CN112018254B - Quantum dot light-emitting diode based on phenylthiol derivative and preparation method thereof - Google Patents
Quantum dot light-emitting diode based on phenylthiol derivative and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a quantum dot light-emitting diode based on a phenylthiol derivative and a preparation method thereof. According to the invention, the small molecule of the phenylthiol derivative is selected as a target molecule to carry out interface modification of the hole transport layer/quantum dot layer, so that the hole injection potential barrier is reduced, and the hole injection efficiency is enhanced. On the other hand, in order to improve the electron injection efficiency, the problems of electron injection surplus caused by energy band matching, exciton quenching caused by high-density interface state of an electron transport layer and the like are solved, the mobility of the electron transport layer is reduced, the electron transport/injection efficiency is inhibited, and therefore the charge injection balance in the device is improved, and the luminous efficiency of the device is improved.
Description
Technical Field
The invention belongs to the technical field of display, and particularly relates to a quantum dot light emitting diode based on a phenylthiol derivative and a preparation method thereof.
Background
Most commercial Light Emitting Diodes (LEDs) are group III-V semiconductors manufactured by vacuum-based epitaxy techniques. Along with the continuous development of technology and the pursuit of more comfortable life by human beings, higher requirements are continuously put on the illumination display devices, and development and research of more reliable high-performance display devices are promoted. Currently, the emerging LED material is an organic molecule capable of efficiently emitting light, and the Organic LED (OLED) has the advantages of full solid structure, flexibility, quick response, low energy consumption and the like, and is widely applied to display of small-area intelligent terminals. State of the art LED devices based on colloidal Quantum Dots (QDs) that can be solution prepared are recently developed. These quantum dot materials combine the properties of conventional inorganic semiconductors with the chemical flexibility of organic molecules. In addition, they have emission wavelengths that are size tuned, color purity from narrow emission, and fluorescence quantum yields approaching 100%. Related studies of QLEDs have developed efficient devices that can operate in various visible and near infrared wavelength ranges over twenty years, making them promising as powerful supplements to OLEDs as a later-coming feature in the next-generation lighting and display fields.
Like conventional light emitting diodes, QLEDs generally have a p-i-n structure that includes an anode, a hole transport layer, a quantum dot light emitting layer, an electron transport layer, and a cathode. Under forward bias, electrons and holes are injected from the respective electrodes and transported through the charge transport layer to the quantum dot EML, and recombine to generate light.
The cadmium-based quantum dot has higher performance in a QLED device, but CdSe, znS and other materials have higher ionization potential (6-8 eV), and meanwhile, the ionization potential of a common hole transport material is lower (5.2-5.6 eV), so that holes have larger injection potential barriers. Simultaneously therewith, an almost unobstructed electron transport channel from the electron transport layer (e.g. ZnO) to the quantum dot causes an excess electron injection, eventually the quantum dot has excess electrons and causes charging of the quantum dot causing auger recombination. In order to improve the energy level alignment and improve the carrier balance of the device, hole injection efficiency may be improved or electron injection efficiency may be suppressed.
Common methods for reducing the hole injection barrier mainly reduce the band offset of the HOMO of the hole transport layer and the valence band of the quantum dots, which include selecting hole transport materials with deeper HOMO energy levels and improving the valence band position of the quantum dots. However, in general, it is difficult to synthesize a novel hole transport material with a deep HOMO level. Secondly, the valence band of the quantum dot can be raised by ligand exchange on the quantum dot so as to lower the hole injection barrier, but the quantum yield of the quantum dot is generally reduced to a certain extent after ligand exchange.
In order to inhibit the electron injection efficiency, in general, the introduction of a modification layer at the interface of the electron transport layer and the quantum dot helps to improve the device performance. However, most reported interface modification layers are insulating polymer materials, and the magnitude of current density and power efficiency may be limited in view of the relative insulating properties of these materials.
Accordingly, the prior art has yet to be further studied and developed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a quantum dot light emitting diode based on a phenylthiol derivative and a preparation method thereof, and aims to solve the phenomenon of unbalanced carriers in the existing device, thereby improving the light emitting efficiency of the device.
In order to solve the technical problems, the invention adopts the following technical scheme:
the quantum dot light-emitting diode based on the benzenethiol derivative comprises an anode substrate, a hole transmission layer, a quantum dot light-emitting layer, an electron transmission layer and a metal cathode from bottom to top, and further comprises a first benzenethiol derivative material layer arranged on the surface of the hole transmission layer, which is close to the quantum dot light-emitting layer, and/or a second benzenethiol derivative material layer arranged on the surface of the electron transmission layer, which is close to the quantum dot light-emitting layer. Further, the first layer of phenyl mercaptan derivative material has a thickness <10nm and the second layer of phenyl mercaptan derivative material has a thickness <10 nm.
Further, the first layer of benzenethiol derivative material is made of positive dipole moment molecules, wherein the benzenethiol derivative of the positive dipole moment molecules comprises at least one of 4-fluorobenzene thiol, 4-chlorobenzenethiol or 4-nitrobenzenethiol.
Further, the second phenylthiol derivative material layer is made by selecting a negative dipole moment molecule, and the phenylthiol derivative of the negative dipole moment molecule comprises at least one of 4-methoxybenzenethiol and 4-methylbenzene thiol.
The preparation method of the quantum dot light emitting diode based on the phenylthiol derivative comprises the following steps:
s10, providing an anode substrate;
s20, preparing a hole transport layer on the anode substrate;
s30, preparing a first layer of phenylthiol derivative material layer on the surface of the hole transport layer;
s40, preparing a quantum dot luminescent layer on the first layer of the phenylthiol derivative material layer;
s50, preparing a second phenylthiol derivative material layer on the quantum dot luminescent layer;
s60, preparing an electron transport layer on the second layer of phenylthiol derivative material;
and S70, depositing a metal cathode on the electron transport layer.
Further, the preparation steps of the S30 are as follows: preparing a solution containing a phenylthiol derivative, depositing the solution on the surface of the hole transport layer, and then performing annealing treatment; wherein the solvent in the solution is an organic solvent.
Further, the concentration of the benzenethiol derivative of S30 dissolved in the organic solvent is 0.4-1.6 mg/mL.
Further, the S30 method for preparing the phenylthiol derivative material layer includes a solution film forming method, a spin coating method, a printing method, a blade coating method, a dip-coating method, a dipping method, a spraying method, a roll coating method, a casting method, a slit coating method, or a bar coating method.
Further, the temperature of the annealing treatment is 60-150 ℃, and the time of the annealing treatment is 5-30 min.
Further, the method for preparing the second benzenethiol derivative material layer on the quantum dot light-emitting layer at S50 is the same as that of the first benzenethiol derivative material layer.
The interface modification material is adopted to avoid the influence of the hole transport material on the carrier transport of the device. The interface modification does not need to consider the characteristics of carrier migration and the like of the modified material, and has a wide material selection range. The molecular modification is a powerful tool for changing the surface energy level of the whole semiconductor, and takes HOMO energy level, polarizability and other factors into consideration, so that the benzene thiol derivative molecule is locked as an interface modifier, and the molecule is used as a ligand for the surface chemical modification of the quantum dot.
On one hand, in order to improve the hole injection capability, a series of small molecules of the phenylthiol derivative are selected as target molecules to carry out interface modification of the hole transport layer/quantum dot layer, so that the hole injection potential barrier is reduced, and the hole injection efficiency is enhanced. On the other hand, in order to improve the electron injection efficiency, other small molecules (negative dipoles) of the phenylthiol derivative are selected as target molecules to carry out interface modification of the electron transport layer/quantum dot layer, so that the problems of excessive electron injection caused by energy band matching, exciton quenching caused by high-density interface states of the electron transport layer and the like are solved, the mobility of the electron transport layer is reduced, the electron transport/injection efficiency is inhibited, and the charge injection balance in the device is improved.
The invention has the beneficial effects that: in the invention, the first and/or second benzene thiol derivative material layers are adopted to improve the photoelectric performance of the QLED device, and the advantages are as follows: first, the intrinsic dipole of the benzenethiol derivative can change the energy band position of the semiconductor, which changes the injection barrier of carriers through the change of the energy level position; second, the chain length of the benzenethiol derivative can influence the dot spacing after the light-emitting layer or the electron transport layer is formed, which changes the coupling degree and the carrier transport capacity between the light-emitting layer or the electron transport layer thin films; thirdly, the side chain functional group of the benzenethiol derivative affects the dispersing capability of the quantum dot or the electron transport material in solvents with different polarities, which is beneficial to the research of various functional layer film forming processes.
According to the first phenylthiol derivative material, when the phenylthiol derivative material with positive dipole moment modifies the hole transport layer, on one hand, the energy level of the hole transport layer can be effectively moved downwards, the hole injection efficiency is enhanced, and the carrier injection is more balanced; on the other hand, in the process of preparing a film by a solution method and constructing a device by the solution method, the selection of a solvent is particularly important because the solvent greatly influences the film forming condition of the material. The benzene mercaptan adopts polar organic solvent (such as ethanol) to help to form a compact and flat quantum dot layer thereon, so as to reduce the electric leakage phenomenon of the device, thereby prolonging the service life of the device.
According to the invention, the second phenylthiol derivative passivates the surface defect of the electron transport layer on one hand, and reduces the quenching position of the interface-OH exciton, so that the non-radiative recombination channel is inhibited. On the other hand, polar groups of the negative dipole moment molecules cause the energy level of the quantum dot layer to move upwards, so that the injection of carriers in the QLED is balanced, and the non-radiative channel at the interface of the quantum dot luminescent layer/electron transmission layer is reduced and has good film morphology, thereby improving the luminescent efficiency of the device.
Drawings
Fig. 1 is a schematic structural diagram of a quantum dot light emitting diode based on a phenylthiol derivative according to embodiment 1 of the present invention;
fig. 2 is a schematic structural diagram of a quantum dot light emitting diode based on a phenylthiol derivative according to embodiment 2 of the present invention;
fig. 3 is a schematic structural diagram of a quantum dot light emitting diode based on a phenylthiol derivative according to embodiment 3 of the present invention;
FIG. 4 is an AFM topography (a-c) of spin-coating a different organic solvent-dissolved first benzenethiol derivative onto a hole transport layer and an AFM topography (d-f) of preparing a quantum dot light emitting layer on a different organic solvent-dissolved first benzenethiol derivative.
Fig. 5 is a schematic diagram showing changes in UPS energy spectrum (a) secondary electron cutoff region (b) HOMO region and (c) hole injection barrier of the hole transport material after modification with the first phenylthiol derivative.
Fig. 6 is a graph of transient fluorescence spectra of sample glass/quantum dot, glass/anode/hole transport layer/quantum dot/electron transport layer, and glass/anode/hole transport layer/quantum dot/second phenylthiol derivative/electron transport layer.
FIG. 7 is (a) a plot of current density versus voltage versus luminance for four devices; (b) External quantum efficiency vs. voltage diagram
Standard device: substrate/anode/hole transport layer/quantum dot/electron transport layer/cathode
Device 1: substrate/anode/hole transport layer/first phenylthiol derivative/quantum dot/electron transport layer/cathode
Device 2: substrate/anode/hole transport layer/quantum dot/second phenylthiol derivative/electron transport layer/cathode
Device 3: substrate/anode/hole transport layer/first benzenethiol derivative/quantum dot/second benzenethiol derivative/electron transport layer/cathode.
Detailed Description
The invention will be further illustrated with reference to specific examples. It is to be understood that the following examples are intended to illustrate the present invention and are not to be construed as limiting the scope of the invention, and that numerous insubstantial modifications and adaptations can be made by those skilled in the art in light of the foregoing disclosure.
Example 1
As shown in fig. 1, the embodiment provides a quantum dot light emitting diode, which comprises an anode substrate, a metal cathode and a quantum dot light emitting layer arranged between the anode substrate and the metal cathode, wherein an electron transport layer is arranged between the quantum dot light emitting layer and the cathode, a hole transport layer is arranged between the quantum dot light emitting layer and the anode substrate, and a first phenylthiol derivative material layer is arranged on the surface of the hole transport layer, which is close to the quantum dot layer.
In an embodiment of the present invention, the thickness of the first layer of phenylthiol derivative material is less than 10 a nm a.
Further, in an embodiment of the present invention, the first benzenethiol derivative material is a positive dipole moment molecule, and the benzenethiol derivative is at least one selected from 4-fluorobenzene thiol, 4-chlorobenzene thiol and 4-nitrobenzene thiol.
According to the quantum dot light emitting diode provided by the embodiment of the invention, the first phenylthiol derivative material is arranged on the surface, close to the quantum dot layer, of the hole transport layer, and when the hole transport layer is modified by the phenylthiol derivative material with positive dipole moment, on one hand, the energy level of the hole transport layer can be effectively moved downwards, the hole injection efficiency is enhanced, and the carrier injection is more balanced; on the other hand, in the process of preparing a film by a solution method and constructing a device by the solution method, the selection of a solvent is particularly important because the solvent greatly influences the film forming condition of the material. The benzene mercaptan adopts polar organic solvent (such as ethanol) to help to form a compact and flat quantum dot layer thereon, so as to reduce the electric leakage phenomenon of the device, thereby prolonging the service life of the device.
Further, the invention also provides a preparation method of the quantum dot light emitting diode with the formal structure shown in fig. 1, which comprises the following steps:
s10, providing an anode substrate;
s20, preparing a hole transport layer on the anode substrate;
s30, preparing a first layer of phenylthiol derivative material on the surface of the hole transport layer;
s40, preparing a quantum dot luminescent layer on the first layer of phenylthiol derivative material;
s50, preparing an electron transport layer on the quantum dot luminescent layer;
and S60, depositing a metal cathode on the electron transport layer.
A step of preparing a layer of a phenylthiol derivative material on the above substrate: a solution containing a benzenethiol derivative is prepared, deposited on the substrate, and then annealed. Wherein the solvent in the solution is an organic solvent.
Wherein the concentration of the benzenethiol derivative dissolved in the organic solvent is 0.4-1.6 mg/mL. The method for preparing the phenylthiol derivative material layer is a solution film forming method, and includes, but is not limited to, one or more of spin coating, printing, knife coating, dip-coating, dipping, spraying, roll coating, casting, slit coating, and bar coating.
The temperature of the annealing treatment is 60-150 ℃; the annealing treatment time is 5-30 min.
The preparation method of the quantum dot light-emitting diode provided by the embodiment of the invention has the advantages of simple process and low cost, the phenylthiol derivative material layer is directly prepared on the hole transport layer and can be coated on different functional layers, and the prepared phenylthiol derivative material layer is directly used for modifying the functional layers, so that the light-emitting performance of the device can be improved.
Example 2
As shown in fig. 2, the embodiment provides a quantum dot light emitting diode, which comprises an anode substrate, a metal cathode and a quantum dot light emitting layer arranged between the anode substrate and the metal cathode, wherein a hole transport layer is arranged between the quantum dot light emitting layer and the anode substrate, an electron transport layer is arranged between the quantum dot light emitting layer and the cathode, and a second phenylthiol derivative material layer is arranged on the surface of the electron transport layer, which is close to the quantum dot layer.
In the above embodiment of the present invention, the thickness of the second layer of the thiophenol derivative material is <10 a nm a.
Further, in the above-described embodiment of the present invention, the second layer of benzenethiol derivative material is different from the first layer of benzenethiol derivative material in that a negative dipole moment molecule is selected, and the benzenethiol derivative is at least one selected from 4-methoxyphenylthiol and 4-methylbenzenethiol.
The second phenylthiol derivative passivates the surface defect of the electron transport layer on the one hand and reduces the quenching position of the interface-OH exciton so as to inhibit a non-radiative recombination channel. On the other hand, polar groups of the negative dipole moment molecules cause the energy level of the quantum dot layer to move upwards, so that the injection of carriers in the QLED is balanced, and the non-radiative channel at the interface of the quantum dot luminescent layer/electron transmission layer is reduced and has good film morphology, thereby improving the luminescent efficiency of the device.
Further, the invention also provides a preparation method of the quantum dot light emitting diode with the formal structure shown in fig. 2, which comprises the following steps:
s10, providing an anode substrate;
s20, preparing a hole transport layer on the anode substrate;
s30, preparing a quantum dot luminescent layer on the surface of the hole transport layer;
s40, preparing a second phenylthiol derivative material layer on the quantum dot luminescent layer; for the second phenylthiol derivative material layer: the preparation process is basically the same as that of the first phenylthiol derivative material layer, and the electron transport layer is positioned on the surface close to the quantum dot luminescent layer;
s50, preparing an electron transport layer on the second layer of the phenylthiol derivative material.
And S60, depositing a metal cathode on the electron transport layer.
A step of preparing a second phenylthiol derivative material layer on the substrate: a solution containing a benzenethiol derivative is prepared, deposited on the substrate, and then annealed. Wherein the solvent in the solution is an organic solvent.
Wherein the concentration of the benzenethiol derivative dissolved in the organic solvent is 0.4-1.6 mg/mL. The method for preparing the phenylthiol derivative material layer is a solution film forming method, and includes, but is not limited to, one or more of spin coating, printing, knife coating, dip-coating, dipping, spraying, roll coating, casting, slit coating, and bar coating.
The temperature of the annealing treatment is 60-150 ℃; the annealing treatment time is 5-30 min.
The preparation method of the quantum dot light-emitting diode provided by the embodiment of the invention has the advantages of simple process and low cost, the phenylthiol derivative material layer is directly prepared on the hole transport layer and can be coated on different functional layers, and the prepared phenylthiol derivative material layer is directly used for modifying the functional layers, so that the light-emitting performance of the device can be improved.
Example 3
As shown in fig. 3, the embodiment provides a quantum dot light emitting diode, which comprises an anode substrate, a metal cathode and a quantum dot light emitting layer arranged between the anode substrate and the metal cathode, wherein a hole transport layer is arranged between the quantum dot light emitting layer and the anode, a first phenylthiol derivative material layer is arranged on the surface of the hole transport layer, which is close to the quantum dot light emitting layer, and an electron transport layer is arranged between the quantum dot light emitting layer and the cathode, and a second phenylthiol derivative material layer is arranged on the surface of the electron transport layer, which is close to the quantum dot light emitting layer.
The first layer of benzenethiol derivative material has a thickness <10nm and the second layer of benzenethiol derivative material has a thickness <10 nm.
Further, in an embodiment of the present invention, the first benzenethiol derivative material is a positive dipole moment molecule, and the benzenethiol derivative is at least one selected from 4-fluorobenzene thiol, 4-chlorobenzene thiol and 4-nitrobenzene thiol.
Further, in the above-described embodiment of the present invention, the second layer of benzenethiol derivative material is different from the first layer of benzenethiol derivative material in that a negative dipole moment molecule is selected, and the benzenethiol derivative is selected from at least one of 4-methoxyphenylthiol and 4-methylbenzenethiol.
Further, the invention also provides a preparation method of the quantum dot light emitting diode with the formal structure shown in fig. 3, which comprises the following steps:
s10, providing an anode substrate;
s20, preparing a hole transport layer on the anode substrate;
s30, preparing a first layer of phenylthiol derivative material on the surface of the hole transport layer;
s40, preparing a quantum dot luminescent layer on the first layer of phenylthiol derivative material;
s50, preparing a second phenylthiol derivative material layer on the quantum dot luminescent layer; for the second phenylthiol derivative material layer: the preparation process is basically the same as that of the first phenylthiol derivative material layer, and the electron transport layer is positioned on the surface close to the quantum dot luminescent layer;
s60, preparing an electron transport layer on the second layer of the phenylthiol derivative material.
And S70, depositing a metal cathode on the electron transport layer.
A step of preparing a layer of a phenylthiol derivative material on the above substrate: a solution containing a benzenethiol derivative is prepared, deposited on the substrate, and then annealed. Wherein the solvent in the solution is an organic solvent.
Wherein the concentration of the benzenethiol derivative dissolved in the organic solvent is 0.4-1.6 mg/mL. The method for preparing the phenylthiol derivative material layer is a solution film forming method, and includes, but is not limited to, one or more of spin coating, printing, knife coating, dip-coating, dipping, spraying, roll coating, casting, slit coating, and bar coating.
The temperature of the annealing treatment is 60-150 ℃; the annealing treatment time is 5-30 min.
The preparation method of the quantum dot light-emitting diode provided by the embodiment of the invention has the advantages of simple process and low cost, the phenylthiol derivative material layer is directly prepared on the hole transport layer and can be coated on different functional layers, and the prepared phenylthiol derivative material layer is directly used for modifying the functional layers, so that the light-emitting performance of the device can be improved.
In examples 1-3 of the present invention, the benzenethiol derivative is a colorless liquid (without affecting light transmittance) at room temperature, wherein the mercapto group is considered to be capable of strongly anchoring to the metal and its oxide, and the self-assembled layer formed has a highly uniform and ordered monolayer on the one hand, and the dipole size and orientation thereof are controlled by the molecular structure on the other hand. The thiol and thiol molecules are intensively studied and widely applied in the fields of photoelectronic devices, quantum dot surface chemical modification and the like, and mainly focus on the adjustment of the work function of a substrate.
The natural dipole of the benzenethiol derivative can change the energy band position of the semiconductor material, and the change of the energy level position enables the natural dipole to change the injection barrier of carriers; secondly, the chain length of the phenylthiol molecules influences the compactness of the film, so that the electric leakage phenomenon is indirectly reduced, and the coupling degree and the carrier transmission capacity between the functional layers are changed; third, the side chain functional group of the benzenethiol derivative determines the self-dispersing capability in solvents with different polarities, which is beneficial to the research of the film forming process of a solution method device.
By utilizing the special properties of the phenylthiol derivative material, a phenylthiol liquid material layer composed of phenylthiol is arranged on the surface of the quantum dot in the device.
The benzene mercaptan derivative material layer is used as an interface modification layer and is arranged on the surface of the hole transmission layer close to the quantum dot layer and the surface of the electron transmission layer close to the quantum dot layer, so that two benzene mercaptan derivative layers are formed, and the balance of carriers in the device is further improved through synergistic effect, so that high luminous efficiency is obtained.
In the above embodiment of the present invention, preferably, the material of the anode is selected from doped metal oxides; wherein the doped metal oxide includes, but is not limited to, one or more of indium doped tin oxide (ITO), fluorine doped tin oxide (FTO), antimony doped tin oxide (ATO), aluminum doped zinc oxide (AZO), gallium doped zinc oxide (GZO), indium doped zinc oxide (IZO), magnesium doped zinc oxide (MZO), aluminum doped magnesium oxide (AMO).
In the above-described embodiments of the present invention, it is preferable that the material of the hole transport layer is selected from organic materials having good hole transport ability, and may be, for example, one or more of Poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) (TFB), polyvinylcarbazole (PVK), poly (N, N ' -bis (4-butylphenyl) -N, N ' -bis (phenyl) benzidine) (Poly-TPD), 4', 4' -tris (carbazole-9-yl) triphenylamine (TCTA), 4' -bis (9-Carbazole) Biphenyl (CBP), N ' -diphenyl-N, N ' -bis (3-methylphenyl) -1, 1' -biphenyl-4, 4' -diamine (TPD), N ' -diphenyl-N, N ' - (1-naphthyl) -1, 1' -biphenyl-4, 4' -diamine (NPB). The HOMO energy level of the hole transport layers is approximately 5.2-5.6 eV, so that holes have larger injection potential barriers, and the improvement of hole injection efficiency of the hole transport layer/quantum dot light-emitting layer interface can be effectively realized through the introduction of the first phenylthiol derivative, and the light-emitting efficiency of the device is improved.
In the above embodiment of the present invention, preferably, the material of the quantum dot light emitting layer is selected from one or more of red quantum dots, green quantum dots, and blue quantum dots, and may also be selected from yellow quantum dots. Specifically, the material of the quantum dot luminescent layer is selected from one or more of CdS, cdSe, cdTe, znO, znS, znSe, znTe, gaAs, gaP, gaSb, hgS, hgSe, hgTe, inAs, inP, inSb, alAs, alP, cuInS, cuInSe and quantum dots with various core-shell structures or quantum dots with alloy structures. The quantum dots of the present invention may be selected from cadmium-containing or cadmium-free quantum dots. The quantum dot luminescent layer of the material has the characteristics of wide excitation spectrum, continuous distribution, high emission spectrum stability and the like.
In the above embodiment of the present invention, further, the material of the electron transport layer is one or more nanoparticles of a transition metal oxide. The transition metal oxide comprises one or more of ZnO, tiO2, snO2, ta2O3, zrO2 and NiO, tiLiO, znAlO, znMgO, znSnO, znLiO, inSnO. The interface of the nanoparticle and the quantum dot luminescent layer often has the phenomena of machine quenching and excessive electron injection, and the introduction of the second phenylthiol derivative material layer can passivate the surface defect of the electron transport layer, so that the quenching position of the interface-OH exciton is reduced, and the non-radiative recombination channel is inhibited. On the other hand, polar groups of the negative dipole moment molecules cause the energy level of the quantum dot layer to move upwards, so that the injection of carriers in the QLED is balanced, and the non-radiative channel at the interface of the quantum dot luminescent layer/electron transmission layer is reduced and has good film morphology, thereby improving the luminescent efficiency of the device.
In the above-described embodiment of the present invention, it is preferable that the material of the cathode is selected from one or more of a conductive metal oxide material and a metal material; conductive metal oxide materials include, but are not limited to, one or more of ITO, FTO, ATO and AZO; the metallic material includes, but is not limited to Al, ag, cu, mo, au, or alloys thereof.
Because of the existence of the thiol group in the phenylthiol derivative, the phenylthiol derivative has better solubility in high-polarity and low-polarity organic solvents, and the solvent of the first phenylthiol derivative is selected from orthogonal solvent ethanol and non-orthogonal solvent toluene to influence film forming and devices. And carrying out morphology characterization on the hole transmission layer, the first benzenethiol diffractor thin film layer dissolved by different organic solvents and the subsequent quantum dot film forming by using an atomic force microscope, wherein a morphology chart is shown in fig. 4. As can be seen from fig. 4, after film formation based on toluene as a solvent, the film roughness increased from 0.45. 0.45 nm to 0.75. 0.75 nm, and pinhole-like holes appeared, indicating that the first benzenethiol derivative has a corrosive effect on the hole transport layer when toluene is selected as a solvent. After film formation based on ethanol as a solvent, the film roughness did not change significantly, indicating that the hole transport layer was not corroded by the orthogonal solvent. The spin coating of the quantum dots based on the three films described above, it was found from the AFM topography (fig. 4 d-f) that the roughness of the quantum dot layer (1.67 nm,1.65 nm, 1.68 nm, respectively) did not change, indicating that the solvent described above did not affect the subsequent topography of the quantum dot layer.
For the photoelectric device, the ultraviolet light electronic energy spectrum characterization means can help to know the energy band arrangement condition of each layer of thin film of the device. UPS characterization was performed for the first phenylthiol derivative modified hole transport film, and fig. 5a and 5b are the measured secondary electron cutoff and HOMO regions, respectively. It can be seen that the secondary electron truncated edge of the hole transport layer was shifted by 0.2 eV towards the low binding energy after the modification with the first phenylthiol derivative, which suggests that the fermi level of the hole transport layer was raised by 0.2 eV after the modification. This allows the injection barrier to be reduced when holes are injected into the quantum dots after device assembly.
After introducing the second phenylthiol derivative into the device, in order to obtain a relationship between-OH bonds on the surface of the electron transport material and PL quenching, time-resolved PL (TR-PL) test was performed on samples having glass/quantum dot, glass/anode/hole transport layer/quantum dot/electron transport layer and glass/anode/hole transport layer/quantum dot/second phenylthiol derivative/electron transport layer, as shown in fig. 6. The PL decay curve of a pure quantum dot film exhibits nearly monoexponential characteristics, with a lifetime of about 7.92 ns, almost all due to the inherent radiation decay of quantum dots, which is the basis for the extremely high photoelectric efficiency that the device can produce. When the quantum dots were in direct contact with the electron transport layer, the exciton lifetime of the quantum dots was slightly reduced to 6.00 ns, indicating that some of the excitons in the light emitting layer were significantly quenched by the metal oxide. Quenching of excitons is primarily caused by non-radiative recombination processes and/or interfacial charge transfer. Fortunately, by the introduction of the second phenylthiol derivative, the exciton lifetime of the quantum dots was restored by 6.37 ns. This result is mainly due to the reduced quenching of quantum dots by hydroxyl groups as exciton quenching sites after passivation by the second phenylthiol derivative. In summary, the introduction of the second phenylthiol derivative suppresses exciton quenching at the quantum dot/electron transport layer interface, which favors efficient radiative recombination in the quantum dot.
In order to explore the influence on the photoelectric performance of the device based on the single or simultaneous existence of the first and second modification layers, a QLED device is constructed based on the four structures. As can be seen from fig. 7, the three devices based on the first benzenethiol derivative (device 1), the second benzenethiol derivative (device 2), and the first and second benzenethiol derivatives (device 3) all have lower current densities in the low voltage region than the standard device. The maximum external quantum efficiency of the devices based on the first and second benzenethiol derivatives was improved by 60.7% compared to the standard devices (see table 1).
Table 1 shows the photoelectric properties of four QLED devices
The foregoing has shown and described the basic principles and main features of the present invention and the advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (9)
1. A quantum dot light emitting diode based on a benzenethiol derivative, characterized by: the quantum dot light emitting diode sequentially comprises an anode substrate, a hole transmission layer, a quantum dot light emitting layer, an electron transmission layer, a metal cathode, a first phenylthiol derivative material layer arranged on the surface of the hole transmission layer, which is close to the quantum dot light emitting layer, and a second phenylthiol derivative material layer arranged on the surface of the electron transmission layer, which is close to the quantum dot light emitting layer,
or a second phenylthiol derivative material layer arranged on the surface of the electron transport layer, which is close to the quantum dot light-emitting layer;
the first phenylthiol derivative material layer is made of positive dipole moment molecules;
the second phenylthiol derivative material layer is made of negative dipole moment molecules, and the phenylthiol derivative of the negative dipole moment molecules comprises at least one of 4-methoxyl phenylthiol and 4-methyl phenylthiol.
2. The benzenethiol derivative-based quantum dot light emitting diode of claim 1, wherein: the first layer of benzenethiol derivative material has a thickness <10nm and the second layer of benzenethiol derivative material has a thickness <10 nm.
3. The benzenethiol derivative-based quantum dot light emitting diode of claim 1, wherein: the benzenethiol derivative of the positive dipole moment molecule comprises at least one of 4-fluorobenzene thiol, 4-chlorobenzene thiol or 4-nitrobenzene thiol.
4. A process for the preparation of a quantum dot light emitting diode based on a benzenethiol derivative as claimed in any one of claims 1 to 3,
the method is characterized by comprising the following steps of:
s10, providing an anode substrate;
s20, preparing a hole transport layer on the anode substrate;
s30, preparing a first phenylthiol derivative material layer on the surface of the hole transport layer;
s40, preparing a quantum dot luminescent layer on the first phenylthiol derivative material layer;
s50, preparing a second phenylthiol derivative material layer on the quantum dot luminescent layer;
s60, preparing an electron transport layer on the second phenylthiol derivative material layer;
and S70, depositing a metal cathode on the electron transport layer.
5. The method of manufacturing according to claim 4, wherein: the preparation steps of the S30 are as follows: preparing a solution containing a phenylthiol derivative, depositing the solution on the surface of the hole transport layer, and then performing annealing treatment; wherein the solvent in the solution is an organic solvent.
6. The method of manufacturing according to claim 5, wherein: the concentration of the benzenethiol derivative of S30 dissolved in the organic solvent is 0.4-1.6 mg/mL.
7. The method of manufacturing according to claim 5, wherein: the method for preparing the phenylthiol derivative material layer in S30 includes a solution film forming method, a spin coating method, a printing method, a blade coating method, a dip-coating method, a dipping method, a spraying method, a roll coating method, a casting method, a slit coating method, or a bar coating method.
8. The method of manufacturing according to claim 5, wherein: the temperature of the annealing treatment is 60-150 ℃, and the time of the annealing treatment is 5-30 min.
9. The method of any one of claims 5-8, wherein: the method for preparing the second benzenethiol derivative material layer on the quantum dot light-emitting layer by S50 is the same as that of the first benzenethiol derivative material layer.
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| CN114242923A (en) * | 2021-11-12 | 2022-03-25 | 华南理工大学 | Method for improving performance of electroluminescent device by modifying indium phosphide quantum dots through thiol compound interface |
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