CN111697145B - Non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode - Google Patents
Non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode Download PDFInfo
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Abstract
The invention belongs to the technical field of thermally activated delayed fluorescence electroluminescent diodes, and discloses a non-doped solution processing type dendritic thermally activated delayed fluorescence electroluminescent diode. The non-doped solution processing type dendritic thermal activation delayed fluorescence electroluminescent diode comprises a substrate, an anode, a hole transport layer, a short excited state life dendritic thermal activation delayed fluorescence light-emitting layer, an electron transport layer and a cathode which are sequentially stacked; the excited state lifetime of the short excited state lifetime dendritic thermal activation delayed fluorescence luminescent material of the luminescent layer is less than or equal to 5 microseconds. The non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode has the characteristics of low turn-on voltage, low efficiency roll-off and long service life, does not need any complex metal doped transmission layer or blending transmission layer, and has good application prospect.
Description
Technical Field
The invention relates to the field of organic photoelectric devices, in particular to a non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode and a preparation method thereof.
Background
At present, Organic Light Emitting Diodes (OLEDs) have been applied and popularized in the display fields of smart phones, tablet computers, liquid crystal televisions, and the like. The traditional fluorescent material only utilizes 25% of singlet excitons, while the phosphorescent material contains noble metal, so that the manufacturing cost is very high, and the industrial application of the organic light-emitting diode is hindered to a certain extent. Pure organic compounds with the characteristics of Thermally Activated Delayed Fluorescence (TADF) successfully circumvent the two problems, and become the most potential organic luminescent materials of the third generation. At present, the processing technology of the vacuum evaporation type TADF-OLEDs is complex, complex and high in manufacturing cost, and is not beneficial to realizing the flexible and large-area display of the OLED. The TADF-OLED prepared by the solution processing technology has low cost and very simple technology, and particularly when a multi-element doping system is faced, the TADF-OLED only needs to be blended in proportion, so that the TADF-OLED is a hot-handable technology in the fields of future display and illumination.
When the current TADF micromolecule-based electroluminescent diode is used for preparing a multilayer device structure, the phenomenon of mutual solubility between layers generally occurs due to poor solvent resistance, so that a luminescence quenching center is generated, and the very serious device efficiency roll-off under high brightness is caused. In addition, these efficient small molecule systems are generally obtained by host-guest blending, which is very limited by the properties of the host material, such as the host material needs to have high T1, bipolar transport property, good solubility, and the like. However, in practice, the number of the main materials of solution processing type is very large, which increases the manufacturing cost of the solution processing device and limits the improvement of the performance of the device in various aspects including efficiency, roll-off, starting voltage and the like.
In 2017, C.Z.Lu et al designed and synthesized a Blue efficient TADF material B-oTC (Combining Charge-Transfer Pathways to Achieve Unique thermal Activated layered emissions Emitters for High-Performance Solution-Processed, Non-Processed Blue OLEDs, Angew.chem.int.Ed.2017,56, 15006-. The B-oTC-based blue undoped organic blue light emitting diode prepared by the solution method achieved an external quantum efficiency as high as 19.1%. However, devices based on this material are at 1000cd m-2The efficiency is only 9.7%, and the ignition voltage is up to 3.9V. The molecule has an excited state lifetime of up to 15 microseconds, and the design and selection of such a light emitting layer is undoubtedly the main factor contributing to the aggravation of exciton-exciton quenching at high current densities. It is well known that the two disadvantages of severe roll-off efficiency and high turn-on voltage are fatal to the development of the application of the flexible, large-area display of the solution-processed TADF-OLED.
Yamamoto et al report that after 40 minutes of lifetime of a non-doped solution processed TADF-OLED (Thermally activated delayed fluorescence OLEDs with full solution illumination of organic layers outside inhibiting new-10% external quantum efficiency. chem. Commun.,2017,53, 2439-2442), the lifetime problem of non-doped solution processed Thermally activated delayed fluorescence devices has not been substantially improved.
Therefore, in view of the current situation that the efficiency roll-off, the turn-on voltage and the service life of the conventional undoped solution processed electroluminescent diode are not ideal enough, the exploration and development of the undoped solution processed dendritic thermal activation delayed fluorescence electroluminescent diode with low turn-on voltage, low efficiency roll-off and long service life and the preparation method thereof are particularly important for promoting the flexible and large-area application of the OLED.
Disclosure of Invention
In order to solve the defects and shortcomings of the prior art, the invention aims to provide a non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode.
The luminous layer in the thermal activation delayed fluorescence electroluminescent diode is a dendritic thermal activation delayed fluorescence luminous material, in particular to a dendritic thermal activation delayed fluorescence material with the excitation state life shorter than 5 microseconds. The dendritic self-body thermal activation delayed fluorescence material with the excited state life shorter than 5 microseconds is used for replacing the traditional luminous micromolecule or host-object doping system, and the problems of poor solvent resistance and film forming property, phase separation of host-object doping, triplet exciton limitation and the like are solved. Since quenching of triplet excitons between host and host, quenching of triplet excitons between host and guest, and quenching of triplet excitons between guest and guest are easily involved in a doping system, these quenching effects lead to generation of high-energy-state excitons. These high-energy excitons, which have a very high excited-state energy, are dissipated via non-radiative transitions, resulting in a significant waste of triplet excitons. The dendritic self-body thermal activation delayed fluorescence molecules with short excited state service life can effectively avoid the influence, and can ensure a rapid and effective reverse intersystem crossing process, rapidly convert high-concentration triplet excitons into singlet excitons through the intersystem crossing process, participate in radiative transition, release photons and further improve the problem of serious efficiency roll-off of the device under high current density. Furthermore, a simple device structure without any metal doped transport layer or multiple transport material blending participation achieves significantly extended device lifetimes.
The starting voltage of the non-doped solution processed dendritic thermal activation delay fluorescence electroluminescent diode is less than or equal to 2.7V and is 1000cd m-2The efficiency at luminance can still be maintained at 90% or more of the maximum external quantum efficiency at an initial luminance of 500cd m-2The device lifetime is greater than 6 hours.
The purpose of the invention is realized by the following technical scheme:
a non-doped solution processing type dendritic thermal activation delayed fluorescence electroluminescent diode comprises a substrate, an anode, a hole transport layer, a short excited state life dendritic thermal activation delayed fluorescence luminescent layer, an electron transport layer and a cathode which are sequentially stacked; the excited state lifetime of the short excited state lifetime dendritic thermal activation delayed fluorescence luminescent material of the luminescent layer is less than or equal to 5 microseconds.
The short excited state lifetime dendritic thermal activation delayed fluorescence material is more than one of T1-T12 molecular structure materials:
the number of layers of the light emitting layer is not less than 1 and is an integer. When the light-emitting layer is a plurality of layers, the material of each layer is the same or different.
The electron transport layer is made of more than one of E1-E19 molecular structure materials:
the hole transport layer is made of more than one of H1-H6 molecular structure materials:
no exciton blocking layer or an exciton blocking layer is added between the hole transport layer and the light-emitting layer; an exciton blocking layer is not added or added between the electron transport layer and the light emitting layer, and the transport layer does not need any metal doping. The exciton blocking layer is preferably a layer.
The non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode further comprises a cathode buffer layer, and the cathode buffer layer is arranged between the electron transport layer and the cathode.
The substrate is glass, quartz, sapphire, polyimide, polyethylene terephthalate, polyethylene naphthalate, metal, alloy or stainless steel film.
The anode and the cathode are independently metal or metal oxide; the metal oxide is at least one of indium tin oxide, fluorine-doped tin dioxide, zinc oxide and indium gallium zinc oxide.
The preparation method of the non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode comprises the following steps:
and taking a substrate with an anode layer, and then sequentially preparing a hole transport layer, a dendritic thermal activation delayed fluorescence light-emitting layer, an electron transport layer and a cathode on the anode layer to obtain a non-doping solution for processing the dendritic thermal activation delayed fluorescence electroluminescent diode.
Preparing or not preparing an exciton blocking layer between the hole transport layer and the light-emitting layer; an exciton blocking layer is prepared or not prepared between the electron transmission layer and the luminous layer.
And a cathode buffer layer is prepared between the electron transport layer and the cathode.
The preparation process comprises one or more of spin coating, brush coating, spray coating, dip coating, roll coating, evaporation coating, printing or ink-jet printing.
The starting voltage of the non-doped solution processed dendritic thermal activation delay fluorescence electroluminescent diode is less than or equal to 2.7V and is 1000 cd.m-2The efficiency at luminance can be maintained at 90% or more of the maximum external quantum efficiency, and the luminance at the initial luminance is 500 cd-m-2The device lifetime is greater than 6 hours.
The invention introduces the dendritic self-body thermal activation delayed fluorescence material with the excited state life shorter than 5 microseconds as the luminous layer, reduces the exciton-exciton quenching effect and the exciton-polaron effect under the high current density, simultaneously realizes the low starting voltage and the low efficiency roll-off, has obviously prolonged device life, does not need any complex metal doping transmission layer or blending transmission layer, and has good application prospect.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) according to the invention, the dendritic host thermal activation delayed fluorescence material with the excited state life shorter than 5 microseconds is selected to replace the traditional host-guest doping system and small molecule system, so that the macroscopic device process problems of host-guest phase separation, difficult host material selection, poor film forming property, solvent resistance and the like are successfully avoided. Since quenching of triplet excitons between host and host, quenching of triplet excitons between host and guest, and quenching of triplet excitons between guest and guest are easily involved in a doping system, these quenching effects lead to generation of high-energy-state excitons. These high-energy excitons, which have a very high excited-state energy, are dissipated via non-radiative transitions, resulting in a significant waste of triplet excitons. The dendritic self-body thermal activation delayed fluorescence molecules with short excited state service life can effectively avoid the influence, and can ensure a rapid and effective reverse intersystem crossing process, rapidly convert high-concentration triplet excitons into singlet excitons through the intersystem crossing process, participate in radiative transition, release photons and further improve the problem of serious efficiency roll-off of the device under high current density.
(2) The starting voltage of the non-doped solution processing type dendritic thermal activation delay fluorescent device non-doped solution processing dendritic thermal activation delay fluorescent electroluminescent diode related by the invention is less than or equal to 2.7V, and can almost be compared with the starting voltage of an evaporation device, and is 1000cd m-2The efficiency at luminance still maintains 90% or more of the maximum external quantum efficiency.
(3) The design of the luminescent layer can reduce the difficulty of selecting a transmission layer with energy level matching, simplify the manufacturing cost and the device structure, and avoid a multi-layer complex structure of metal doping or multiple transmission material blending used by the traditional stable device. The initial brightness of the undoped solution processed thermally activated delayed fluorescence device is 500cd m-2And the service life of the device is longer than 6 hours, which is better than the service life of the solution processing type non-doping heat activation delayed fluorescence device reported in the literature.
Drawings
FIG. 1 is a schematic structural diagram of a non-doped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode according to the present invention; 1-substrate with anode, 2-hole transmission layer, 3-luminous layer, 4-electron transmission layer, 5-cathode buffer layer and cathode;
FIG. 2 is a graph of 2- (a) current density-voltage-luminance of the undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode obtained in example 1; 2- (b) external quantum efficiency-luminance plot; 2- (c) electroluminescence spectrum at a current density of 10 milliampere/square centimeter; 2- (d) transient fluorescence lifetime spectrogram; 2- (e) luminance-time decay profile;
FIG. 3 is a graph of 3- (a) current density-voltage-luminance of the undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode obtained in example 2; 3- (b) external quantum efficiency-luminance plot; 3- (c) electroluminescence spectrum at a current density of 10 milliampere/square centimeter; 3- (d) transient fluorescence lifetime spectrogram; 3- (e) luminance-time decay profile;
FIG. 4 is a graph of 4- (a) current density-voltage-luminance of the undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode obtained in example 3; 4- (b) external quantum efficiency-luminance plot; 4- (c) electroluminescence spectrum at a current density of 10 milliampere/square centimeter; 4- (d) transient fluorescence lifetime spectrogram; 4- (e) luminance-time decay curve.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
The structural schematic diagram of the non-doped solution processing type dendritic thermal activation delayed fluorescence electroluminescent diode is shown in fig. 1, and the non-doped solution processing type dendritic thermal activation delayed fluorescence electroluminescent diode comprises a substrate 1 with an anode, a hole transport layer 2, a light-emitting layer 3, an electron transport layer 4, a cathode buffer layer and a cathode 5 which are sequentially stacked. No exciton blocking layer or an exciton blocking layer is added between the hole transport layer and the light-emitting layer; and no exciton blocking layer or an exciton blocking layer is added between the electron transport layer and the light-emitting layer.
The process of diode preparation herein includes one or a mixture of spin coating, brush coating, spray coating, dip coating, roll coating, evaporation, printing, or ink jet printing.
And annealing treatment is carried out after the hole transport layer and the light-emitting layer are coated. When preparing the exciton blocking layer between the hole transport layer and the light emitting layer, annealing treatment is carried out after coating. The electron transmission layer, the exciton blocking layer prepared between the electron transmission layer and the luminous layer and the cathode buffer layer can be prepared in an evaporation mode.
The thickness of the hole transport layer is 30-50 nm; the thickness of the luminous layer is 30-50 nm; the thickness of the electron transmission layer is 30-60 nm; the thickness of the exciton blocking layer between the hole transport layer and the light emitting layer is 20-50 nm; the thickness of the exciton blocking layer prepared between the electron transmission layer and the luminous layer is 5-20 nm; the thickness of the cathode buffer layer is 1-2 nm.
The material of the exciton blocking layer between the hole transport layer and the light emitting layer is selected from the H1-H6 molecular structure materials described above. The material of the exciton blocking layer between the electron transport layer and the light emitting layer is selected from the molecular structural materials E1-E19.
Example 1
The non-doped solution-processed dendritic thermal activation delayed fluorescence electroluminescent diode with low turn-on voltage, low efficiency roll-off and considerable device life of the embodiment is composed of a substrate with an anode, a hole transport layer, an exciton blocking layer, a light emitting layer, an exciton blocking layer, an electron transport layer, a cathode buffer layer and a cathode which are sequentially stacked.
The luminescent layer is
The hole transport layer is PEDOT: PSS,
the exciton blocking layer between the hole transport layer and the light emitting layer is PVK,
an exciton blocking layer T2T between the light emitting layer and the electron transporting layer,
the electron transport layer NBphen is provided,
the cathode buffer layer is made of CsF layer, and Al is used as a cathode.
In order to show the superiority of the performance of the dendritic thermal activation delayed fluorescence light-emitting layer, the light-emitting layer P1 is used as a comparison, and the structural formula of P1 is as follows:
the preparation method of the undoped solution processing type thermal activation delay fluorescence electroluminescent diode comprises the following steps:
a plurality of ITO conductive glass substrates of the same batch number are taken, the specification is 15 mm multiplied by 15 mm, the thickness of the ITO is about 100 nm, and the square resistance of the ITO conductive glass substrates is about 10 ohm/square. The substrate was thoroughly cleaned in an ultrasonograph with tetrahydrofuran, isopropanol, detergent, deionized water, acetone and isopropanol in sequence, each cleaning step lasting 10 minutes to thoroughly remove dust, photoresist, etc. from the surface of the substrate, and then placed in a clean, dust-free oven to dry overnight at 75 ℃. When the device is formally prepared, firstly, O is used2The plasma is used for carrying out surface plasma treatment for 1 minute, so that the surface work function of the ITO is reduced, and the surface wettability and the film forming uniformity are improved. Then, PSS, a hole transport layer, PEDOT, was spin-coated onto a previously cleaned ITO glass substrate to a thickness of 40nm at 3000 rpm in a dry, dust-free, oxygen-free glove box, and annealed at 150 ℃ for 10 minutes to completely remove the water. Then transferred quickly to another anhydrous oxygen-free glove box filled with high purity nitrogen. A PVK hole transport layer (dissolved in chlorobenzene at a concentration of 8 mg/ml) was spin-coated at 3000 rpm for 10 minutes with a film thickness of 35nm and an annealing temperature of 125 ℃. Then spin coating prepared and filtered T1 or P1 chlorobenzene solution as light emitting layer material onto PVK layer at a certain speed of 3000 r/min to form light emitting layer with thickness of 40nm (PVK can be used as both transmission and exciton blocking), and then coating the light emitting layer material on the PVK layerAnnealing at 100 deg.C for 10 min to completely remove the solvent. Finally, the film is quickly transferred to a vacuum degree of 5.5-6.0X 10-5In the vacuum vapor deposition chamber of Pa, a thermal vapor deposition operation was started. First in turn with
And
the exciton blocking layer T2T (10nm) and the electron transport layer NBphen (40nm) were successively evaporated onto the spin-coated light-emitting layer at the evaporation rate of (1)
At a rate of evaporating a CsF layer (1.2nm) of cathode buffer layer material and
as a cathode (120nm), the electron transport layer was continuously evaporated with Al to obtain a complete device.
This example performs a photoelectric performance test on the above-described device. After the evaporation is finished, after the evaporation bin is cooled to the room temperature, the device is taken down after the bin is opened, and the device is simply packaged by utilizing the glass cover plate under the adhesion and solidification of the epoxy resin encapsulating glue. And finally, taking the device out of the glove box, and sequentially testing the performance of the device. The Electroluminescence (EL) spectrum is recorded by an optical analyzer PR 745. The current density and luminance dependence on the drive voltage and device lifetime were measured by Keithley-2400 and Konika Mentada chromatograph CS-200. From the lambertian distribution, the External Quantum Efficiency (EQE) of the device was calculated from the luminance, current density and EL spectra.
In this example, the transient fluorescence lifetime test was performed on the above light-emitting layer film. T1 and P1 thin films with the same thickness are prepared on clean and dust-free quartz wafers according to the processes of completely consistent spin coating speed, annealing temperature and the like in the device preparation process. The transient fluorescence lifetime is measured and recorded by a C4334 fluorescence lifetime measuring instrument.
The current density-voltage-luminance graph, the external quantum efficiency-luminance graph, the electroluminescence spectrogram at the current density of 10 milliampere/square centimeter, the transient fluorescence lifetime spectrogram and the luminance-time decay graph of the undoped solution processing device (the undoped solution processing type dendritic thermal activation delayed fluorescence electroluminescence light-emitting diode) obtained in the embodiment are shown in fig. 2- (a) to (e).
Table 1 summarizes the device performance data for this example.
Table 1 device performance data for example 1
As can be seen from FIGS. 2- (a) to (e) and the data in Table 1: the blue-green light non-doped dendritic thermal activation delayed fluorescence device obtained by the embodiment simultaneously realizes the extremely low turn-on voltage of 2.7V, the maximum external quantum efficiency of 10.70 percent and 1000cd m-2The lower extremely suppressed efficiency decays. Initial luminance of 500cd m-2The life half-life was measured to be over 6.5 hours. Compared with a reference device, the excellent device performance shows that the dendritic self-body thermal activation delayed fluorescent material with the excited state life shorter than 5 microseconds is used as the light emitting layer, so that a very quick reverse intersystem crossing process is realized, the utilization rate of triplet excitons is improved, the exciton-exciton annihilation effect under high current density is effectively inhibited, better carrier transmission balance can be realized, and finally the improvement of the turn-on voltage, the efficiency roll-off and the device life is realized. It is noted that the device lifetime of this example can reach 6.74 hours, which is a substantial improvement on the lifetime problem of non-doped solution processed TADF-OLEDs.
Example 2
In this example, the undoped light-emitting layer with short excited state lifetime was changed to T7, and the other conditions were the same as in example 1.
T7 has a structure of
This example was conducted in the same manner as example 1, and the photoelectric properties of the above-described device were measured.
In this example, the transient fluorescence lifetime test was performed on the above light-emitting layer film in the same manner as in example 1.
The current density-voltage-luminance graph, the external quantum efficiency-luminance graph, the electroluminescence spectrogram at the current density of 10 milliampere/square centimeter, the transient fluorescence lifetime spectrogram and the luminance-time decay graph of the undoped solution processing device (the undoped solution processing type dendritic thermal activation delayed fluorescence electroluminescence light-emitting diode) obtained in the embodiment are shown in fig. 3- (a) to (e).
Table 2 summarizes the device performance data for this example.
Table 2 device performance data for example 2
As can be seen from the data in FIGS. 3- (a) to (e) and Table 2: the blue-green light non-doped dendritic thermal activation delayed fluorescence device obtained by the embodiment simultaneously realizes the extremely low turn-on voltage of 2.7V, the maximum external quantum efficiency of 7.70 percent and 1000cd m-2The maximum efficiency of 91% can still be maintained. Initial luminance of 500cd m-2The life half-life was measured to be over 6 hours. The excellent performance of the device shows that the dendritic self-body thermal activation delayed fluorescent material with the excited state life shorter than 5 microseconds is used as the luminescent layer, so that the exciton-exciton annihilation effect under high current density can be effectively inhibited, the better carrier transmission balance can be realized, and finally the improvement of the lighting voltage, the efficiency roll-off and the device life is realized at the same time. It is noted that the device lifetime of this example can reach 6.17 hours, which is a substantial improvement on the lifetime problem of non-doped solution processed TADF-OLEDs.
Example 3
The non-doped solution processed dendritic thermally activated delayed fluorescence electroluminescent diode of the present example is composed of a substrate with an anode, a hole transport layer, a light emitting layer, an electron transport layer, a cathode buffer layer and a cathode, which are sequentially stacked.
The luminescent layer is
The hole transport layer is PEDOT: PSS,
the electron transport layer TPBi is provided with,
the cathode buffer layer is made of CsF layer, and Al is used as a cathode.
In order to show the superiority of the performance of the dendritic thermal activation delayed fluorescence light-emitting layer, the light-emitting layer P1 is used as a comparison, and the structural formula of P1 is as follows:
the preparation method of the undoped solution processing type thermal activation delay fluorescence electroluminescent diode comprises the following steps:
a plurality of ITO conductive glass substrates of the same batch number are taken, the specification is 15 mm multiplied by 15 mm, the thickness of the ITO is about 100 nm, and the square resistance of the ITO conductive glass substrates is about 10 ohm/square. The substrate was thoroughly cleaned in turn with tetrahydrofuran, isopropanol, detergent, deionized water, acetone and isopropanol in an ultrasonic instrument, wherein each cleaning step lasted 10 minutes to thoroughly remove dust, photoresist, etc. from the surface of the substrate, and then placed in a clean, dust-free oven for overnight drying at 75 ℃. When the device is formally prepared, firstly, O is used2The plasma is used for carrying out surface plasma treatment for 1 minute, so that the surface work function of the ITO is reduced, and the surface wettability and the film forming uniformity are improved. Then, PSS, a hole transport layer, PEDOT, was spin-coated onto a previously cleaned ITO glass substrate to a thickness of 40nm at 3000 rpm in a dry, dust-free, oxygen-free glove box, and then annealed at 150 ℃ for 10 minutes to completely remove the water. And then quickly transferred to another anhydrous oxygen-free glove box filled with high purity nitrogen. Then spin coating the prepared and filtered T9 or P1 chlorobenzene solution at a certain speed of 3000 r/min to form a thick filmThe light-emitting layer having a thickness of 40nm was annealed at 150 ℃ for 10 minutes, and the solvent was completely removed. Finally, the film is quickly transferred to a vacuum degree of 5.5-6.0X 10-5In the vacuum vapor deposition chamber of Pa, a thermal vapor deposition operation was started. First, respectively
The electron transport layer TPBi (50nm) is continuously evaporated onto the spin-coated luminescent layer at the evaporation rate of (2) and finally, respectively
And
the buffer layer material CsF layer (1.2nm) and Al (120nm) are continuously evaporated on the electron transport layer to be used as a cathode, and a complete device is obtained.
This example performs a photoelectric performance test on the above-described device. After the evaporation is finished, after the evaporation bin is cooled to the room temperature, the device is taken down after the bin is opened, and the device is simply packaged by utilizing the glass cover plate under the adhesion and solidification of the epoxy resin encapsulating glue. And finally, taking the device out of the glove box, and sequentially testing the performance of the device. The Electroluminescence (EL) spectrum is recorded by an optical analyzer PR 745. The current density and luminance dependence on the drive voltage and device lifetime were measured by Keithley-2400 and Konika Mentada chromatograph CS-200. From the lambertian distribution, the External Quantum Efficiency (EQE) of the device was calculated from the luminance, current density and EL spectra.
In this example, the transient fluorescence lifetime test was performed on the above light-emitting layer film. And preparing the T1 film with the same thickness on a clean dust-free quartz plate according to the completely consistent processes of spin coating speed, annealing temperature and the like in the device preparation process. The transient fluorescence lifetime is measured and recorded by a C4334 fluorescence lifetime measuring instrument.
The current density-voltage-luminance graph, the external quantum efficiency-luminance graph, the electroluminescence spectrogram at the current density of 10 milliampere/square centimeter, the transient fluorescence lifetime spectrogram and the luminance-time decay graph of the undoped solution processing device (the undoped solution processing type dendritic thermal activation delayed fluorescence electroluminescence light-emitting diode) obtained in the embodiment are shown in fig. 4- (a) to (e).
Table 3 summarizes the device performance data for this example.
Table 3 device performance data for example 3
As can be seen from FIGS. 4- (a) to (e) and the data in Table 3: the blue-green light non-doped dendritic thermal activation delayed fluorescence device obtained in the embodiment only adopts a three-layer structure except for the electrodes at two ends, and simultaneously realizes the extremely low turn-on voltage of 2.7V and the maximum external quantum efficiency of 8.23%, and is 1000cd m-2The maximum efficiency of 91% can still be maintained. Most notably at an initial luminance of 500cd m-2The half life period of the measured life time reaches 16 hours, and the excellent performance of the devices shows that the dendritic self-body thermal activation delayed fluorescent material with the excited state life shorter than 5 microseconds is used as a light emitting layer, so that the exciton-exciton annihilation effect under high current density can be effectively inhibited, better carrier transmission balance can be realized, and finally, the improvement of the lighting voltage, the efficiency roll-off and the device life can be realized at the same time. It is noteworthy that the half-life of up to 16 hours for this example is a dramatic improvement over the lifetime problem of undoped solution processed TADF-OLEDs compared to the reference device.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (8)
1. A non-doped solution processing type dendritic thermal activation delay fluorescence electroluminescent diode is characterized in that: the device comprises a substrate, an anode, a hole transport layer, a short excited state lifetime dendritic thermal activation delayed fluorescence luminescent layer, an electron transport layer and a cathode which are sequentially stacked; the excited state lifetime of the short excited state lifetime dendritic thermal activation delayed fluorescence luminescent material of the luminescent layer is less than or equal to 5 microseconds;
the short excited state lifetime dendritic thermal activation delayed fluorescence luminescent layer is more than one of molecular structure materials T1-T2, T4-T8 and T10-T12:
and a cathode buffer layer is arranged between the electron transport layer and the cathode.
2. The undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode of claim 1, wherein: the electron transport layer is made of more than one of E1-E19 molecular structure materials:
3. the undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode of claim 1, wherein: the hole transport layer is made of more than one of H1-H6 molecular structure materials:
4. the undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode of claim 1, wherein: no exciton blocking layer or an exciton blocking layer is added between the hole transport layer and the light-emitting layer; an exciton blocking layer is not added or added between the electron transport layer and the light emitting layer, and the transport layer does not need any metal doping.
5. The undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode of claim 1, wherein: the substrate is glass, quartz, sapphire, polyimide, polyethylene terephthalate, polyethylene naphthalate, metal, alloy or stainless steel film.
6. The undoped solution-processed dendritic thermally activated delayed fluorescence electroluminescent diode of claim 1, wherein: the anode and the cathode are independently metal or metal oxide; the metal oxide is at least one of indium tin oxide, fluorine-doped tin dioxide, zinc oxide and indium gallium zinc oxide.
7. The method for preparing the non-doped solution processed dendritic thermal activation delayed fluorescence electroluminescent diode according to any one of claims 1 to 6, wherein the method comprises the following steps: the method comprises the following steps: taking a substrate with an anode layer, and then sequentially preparing a hole transport layer, a dendritic thermal activation delayed fluorescence light-emitting layer, an electron transport layer and a cathode on the anode layer to obtain a non-doped solution processed dendritic thermal activation delayed fluorescence electroluminescent diode;
and a cathode buffer layer is prepared between the electron transport layer and the cathode.
8. The method for preparing the non-doped solution processed dendritic thermal activation delayed fluorescence electroluminescent diode according to claim 7, wherein the method comprises the following steps: preparing or not preparing an exciton blocking layer between the hole transport layer and the light-emitting layer; preparing or not preparing an exciton blocking layer between the electron transmission layer and the luminous layer;
the preparation process comprises one or more of spin coating, brush coating, spray coating, dip coating, roll coating, evaporation coating, printing or ink-jet printing.
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