CN106684159A - Design and preparation method of a surface film with atomic oxygen protection function - Google Patents

Abstract

The invention provides a design and preparation method of a surface film with an atomic oxygen protection function, wherein the surface film is designed by adopting a combined film layer and has the following structure: AIR |. H_SiO2L_SiO2| GLASS, AIR as the incident medium, H_SiO2SiO having a refractive index of 1.45. + -. 0.01₂Film layer with thickness of 20 +/-1 nm and thickness of L_SiO2SiO with refractive index of 1.28 +/-0.02₂The thickness of the film layer is 95 +/-5 nm, GLASS is a GLASS cover plate doped with cerium dioxide, and 2 layers of films are deposited on the GLASS cover plate layer by layer in an electron beam thermal evaporation mode. The invention has the beneficial effect that the main material of the surface film prepared by the method is SiO₂The surface film can not be denatured by the oxidation of high-activity atomic oxygen, and the chemical stability of the surface film is improved. Meanwhile, the film is specially designed for the anti-radiation glass cover plate for space, the refractive index of the material is well matched with that of the glass cover plate, and the transmissivity of the cover plate after coating is higherThe method is high, and is beneficial to improving the working efficiency of the solar cell module.

Description

Design and preparation method of a surface film with atomic oxygen protection function

technical field

The invention belongs to the field of optical film design, and in particular relates to a design and preparation method of a surface film with atomic oxygen protection function.

Background technique

At present, artificial satellites, spaceships, space stations and other spacecraft all use solar cells to obtain energy for continuous operation. In order to protect the solar cell from the radiation and bombardment of high-energy rays and charged particles in space and prolong the service life of the solar cell, an anti-radiation glass cover sheet for space is often pasted on the surface of the solar cell. The radiation-resistant cover glass is doped with cerium oxide, which can effectively absorb the light in the ultraviolet band of sunlight, and greatly reduce the color centers in the cover glass caused by the irradiation of high-energy particles, thereby reducing the impact of radiation on the cover glass. The attenuation of transmittance caused by illumination ensures the stable and long-lasting output power of solar cells.

The refractive index of the cover glass is about 1.51. When the sunlight is vertically irradiated on the surface of the cover glass, there is about 4% light reflection loss (single surface reflection loss). In order to reduce this part of light loss, the existing process is to deposit a MgF ₂ film with an optical thickness of 1/4 wavelength on the surface of the cover glass. The refractive index of MgF ₂ is 1.38, which can theoretically reduce the surface reflectance of sunlight to 1.3% (single surface reflection loss), which further improves the conversion efficiency of solar cell components.

In the low earth orbit area (Low Earth Orbit LEO, 200km ~ 600km), the gas pressure is 10 ^-5 -10 ^{- 7} Pa, and the environmental components contain N ₂ , O ₂ , Ar, He, H ₂ and atomic oxygen (AO ), of which the content of atomic oxygen is the highest, accounting for about 80%. Atomic oxygen is formed by the decomposition of oxygen under the irradiation of ultraviolet rays. It is highly active and has strong oxidizing properties. Although in the LEO orbit, the space density of AO is only 10 ⁵ ~10 ⁹ /cm ³ , but since the spacecraft flies at a speed close to 8 km/s, the atomic oxygen flux on the windward side can reach up to 10 ¹⁵ /(cm ² · s), and a small number of atoms of oxygen are still in an excited state, which has the ability to transmit additional energy to the surface of the material, which is enough to cause chain scission of the polymer material and form low molecular substances, and the volatilization of these substances and their oxides causes the denudation of the material . In addition, atomic oxygen will collide with the surface of the spacecraft to produce glow discharge, which will cause surface cracking, cracking, local combustion and melting of the material, etc. The joint action of solar ultraviolet rays, especially vacuum ultraviolet rays, and atomic oxygen will also intensify the damage of atomic oxygen to some materials. The denudation effect seriously affects the performance and service life of the spacecraft. Flight experiments, long-term exposure experiments, and limited-term selective exposure experiments conducted by NASA and other institutions have further confirmed that atomic oxygen is the main cause of performance changes in spacecraft surface materials.

The above-mentioned problems will also occur in the solar cell module pasted with the glass cover sheet in LEO. Under the action of the strong oxidation of atomic oxygen, MgF ₂ is gradually oxidized to MgO. Since the refractive index of MgO is about 1.74, when the MgF ₂ on the surface of the cover glass is oxidized, the surface reflectance of the cover will increase to 11.0%, which greatly increases the surface light reflection loss of the solar cell module, and the corresponding output of the solar cell There is a noticeable drop in power.

The existing method for preparing the atomic oxygen protective coating is obtained by depositing by means of magnetron sputtering after preparing the ITO/MgF ₂ composite target. The circular ITO target is used as the main substrate, and the sheet-shaped fan-shaped MgF ₂ material is pasted on the surface of the ITO target with conductive adhesive to achieve partial coverage of the ITO target. The composite coating was prepared by magnetron sputtering under argon atmosphere. The coverage area ratio of flake MgF ₂ to the ITO substrate target is about 15% to 20%, which directly affects the proportion of MgF ₂ in the composite coating.

Since the composite coating is made of a mixture of ITO and MgF ₂ materials, although MgF ₂ accounts for a small proportion, it will still be denatured due to the oxidation of atomic oxygen. At the same time, the refractive index of ITO is about 1.7 to 1.9. Although a small amount of MgF ₂ is mixed in, the overall refractive index of the composite coating is still significantly higher than that of the cover glass, so this composite coating cannot be used for the cover glass. Bring good anti-reflection effect.

To sum up, the above-mentioned composite coating is not suitable for the radiation-resistant glass cover slips used in space. There is a need to propose a new type of surface film that is both resistant to atomic oxygen shielding and capable of providing good anti-reflection effects for the cover slip.

Contents of the invention

The problem to be solved by the present invention is to provide a design and preparation method of a surface film with atomic oxygen protection function, which is especially suitable for the surface film of the radiation-resistant glass cover sheet used in space, and solves the problem of MgF2 film _on the surface of the radiation-resistant glass cover sheet. The problem of oxidative denaturation by atomic oxygen in the LEO orbital.

In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is: a surface film with atomic oxygen protection function, including two layers of film H _SiO2 and L _SiO2 , its structure is as follows: AIR∣H _SiO2 L _SiO2∣GLASS , AIR is Incident medium, H _SiO2 is a SiO ₂ film with a refractive index of 1.45±0.01, with a thickness of 20±1nm, L _SiO2 is a SiO ₂ film with a refractive index of 1.28±0.02, with a thickness of 95±5nm, and GLASS is a film doped with ceria glass cover slip.

Further, the thickness of the H _SiO2 SiO ₂ film is 20 nm, and the refractive index is 1.45.

Further, the thickness of the L _SiO 2 SiO ₂ film is 95 nm, and the refractive index is 1.28.

Further, the incident medium is air or vacuum.

A method for preparing a surface film with an atomic oxygen protection function, using electron beam thermal evaporation to deposit two layers of film on a cover glass layer by layer, comprising the following steps:

(1) The glass coverslip is cleaned and pretreated;

(2) Deposit the first layer of L _SiO2 film on the cover glass, using an oblique deposition method, the angle between the deposition direction of the evaporation source and the cover glass is 15°±2°, and the thickness of the first layer of L _SiO2 film deposited is 95± 5nm, the refractive index is 1.28±0.02, no baking heating in the vacuum chamber;

(3) The physical thickness and refractive index of the deposited first layer of L _SiO2 film at the reference wavelength are measured by spectroscopic ellipsometer;

(4) Deposit the second layer of H _SiO2 film on the first layer of L _SiO2 film, using the normal deposition process method, the angle between the direction of the evaporation source and the glass cover is 75 ° ± 2 °, the second layer of deposition H _SiO2 The thickness of the film is 20±1nm, the refractive index is 1.45±0.01, it is baked and heated to 150°C in a vacuum chamber, and an ion source is used for assisted deposition during the deposition process;

(5) Spectroscopic ellipsometer is used to measure the physical thickness and lower refractive index of the deposited second layer of H _SiO2 film under the reference wavelength;

(6) After the coating is completed, use a spectrophotometer to measure the transmittance curve of the cover glass in the range of 280nm to 1800nm.

Wherein, the evaporation source is SiO ₂ particles, and the reference wavelength in step (3) and step (5) is 628nm.

The advantages and positive effects of the present invention are: due to the adoption of the above technical scheme, the main material of the prepared surface film is SiO ₂ , which will not be denatured due to oxidation by highly active atomic oxygen, and the chemical stability of the surface film is improved. At the same time, the film is specially designed for the radiation-resistant glass cover used in space. The refractive index of the material matches well with the glass cover. The transmittance of the coated cover is high, which is conducive to improving the working efficiency of solar cell modules. .

Description of drawings

Figure ₁ is the transmittance curve of the actually prepared glass cover slip deposited with 1/4 wavelength optical thickness of MgF2 and _SiO2

Fig. 2 is a schematic diagram of the surface film structure of the present invention with atomic oxygen protection function

Fig. 3 is the oblique deposition L _SiO of the present invention Film layer schematic diagram

Fig. 4 is the normal process deposition H _SiO of the present invention Film layer schematic diagram

Figure ₅ is the transmittance curve of the actually prepared MgF2 cover glass deposited with 1/4 wavelength optical thickness and the cover glass deposited with a surface film with atomic oxygen protection function

In the picture:

1. Substrate 2. Cover glass 3. Evaporation source deposition direction

4. Evaporation source

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

In order to solve the problem that the MgF2 film _on the surface of the radiation-resistant glass cover is oxidized and denatured by the atomic oxygen in the LEO orbit, the present invention provides a design and preparation method of a surface film with the protection function of atomic oxygen, which is suitable for the space radiation-resistant glass cover use. Among them, a surface film with atomic oxygen protection function, the design of the surface film adopts the composite film design, including H _SiO2 and L _SiO2 two-layer film, its structure is as follows: AIR∣H _SiO2 L _SiO2∣GLASS , as shown in Figure 2 AIR is the incident medium, and the incident medium is air or vacuum; H _SiO2 is a SiO ₂ film with a refractive index of 1.45±0.01, with a thickness of 20±1nm; L _SiO2 is a SiO ₂ film with a refractive index of 1.28±0.02, with a thickness of 95±5nm; GLASS is a cover glass doped with ceria. Preferably, the H _SiO2 SiO ₂ film has a thickness of 20 nm and a refractive index of 1.45. Preferably, the L _{SiO2 SiO2} film has a thickness of 95 nm and a refractive index of 1.28.

Using oxides to prepare reflective films on the surface of glass coverslips can avoid the problem of being oxidized by atomic oxygen, but SiO ₂ has the lowest refractive index among common oxide film materials, with a refractive index of 1.45. If the SiO ₂ anti-reflection film is prepared by using the normal process, the effect of the anti-reflection film will be reduced. As shown in Figure ₁ , the figure shows the transmittance curve of the actually prepared glass cover glass deposited with 1/4 wavelength optical thickness of MgF2 and _SiO2 , in the wavelength range of 400nm to 1100nm (this wavelength range is silicon The working wavelength range of the solar cell is also an important working wavelength range of the triple-junction gallium arsenide solar cell) and the average transmittances of the two are 94.38% and 93.65% respectively. Therefore, it is necessary to prepare a SiO ₂ film with a low refractive index, which will not be denatured by atomic oxygen oxidation, and which matches the refractive index of the cover glass and has a good transmission effect.

The preparation method of the surface film with atomic oxygen protection function is to deposit two layers of film on the cover glass layer by layer by means of electron beam thermal evaporation, including the following steps:

(1) The glass coverslip 2 is cleaned and pretreated;

(2) Deposit the first layer of L _SiO on the cover glass ₂ Thin film, in order to obtain the SiO of low refractive index Thin film, adopt oblique deposition mode, as shown in Figure 3, between evaporation source 4 deposition direction 3 and glass cover 2 The included angle is 15°±2°, that is, to reduce the included angle between the deposition direction 3 of the evaporation source 4 and the cover glass 2, and deposit the first layer of L _SiO2 film with a thickness of 95±5nm and a refractive index of 1.28±0.02 in a vacuum Indoor heating without baking. Depositing the thin film by oblique deposition can increase the porosity of the thin film, thereby reducing the effective refractive index of the thin film; during oblique deposition, the vacuum degree of the vacuum chamber is 2.5×10 ^-3 Pa.

(3) The physical thickness and refractive index of the deposited first layer of L _SiO2 film at the reference wavelength are measured by spectroscopic ellipsometer;

(4) Due to the large porosity of the L _SiO2 film obtained by oblique deposition, in order to make the film firmer and reduce the adsorption of impurity gases and water vapor, a second layer of H _SiO2 film is deposited on the first layer of L _SiO2 film , using the normal deposition process method, as shown in Figure 4, the angle between the evaporation source direction 3 and the cover glass 2 is 75°±2°, the thickness of the second layer deposited H _SiO2 film is 20±1nm, and the refractive index is 1.45±0.01, baked and heated to 150°C in a vacuum chamber, and an ion source was used for auxiliary deposition during the deposition process. This layer of film mainly plays a protective role, protecting the first layer of L _SiO2 film from being hit by space atomic oxygen and causing surface cracking and turtles. Cracking, partial combustion and melting; during pre-deposition, the vacuum degree of the vacuum chamber is 3.0×10 ^-3 Pa, the medium gas is argon, the ion energy is 80eV, and the beam current is 5A.

When using an ion source to assist deposition: the inert gas is ionized to form ions, and the ions are accelerated by an electric field and then bombard to the cover glass 2 . The ion bombardment provides sufficient kinetic energy to the film material particles reaching the cover glass 2, thereby improving the mobility of the deposited particles, increasing the aggregation density of the film layer, and filling the void defects in the film. (5) The thickness and the lower refractive index of the deposited second layer of H _SiO2 film at the reference wavelength are measured by spectroscopic ellipsometer;

(6) After the coating is completed, measure the transmittance curve of the cover glass 2 in the range of 280nm-1800nm with a spectrophotometer. As shown in FIG. 5 , the average transmittance of the cover glass 2 deposited with the surface film in the range of 400nm-1100nm is 95.11%, which is better than the 94.38% of the cover glass of MgF ₂ .

Wherein, the evaporation source 4 is made of SiO ₂ particles with a diameter of 2mm-4mm. The reference wavelength in step (3) and step (5) is 628nm.

The surface film is prepared on the cover glass doped with cerium oxide. The average transmittance of the cover glass is 92.2% in the range of 400nm-1800nm, and the cut-off absorption wavelength is 330nm. The prepared surface film is in the range of 400nm-1100nm. The average transmittance is 95.11%, forming a good match with the cover glass, and the transmittance of the cover glass after coating is relatively high.

The advantages and positive effects of the present invention are: due to the adoption of the above technical scheme, the main material of the prepared surface film is SiO ₂ , which will not be denatured due to oxidation by highly active atomic oxygen, and the chemical stability of the surface film is improved. At the same time, the film is specially designed for the radiation-resistant glass cover used in space. The refractive index of the material matches well with the glass cover. The transmittance of the coated cover is high, which is conducive to improving the working efficiency of solar cell modules. .

An embodiment of the present invention has been described in detail above, but the content described is only a preferred embodiment of the present invention, and cannot be considered as limiting the implementation scope of the present invention. All equivalent changes and improvements made according to the application scope of the present invention shall still belong to the scope covered by the patent of the present invention.

Claims (7)

1. a kind of surface film with elemental oxygen safeguard function, it is characterised in that：Including double-layer filmses H_SiO2And L_SiO2, its knot Structure is as follows：AIR∣H_SiO2 L_SiO2∣ GLASS, the AIR be incident medium, described H_SiO2For refractive index 1.45 ± 0.01 SiO₂Film layer, thickness is 20 ± 1nm, the L_SiO2For the SiO of refractive index 1.28 ± 0.02₂Film layer, thickness is 95 ± 5nm, described GLASS is the cover glass mixed with ceria.

2. the surface film with elemental oxygen safeguard function according to claim 1, it is characterised in that：Described H_SiO2SiO₂Thicknesses of layers is 20nm, refractive index 1.45.

3. the surface film with elemental oxygen safeguard function according to claim 1, it is characterised in that：Described L_SiO2SiO₂Thicknesses of layers is 95nm, refractive index 1.28.

4. the surface film with elemental oxygen safeguard function according to claim 1, it is characterised in that：Described incident Jie Matter is air or vacuum.

5. a kind of method of the surface film with elemental oxygen safeguard function prepared described in claim 1, it is characterised in that：Adopt With the mode of electron beam evaporation by the double-layer filmses layer by layer deposition to the cover glass, comprise the steps：

(1) cover glass carries out cleaning pretreatment；

(2) ground floor L is deposited on the cover glass_SiO2Thin film, using inclined deposition mode, evaporation source deposition direction and institute It is 15 ° ± 2 ° to state the angle between cover glass, the deposition ground floor L_SiO2Film thickness is 95 ± 5nm, and refractive index is 1.28 ± 0.02, without Baking out in vacuum room；

(3) using spectroscopic ellipsometers to the deposition ground floor L_SiO2Physical thickness and refractive index of the thin film under reference wavelength enters Row measurement；

(4) in the ground floor L_SiO2Second layer deposition H is deposited on thin film_SiO2Thin film, using normal sedimentation process, evaporation Angle between source direction and the cover glass is 75 ° ± 2 °, and the second layer deposits H_SiO2The thickness of thin film is 20 ± 1nm, Refractive index is 1.45 ± 0.01, and to 150 DEG C, ion source carries out assistant depositing to Baking out used in deposition process in vacuum room；

(5) using spectroscopic ellipsometers to the deposition second layer H_SiO2Physical thickness and lower refractive index of the thin film under reference wavelength Measure；

(6) after the completion of plated film, the absorbance using spectrophotometer measurement cover glass in the range of 280nm~1800nm is bent Line.

6. the method that preparation according to claim 5 has the surface film of elemental oxygen safeguard function, it is characterised in that：Institute The evaporation source stated is SiO₂Granule.

7. the method that preparation according to claim 5 has the surface film of elemental oxygen safeguard function, it is characterised in that：Institute It is 628nm to state the reference wavelength in step (3) and step (5).