CN102612188B - Luminescent device embedded with self-assembled air-vent photonic crystal film and preparation method thereof - Google Patents

Abstract

A light-emitting device embedded in a self-assembled photonic crystal film, which is composed of a glass layer, an ITO layer, an air-hole photonic crystal layer and a metal cathode electrode, wherein the air-hole photonic crystal layer is composed of a light-emitting material and air holes filled in it The surface of the air hole is provided with a luminescent material layer; the preparation method is as follows: firstly, the diameter of the air hole in the light-emitting device is calculated by numerical simulation method, and polystyrene nanospheres or polymethyl methacrylate nanospheres having the same diameter as the air hole are selected. Microspheres; self-assembled photonic crystal structure on ITO glass; filling the luminescent material on the nano-microsphere film layer, removing the nano-microspheres at high temperature to form air holes, and finally evaporating metal cathode electrodes. The invention has the advantages that: the optoelectronic device is embedded in a layer of photonic crystal structure, and the photonic bandgap is used to increase the light output in the vertical direction, reduce total internal reflection, and improve the luminous efficiency of the light emitting device; the preparation method is simple in process and low in cost, and is conducive to realizing Industrial production.

Description

Light-emitting device embedded in self-assembled air hole photonic crystal thin film and its preparation method

technical field

The invention belongs to the field of flat light-emitting devices, and in particular relates to a light-emitting device embedded in a self-assembled air hole photonic crystal film and a preparation method thereof.

Background technique

A photonic crystal is a dielectric material whose dielectric constant changes periodically in space. The dispersion curve of the light wave propagating in it will form a band structure, and a photonic band gap (photonic band gap) similar to the semiconductor band gap appears between the bands. , light whose frequency lies in the band gap cannot propagate in the photonic crystal.

Light Emitting Diode (LED) is increasingly becoming an attractive alternative to traditional light sources due to its small size, high efficiency, and long life. High-brightness LEDs have always been the goal pursued by people. In order to achieve high brightness, the internal quantum efficiency and external quantum efficiency of LED must be improved. With the help of advanced manufacturing technology, the internal quantum efficiency can be significantly improved, but the external quantum efficiency is difficult to be effectively improved because of total reflection. The periodic structure of photonic crystals can cause Bragg scattering, thereby reducing total reflection. At the same time, the band gap of photonic crystals can be used to guide the guided mode in LEDs to improve external quantum efficiency. Therefore, how to use photonic crystals in LEDs to improve luminous efficiency has become one of the hot spots of research at home and abroad. There are two main mechanisms for photonic crystals to improve the luminous efficiency of electroluminescent devices: one is to use the Bragg scattering caused by the surface periodic structure to reduce the occurrence of total reflection; the other is to use the photonic crystal energy gap to guide the conduction state out to improve External Quantum Effects.

The self-assembly method is a simple and effective method to prepare photonic crystals. Because the lattice constant of self-assembled photonic crystals is usually on the submicron scale, it is an important way to prepare photonic crystals in the visible and near-infrared bands. In the present invention, a single-layer nano-microsphere colloidal crystal film is prepared by self-assembly method, the optimal parameters are calculated in combination with numerical simulation, the colloidal crystal film prepared according to the design is embedded in a light-emitting device, and the photonic crystal film is used to improve the luminous efficiency of the light-emitting device.

Contents of the invention

The purpose of the present invention is to address the common problem of low luminous efficiency of LEDs, to provide a light-emitting device embedded in a self-assembled air-hole photonic crystal film and its preparation method. A layer of photonic crystal structure is embedded in the optoelectronic device to utilize the The light output in the vertical direction is improved, the total internal reflection is reduced, and the luminous efficiency of the light-emitting device is improved.

Technical scheme of the present invention:

A light-emitting device embedded in a self-assembled air-hole photonic crystal film, which is composed of a glass layer, an ITO layer, an air-hole photonic crystal layer and a metal cathode electrode, wherein the air-hole photonic crystal layer is composed of a light-emitting material and air holes filled therein And there is a layer of luminescent material layer with a thickness of 50-200 nanometers on the surface of the air hole, the thickness of the ITO layer is 100-200 nanometers, the thickness of the photonic crystal layer of the air hole is 100 nanometers-1 micron, and the thickness of the metal cathode electrode is 100-200 nanometers. Nano.

The luminescent material is lead sulfide, zinc sulfide or zinc oxide.

The metal cathode is aluminum, silver or gold.

A method for preparing a light-emitting device embedded in a self-assembled air hole photonic crystal film, the steps are as follows:

1) Use the open source software MPB to calculate the energy band structure of the photonic crystal material: first use the numerical simulation method to calculate the position ω _min -ω _max of the photonic structure band gap in the light-emitting device to be prepared, where ω _min is the lowest position of the band gap, ω _max is the highest position of the bandgap, and the average value of the bandgap position is ω _m = 1/2(ω _max -ω _min ), and the peak emission spectrum of the device is known to be λ, and the photonic crystal lattice is calculated by the formula ω _m = a/λ The constant a is the diameter of the air hole, and select polystyrene nanospheres or polymethyl methacrylate nanospheres equal to the diameter of the air hole;

2) Self-assembled photonic crystal structure on pre-cleaned ITO glass: the self-assembly method is to ultrasonically disperse the above-mentioned nano-microspheres in anhydrous ethanol solution to form an ethanol suspension of nano-microspheres, and the mass percentage concentration of the suspension is 0.5 -3%, stack two pieces of ITO glass together, put a glass gasket with a thickness of 0.2 mm at one end between the two ITO glass pieces, and then inject the prepared suspension between the two ITO glass pieces , after 2 days in a drying oven at a constant temperature of 30 degrees Celsius, a single-layer self-assembled nano-microsphere film can be obtained on the surface of a piece of ITO glass below;

3) Preparation of the light-emitting layer and negative electrode of the electroluminescence device: on the nano-microsphere thin film layer, vacuum evaporation method or spin coating method is used to fill the light-emitting material to form a composite layer of the nano-microsphere film and the light-emitting material, and then in 250-450 The temperature is kept at ℃ for 2-3 hours to remove the air holes formed by the nanometer microspheres, and finally the metal cathode electrode is evaporated on the photonic crystal layer of the air holes.

Principle and basis of the present invention:

In photonic crystals, the refractive index changes periodically, and its period size is on the order of the wavelength of light. When light propagates in photonic crystals, photon band gap will appear due to periodic scattering, and photons whose frequency falls within the photonic band gap will not be able to propagate. By changing the size of the air hole, the lattice constant of the photonic crystal changes, and the band gap changes, which can limit the light output in the horizontal direction of different luminescent materials, so that more light can be emitted from the direction vertical to the substrate, and the light output of the device can be improved. efficiency and directionality.

The advantages of the present invention are: the optoelectronic device is embedded in a layer of air hole photonic crystal structure, and the photonic band gap is used to improve the light output in the vertical direction, reduce total internal reflection, and improve the luminous efficiency of the light emitting device, which can be applied to inorganic light emitting devices or organic electroluminescent devices. A light-emitting device; the preparation method is simple in process, easy to implement and low in cost, and is conducive to realizing industrialized production.

Description of drawings

The accompanying drawing is a structural schematic diagram of the light emitting device.

In the figure: 1. Glass layer 2. ITO layer 3. Air holes 4. Luminescent material

5. Metal cathode electrode

Detailed ways

Example:

A light-emitting device embedded in a self-assembled air-hole photonic crystal film, as shown in the accompanying drawing, is composed of a glass layer 1, an ITO layer 2, an air-hole photonic crystal layer and a metal cathode electrode 5, wherein the air-hole photonic crystal layer consists of a light-emitting The material 4 and the air hole 3 filled therein constitute and are provided with a luminescent material layer with a thickness of 100 nm on the surface of the air hole, the thickness of the ITO layer 2 is 180 nm, the thickness of the photonic crystal layer of the air hole is 540 nm, and the metal cathode electrode 5 The thickness is 150 nm.

A method for preparing a light-emitting device embedded in a self-assembled air hole photonic crystal film, the steps are as follows:

1) Use the open source software MPB to calculate the energy band structure of the air-hole two-dimensional photonic crystal formed by PbS (refractive index 3.912). Get ω _m =0.267, be 1100 nanometers for the luminescence peak of PbS, calculate the photonic crystal lattice constant a, promptly the diameter of air hole is 440 nanometers, and select the polystyrene nano-microsphere (PS) equal to air hole diameter ;

2) Cut the ITO glass into 12×30mm glass pieces, soak them in a mixed solution of H ₂ SO ₄ and H ₂ O ₂ with a volume ratio of 4:1 at 80°C for 10 min, and then rinse them with deionized water. Clean up the ITO glass, using The method prepares monodisperse PS microspheres with a diameter d of 440 nanometers, and the particle size deviation of the microspheres is less than 5%. The method is to ultrasonically disperse the nanospheres in an absolute ethanol solution to form an ethanol suspension of the nanospheres. The mass percent concentration is 1%, and it is ultrasonically dispersed in an ultrasonic instrument to obtain a monodisperse suspension. Two pieces of ITO glass are stacked together, and a piece of thick ITO glass is placed at one end between the two ITO glass pieces. 0.2mm glass spacer, and then inject the prepared suspension between two ITO glass sheets, and after standing for 2 days in a drying oven at a constant temperature of 30 degrees Celsius, a monolayer can be self-assembled on the surface of the ITO glass below Self-assembled nano-microsphere film (the self-assembled nano-microsphere monolayer film adopts literature T.Yamasaki and T.Tsutsui, "Fabrication and optical properties of two-dimensional ordered arrays of silica microspheres," Japanese Journal of Applied Physics, vol.38, p.5916, 1999. disclosed method);

3) Preparation of the light-emitting layer and negative electrode of the electroluminescent device: PbS nanocrystals are filled in the gap of the PS colloidal crystal film on the homogenizer, and a 50-nanometer thick PbS layer is formed on the surface of the PS colloidal crystal film, and PS will grow. The glass sheet of the colloidal crystal film is placed in a muffle furnace, and the temperature is raised to 250°C at a heating rate of 0.2°C/min and kept for 3 hours to remove the PS template to form air holes to obtain a single-layer PbS array material, and then evaporate a layer of thickness with an electron beam A 100nm aluminum film is used as the cathode electrode of the device.

The bandgap values of lead sulfide two-dimensional photonic crystals in this light-emitting device are shown in Table 1.

Table 1

In Table 1, r/a is the ratio of the radius of the two-dimensional photonic crystal dielectric column to the lattice constant, ω _min and ω _max are the minimum and maximum values of the bandgap frequency, ωm _is the median value of the bandgap frequency, and Δω/ω _m is the relative size of the band gap.

It can be seen from the above table that the lead sulfide hollow hole photonic crystal structure has a photonic band gap in the direction parallel to the glass layer, and the photonic band gap can be used to improve the light output in the vertical direction; the hollow structure reduces the equivalent refractive index of the light-emitting layer and reduces the light in the device. Total reflection improves the light extraction efficiency of the light emitting device.

Claims (1)

1. one kind embeds the preparation method of the luminescent device of self assembly airport photon crystal film, described luminescent device is made up of glassy layer, ITO layer, airport layer of photonic crystals and the stack of metal negative electrode, wherein airport layer of photonic crystals is by luminescent material with fill up airport wherein and form and be provided with the luminous material layer that a layer thickness is 50-200 nanometer on airport surface, ITO layer thickness is 100-200 nanometer, airport photonic crystal layer thickness is 100 nanometer-1 micron, and the thickness of metal negative electrode is 100-200 nanometer; Described luminescent material is vulcanized lead, zinc sulphide or zinc oxide; Described metal negative electricity is aluminium, silver or golden very;

It is characterized in that step is as follows:

1) utilize open source software MPB to calculate the band structure of photon crystal material: the position ω that first calculates photon structure band gap in the luminescent device that will prepare with method for numerical simulation _min-ω _max, wherein ω _minfor band gap extreme lower position, ω _maxfor band gap extreme higher position, obtain band gap position mean ω _m=1/2 (ω _max-ω _min), known device Emission Spectrum Peals is λ, by formula ω _m=a/ λ calculates photonic crystal lattice constant a, i.e. the diameter of airport, and choose and Properties of Polystyrene Nano Particles or the polymethyl methacrylate nano microballoon of airport equal diameters;

2) self-assembling photonic crystal structure on the ito glass of pre-cleaning: self-assembly method is the alcohol suspension that forms Nano microsphere in being dispersed in ethanol solution by ultrasonic above-mentioned Nano microsphere, the mass percent concentration of this suspension is 0.5-3%, two ito glasses are stacked together, it is the glass gasket of 0.2 millimeter that a thickness is put in one end between two ito glass sheets, then the suspension preparing is injected between two ito glass sheets, quiet putting after 2 days in the drying box of 30 degrees Celsius of constant temperature, ito glass surface that can be below obtains the Nano microsphere film of individual layer self assembly,

3) preparation of electroluminescent device luminescent layer and negative electrode: adopt vacuum evaporation method or spin coating method to fill luminescent material on Nano microsphere thin layer, form the composite bed of Nano microsphere film and luminescent material, then at 250-450 DEG C, be incubated 2-3 hour, form airport, finally evaporation metal negative electrode on airport layer of photonic crystals to remove Nano microsphere.