A method for preparing an aromatic carbon nitride warm white light emitting diode

Abstract

The present application relates to a kind of preparation aromatic carbon nitride warm white light emitting diode method, belong to white light emitting diode field, solve the problem of exploring white light origin.This paper is prepared by aromatic treatment to original carbon nitride material, a kind of aromatic carbon nitride with wideband electroluminescence covering visible light range, and it is used as single-component emission layer, for the design of white light emitting diode, successfully realized bright warm white light electroluminescence.The present application widens the application field of carbon nitride material, provides material selection for physical chemistry principle research and photoelectric application.The present application provides a brand-new way for the material selection and low-cost design of white light emitting diode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of white light emitting diodes, and relates to a method for preparing aromatic carbon nitride warm white light emitting diodes. BACKGROUND

[0002] In recent years, white light emitting diodes (WLEDs) as high-efficiency solid-state lighting have increasingly replaced incandescent bulbs and fluorescent tubes to solve energy-saving and carbon-neutral problems. Commercial WLEDs are composed of a blue light emitting LED chip and a yellow-emitting phosphor coating, which are multi-color hybrid devices. Due to different degradation rates of emitters and energy loss caused by overlapping absorption, the light-emitting color of the devices is unstable over time. Therefore, a single-component material with broadband electroluminescence (EL) covering the visible spectrum is an ideal material for the next generation of artificial lighting, which can solve these problems and further simplify the manufacturing process. On the contrary, such a material is extremely rare because electron-hole pairs tend to reach the lowest energy state and result in monochromatic emission. The aromatic carbon nitride (PhCN) prepared by the present application successfully realizes broadband electroluminescence covering the visible spectrum. A high-efficiency bright warm white EL device based on PhCN as a single-component emitting layer is prepared by a vacuum deposition process. The present application makes g-CN a promising light-emitting material in the field of EL devices after organic small molecules, polymer molecules and perovskites, not only providing material selection for physical and chemical principle research and optoelectronic applications, but also providing a new way for the development of low-cost WLEDs. SUMMARY

[0003] The present application prepares PhCN with broadband electroluminescence by aromatizing the original graphite phase carbon nitride (g-CN) through a one-step thermal polymerization method, using 2,4-diamino-6-phenyl-1,3,5-triazine as a precursor. To adjust the carrier balance and improve the performance of the device, the electron / hole transport material is adjusted multiple times. By a vacuum deposition process, PhCN is used as a single-component emitting layer to prepare three different structures of WLEDs, all of which exhibit bright warm white electroluminescence. The specific device structure is as follows: device I: indium tin oxide (ITO) / poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) / poly(9-vinylcarbazole) (PVK, 2.5 mg ml -1 ) / PhCN (5 nm) / 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi, 40 nm) / LiF (1 nm) / Al (80 nm); device II: ITO / PEDOT:PSS / poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'- (N-(4-sec-butylphenyl) diphenylamine)] (TFB, 2.5 mg ml -1PVK (2.5 mg ml -1 PhCN (5 nm) / TPBi (40 nm) / LiF (1 nm) / Al (80 nm);device Ⅲ: ITO / PEDOT:PSS / TFB (2.5 mg ml -1 PVK (2.5 mg ml -1 PhCN (5 nm) / 4,6-bis(3,5-di(3-pyridyl)phenyl)-2-methylpyrimidine (B3PYMPM, 40 nm) / LiF (1 nm) / Al (80 nm).

[0004] The structure of the product and the performance of the device obtained by the present application are as follows:

[0005] Figure 1 A schematic diagram of PhCN prepared from the precursor by one-step thermal polymerization process.

[0006] (2) Figure 2 Optical properties of PhCN: (a) Photoluminescence (PL) spectrum of PhCN. (b) Normalized PL spectra of PhCN under different excitation lights. (c) PL spectra of PhCN under different intensities of 385 nm excitation light (inset: power dependence curve of luminescence intensity). (d) PL decay curve of PhCN under 375 nm picosecond laser.

[0007] (3) Figure 3 EL performance of PhCN-based LEDs: (a-c) Structure of LED device. (d) Current density-voltage curve, (e) luminance-voltage curve and (f) EQE-voltage-power efficiency curve (hollow circles represent EQE, and solid circles represent power efficiency) of device Ⅰ, Ⅱ, Ⅱc and Ⅲ.

[0008] Advantages and positive effects of the present application:

[0009] The present application uses a carbon nitride material with simple preparation, ultra-low cost and wide-band electroluminescence as a single-component emission layer of WLEDs, and realizes bright warm white electroluminescence through device structure optimization. The present application proves that the application of carbon nitride material is not limited to the field of photocatalysis, which broadens its application range and adds a new material to the research of optoelectronic field. The present application provides a new idea for the further development of WLEDs and promotes the low-cost of WLEDs. It should be clear that the claims of the present application can be varied and changed within the limited range. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 A schematic diagram of the polymerization mechanism of aromatic carbon nitride.

[0011] Figure 2 Optical properties of PhCN. (a) Fluorescence spectra of PhCN; (b) Fluorescence spectra of PhCN under different excitation wavelengths; (c) Fluorescence spectra of PhCN under different laser intensities; (d) Fluorescence lifetime of PhCN in different wavelength ranges.

[0012] Figure 3 Performance of PhCN-based LEDs. (a-c) Energy level diagrams of different LED device structures; (d) Voltage-current curves of LEDs; (e) Voltage-brightness curves of LEDs; (f) Voltage-external quantum efficiency curves of LEDs. DETAILED DESCRIPTION

[0013] For a further understanding of the present application, the application will be described further in conjunction with the accompanying drawings and examples, but the application is not limited in any way by the drawings and examples.

[0014] Synthesis Example

[0015] (1) Synthesis of PhCN:

[0016] 5 grams of 2,4-diamino-6-phenyl-1,3,5-triazine was placed in an alumina crucible with a lid, then transferred to a tube furnace, then heated at 400°C for 40 minutes under a high-purity nitrogen gas (purity: 99.999%) atmosphere (10 ml min-1) at a temperature increasing rate of 2.3°C min-1, and finally naturally cooled to room temperature. The sample in the crucible was taken out and ground to obtain a PhCN sample.

[0017] (2) Preparation of PhCN-based LEDs:

[0018] ITO glass of 2 cm x 2 cm was cleaned with deionized water, acetone and isopropanol in an ultrasonic bath for 10 minutes each and treated with oxygen plasma for 10 minutes. PEDOT:PSS solution was diluted with ultrapure water at a ratio of 1 : 1 and then spin-coated on ITO glass at 4000 rpm for 60 seconds, followed by annealing at 150 °C in air for 20 minutes. TFB or PVK was dissolved in chlorobenzene (CB) at a concentration of 2.5 mg ml-1. In a nitrogen-filled glovebox, TFB / CB solution (70 μL) was spin-coated at 2000 rpm for 45 seconds, followed by annealing at 150 °C for 30 minutes. After that, CB (70 μL) was dropped onto the substrate coated with TFB film, then spin-coated at 2000 rpm for 45 seconds and annealed at 120 °C for 30 seconds to obtain a thin TFB film. In a nitrogen-filled glovebox, PVK / CB solution (70 μL) was spin-coated at 4000 rpm for 60 seconds and annealed at 120 °C for 20 minutes. Finally, the substrate was transferred to a vacuum deposition chamber and PhCN (5 nm), TPBi or B3PYMPM (40 nm), LiF (1 nm) and Al (80 nm) were sequentially deposited by thermal evaporation in a vacuum of about 5 x 10-7 torr.

[0019] (3) LEDs device performance test:

[0020] All devices were tested in a nitrogen-filled glovebox. A Keithley 2450 source meter (Keithley, America) was used to provide stable current and voltage output for the devices, and then a QEPro spectrometer (Ocean Optics, America) connected to an integrating sphere was used to collect the optical signal of LEDs devices.

[0021] (4) Characterization of aromatic carbon nitride (PhCN):

[0022] PL spectra were measured at different excitation wavelengths and different power densities using a QEPro spectrometer (Ocean Optics, America). Time-resolved PL (TR-PL) spectra were measured using a FLS1000 fluorescence spectrometer (Edinburgh Instruments, UK) and a 375 nm picosecond pulsed laser.

Claims

1. A method of making an aromatic carbon nitride warm white light emitting diode, characterized by: Aromatic carbon nitride with broadband electroluminescence is prepared by one-step thermal polymerization method with 2,4-diamino-6-phenyl-1,3,5-triazine as precursor, and a warm white light emitting diode is prepared by vacuum deposition process with the obtained aromatic carbon nitride as single-component emitting layer; the structure of the prepared warm white light emitting diode is: indium tin oxide / poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) / poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-((N-(4-sec-butylphenyl)diphenylamine))] / poly(9-vinylcarbazole) / aromatic carbon nitride / 4,6-bis(3,5-di(3-pyridyl)phenyl)-2-methylpyrimidine / LiF / Al. wherein indium tin oxide is denoted ITO; poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) is denoted PEDOT:PSS; poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'- (N-(4-sec-buty lphenyl) diphenylamine)] is denoted TFB, at a concentration of 2.5 mg ml -1 ; Poly(9-vinylcarbazole) is denoted PVK and has a concentration of 2.5 mg ml -1 ; aromatic carbon nitride is denoted PhCN and has a thickness of 5 nm; 4,6-bis(3,5-di(3-pyridyl)phenyl)-2-methylpyrimidine is denoted B3PYMPM and has a thickness of 40 nm; LiF has a thickness of 1 nm; Al has a thickness of 80 nm.

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