are mixed in a certain proportion in a doped optoelectronic device; to avoid the irregular film forming phenomenon caused by the mutual dissolution of adjacent droplets in the horizontal direction; to avoid the problems of inconvenient solute ratio adjustment and complicated operation in multi-solute luminescent inks, and the problems of voids and irregular defects between the luminescent layer and the transmission layer. It is worth noting that separating the materials in the doping system not only maintains the original energy transfer effect, but also does not rely on the use of orthogonal solvents when depositing the luminescent layer film.

[0043] Example 1

[0044] The thin film is formed by inkjet printing a single solute ink on a substrate with a growth seed layer. The specific process steps are as follows:

[0045] Preparation of hole injection layer: Figure 1 As shown, the surface of the indium tin oxide (ITO) glass substrate 101 is rinsed with clean water, and then the glass is ultrasonically cleaned with acetone and ethanol at 20 degrees Celsius for 10 minutes each, and then the ITO glass substrate 101 is blown dry with nitrogen and placed in a UV ozone treatment device for 20 minutes. Then, a layer of poly (3,4-ethylenedioxythiophene) - polystyrene sulfonic acid (PEDOT:PSS) is grown on the surface of the ITO glass substrate 101 at a speed of 4000 revolutions per minute for 30 seconds to form a hole injection layer 102, and then the formed hole injection material is placed on a heating table and annealed at 120 degrees Celsius for 10 minutes.

[0046] Preparation of the growth seed layer: First, a chlorobenzene solution (5 mg / ml) of 1,3-dicarbazole-9-ylbenzene (mCP) and a chlorobenzene solution (5 mg / ml) of polyvinylcarbazole (PVK) were mixed in a mass ratio of 80:20, and then the above solution was spin-coated on the hole injection layer 102 at a speed of 1000 rpm for 30 seconds to form a growth seed layer 103.

[0047] Inkjet printing of the luminescent layer: 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile (4CzIPN) was prepared with cyclohexanone and isopropanol at a volume ratio of 70:30 to form an ink with a concentration of 1 mg / ml. 1.5 ml of the ink was then injected into the ink bag using a syringe. The aforementioned substrate was placed on the inkjet printer operating platform to observe the ink droplets before printing. By adjusting the pulse waveform (as shown in the attached figure), the ink droplets were observed. Figure 2 As shown in the figure, the ink droplets are observed to fall vertically and evenly without satellite droplets by the built-in camera. A rectangular printing range of 3 mm × 11 mm is drawn on the software drawing interface, and the inkjet printing height is 1.2 mm. The substrate is preheated at 40 degrees Celsius, and inkjet printing is performed on the required area on the substrate with a printing spacing of 50 microns to obtain the first light-emitting layer 104. After printing, the sample is taken out for fluorescence experiment.

[0048] As a comparison, the luminescent ink was directly printed on the hole injection layer 102 with the above printing parameters. The photoluminescence spectra of the two prepared luminescent films are shown in FIG. Figure 3 As shown in the figure, it can be seen that the luminescence spectrum of the thin film with the growth seed layer has a certain blue shift because the first growth seed layer 103 containing the main function in the post-doped luminescent layer avoids aggregation, and the luminescence intensity is significantly enhanced because the post-doping process avoids the concentration quenching effect. This host-guest separation structure is difficult to achieve with traditional inkjet printing and other solution preparation methods without the help of orthogonal solvents.

[0049] Example 2

[0050] The inkjet printing optoelectronic device with post-doping based on a single solute ink is as follows:

[0051] Preparation of hole injection layer: Figure 4 As shown, the surface of the indium tin oxide (ITO) glass substrate 201 is rinsed with clean water, and then the glass is ultrasonically cleaned with acetone and ethanol at 20 degrees Celsius for 10 minutes each, and then the ITO glass substrate 201 is blown dry with nitrogen and placed in a UV ozone treatment device for 20 minutes. Then, a layer of poly (3,4-ethylenedioxythiophene) - polystyrene sulfonic acid (PEDOT:PSS) is grown on the surface of the ITO glass substrate 201 at a speed of 4000 rpm for 30 seconds to form a hole injection layer 202, and then the formed hole injection material is placed on a heating table and annealed at 120 degrees Celsius for 10 minutes.

[0052] Preparation of the growth seed layer: First, a chlorobenzene solution (5 mg / ml) of 1,3-dicarbazole-9-ylbenzene (mCP) and a chlorobenzene solution (5 mg / ml) of polyvinylcarbazole (PVK) were mixed in a mass ratio of 80:20, and then the above solution was spin-coated on the hole injection layer 202 at a speed of 1000 rpm for 30 seconds to form a growth seed layer 203.

[0053] Inkjet printing of the luminescent layer: 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile (4CzIPN) was prepared with cyclohexanone and isopropanol at a volume ratio of 70:30 to form an ink with a concentration of 1 mg / ml. 1.5 ml of the ink was then injected into the ink bag using a syringe. The aforementioned substrate was placed on the inkjet printer operating platform to observe the ink droplets before printing. By adjusting the pulse waveform (as shown in the attached figure), the ink droplets were observed. Figure 2 As shown in the figure, the ink droplets are observed to fall vertically and evenly without satellite droplets by the built-in camera. A rectangular printing range of 3 mm × 11 mm is drawn on the software drawing interface, and the inkjet printing height is 1.2 mm. The substrate is preheated at 40 degrees Celsius, and inkjet printing is performed on the required area on the substrate. The printing spacing is set to 30 microns, 50 microns, 70 microns, and 90 microns, respectively, to form the corresponding second light-emitting layer 204. After printing, the sample is taken out.

[0054] Preparation of other functional layers: After the inkjet printing, the substrate was moved to a vacuum evaporation chamber to sequentially evaporate a hole blocking layer [2-((oxy)diphenylphosphino)phenyl]ether (DPEPO, 10 nm), an electron transport layer 1,3,5-tris(3-(3-pyridyl)phenyl)benzene (TmPyPB, 50 nm), an electron injection layer octahydroxyquinoline lithium (Liq, 1 nm) and a metal aluminum cathode (100 nm), corresponding to Figure 4 Middle functional layers 205 , 206 , 207 and 208 .

[0055] After the device is prepared, the evaporation chamber is taken out and the electroluminescence performance is tested in the atmosphere. The normalized electroluminescence spectra of the devices with four different inkjet printing spacings are shown in Figure 2. Figure 5 As shown. Figure 5 It can be seen that as the printing spacing increases, the spectrum has a slight blue shift. The electroluminescence brightness of the device is shown in Figure 6 As shown, when the printing spacing reaches 50 microns, the brightness of the device is maximum at the same voltage, and the external quantum efficiency of the device can reach 16.3%.

[0056] Example 3

[0057] Inkjet printing of narrow emission spectrum organic electroluminescent devices, the specific steps are as follows:

[0058] Preparation of hole injection layer: Figure 7 As shown, an indium tin oxide (ITO) glass substrate 301 is ultrasonically cleaned with acetone and ethanol at 20 degrees Celsius for 10 minutes each, and then the glass substrate is blown dry with nitrogen and placed in a UV ozone treatment device for 20 minutes. Then, a layer of poly (3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) is grown on the ITO glass substrate 301 at a speed of 4000 rpm for 30 seconds to form a hole injection layer 302, and then the substrate is placed on a heating table and annealed at 120 degrees Celsius for 10 minutes.

[0059] Preparation of growth seed layer: A chlorobenzene solution (5 mg / ml) of a sensitizer thermally activated delayed fluorescent material bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) and a chlorobenzene solution (5 mg / ml) of polyvinylcarbazole (PVK) were mixed at a mass ratio of 80:20, and then spin-coated on the aforementioned substrate at a speed of 1000 rpm for 30 seconds to prepare a growth seed layer 303.

[0060] Inkjet printing of luminescent layer: The organic boron nitrogen luminescent material (BCzBN) with a narrow emission spectrum is prepared with solvents cyclohexanone and isopropanol in a volume ratio of 70:30 to form an ink with a concentration of 1 mg per ml, and then 1.5 ml of ink is taken with a syringe and injected into the printing ink bag. Before printing, the ink droplets need to be observed with the built-in camera of the inkjet printer. Adjust the voltage until the ink droplets are observed to fall vertically and evenly without satellite droplets. Draw a 3 mm × 11 mm rectangular pixel pattern on the software drawing interface, with a print height of 1.2 mm, heat the substrate at 40 degrees Celsius, and perform inkjet printing in a suitable area with parameters of printing dot spacing of 40 microns, 60 microns, 80 microns, and 100 microns, respectively, to form the second luminescent layer 304. After printing, take out the sample.

[0061] Preparation of other functional layers: Hole blocking layer [2-((oxy)diphenylphosphino)phenyl]ether (DPEPO, 10 nm), electron transport layer 1,3,5-tris(3-(3-pyridyl)phenyl)benzene (TmPyPB, 50 nm), electron injection layer octahydroxyquinoline lithium (Liq, 1 nm) and cathode aluminum electrode (100 nm) were sequentially deposited in a vacuum deposition chamber, corresponding to Figure 7 Middle functional layers 305 , 306 , 307 and 308 .

[0062] Figure 8 The normalized electroluminescence spectra of narrow emission light-emitting devices with different inkjet printing spacings. From the spectrum, it can be seen that the narrow emission device prepared by post-doping based on this single solute ink still has a good energy transfer effect even if the sensitizer and the luminescent material are separated. The half-peak width of the device with different printing spacings is only slightly different. When the printing spacing is 80 microns, the half-peak width of the device spectrum is only 38 nanometers.

[0063] Example 4

[0064] Inkjet printing of white organic electroluminescent devices, the specific steps are as follows:

[0065] Preparation of hole injection layer: Figure 7 As shown, an indium tin oxide (ITO) glass substrate 401 is ultrasonically cleaned with acetone and ethanol at 20 degrees Celsius for 10 minutes each, and then the glass substrate is blown dry with nitrogen and placed in a UV ozone treatment device for 20 minutes. Then, a layer of poly (3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) is grown on the ITO glass substrate 301 at a speed of 4000 rpm for 30 seconds to form a hole injection layer 402, and then the substrate is placed on a heating table and annealed at 120 degrees Celsius for 10 minutes.

[0066] Preparation of growth seed layer: A chlorobenzene solution (5 mg / ml) of a sensitizer thermally activated delayed fluorescent material bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) and a chlorobenzene solution (5 mg / ml) of polyvinylcarbazole (PVK) were mixed at a mass ratio of 80:20, and then spin-coated on the aforementioned substrate at a speed of 1000 rpm for 30 seconds to prepare a growth seed layer 403.

[0067] Inkjet printing of the luminescent layer: The phosphorescent material (acetylacetone) bis(2-methyldibenzo[F,H]quinoxaline) iridium (Ir(MDQ)2acac) is prepared with solvents cyclohexanone and isopropanol in a volume ratio of 80:20 to form an ink with a concentration of 1 mg per ml, and then 1.5 ml of the ink is taken with a syringe and injected into the printing ink bag. Before printing, the ink droplets need to be observed with the built-in camera of the inkjet printer. Adjust the voltage until the ink droplets are observed to fall vertically and evenly without satellite droplets. Draw a 3 mm × 11 mm rectangular pixel pattern on the software drawing interface with a print height of 1.2 mm, heat the substrate at 40 degrees Celsius, and perform inkjet printing in a suitable area with a print dot spacing of 140 microns to form the third luminescent layer 404. After printing, remove the sample.

[0068] Preparation of other functional layers: Hole blocking layer [2-((oxy)diphenylphosphino)phenyl]ether (DPEPO, 10 nm), electron transport layer 1,3,5-tris(3-(3-pyridyl)phenyl)benzene (TmPyPB, 50 nm), electron injection layer octahydroxyquinoline lithium (Liq, 1 nm) and cathode aluminum electrode (100 nm) were sequentially deposited in a vacuum deposition chamber, corresponding to Fig. 9 Middle functional layers 405 , 406 , 407 and 408 .

[0069] Fig.10 The normalized electroluminescent white light spectrum of the inkjet-printed device is shown in Figure 2. As can be seen from the spectrum, due to the incomplete energy transfer between the sky blue light material DMA-DPS in the growth seed layer and the inkjet-printed red phosphorescent material Ir(MDQ)2acac, warm white light emission is achieved, with color coordinates of (0.45, 0.43). In addition, the brightness of the device at 11V exceeds 4000 candela per square meter, and the maximum external quantum efficiency is 15%.

[0070] The specific embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. A method for doping a light-emitting layer thin film after printing with a single-solvent ink, characterized in that: The following steps are involved: Preparation of hole injection layer: preparing a hole injection layer on a substrate; Preparation of the growth seed layer: spin coating a solution containing a growth seed layer material on the hole injection layer to obtain the growth seed layer; the growth seed layer material is a single host material, a mixed host material, or a mixed material of a host material and a luminescent sensitizer that provides carrier transport and energy transfer; Preparation of inkjet-printed luminescent layer: a single solute is dissolved in a solvent to form an inkjet-printed luminescent ink, which is deposited on a growth seed layer by inkjet printing, and the electroluminescent performance is adjusted by regulating inkjet printing parameters during inkjet printing; the singlet and triplet energy levels of the growth seed layer material are higher than the energy levels of the inkjet-printed luminescent ink; the growth seed layer and the luminescent ink are partially miscible and doped to form a luminescent layer through energy transfer.

2. The method according to claim 1, characterized in that: The substrate is a flat plane with a surface roughness less than 1 micron, including one of an ITO glass substrate, stainless steel, a flexible substrate polyimide or a silicon wafer.

3. The method according to claim 1, characterized in that: The hole injection layer is poly(3,4-ethylenedioxythiophene)-polystyrene sulfone.

4. The method according to claim 1, characterized in that: The host material is selected from 1,3-di-9-carbazolylbenzene (mCP) and polyvinylcarbazole (PVK), and the triplet energy level of the host material is higher than the triplet energy level of the luminescent sensitizer.

5. The method according to claim 1, characterized in that: The luminescence spectrum of the luminescence sensitizer and the absorption spectrum of the solute have a certain overlap, and the luminescence peak of the photosensitizer is quenched, disappears or weakened due to energy transfer during the electroluminescence process. The luminescence sensitizer is selected from bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone.

6. The method according to claim 1, characterized in that: The solvent in the solution containing the growth seed layer material is selected from one or more mixtures of chlorobenzene, toluene, tetrahydrofuran, dichlorobenzene, dichloromethane, chloroform and acetonitrile.

7. The method according to claim 1, characterized in that: The solute of the inkjet printing luminescent ink is selected from 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile, organic boron nitrogen luminescent materials, and phosphorescent materials; the solvent of the luminescent ink includes a mixture of one or more of cyclohexanone, ethanol, methanol, isopropanol, chlorobenzene, toluene, acetonitrile, tetrahydrofuran, o-dichlorobenzene, dodecane, and n-octane, with a concentration of less than 10 mg / ml.

8. The method according to claim 1, characterized in that: The inkjet printing parameters include printing times, inkjet printing spacing, printing pulse waveform and substrate heating temperature.

9. A thin film doped with a luminescent layer after printing with a single-solvent ink, characterized in that: The method is prepared by any one of claims 1 to 8.

10. An electroluminescent device with a light-emitting layer doped after printing with a single-solvent ink, characterized in that: It includes the single-solute ink-printed doped luminescent layer film as described in claim 9, and also includes a hole blocking layer, an electron transport layer, an electron injection layer and a metal cathode arranged in sequence on the inkjet-printed luminescent layer. White light emission can be achieved by regulating the size of the spatial distribution area of ​​the growth seed layer and the single-solute luminescent ink.

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