WO2016082486A1

WO2016082486A1 - Structure and method for improving light extraction efficiency

Info

Publication number: WO2016082486A1
Application number: PCT/CN2015/079143
Authority: WO
Inventors: 王祎君; 陆建钢; 谢汉萍
Original assignee: 上海交通大学
Priority date: 2014-11-25
Filing date: 2015-05-18
Publication date: 2016-06-02
Also published as: CN104466019A

Abstract

A structure and method for improving light extraction efficiency. A medium layer (2) is provided between a light source side (1) and an external medium side (3), the medium layer (2) is internally provided with a micro-structure (4) for changing the direction of light propagation, the micro-structure (4) is in a spherical shape, or a rod shape or a conical shape, the micro-structure (4) is a micro structure with the medium layer (2) surrounding the air, or the micro-structure (4) is a structure consisting of the same medium, but the arrangement of crystal lattice therein changed, which presents refractive index distribution different from that on other positions in the medium layer. The structural design of micro-optics is realized inside the medium layer (2), the micro-optics structure changes a propagation path of light in the medium, and the occurrence of total reflection phenomenon is avoided, such that the light energy which cannot be used due to the total reflection can be used, the efficiency for coupling light via the medium is increased, and the utilization rate of the light energy is remarkably increased.

Description

Structure and method for improving light extraction efficiency

Technical field

The present invention relates to a structure and method for improving light extraction efficiency.

Background technique

In the field of display and illumination, the light-emitting efficiency of light sources greatly affects the use time of electronic devices, which is more obvious for mobile devices. Among many illuminating light sources, light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs) have gradually replaced the previous cold cathode tubes (CCFLs) and other light-emitting devices, becoming the mainstream light source in the market. The organic light emitting diode (OLED) is a thin film light emitting device, and by applying a certain voltage to both ends of the light emitting body, electrons and holes in the light emitting material are continuously combined to emit light. The field of application can be extended from lighting to display and is a very promising technology. The light-emitting efficiency of OLED has always been one of the focuses of this technology research. The total light-emitting efficiency of OLED is determined by the internal quantum efficiency and the external quantum efficiency. In recent years, the internal quantum efficiency of OLED has been able to achieve nearly 100% efficiency. External quantum efficiency is also limited to a lower 20%. Light is trapped in the OLED in three modes (surface plasmon mode, waveguide mode, substrate mode) and cannot be coupled out of the OLED device. For OLEDs, today's methods for improving the efficiency of external extraction are roughly divided into several types: 1 arrangement of microlens arrays on the outer surface of the substrate glass; 2 roughening of the outer surface of the glass substrate; 3 filling between the inner surface of the glass and the ITO or Growing a substance or material. The first scheme will change the original Lambertian distribution of the light source and change the divergence angle. If there is a situation in which the image is blurred, the second scheme is not suitable for display, because the screen will be in the case of not lighting the pixel. The scattering phenomenon, the third solution needs to change the current process of OLED manufacturing, and is not suitable for large-scale manufacturing. On the other hand, light-emitting diodes (LEDs) are made of III-IV compounds, such as GaAs (gallium arsenide). Made of semiconductors such as GaP (gallium phosphide) and GaAsP (phosphorus gallium arsenide), the core of which is the PN junction. Under certain conditions, it has luminescent properties. At the forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. A part of the minority carriers (small children) entering the other area is combined with the majority carriers (multiple sub-groups) to emit light. The total light extraction efficiency of the LED is also determined by the internal quantum efficiency and the external quantum efficiency. The internal quantum efficiency can be greater than 50% under optimal conditions, while the external quantum efficiency is only 0.1% to 0.7%. When the light-emitting chip is wrapped with a medium having a high refractive index, the external quantum efficiency can be increased to 20% to 30%. For LEDs, the method of extracting the external extraction efficiency is generally to change the shape of the high refractive index material of the packaged light emitting chip, to destroy total reflection, or to use a reflective cup to improve utilization. The problem is that it will change the divergence angle of the Lambertian distribution of light emitted by the original chip, and there is a problem that the angular luminance is unevenly illuminated. At the same time, the volume of the LED is increased due to the change of the package shape of the LED outside, which is disadvantageous for improving the system. Integration.

When the light-emitting layer needs to be coupled to the outside through a certain material or medium, since the optical transmission medium has a difference in refractive index between the medium coupled to the outside and the medium in which the light source itself is located, a total reflection phenomenon occurs at each medium interface. This phenomenon causes light to be reflected back to the medium in which the light source is located or confined to the dielectric layer through which the light needs to penetrate, and cannot be coupled to an external medium (such as air), resulting in loss of this portion of the optical energy.

Summary of the invention

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the deficiencies of the prior art and to provide a structure and method for improving light extraction efficiency.

The object of the invention is achieved by the following technical solutions:

A structure for improving light extraction efficiency is characterized in that a dielectric layer is provided between a light source side and an external medium side, and a microstructure for changing a light propagation direction is provided in the dielectric layer.

Further, the above structure for improving light extraction efficiency, wherein the microstructure is spherical or rod-shaped or tapered.

Further, in the above structure for improving light extraction efficiency, the microstructure is a microstructure in which the inside is a dielectric layer outside the air.

Furthermore, the above structure for improving light extraction efficiency, wherein the microstructure is a structure composed of the same medium but changing its internal lattice arrangement, exhibits a refractive index distribution different from other positions in the dielectric layer.

Further, the above structure for improving the light extraction efficiency, wherein the microstructure is formed by engraving a pulsed laser inside the dielectric layer.

Furthermore, the above structure for improving light extraction efficiency, wherein the microstructure extends along the length direction to the surface of the dielectric layer.

Further, in the above structure for improving light extraction efficiency, the refractive index on the light source side is n1, the refractive index of the dielectric layer is n2, and the refractive index on the external medium side is n3, n1≠n2, n2≥n3.

The method for improving the light extraction efficiency of the invention, the light is incident from the light source side to the dielectric layer, and the microstructure in the dielectric layer changes the propagation direction of the light during the process of coupling the dielectric layer to the external medium side, so that the light energy meets the emission condition, that is, the emission The angle is less than the critical angle so the light energy is coupled into the external medium.

Further, in the above method for improving light extraction efficiency, the refractive index of the light source side is n1, the refractive index of the dielectric layer is n2, and the refractive index of the external medium side is n3, which satisfies n1≠n2, n2≥n3 .

The outstanding substantive features and significant progress of the technical solution of the present invention are mainly embodied in:

1 The invention realizes the micro-optical structure design inside the dielectric layer, and the micro-optical structure changes the propagation path of light in the medium to avoid the occurrence of total reflection phenomenon, so that the light energy that cannot be utilized due to total reflection is utilized, and the optical energy is greatly improved. Utilization of light energy;

2 Designed for the dielectric layer of optical transmission, the optical coupling efficiency is significantly improved without changing the shape of the penetrating medium required for light, and the process flow for fabricating the photovoltaic device is not changed;

3 is very suitable for large-area and industrial mass production, with significant economic and social effects. It is a good technology with novelty, creativity and practicality.

DRAWINGS

The technical solution of the present invention is further described below with reference to the accompanying drawings:

Figure 1: Schematic diagram of the structure of the present invention.

detailed description

The present invention proposes a new design method aimed at reducing the proportion of light energy confinement in various modes, thereby improving overall luminous efficiency.

As shown in FIG. 1, the structure for improving the light extraction efficiency has a dielectric layer 2 between the light source side 1 and the external medium side 3, and the dielectric layer 2 is provided with a microstructure 4 for changing the direction of light propagation.

The microstructure 4 is spherical or rod-shaped or tapered, and the microstructure can be fabricated by various means. For example, a pulsed laser is engraved in the interior of the dielectric layer, and the manner of forming the microstructure is not limited to a pulsed laser, but also The space for the microstructure is reserved when the glass is made, and the structure is designed at the time of production.

The microstructure 4 is a microstructure in which the outside of the air is a dielectric layer, or the microstructure 4 is a structure composed of the same medium but changing its internal lattice arrangement, exhibiting a refractive index distribution different from other positions in the dielectric layer. .

The length of the microstructure 4 can be designed to extend to the surface of the dielectric layer or only within the dielectric layer without destroying the surface topography of the dielectric layer. The shape and length of the microstructure can be controlled by different technical means (such as adjusting the wavelength of the laser emitting light, pulse frequency, duration, energy of a single pulse, etc.). According to different requirements, the arrangement of the microstructures may be random or arranged in an array manner, and even the depth position of the microstructures in the dielectric layer may be flexibly arranged and changed.

In a specific application, light is incident from the light source side 1 to the dielectric layer 2, and during the coupling of the dielectric layer 2 to the external medium side 3, the microstructure 4 in the dielectric layer 2 changes the direction of light propagation, so that the light energy satisfies the emission condition. The exit angle is less than the critical angle so the light energy is coupled into the external medium. The micro-optical structure design is realized inside the dielectric layer, and the micro-optical structure can destroy the propagation path of light in the medium. The diameter avoids the occurrence of total reflection, so that light energy that cannot be utilized due to total reflection is utilized, and the efficiency of coupling light out through the medium increases.

The light source side represents the light incident from the side into the dielectric layer, and does not mean that the dielectric layer must be close to the light source side, and the light source may be in close contact with the dielectric layer, or the light source may enter the upper dielectric layer through the medium of the layer. The refractive index of the layer is n1, the refractive index of the dielectric layer to be penetrated by light is n2, and the refractive index of the external medium side is n3, n1≠n2, n2≥n3. Under normal circumstances, when the light source is coupled to the external medium through the dielectric layer, the light will be totally reflected on the interface of the medium, and the light will not be coupled to the external medium, and the energy will be lost. The present invention designs the dielectric layer so that the dielectric layer has some microstructures, and the microstructure destroys the original propagation direction of the light, destroying the total reflection effect, so that the light energy satisfies the exit condition (the exit angle is smaller than the critical angle), and thus the light Can be coupled to an external medium to improve the utilization of light energy.

The density of the microstructure has an effect on the amount of light energy that is ultimately coupled out. The amount of light coupled out increases with the increase of the microstructure density, but is coupled when the microstructure density increases to a certain extent. The energy of the light can no longer increase and gradually reach a degree of saturation, so the density of the microstructure has an optimum value. The depth position of the microstructure in the medium is insensitive to the effect of the amount of light energy. The shape of the microstructure arrangement is insensitive to the effect of the amount of light energy in the case of a nearly uniform arrangement. The shape of the microstructure changes the appearance of the light. If it is a cone-shaped structure, the light type will be concentrated. If it is circular, it will cause the light type to be divergent. The shape, arrangement, density, etc. of the microstructures do not cause the spectral lines of the spectrum to drift.

In summary, the present invention is only designed for the dielectric layer of optical transmission, and greatly improves the optical coupling efficiency without changing the shape of the transparent medium required for light, and does not change the current process of fabricating the photovoltaic device, which is very suitable. Large area and industrial mass production have high practicality and economic value.

It is to be understood that the above description is only a preferred embodiment of the present invention, and that those skilled in the art can make several modifications and improvements without departing from the principles of the invention. Retouching should also be considered as the scope of protection of the present invention.

Claims

A structure for improving light extraction efficiency, characterized in that a dielectric layer is provided between a light source side and an external medium side, and a microstructure for changing a light propagation direction is provided in the dielectric layer.
The structure for improving light extraction efficiency according to claim 1, wherein the microstructure is spherical or rod-shaped or tapered.
The structure for improving light extraction efficiency according to claim 1 or 2, wherein the microstructure is a microstructure in which the inside is a dielectric layer outside the air.
The structure for improving light extraction efficiency according to claim 1 or 2, wherein the microstructure is a structure which is composed of the same medium but changes its internal lattice arrangement, and exhibits a different position from other positions in the dielectric layer. The refractive index distribution.
The structure for improving light extraction efficiency according to claim 1 or 2, wherein the microstructure is formed by engraving a pulsed laser light inside the dielectric layer.
The structure for improving light extraction efficiency according to claim 1 or 2, wherein the microstructure extends in the length direction to the surface of the dielectric layer.
The structure for improving light extraction efficiency according to claim 1, wherein the material of the dielectric layer is glass or PC film or PE or PMMA.
The structure for improving light extraction efficiency according to claim 1, wherein the refractive index of the light source side is n1, the refractive index of the dielectric layer is n2, and the refractive index of the external medium side is n3, n1≠n2, n2. ≥n3.
A method for improving light extraction efficiency according to the structure of claim 1, characterized in that light is incident from the light source side to the dielectric layer, and in the process of coupling the dielectric layer to the external medium side, the microstructure in the dielectric layer changes the direction of light propagation. Therefore, the light energy satisfies the exit condition, that is, the exit angle is smaller than the critical angle, and thus the light energy is coupled into the external medium.
The method for improving light extraction efficiency according to claim 9, wherein the refractive index of the light source side is n1, the refractive index of the dielectric layer is n2, and the refractive index of the external medium side is n3, which satisfies n1≠n2, N2 ≥ n3.