CN111200044A - Thin film type white light LED chip - Google Patents

Thin film type white light LED chip Download PDF

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CN111200044A
CN111200044A CN202010032945.7A CN202010032945A CN111200044A CN 111200044 A CN111200044 A CN 111200044A CN 202010032945 A CN202010032945 A CN 202010032945A CN 111200044 A CN111200044 A CN 111200044A
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layer
light
injection layer
transparent electrode
led chip
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CN111200044B (en
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陈梓铭
叶轩立
黎振超
曹镛
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South China University of Technology SCUT
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South China University of Technology SCUT
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/40—Materials therefor
    • H01L33/42—Transparent materials
    • H—ELECTRICITY
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    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/20—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/38—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes with a particular shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/50—Wavelength conversion elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/50—Wavelength conversion elements
    • H01L33/501—Wavelength conversion elements characterised by the materials, e.g. binder
    • H01L33/502—Wavelength conversion materials
    • H01L33/504—Elements with two or more wavelength conversion materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/115—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising active inorganic nanostructures, e.g. luminescent quantum dots
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/125—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers specially adapted for multicolour light emission, e.g. for emitting white light
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/17—Carrier injection layers
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/17—Carrier injection layers
    • H10K50/171—Electron injection layers
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    • H10K50/80—Constructional details
    • H10K50/805—Electrodes

Abstract

The invention discloses a thin-film white light LED chip which comprises a transparent substrate, a first transparent electrode, a light-emitting structure, a second transparent electrode and a first fluorescent powder layer which are sequentially arranged, wherein the light-emitting structure comprises a light-emitting layer, an electron injection layer and a hole injection layer which are arranged on two sides of the light-emitting layer, and the total thickness (inverted structure) of the electron injection layer and the second transparent electrode or the total thickness (upright structure) of the hole injection layer and the second transparent electrode is less than the length of one light-emitting wavelength of the light-emitting layer. The arrangement of the second transparent electrode enables photons emitted by the light emitting layer to penetrate the first fluorescent powder layer, and the total thickness (inverted structure) of the electron injection layer and the second transparent electrode or the total thickness (inverted structure) of the hole injection layer and the second transparent electrode is smaller than the length of one light emitting wavelength of the light emitting layer, so that an evanescent wave generated by total reflection can penetrate the first fluorescent powder layer and is absorbed by the first fluorescent powder layer to emit light, and the integral external quantum efficiency of the LED chip is improved.

Description

Thin film type white light LED chip
Technical Field
The invention relates to the technical field of Light Emitting Diodes (LEDs), in particular to a thin film type white light LED chip with high external quantum efficiency and low production cost.
Background
White light illumination is closely related to the work life of human beings, and the white light illumination technology has been greatly developed so far, wherein a white Light Emitting Diode (LED) has become one of the best choices for replacing the traditional illumination light emitting elements (such as incandescent lamps and fluorescent lamps), and the use of a green, energy-saving and environment-friendly white light LED as a main illumination element is also in great tendency. The thin film type white light LED has the advantages of nanometer-level thickness of each layer, small material consumption, compatibility with processes such as blade coating, printing and the like, lower cost and realization of large-area preparation and surface light source emission, thereby gradually replacing the traditional white light LED emitted by a point light source.
Referring to fig. 1, the following solutions are mainly used to realize the film-type white LED lighting in the present stage: the scheme A is that a blue light LED chip (with the luminous peak position of 430nm-500nm) is utilized to excite red light (with the luminous peak position of 600nm-780nm) and green light (with the luminous peak position of 500nm-560nm) double-color fluorescent powder, or excite single-color yellow light (with the luminous peak position of 560nm-600nm) fluorescent powder to emit light, and the fluorescent powder is integrally mixed into white light to emit light. And in the scheme B, a purple light LED chip (the light-emitting peak position is 200nm-430nm) is utilized to excite red, green and blue (or complementary color) fluorescent powder to emit light, and the red, green and blue fluorescent powder is integrally mixed to form white light for emitting light. The two implementation modes of the 'electroluminescent + photoluminescent' white light LED have the advantages that the circuit driving and the LED preparation process are relatively simple, the overall cost is relatively low, and meanwhile, the fluorescent powder with various colors is usually added into the packaging layer of the blue light (or purple light) LED chip and is far away from the light emitting layer of the blue light (or purple light) LED chip, so that far-field excitation is realized, and the fluorescent powder only carries out down-conversion on the energy of photons capable of emitting out of the LED chip.
Continuing to refer to fig. 1, scheme C is to construct a full electroluminescent LED chip with a longitudinal stack of three colors, red, green and blue, which are blended into white light; and the scheme D is to construct a red, green and blue transversely-stacked all-electric light-emitting LED chip, and blend three colors into white light. Both schemes are realized in a full-electroluminescence mode, and because the external quantum efficiency of the red light LED and the green light LED is higher than that of the blue light LED, the white light LED efficiency higher than that of the scheme A and the scheme B can be obtained; meanwhile, in the scheme D, the red, green and blue LEDs can be independently driven, so that the proportion of red, green and blue can be regulated and controlled to realize the controllability of the color temperature of white light.
Referring to fig. 2, in the conventional schemes a and B, since the refractive index of the blue and violet LED chips 100 is much higher than that of the external encapsulation medium 200 (usually epoxy resin) containing the phosphor 210, photons are incident from the optically dense medium to the optically sparse medium, resulting in a large amount of total reflection inside the chip 100 (as shown by the arrow in fig. 2), which limits the external extraction of photons, however, the phosphor 210 is added into the encapsulation medium 200, away from the LED chip, in a far-field position (the actual distance between the phosphor 210 and the light emitting layer of the LED chip 100 is at least several times greater than the light emitting wavelength), so only within the total reflection angle, photons that can exit to the outside of the chip and reach the encapsulation medium 200 can be absorbed by the phosphor 210, and then the fluorescence emission of the phosphor 210 is performed. However, the external quantum efficiency of blue and violet LEDs is low, and the fluorescent quantum efficiency of the phosphor is less than 100%, which seriously affects the overall efficiency of the white LED, so that the white LED in the form of "electroluminescence + photoluminescence" is much lower in efficiency. In addition, for the case of the solution B only, the strong uv component in the spectrum has a certain harm to human body, especially under the condition of long-time irradiation, therefore, in consideration of the influence of uv to human body, in the white light implementation of "electro + photo", exciting red green (or yellow) phosphor with blue LED chip (solution a) is still the first choice of the white light LED commercialized at present, although its efficiency is low.
Referring again to fig. 1, for scheme C, although this approach can obtain a high-efficiency white LED chip, the device manufacturing process is complicated, and the whole chip involves more than a dozen layers of thin film deposition processes, which is very costly. For the scheme D, since the red, green and blue LEDs all need independent driving circuits, the number of each white LED driving circuit is increased to three, and the driving circuits are complex in design, also need very high cost, and sacrifice the lateral size, and are not usually used as lighting elements. The market share of the two white light illumination schemes of scheme C and scheme D is very low due to manufacturing cost issues.
Therefore, there is a need to provide a thin film type white LED chip which can significantly improve the light emitting efficiency of an "electro + photo" type mainstream white LED, reduce the illumination energy consumption of the white LED, and has a low production cost, so as to solve the above problems in the prior art.
Disclosure of Invention
The invention aims to provide a thin-film type white light LED chip which can obviously improve external quantum efficiency, reduce illumination energy consumption and has low production cost.
In order to achieve the purpose, the technical scheme of the invention is as follows: the thin-film white light LED chip comprises a transparent substrate, a first transparent electrode, a light-emitting structure, a second transparent electrode and a first fluorescent powder layer which are sequentially arranged, wherein the light-emitting structure comprises a light-emitting layer, and an electron injection layer and a hole injection layer which are arranged on two sides of the light-emitting layer, and the total thickness (inverted structure) of the electron injection layer and the second transparent electrode or the total thickness (inverted structure) of the hole injection layer and the second transparent electrode is smaller than the length of one light-emitting wavelength of the light-emitting layer.
Preferably, the light-emitting layer includes a violet light-emitting material having an emission wavelength of 200nm to 430nm or a blue light-emitting material having an emission wavelength of 430nm to 500 nm.
Preferably, the light-emitting structure includes the hole injection layer, the light-emitting layer, and the electron injection layer, which are sequentially disposed, the electron injection layer is adjacent to the second transparent electrode, the thickness of the electron injection layer is less than 200nm, and the thickness of the hole injection layer is less than 1000 nm.
Preferably, the light-emitting structure includes the electron injection layer, the light-emitting layer, and the hole injection layer, which are sequentially disposed, the hole injection layer is adjacent to the second transparent electrode, the thickness of the hole injection layer is less than 200nm, and the thickness of the electron injection layer is less than 1000 nm.
Preferably, the materials of the electron injection layer and the hole injection layer are both at least one of organic polymers and small molecules, metal oxides, inorganic semiconductor materials and organic-inorganic composites, and the optical material of the light-emitting layer is at least one of organic light-emitting materials, quantum dots and nanocrystalline materials, inorganic light-emitting materials and organic-inorganic hybrid light-emitting materials.
Preferably, the thickness of the second transparent electrode is less than 100nm, the thickness of the first transparent electrode is less than 1000nm, and the materials of the second transparent electrode and the first transparent electrode are at least one of an ultrathin metal film, a patterned metal film, a metal nanowire, a metal nanorod, a metal nanoparticle, an organic polymer, a small molecule, a metal oxide, and an organic-inorganic composite.
Preferably, the thin-film white LED chip further includes a second phosphor layer, the second phosphor layer is disposed on a side of the transparent substrate away from the first transparent electrode, and thicknesses of the first phosphor layer and the second phosphor layer are both less than 1 mm.
Preferably, the first phosphor layer and the second phosphor layer each include at least one of a blue phosphor material with an emission band of 430nm to 500nm, a green phosphor material with an emission band of 500nm to 560nm, a yellow phosphor material with an emission band of 560nm to 600nm, and a red phosphor material with an emission band of 600nm to 780 nm.
Preferably, the fluorescent materials of the first and second phosphor layers are at least one of organic fluorescent materials, quantum dot and nanocrystal materials, inorganic fluorescent materials, and organic-inorganic hybrid fluorescent materials.
Preferably, the first transparent electrode, the light emitting layer, the electron injection layer, the hole injection layer, the second transparent electrode, the first phosphor layer, and the second phosphor layer are formed by vapor deposition, sputtering, spin coating, blade coating, evaporation, ink jet printing, drop coating, roll-to-roll printing, slit coating, screen printing, spray coating, or mechanical stamping.
Compared with the prior art, the thin-film white light LED chip comprises a transparent substrate, a first transparent electrode, a light-emitting structure, a second transparent electrode and a first fluorescent powder layer which are sequentially arranged, wherein the light-emitting structure comprises a light-emitting layer, and an electron injection layer and a hole injection layer which are arranged on two sides of the light-emitting layer, and the total thickness (inverted structure) of the electron injection layer and the second transparent electrode or the total thickness (upright structure) of the hole injection layer and the second transparent electrode is smaller than the length of one light-emitting wavelength of the light-emitting layer. Firstly, because the reflective metal electrode in the prior art is replaced by the second transparent electrode, photons emitted by the light-emitting layer can not be completely reflected in the direction, but have a chance to permeate into the first fluorescent powder layer; secondly, through the arrangement that the total thickness (inverted structure) of the electron injection layer and the second transparent electrode or the total thickness (upright structure) of the hole injection layer and the second transparent electrode is smaller than the length of one light-emitting wavelength of the light-emitting layer, the evanescent wave generated by total reflection can penetrate into the first fluorescent powder layer and be absorbed by the first fluorescent powder layer, and the actual utilization rate of photons inside the chip is improved by a mode of absorbing the evanescent wave and emitting fluorescence, so that the overall external quantum efficiency of the LED chip is improved, the illumination energy consumption is reduced, the white light emission can be ensured, and the production cost is low.
Drawings
Fig. 1 is a schematic diagram of a thin film type white LED in the prior art.
Fig. 2 is a schematic diagram of a light emitting principle of a thin film type white LED chip in the prior art.
Fig. 3a is a schematic structural diagram of an embodiment of a thin film type white LED chip with an inverted structure according to the present invention.
FIG. 3b is a schematic structural diagram of another embodiment of the inverted thin film type white LED chip of the present invention.
Fig. 4a is a schematic structural diagram of an embodiment of a thin film type white LED chip with a front-mounted structure according to the present invention.
FIG. 4b is a schematic structural diagram of another embodiment of a thin film type white LED chip with a front-mounted structure according to the present invention.
Fig. 5a is a schematic diagram of an evanescent wave generated when a light wave is incident from an optically dense medium to an optically thinner medium and totally reflected.
Fig. 5b is a schematic diagram of evanescent wave penetration of a light wave from an optically dense medium into an optically thinner medium with a third layer of medium that absorbs photons.
Fig. 6a is a voltage-current density curve of quantum dot blue and bicolor white LED chips.
Fig. 6b is a current density-external quantum efficiency curve for quantum dot blue and bicolor white LED chips.
Fig. 7a is a spectrum diagram of a quantum dot bichromatic white LED chip.
Fig. 7b is a color coordinate diagram of a quantum dot bicolor white LED chip.
Fig. 8a is a voltage-current density curve for perovskite blue and three-color white LED chips.
Fig. 8b is a current density-external quantum efficiency curve for perovskite blue and three-color white LED chips.
Fig. 9a is a spectrum of a perovskite three-color white LED chip.
Fig. 9b is a color coordinate diagram of a perovskite three-color white LED chip.
Detailed Description
Embodiments of the present invention will now be described with reference to the drawings, wherein like element numerals represent like elements.
Referring to fig. 3a to fig. 4b, the thin film type white LED chip 100 of the present invention includes a transparent substrate 110, a first transparent electrode 120, a light emitting structure 130, a second transparent electrode 140, and a first phosphor layer 150, which are sequentially disposed. The light emitting structure 130 includes a light emitting layer 131, and a hole injection layer 132 and an electron injection layer 133 disposed on two sides of the light emitting layer 131, and a total thickness (inverted structure) of the electron injection layer 133 and the second transparent electrode 140 or a total thickness (forward structure) of the hole injection layer 132 and the second transparent electrode 140 is smaller than a light emitting wavelength length of the light emitting layer 131 (described in detail later).
Furthermore, the thin film type white LED chip 100 of the present invention may further include a second phosphor layer 160, wherein the second phosphor layer 160 is disposed on a side of the transparent substrate 110 away from the first transparent electrode 120.
Referring to fig. 3a-4b, different embodiments of the thin film type white LED chip 100 of the present invention will be described.
Referring to fig. 3a, in an embodiment of the thin-film white LED chip 100 of the present invention, the thin-film white LED chip 100 is an inverted structure, and specifically includes a transparent substrate 110, a first transparent electrode 120, a light-emitting structure 130, a second transparent electrode 140, and a first phosphor layer 150, which are sequentially disposed, wherein the light-emitting structure 130 includes a hole injection layer 132, a light-emitting layer 131, and an electron injection layer 133, which are sequentially disposed, the hole injection layer 132 is formed between the first transparent electrode 120 and the light-emitting layer 131, the electron injection layer 133 is formed between the light-emitting layer 131 and the second transparent electrode 140, meanwhile, the thickness of the hole injection layer 132 is less than 1000nm, the thickness of the electron injection layer 133 is less than 200nm, and the total thickness of the electron injection layer 133 and the second transparent electrode 140 is less than one light-emitting wavelength length of the light-emitting layer 131.
In the present embodiment, the light emitting layer 131 includes a violet light emitting material having an emission wavelength of 200nm to 430nm or a blue light emitting material having an emission wavelength of 430nm to 500nm, and thus, the total thickness of the electron injection layer 133 and the second transparent electrode 140 is preferably less than 200nm or less than 430nm, and is flexibly set according to different light emitting materials of the light emitting layer 131.
With continued reference to fig. 3a, the light emitting material of the light emitting layer 131 is preferably at least one of an organic light emitting material, a quantum dot and nanocrystal material, an inorganic light emitting material, and an organic-inorganic hybrid light emitting material, but not limited thereto. In addition, the materials of the electron injection layer 133 and the hole injection layer 132 may be at least one of organic polymers and small molecules, metal oxides, inorganic semiconductor materials, and organic-inorganic composites, but are not limited thereto.
Referring again to fig. 3a, in the present embodiment, the thickness of the first transparent electrode 120 is less than 1000nm, the thickness of the second transparent electrode 140 is less than 100nm, and as mentioned above, the thickness of the electron injection layer 133 is less than 200nm, and the total thickness of the electron injection layer 133 and the second transparent electrode 140 is preferably less than 200 nm. In addition, the material of each of the first transparent electrode 120 and the second transparent electrode 140 may be at least one of an ultrathin metal film, a patterned metal film, a metal nanowire, a metal nanorod, a metal nanoparticle, an organic polymer and a small molecule, a metal oxide, and an organic-inorganic composite, but is not limited thereto. The transparent substrate 110 is a transparent non-conductive substrate, which may be a rigid inorganic substrate or a flexible organic polymer substrate.
Referring again to fig. 3a, the first phosphor layer 150 must be present in the device structure, and the thickness of the first phosphor layer 150 is less than 1 mm. The first fluorescent powder layer 150 comprises at least one of a blue fluorescent material with a light-emitting waveband of 430nm-500nm, a green fluorescent material with a light-emitting waveband of 500nm-560nm, a yellow fluorescent material with a light-emitting waveband of 560nm-600nm, and a red fluorescent material with a light-emitting waveband of 600nm-780 nm. In the present embodiment, the fluorescent material of the first phosphor layer 150 is preferably at least one of an organic fluorescent material, a quantum dot and nanocrystal material, an inorganic fluorescent material, and an organic-inorganic hybrid fluorescent material, but is not limited to these materials.
Referring to fig. 3b, in another embodiment of the thin-film white LED chip 100 with an inverted structure according to the present invention, the thin-film white LED chip may further include a second phosphor layer 160, the second phosphor layer 160 is disposed on a side of the transparent substrate 110 away from the first transparent electrode 120, and a thickness of the second phosphor layer 160 is less than 1mm, the second phosphor layer 160 is not necessarily present in the device structure, and mainly functions to supplement a light-emitting wavelength band that the first phosphor layer 150 cannot cover.
In addition, the fluorescent material of the second phosphor layer 160 is the same as that of the first phosphor layer 150, that is, the fluorescent material of the second phosphor layer 160 also includes at least one of a blue fluorescent material having an emission band of 430nm to 500nm, a green fluorescent material having an emission band of 500nm to 560nm, a yellow fluorescent material having an emission band of 560nm to 600nm, and a red fluorescent material having an emission band of 600nm to 780 nm. In this embodiment, the fluorescent material of the second phosphor layer 160 is preferably at least one of an organic fluorescent material, a quantum dot and nanocrystal material, an inorganic fluorescent material, and an organic-inorganic hybrid fluorescent material, and the fluorescent material of the second phosphor layer 160 is not limited to those listed herein.
Referring to fig. 3a-3b again, all the structural layers of the thin film type white LED chip 100 with the inverted structure of the present embodiment may be formed by vapor deposition, sputtering, spin coating, blade coating, evaporation, inkjet printing, drop coating, roll-to-roll printing, slit coating, screen printing, spray coating or mechanical imprinting, that is, the first transparent electrode 120, the hole injection layer 132, the light emitting layer 131, the electron injection layer 133, the second transparent electrode 140, the first phosphor layer 150 and the second phosphor layer 160 may be formed by one of the above methods, so that the forming process of the thin film type white LED chip 100 is simple and the production cost is reduced.
Referring now to fig. 4a-4b, another embodiment of the thin film type white LED chip 100 of the present invention is a front-up structure, and the front-up structure of the thin film type white LED chip 100 is different from the above-mentioned upside-down structure only in that: the light emitting structure 130 is disposed differently.
Specifically, the light emitting structure 130 includes an electron injection layer 133, a light emitting layer 131 and a hole injection layer 132 sequentially disposed, wherein the electron injection layer 133 is formed between the first transparent electrode 120 and the light emitting layer 131, the hole injection layer 132 is formed between the light emitting layer 131 and the second transparent electrode 140, the thickness of the electron injection layer 133 is less than 1000nm, the thickness of the hole injection layer 132 is less than 200nm, and the total thickness of the hole injection layer 132 and the second transparent electrode 140 is less than one light emitting wavelength length of the light emitting layer 131.
As in the above-described embodiment, the total thickness of the hole injection layer 132 and the second transparent electrode 140 is flexibly set according to the different light emitting materials of the light emitting layer 131, for example, when the light emitting layer 131 includes a violet light emitting material having an emission wavelength between 200nm and 430nm or a blue light emitting material having an emission wavelength between 430nm and 500nm, the total thickness of the hole injection layer 132 and the second transparent electrode 140 is preferably less than 200nm or less than 430 nm. In a preferred embodiment, the total thickness of the hole injection layer 132 and the second transparent electrode 140 is less than 200 nm.
In addition, the film-type white LED chip 100 with the front-mounted structure shown in fig. 4a is only provided with the first phosphor layer 150, and the film-type white LED chip 100 with the front-mounted structure shown in fig. 4b is provided with the first phosphor layer 150 and the second phosphor layer 160 at the same time, but except for the arrangement of the light emitting structure 130, the structure, the material and the forming manner of other parts of the film-type white LED chip 100 with the front-mounted structure of the present embodiment are the same as those of the film-type white LED chip 100 with the inverted structure, and therefore, the description thereof is omitted.
Referring to fig. 5a, an evanescent wave generated when an optical wave is incident from an optically dense medium to an optically sparse medium and totally reflected will be described. As shown in FIG. 5a, the first layer of medium is an optically dense medium with a refractive index n1The second medium is an optically thinner medium with refractive index n2And n is1>n2When the optical wave E is incident to the light sparse medium from the optical dense medium and the incident angle is larger than the total reflection angle, total reflection occurs, the total reflection light E 'is reflected to the first layer of medium, under the condition that the total reflection occurs, according to the wave property of light, an evanescent wave E' penetrating into the second layer of medium appears on the interface, the evanescent wave E 'is a plane wave in the direction parallel to the interface, the Goos-Hanchen displacement D is caused, the intensity of the evanescent wave E' decreases with the depth index in the direction F vertical to the interface, and the penetration depth is about the order of magnitude of one wavelength. However, since the average poynting vector of the evanescent wave in the vertical direction is 0, there is no actual energy flow in this direction that can propagate in the far field, and all photons are totally reflected into the first layer of medium.
If a third layer of a medium absorbing photon energy is introduced before the evanescent wave intensity is completely attenuated, its refractive index n is shown in FIG. 5b3The energy of the evanescent wave can be partially absorbed, so that the energy reflected to the first layer of medium is reduced, and the occurrence of total reflection is destroyed. Furthermore, if the third layer of medium is absorbing the evanescent wave energyThen, the light can be down-converted into fluorescence, photons in the first layer of medium outside the total reflection angle can be down-converted into photons in the third layer of medium to be emitted, and the efficiency of the whole process depends on the fluorescence quantum efficiency of the third layer of medium and the thickness of the second layer of medium. Therefore, through the whole coupling of the near-field optics of the device, photons which are originally bound in the device by total reflection are slowly absorbed and consumed by the third layer of medium by taking the evanescent wave as a medium, and then are converted into actual photons which can be emitted to an external space, so that the external quantum efficiency of the whole LED chip is greatly improved.
As shown in fig. 3a to 4b and fig. 5b, the refractive index of the light emitting layer 131 in the LED chip 100 is larger than the refractive index of the electron injection layer 133/hole injection layer 132 in most cases. According to the principle shown in fig. 5b, when the first layer of medium is the light emitting layer 131, the second layer of medium is a composite layer of the electron injection layer 133 and the second transparent electrode 140 with an inverted structure (see fig. 3a-3b) or a composite layer of the hole injection layer 132 and the second transparent electrode 140 with an inverted structure (see fig. 4a-4b), and the third layer of medium is the first phosphor layer 150, white light emission can be realized while the overall external quantum efficiency of the LED chip 100 is improved, and the low efficiency mode that the white light LED can only excite far-field phosphor through a blue (or violet) LED chip at present is solved.
Referring to fig. 3a again, a specific implementation of the thin film type white LED chip 100 of the present invention will be described by taking an inverted quantum dot bicolor white LED chip as an example.
Specifically, the structure of the quantum dot bi-color white LED chip 100 is shown in fig. 3a, wherein the transparent substrate 110 is glass, the first transparent electrode 120 is an indium tin oxide transparent electrode (ITO), the hole injection layer 132 is poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS), the light emitting layer 131 is cadmium selenide (CdSe) quantum dots, the electron injection layer 133 is 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi), and the second transparent electrode 140 is lithium fluoride/aluminum (LiF/Al); in addition, a first phosphor layer 150 is deposited on the second transparent electrode 140, and the first phosphor layer 150 is a red quantum dot phosphor (CdTe). It should be noted that if the first phosphor layer 150 is not deposited, the quantum dot blue LED chip with the inverted structure is formed.
Referring to fig. 3a again, the quantum dot bi-color white LED chip 100 of the present embodiment is prepared by the following steps: before the preparation, the ITO conductive glass is ultrasonically cleaned by isopropanol, deionized water, a detergent, deionized water and isopropanol in sequence, and then is placed in an oven to be dried; in addition, before use, the ITO conductive glass sheet needs to be cleaned in a plasma surface cleaner for 4 minutes.
When the preparation is started, firstly, poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS) (CLEVOS P VP CH 8000) is coated on ITO conductive glass in a high-speed spin coating mode by a spin coater (KW-4A) with the thickness of about 30nm, and annealing is carried out for 20min at 120 ℃ to obtain a hole injection layer 132; then, cadmium selenide (CdSe) was spin-coated on the hole injection layer 132 to obtain the light emitting layer 131, the thickness of the light emitting layer 131 being about 20 nm; next, forming the electron injection layer 133 and the second transparent electrode 140, specifically, depositing the TPBi electron injection layer material, the electron injection interface LiF, and the ultra-thin Al electrode on the CdSe light-emitting layer 131 in sequence by evaporation, with thicknesses of 35nm, 1nm, and 10nm, respectively; finally, a first phosphor layer 150(CdTe) was deposited on the ultra-thin Al electrode by spin coating to a thickness of about 100 nm. The above steps are completed to obtain the quantum dot bicolor white LED chip 100, and if the first fluorescent powder layer 150 is not deposited, the quantum dot blue LED chip with the inverted structure is obtained.
Referring to fig. 3a and fig. 6a-6b, the electrical characteristics and external quantum efficiency of the quantum dot blue LED chip with the inverted structure and the quantum dot bichromatic white LED chip 100 of the present invention are compared. Fig. 6a shows a voltage-current density curve of a quantum dot blue light and quantum dot bichromatic white LED chip, and it can be seen from the graph that the deposition of the first fluorescent powder layer 150 does not affect the electrical characteristics of the blue light quantum dot LED chip. In addition, as can be seen from the current density-external quantum efficiency curve of the quantum dot blue light and quantum dot bicolor white LED chip shown in fig. 6b, since the refractive index (about 2.3) of the quantum dot light emitting layer 131 is much greater than the refractive index (about 1.7) of the TPBi electron injection layer 133, the total reflection will greatly limit the emission of photons, resulting in a low external quantum efficiency (about 4%) of the quantum dot blue LED chip; however, after the first phosphor layer 150 is introduced, since the evanescent wave generated during the total reflection is utilized, the actual utilization rate of photons inside the chip is improved by absorbing the evanescent wave and then emitting fluorescence, so that the external quantum efficiency of the chip is improved to 5.7%, which is improved by about 43%.
Referring to fig. 3a and 7a-7b, since the light emitted by the quantum dot bi-color white LED chip 100 of the present embodiment is composed of sky blue light (emitted by the chip) and red light (emitted by the phosphor), it can be seen from the spectrum diagram shown in fig. 7a that bi-color white light is formed by the complementary color principle, and it can be seen from the color coordinate shown in fig. 7b that the color coordinate of the quantum dot bi-color white LED chip 100 is at the (0.33 ) position, indicating that the light color is pure white light.
Referring to fig. 3b again, another specific implementation of the thin film type white LED chip 100 of the present invention is illustrated by taking the organic-inorganic hybrid perovskite three-color white LED chip 100 with an inverted structure as an example.
Specifically, the structure of the perovskite three-color white light LED chip 100 is shown in fig. 3b, wherein the transparent substrate 110 is glass, the first transparent electrode 120 is an Indium Tin Oxide (ITO) transparent electrode, the hole injection layer 132 is poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS), and the light emitting layer 131 is organic-inorganic hybrid perovskite PEA2Csn-1Pbn(ClxBr3-x)3n+1The electron injection layer 133 is 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi), and the second transparent electrode 140 is lithium fluoride/aluminum (LiF/Al); in addition, a first phosphor layer 150 is deposited on the second transparent electrode 140, and the first phosphor layer 150 is red perovskite phosphor (CsPbBr)0.5I2.5) A second phosphor layer 160 is further deposited on the bottom side of the transparent substrate 110, and the second phosphor layer 160 is green perovskite phosphor (CsPbBr)2.5I0.5)。
It should be noted that if the first phosphor layer 150 and the second phosphor layer 160 are not deposited, the perovskite blue LED chip with the inverted structure is formed.
Referring again to fig. 3b, the organic-inorganic hybrid perovskite three-color white LED chip 100 of the present embodiment is prepared by the following steps: before use, the ITO conductive glass is sequentially cleaned by isopropanol, deionized water, a detergent, deionized water and isopropanol in an ultrasonic mode, then the ITO conductive glass is placed in an oven to be dried, and before manufacturing, the ITO glass sheet needs to be cleaned in a plasma surface cleaning instrument for 4 minutes again.
When the preparation is started, firstly, poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS) (CLEVOS P VP CH 8000) is coated on ITO conductive glass in a high-speed spin coating mode by a spin coater (KW-4A) with the thickness of about 30nm, and annealing is carried out for 20min at 120 ℃ to obtain a hole injection layer 132; then, PEA is added2Csn-1Pbn(ClxBr3-x)3n+1The material is spin-coated on the hole injection layer 132 to a thickness of about 50nm, and annealed at 70 ℃ for 5min to obtain the light-emitting layer 131; next, forming the electron injection layer 133 and the second transparent electrode 140, specifically, depositing the TPBi electron injection layer material, the electron injection interface LiF and the ultra-thin Al electrode on the perovskite light emitting layer 131 in sequence by evaporation, with thicknesses of 35nm, 1nm and 10nm, respectively; then, the first phosphor layer 150 (CsPbBr)0.5I2.5) Depositing the film on the ultrathin Al electrode in a spin coating mode, wherein the thickness of the film is about 100 nm; and a second phosphor layer 160 (CsPbBr)2.5I0.5) Depositing on the glass substrate by spin coating to a thickness of about 50nm, and completing the preparation. In addition, if the first and second phosphor layers 150 and 160 are not deposited, the resulting perovskite blue LED chip has an inverted structure.
Referring to fig. 3b and fig. 8a to 8b, the electrical characteristics and external quantum efficiency of the inverted perovskite blue LED chip are compared with the perovskite three-color white LED chip 100 of the present embodiment. Fig. 8a shows a voltage-current density curve of a perovskite blue light and perovskite three-color white light LED chip, and it can be seen from fig. 8a that the deposition of the first phosphor layer 150 and the second phosphor layer 160 hardly affects the electrical characteristics of the perovskite blue light LED chip.
In addition, as can be seen from the current density-external quantum efficiency curve of the perovskite blue light and perovskite three-color white light LED chip shown in fig. 8b, since the refractive index of the perovskite light emitting layer 131 (about 2.5) is much greater than the refractive index of the TPBi electron injection layer 133 (about 1.7), the total reflection also greatly limits the emission of photons, resulting in a low external quantum efficiency of the perovskite blue light perovskite LED chip (about 3.5%); however, after the first phosphor layer 150 is introduced, since the evanescent wave generated during the total reflection is utilized, the actual utilization rate of photons inside the chip is improved by absorbing the evanescent wave and then emitting fluorescence, so that the external quantum efficiency of the chip is improved to 4.8%, which is about 37%.
It should be noted that the efficiency improvement range is not as wide as that of the aforementioned quantum dot bicolor white LED chip 100, because the second phosphor layer 160 in the far field is introduced, which cannot make a positive contribution to the device efficiency, but rather makes a negative contribution to the off-chip quantum efficiency due to the fluorescence quantum efficiency of less than 100%, but the external quantum efficiency of the perovskite three-color white LED chip of the present embodiment is still much higher than that of the perovskite white LED chip in the prior art.
As shown in fig. 3b and fig. 9a-9b, since the light emitted by the perovskite blue light and perovskite three-color white LED chip of the present embodiment is composed of blue light (emitted by the chip), red light (emitted by the first phosphor layer 150), and green light (emitted by the second phosphor layer 160), as shown in fig. 9a, three-color white light is formed by the three-primary-color principle, and the color coordinates of the perovskite three-color white LED chip are at the (0.29,0.37) position, as shown in fig. 9b, it indicates that the light color is purer positive white light.
In summary, the thin film type white LED chip 100 of the present invention includes a transparent substrate 110, a first transparent electrode 120, a light emitting structure 130, a second transparent electrode 140 and a first phosphor layer 150, which are sequentially disposed, wherein the light emitting structure 130 includes a light emitting layer 131, and an electron injection layer 133 and a hole injection layer 132 disposed on two sides of the light emitting layer, and a total thickness (an inverted structure) of the electron injection layer 133 and the second transparent electrode 140 or a total thickness (an upright structure) of the hole injection layer 132 and the second transparent electrode 140 is smaller than a light emitting wavelength length of the light emitting layer 131. First, since the reflective metal electrode in the prior art is replaced with the second transparent electrode 140, photons emitted from the light emitting layer 131 can penetrate into the first phosphor layer 150 without being completely reflected in the direction; secondly, by setting that the total thickness (inverted structure) of the electron injection layer 133 and the second transparent electrode 140 or the total thickness (upright structure) of the hole injection layer 132 and the second transparent electrode 140 is smaller than the length of one light-emitting wavelength of the light-emitting layer 131, the evanescent wave generated by total reflection can penetrate into the first phosphor layer 150 and be absorbed by the first phosphor layer 150, and then the fluorescence is emitted by absorbing the evanescent wave, so that the actual utilization rate of photons inside the chip is improved, the overall external quantum efficiency of the LED chip is improved, the illumination energy consumption is reduced, the white light emission can be ensured, and the production cost is low.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, therefore, the present invention is not limited by the appended claims.

Claims (10)

1. A thin-film white light LED chip is characterized by comprising a transparent substrate, a first transparent electrode, a light-emitting structure, a second transparent electrode and a first fluorescent powder layer which are sequentially arranged, wherein the light-emitting structure comprises a light-emitting layer, an electron injection layer and a hole injection layer which are arranged on two sides of the light-emitting layer, and the total thickness of the electron injection layer and the second transparent electrode or the total thickness of the hole injection layer and the second transparent electrode is smaller than the light-emitting wavelength length of the light-emitting layer.
2. The thin-film white LED chip of claim 1, wherein the light emitting layer comprises a violet light emitting material having an emission wavelength of 200nm to 430nm or a blue light emitting material having an emission wavelength of 430nm to 500 nm.
3. The thin-film white LED chip of claim 2, wherein the light emitting structure comprises the hole injection layer, the light emitting layer and the electron injection layer in this order, the electron injection layer is adjacent to the second transparent electrode, the thickness of the electron injection layer is less than 200nm, and the thickness of the hole injection layer is less than 1000 nm.
4. The thin-film white LED chip of claim 2, wherein the light-emitting structure comprises the electron injection layer, the light-emitting layer, and the hole injection layer in this order, the hole injection layer is adjacent to the second transparent electrode, the hole injection layer has a thickness of less than 200nm, and the electron injection layer has a thickness of less than 1000 nm.
5. The thin-film white LED chip as claimed in any one of claims 1 to 4, wherein the electron injection layer and the hole injection layer are made of at least one of organic polymers and small molecules, metal oxides, inorganic semiconductor materials, and organic-inorganic composites, and the light emitting layer is made of at least one of organic light emitting materials, quantum dots and nano-crystalline materials, inorganic light emitting materials, and organic-inorganic hybrid light emitting materials.
6. The thin-film white LED chip of claim 1, wherein the thickness of the second transparent electrode is less than 100nm, the thickness of the first transparent electrode is less than 1000nm, and the materials of the second transparent electrode and the first transparent electrode are at least one of an ultrathin metal film, a patterned metal film, a metal nanowire, a metal nanorod, a metal nanoparticle, an organic polymer, a small molecule, a metal oxide, and an organic-inorganic composite.
7. The thin-film white LED chip of claim 1, further comprising a second phosphor layer, wherein the second phosphor layer is disposed on a side of the transparent substrate away from the first transparent electrode, and the first and second phosphor layers are less than 1mm thick.
8. The thin-film white LED chip of claim 7, wherein the first phosphor layer and the second phosphor layer each comprise at least one of a blue phosphor having an emission band of 430nm to 500nm, a green phosphor having an emission band of 500nm to 560nm, a yellow phosphor having an emission band of 560nm to 600nm, and a red phosphor having an emission band of 600nm to 780 nm.
9. The thin-film white LED chip of claim 7, wherein the phosphor materials of the first and second phosphor layers are at least one of organic phosphor materials, quantum dot and nanocrystal materials, inorganic phosphor materials, organic-inorganic hybrid phosphor materials.
10. The thin-film type white LED chip of any one of claims 7 to 9, wherein the first transparent electrode, the light emitting layer, the electron injection layer, the hole injection layer, the second transparent electrode, the first phosphor layer, and the second phosphor layer are formed by vapor deposition, sputtering, spin coating, blade coating, evaporation, inkjet printing, drop coating, roll-to-roll printing, slit coating, screen printing, spray coating, or mechanical embossing.
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