Method for producing diamond-like films for encapsulating solar photocells

FIELD: metal science; protection of materials against external and corrosive attacks.

SUBSTANCE: proposed method for producing diamond-like films designed for encapsulating solar photocells to protect them against chemical, radiation, and mechanical damage includes variation of ion kinetic energy, plasma discharge current, and spatial density distribution of plasma incorporating C+, H+, N+, and Ar+ ions by acting upon ion current from radial source with electric field built up by stop-down, neutralizing, and accelerating electrodes. Spatial plasma distribution is checked for uniformity by measuring plasma current density on solar photocell surface whose temperature is maintained not to exceed 80 oC. In the process substrate holder makes complex axial movement in three directions within vacuum chamber. Diamond-like films produced in the process on solar photocell surface area over 110 cm2 are noted for uniformity, difference in their optical parameters variable within desired range is not over 5%.

EFFECT: enhanced adhesive property, microhardness, and resistance of films to corrosive attacks.

5 cl, 12 dwg, 2 tbl

 

The invention relates to science, to protect materials from external and aggressive actions, in particular to the coating of the working surface of the photovoltaic element (SFE) for protection from chemical, radiation, and mechanical destruction.

Known semiconductor SFE with silicon (Si) base p-n junction and bilateral contacts on the illuminated surface of which has encapsulates diamond-like layer [1]. Diamond-like layer is obtained from the plasma flow from the radial ion source consisting of a cylindrical hollow cathode, anode, and an electromagnetic solenoid. Simplicity of design and reliability of this method of producing diamond-like films make it possible to implement it in the vacuum systems of mass production. The disadvantage of this method is the large variability in the density and the kinetic energy of the plasma flow, which excludes the possibility of obtaining uniform encapsulates diamond-like coatings on SFE area of more than 20 cm2.

There is also known a method of applying a high frequency plasma arc and passivating diamond or diamond composite film on the surface of optoelectronic devices (solar cells or photodetectors) [2].

Closest to the claimed image is the shadow method is applied on the substrate coating, including diamond-like films, in which the parameters of the plasma and the substrate voltage are set independently. The voltage on the substrate includes a constant and pulsating with a frequency of 0.1 kHz to 10 MHz components. The substrate performs a planetary motion relative to the plasma sources. You get a multilayer wear resistant coatings with low friction. The optical characteristics of the coatings do not control. The method allows you to get a diamond-like films on flat substrates of large area [3].

The objective of the invention is the obtaining of a homogeneous (with dispersion values of the optical parameters of not more than 5%) of diamond-like films on the surface chemistry of large area (more than 110 cm2with varied within the specified limits of optical parameters, as well as high adhesion, hardness and resistance to aggressive influences.

The problem is solved as follows. Offered in a method of producing diamond-like films (APT) for the encapsulation of solar photovoltaic elements (SFE) to change the kinetic energy of the ions, the current plasma discharge and the spatial distribution of plasma density with the composition of the ions C+N+N+and AG+the impact on the flow of ions from the radial source of the electric field that is formed diaphragmalysis, neutralizes the m and accelerating ring electrodes. The temperature chemistry in the process of encapsulation support above 80° C.

In addition, it is suggested to control the uniformity of the spatial distribution of the plasma by measuring the current density of the plasma on the surface chemistry.

To obtain a diamond-like films with indicator plomley in the range of 1.48-2,60 average kinetic energy of the ions is encouraged in the range from 20 to 140 eV, the current density of the plasma in the range of 0.2 to 0.8 mA· cm-2and the gas mixture for plasma content of the hydrocarbon to maintain in the range from 2% to 40%.

To further increase the uniformity of diamond-like films proposed to carry out triaxial rotation SFE in a vacuum chamber.

To obtain a diamond-like films with a discrete change in the refractive index in the thickness or diamond-like films with a continuous change in the refractive index in thickness, respectively, discrete or continuous change in the process of obtaining films of the kinetic energy of the ions, the current plasma and gas mixture composition.

This is achieved by obtaining a homogeneous single or multilayer diamond-like films with different values of the refractive index in the range of 1.48 to 2.6 and more on the surface chemistry with an area of more than 110 cm2and films with a given variation in the index of prelamin the thickness. Increases adhesion, microhardness, density and decreases the number of defects in the resulting diamond-like thin films. In the field of photosensitivity Si SFE is provided transmittance T>95%, the reflectance R<5%. The obtained diamond film resistant to the effects of moisture, chemically aggressive environments, ultraviolet radiation, but also to the impact of electrons and protons.

Figure 1 schematically shows the ion source and the electrode system to control the plasma.

Figure 2 shows the spatial distribution of plasma density before the introduction of the electrode diafragmalnaya system (curve 1) and after injection (curve 2), where x-axis is the coordinate perpendicular to the axis of the plasma (cm), and the y - axis the current density of the plasma.

Figure 3 shows a schematic front view of the developed system of rotation of the substrate layer 4 is a top view, and figure 5 is a General view with the electrode system.

Figure 6 presents the Raman spectra for the three samples of diamond-like films, where the horizontal axis represents Raman shift, and the vertical axis represents the intensity in arbitrary units.

Figure 7 shows the spectral dependence of the optical reflectivity (R) of diamond-like films on Si surface in different areas of the film area is provided on the top box).

On Fig presents the spectral dependence of the transmittance for each of three samples of diamond-like films on sapphire substrates grown under different technological regimes.

Figure 9 shows the cross section of the front part of the SFE with nanesennoi contact mesh M and the two diamond-like film: APP1and APP2.

Figure 10 shows the spectral dependence of the reflection coefficient of a two layer of diamond-like coatings on Si surface chemistry.

Figure 11 shows the spectral dependence of imperfetto (A/W) sensitivity SFE when illuminated from the back side without enlightening diamond-like coating (curve 1) and with a diamond-like coating (curve 2).

On Fig shows the spectral dependence of imperfetto (A/W) sensitivity of two samples SFE encapsulated diamond-like film before (curves 1 and 2) and after proton irradiation (curves 3 and 4)and without diamond-like film (curve 5).

Shown in figure 1 radial ion constant current source (anode 7, a cylindrical cathode 2, an electromagnetic solenoid 3) is mounted in the vacuum chamber 4. Between the anode 1 and the cylindrical cathode 2 is supplied with a high voltage from a power source within 1÷ 4 kV. Electromagnetic solenoid 3, the formation of a magnetic field perpendicular to the electric is. The plasma is ignited in the gap between the anode 1 and the cylindrical cathode 2 and the output has the form of a truncated cone. Using a grounded electrode, the diaphragm 5 is the deceleration of electrons and clipping ions propagating at an angle of more than 40° in relation to the axis of the plasma. On an additional electrode-Converter 6, located after the electrode-diaphragm 5, the voltage is in the range of 30÷ 50 that provides emission of electrons in the plasma to neutralize the slow ions and medicationabana radicals (CxHy). As a result, the accelerating electrode 7 enters the ion flux with a small range of energies. The accelerating electrode 7 with a grid 8 with hole sizes of 0.3÷ 0.5 mm, allowing to adjust the average values of the kinetic energies of the ions reaching the surface chemistry 9 on polictial 10. Using the power supply to the accelerating electrode 7 and polictial 10 is fed a negative offset -50÷ 400 In that allows you to control the value of the average kinetic energy of the ions within a 20÷ 150 eV. Through the pipe 11 in the chamber 4 is created preliminary vacuum of 10-3PA.

The original (i.e. without the use of additional electrodes) spatial distribution of current density of approximately described by a Boltzmann function (figure 2., kr). Only near the axis m is tenderly to allocate land area of 10÷ 15 cm2within which the dispersion does not exceed 10%. The use of additional electrodes (diafragmicheskogo, neutralizing and pull) dramatically improves the situation. The density distribution of the plasma acquires a geometric shape of a cylinder with a diameter of 12 cm with a range of density values not exceeding 10% (figure 2, CR). Inside the plasma, the dispersion in the average kinetic energies of the ions C+H+N+and Ar+not exceed 10%. The ratio of the concentrations of these ions varies depending on the initial concentrations of vapours C7H8and gases Ar, N2in the mixture supplied to the ion source.

To increase the uniformity of diamond-like films with a range of mechanical and optical parameters of the film are less than 5% within the surface area of application S≥ 110 cm2and increase the performance of the process, in addition to the above, the system of electrodes and diaphragms developed a system of rotation of podarkticules. Figure 3 shows a schematic representation of the system (front view)figure 4 - top view, and figure 5 is a General view together with a system of electrodes. Primary vertical axis 12 is driven by electric actuators. This ensures that the movement of the mutually perpendicular horizontal axes 13, around which, in turn, rotate the four disk 14. The movement of the disk is in, leads to an additional rotation around their axes attached to the disks of podarkticules 10, which in the end make complex movement relative to the fixed base 15. The speed of the system is maintained within the range of about 10-30./minutes figure 5 also shows the configuration of the plasma 16, the resulting impact of the system of electrodes and diaphragms 5-8, shown in figure 1. Developed a system of spins allows to realize the optimal path of movement of the substrate, ensuring the passage of the substrate through all zones of the plasma flow. Thereby is achieved by the additional uniformity of the deposited diamond-like coating. In addition, the system allows to vary the residence time of the substrate in the area of plasma and abroad and to provide the necessary cooling of the substrate. The surface temperature of the substrate depending on the mode of deposition is in the range 30-80° without the use of other cooling methods.

Obtained using the described technology films are high-quality diamond-like material. Figure 6 presents the Raman spectra of diamond-like films deposited at three different technological regimes and with different thickness: CR d=240 nm, CR d=540 nm and CR d=840 nm. The position of the maxima shows that in the resulting diamond-like films dominate sp3connection.

Achieved with the help used in the invention of homogeneous elements is here optical parameters of diamond-like films is illustrated in Fig.7, which shows the spectral dependence of the optical reflectivity (R) of diamond-like films on Si surface in different areas of the film (the area shown in the inset). It is seen that all parts of the surface with an area of more than 110 cm2the spectral dependence of the R almost the same. The density of diamond-like films in different zones have spread less than 5%, as well as the values of R.

Variations of the current and energy of the ion beam, and the composition of the gas mixture in the chamber allow you to control the properties of the synthesized diamond-like films. Table 1 presents the main parameters characterizing technological conditions obtaining on the surface chemistry of diamond-like films with a thickness of from 60 to 900 nm: Uacthe voltage between the anode 1 and the cylindrical cathode 2 of the ion source, Iac- current plasma discharge between them, Ub- the offset to pull the electrode-diaphragm 7 and polictial 10, <Ek> is the average value of the kinetic energy of the plasma ions reaching the surface chemistry 9, n is the density of the plasma current on the surface chemistry 9, Ipthe refractive index of the deposited diamond-like films, HV - value of micro-hardness diamond-like film. The gas mixture (C7H8N2Ar) in all cases was 55% Ar, the remaining 45% were C7H8and N 2.

Table 1 shows the proportion With7H8.

Table 1
C7H8, %UAC, kVIacmAUbIn<Fk>eVIpmA/cm2nHV kgf/mm2
352,530-300900,201,482500
282,635-3501000,252,002750
242,840-4001400,302,102700
182,280-250600,602,403000
122,3100-300650,652,452950
152,4120-350800,802,353100
101,545-20200,352,552900
81,850-50250,402,602850
42,060-100500,45to 2.572800

As can be seen from the table, the choice of the mode of deposition of the film, characterized by the composition of the gas mixture, the average kinetic energy of the ions in the plasma <Ek> and current density plasma Ipon the surface chemistry, receive a diamond-like films with different values of microhardness HV (2500÷ 3100 kgf/mm2) and refractive index (1,48÷ 2,60). The density of the films varies in the range 1.8÷ 2.35 g/cm3they have a minimum of microdefects and internal stress, high adhesion, and very small values of the friction coefficients. This, in combination with high hardness, high mechanical resistance encapsulates diamond-like film.

Film with a lower refractive index obtained when the ratio of C7H8:N2=40:5 and when the ion energy is not higher than 140 eV. At higher ratio of C7H8:N2films have unacceptably high absorption. At an energy in excess of 140 eV, ions lead to the degradation of the properties of SFE.

When the ion energy is less than 20 eV is observed such a high value is e of the refractive index films, that film unsuitable for enlightenment SFE.

Current reduction of plasma to less than 0,20 mA/cm process performance thin film deposition decreases. Current increases plasma ions to a value of more than 0.80 mA/cm2the number of defects in the films increases.

Variation of deposition conditions allows you to change the spectral dependence of transmittance of diamond-like films and, consequently, the efficiency of SFE. On Fig curves 1 and 2 show the spectral dependence of the transmittance T of the two samples of diamond-like films having the same thickness d=185 nm, but grown under different technological regimes on sapphire substrates; value T of these films differ by 17% if λ =260 nm. (Transmittance T was determined from the expression: T=I/I0(1-R), where I is the intensity of light transmitted through the diamond-like film, I0- the intensity of light falling on the film, and R is the reflection coefficient of the film). In the wavelength range λ =300-620 nm diamond-like film with a thickness of 185 nm is(Fig, CR), and the width of the forbidden zonethat provides a very small loss on the absorption of solar radiation with wavelengths λ >300 nm. It also provides additional opportunities for uluchsheniya properties of diamond-like films in the ultraviolet region and increase the efficiency of SFE. CR (Fig) corresponds to the diamond-like film with thickness d=240 nm, obtained by the process mode different from the mode for the other two films.

The dependence of the refractive index of diamond-like films from cultivation conditions (current and energy of the ion beam, the composition of the gas mixture) allows to obtain a diamond film with a given change in the refractive index n thickness, i.e. either a multilayer structure with a discrete change in n or films with a continuous change in n on the layer thickness. For example, figure 9 shows a cross-section of the front part of the SFE coated with a metal contact grid M and two diamond-like film (APT1: n1=2,4, d1=60 nm and APP2: n2=1,6, d2=80 nm). Figure 10 shows the spectral dependence of the reflection coefficient R of the two diamond-like film on the Si surface chemistry obtained by the sequential deposition of diamond-like layers, first by the middle group of technological modes Table 1 (n1=2,4), and then by the upper group (n2=1,6). After growing the first layer APP1the suspend process and establish a new regime for the application of the second layer APP2. As can be seen from figure 10, the small value of R≤ 5% of diamond-like films in the entire spectral range of photosensitivity Si provides good enlightenment RA is the sight of the Si surface chemistry.

Figure 11 shows that when the wavelength of 0.7 μm imperfecta sensitivity SFE upon excitation from the rear side is covered with the APC increases 1.6 times compared with the value for the uncovered surface, whereas at the expense of enlightenment sensitivity cannot be increased more than 40%. This means that when applying the diamond-like film is significantly reduced surface recombination of Si, leading to increased efficiency more than 40%.

Si SFE with diamond-like films tested following exposure to chemically aggressive environments:

1) Stay in the concentrated acid NGO3when temp° C for 30 min;

2) stay in a 1% solution of acid NGO3at a temperature of 25° C for 1 hour;

3) Stay in the concentrated acid, H2SO4when temp° C for 30 min;

4) stay in a 1% solution of acid (H2SO4at a temperature of 25° C for 1 hour;

5) Stay in a saturated solution of sodium chloride (imitation sea fog) for 40 hours at a temperature of 25-30° C.

After conducting each test values the efficiency of SFE with diamond-like films are practically indistinguishable from the original (see Table 2). The dispersion efficiency of SFE is within measurement error. The values of efficiency, the reflectance spectra of the visual and con the role of surface chemistry with diamond-like film indicate the stability of the encapsulated diamond-like chemistry in relation to the above effects. SFE encapsulated diamond-like films, stand out from the SFE with antireflection coating of ZnS, the efficiency of which, after the same tests decreased by 30% due to the destruction layer of ZnS.

Table 2
<Ek>eVC7H8,%d, NmEfficiency,%
   Si +APP SFEAfter exposure to moisture, Si+APP SFEAfter chemical exposure, Si+APP SFE
5522809,879,859,78
7016809,719,759,58
6513758,908,938,78
6012859,279,239.28 are
7510859,119,189,14
6514808,828,908,80

Ultraviolet (UV), electron and proton irradiation does not affect the properties of diamond-like films and chemistry, Inc. paliwanag this film.

The UV radiation of the xenon lamp high pressure with radiation spectrum similar to sunlight (but higher than the Sun, shares UV) with a density of 0.5 W cm-2over 400 hours did not lead to changes in the efficiency of SFE with diamond-like protective coating, whereas the SFE with antireflection coating of ZnS efficiency decreased by 15%.

Test conditions for resistance to proton irradiation are selected according to well-known models, for example, NASA AP-8, JPL-91 to perform calculations for various orbits of spacecraft. On Fig shows the spectral dependence enervates sensitivity (efficiency) of the two Si SFE encapsulated diamond-like film before (CR and 2) and after (CR and 4) proton radiation, and chemistry without diamond-like coating (CR). From Fig follows that diamond coatings with a thickness of 1-2 μm sustainable and can serve as a protection against solar protons with energies of 10-500 Kev with a dose of 2· 1012÷5· 1011cm-2corresponding period of 11 years).

Thus, the combined use of the invention is the correction of the spatial distribution of plasma density using special electrodes; a complex three-axis rotation of the substrate; variations of the current and energy of the ion beam, and the composition of the gas mixture allows to solve the problem of powereditor, improve the quality and control of optical properties of diamond-like films of large area.

The variation of density and refractive index film on a surface of at least 110 cm2not exceed 5%. The obtained diamond films have low (2÷ 6%) reflectance, high (~98%) optical transparency, high (up to 3100 kgf/mm2) the micro, small internal stress and good adhesion to the substrate surface. Variations in growing conditions allow to obtain a diamond film with a refractive index in the range of 1.48÷ 2,60 and implement a diamond-like film with a given change in the refractive index across the thickness, i.e. either a multilayer structure with a discrete change in n or films with a continuous change in n on the thickness of the layer.

The parameters of diamond-like films and encapsulated them in silicon chemistry resistant to moisture, chemicals, ultraviolet, proton and electron irradiation. Thus, the diamond-like film is a high-quality reliable encapsulant for chemistry, intended for use on earth and in space.

SOURCES of INFORMATION

1. Patent AM No. 851, H 01 L3 1/02, Ganesan, Agapius, Ctorian, Ukonceno, Aurelian, Yengibaryan, Spokeman. Semiconductor photovoltaic is reobrazovateli, Published in the Official Gazette No. 2, 2000.

2. Patent CN No. 1188160, C 23 C 16/26, G 02 B 1/11, 1998. X.Yiben, J.Jianhua, Sh.Weimin. Making of Optical Anti-Reflection Film by Diamond-Like and Diamond Compound Film.

3. Patent US No. 6372303, C 23 C 016/26, 2002. Burger, Kurt, Weber, Thomas, Voigt, Johannes, Lucas, Susanne. Method and Device for Vacuum-Coating a Substrate.

1. A method of obtaining a diamond-like films for the encapsulation of solar photovoltaic elements (SFE), including receiving in a vacuum chamber of a plasma ion composition C+N+N+and Ar+the change in kinetic energy of the ions, the current plasma discharge and spatial distribution of plasma density, characterized in that the change in kinetic energy of the ions, the current plasma discharge and spatial distribution of plasma density exercise influence on the flow of ions from the radial source electric field generated diaphragmalysis, neutralizing and precipitating ring electrodes, and the temperature chemistry in the process of encapsulation support above 80°C.

2. The method according to claim 1, characterized in that the control of the homogeneity of the spatial distribution of the plasma is performed by measuring the current density of the plasma on the surface chemistry.

3. The method according to claim 1, characterized in that to obtain a diamond-like films with a refractive index in the range of 1.48-2,60 average kinetic energy of the ions is maintained within the range of from 20 d is 140 eV, the current density of the plasma in the range of 0.2 to 0.8 mA·cm-2and the gas mixture for plasma content of hydrocarbon maintained within the range of from 2 to 40%.

4. The method according to claim 1, to 3, characterized in that to obtain a multilayer diamond-like films with a discrete change in the refractive index in the thickness or diamond-like films with a continuous change in the refractive index in the thickness of the discrete or continuous change in the process of obtaining films of the kinetic energy of the ions, the current plasma and gas mixture composition.

5. The method according to claim 1, characterized in that conduct triaxial rotation SFE in a vacuum chamber.



 

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