RU2525633C1 - Solar battery for small-size spacecrafts and method of its manufacturing - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: result is achieved by increasing strength of connection of shunting diodes and solar elements, increased repeatability of the process of manufacturing of the solar battery of spacecrafts due to optimisation of the technology of manufacturing of shunting diodes and solar elements of the solar battery, and also switching buses that connect the solar elements and shunting diodes, which are made as multi-layer. The solar battery for small-size spacecrafts comprises the following: panels with modules with solar elements (SE) adhered to them, a shunting diode; switching buses that connect the face and reverse sides of the shunting diodes with solar elements, at the same time the shunting diode is installed in the cut in the corner of the solar element, at the same time switching buses are made as multi-layer, made of molybdenum foil, at two sides of which there are serial layers of vanadium or titanium, a layer of nickel and a layer of silver, accordingly.

EFFECT: increased resistance of solar batteries to thermal shocks, to impact of mechanical and thermomechanical loads, increased manufacturability of design, extended active life of a solar battery of spacecrafts, increased functional capabilities due to expansion of temperature range of functioning and optimisation of design of a solar battery, simplification of a switching system.

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Description

Technical field

The invention relates to electrical engineering, in particular to devices for generating electrical energy by converting light radiation into electrical energy, and can be used in the design and manufacture of small spacecraft with solar batteries (SB).

State of the art

The following requirements are imposed on the SB: maximum energy efficiency with a minimum mass, preservation of electrical and mechanical characteristics during storage, transportation on Earth and putting into the designed orbit, long term active life (CAC) in orbit with minimal degradation, which is expressed in loss of power. In modern SB, SAS reaches 15 years and demands are made to increase it to 20 years.

The main causes of degradation in orbit are disturbances in the structure of active elements, namely photoconverters (FPs) and diodes under the influence of radiation, as well as disturbances resulting from the effects of temperature changes and thermal cycles. In different orbits, the temperature range and the frequency of thermal cycles are different. For operating conditions in the geostationary orbit, the upper temperature value is + 100 ° C, the lower one is 170 ° C, the number of thermal cycles is 2000. In low orbits, the temperature range is less, the upper value is + 100 ° C, the lower one is 100 ° C, but the number of thermal cycles in the duration of the active life in orbit is several tens of thousands.

From the prior art it is known (see N. S. Rauschenbach. The principles and technology of photovoltaic energy conversion. New York, 1980) that the SB consists of separate generators, including chains of solar cells (SE), inside the generators counter-parallel to the solar elements set bypass diodes. In addition to shunt diodes, to ensure reliable operation of the SB, diode protection is used, which is provided by blocking diodes.

In recent years, silicon has been replaced by more efficient solar cells, including several cascades of heterojunctions based on AzB5 compounds grown on a germanium substrate (see PR Sharps, M. A. Stan, DJ Aiken, B. Clevenger, JS Hill and NS Fatemi. High efficiebcy, multi-junction cells with monolithic bypass diodes, NASA / CP.2005-213431. Page 108-115). Each such SC is protected by a diode located with the SC in the same plane, and the diode has the same thickness as the SC. Typically, SCs are made at the corners of the slices in which the triangular diode is placed (see US patents for inventions US 6353176, US 6034322 and US application for invention US 2008/0000523).

The prior art solar spacecraft battery located on a carbon fiber honeycomb panel. The bearing part of the honeycomb panel consists of two layers of carbon fiber, between which there is a honeycomb made of aluminum foil. An electrically insulating film is glued to the carbon fiber surface intended for the installation of solar cells. The power generating part of the solar battery (modules) consists of solar cells connected in series or in series-parallel to each other using switching elements with thermomechanical compensators. A glass plate is glued onto the front surface of each solar cell (see GLOBASTAR. Solar Generator Desigh And Layout For Low Earth Orbit Application in Consideration Of Commercial Aspects And Quanlity Production. D-81663 Munich Germany).

The disadvantages of the known solar battery of spacecraft include low technological design, low temperature range of operation due to the low strength of soldered and welded joints of shunt diodes and solar cells. The high probability of damage to the inter-element switching that protrudes above the front surface of the SB during its manufacturing and routine maintenance, as well as the technological complexity of manufacturing the inter-element switching, due to the need to place thermomechanical compensators in the narrow interelement gaps, leads to the low resistance of the SB to the effects of thermal and mechanical loads .

The closest in technical essence and the achieved effect technical solution (prototype) is the solar battery of spacecraft, containing panels with modules glued to them, consisting of series or series-parallel-connected with the help of switching buses SE, where the switching buses are equipped with thermomechanical compensators, and the front surface of each solar cell is glued a protective glass plate, which is equipped with an additional frame glued to a flat or curved surface They have elastic elements with a given shape and size, where the internal volume of the elastic elements is filled with sealant with the formation of a convex meniscus, and the SEs are pressed to the elastic elements and fixed motionless, and the switching buses with thermomechanical compensators and shunt diodes are welded or soldered to the back contacts of the SE in the zones, free of sealant, and thermomechanical compensators are located between the back side of the solar cell and the supporting surface of the frame in areas free of sealant (see patent of the Russian Federation for the invention RU 2250536).

The disadvantages of the known solar battery of spacecraft include low technological design, low temperature range of operation due to the low strength of soldered and welded joints of shunt diodes and solar cells, poor resistance of the SB to mechanical and thermomechanical loads. A molybdenum tire, 50 microns thick and having a multi-layer special coating, is very stiff. When connecting switching buses by welding, the electrical characteristics of shunt diodes deteriorate, and in some cases, due to a rigid bus, the welding point breaks out with silicon, which leads to a low yield of crystals after thermal cycling tests. At elevated temperatures, degradation of the solar cells occurs after soldering and welding, which leads to delamination of the contacts from the solar cells and, as a result, the SB cells become out of operation.

The prior art method for the manufacture of SB spacecraft with a shunt diode, including the manufacture of SC based on a photovoltaic semiconductor substrate, the formation of shunt diodes on the front side of the SC, the connection of shunt diodes and SC SC spacecraft, connection using commutating buses SE (see US patent US6666507).

The disadvantages of this method include the low reproducibility of the manufacturing process due to the high probability of peeling (loss of adhesion) of metallization on the working and non-working sides. In addition, when connecting the switching buses by welding, it is possible to close the layers of the structure with the switching bus, and the welding point breaks out together with the substrate structure, which leads, as a result, to a low yield of crystals after thermal cycling tests.

The technical solution closest in technical essence and the effect achieved (prototype) is a method for fabricating SB spacecraft with an integrated shunt diode, which includes fabricating solar cells based on a photoelectric semiconductor substrate with recesses for placing discrete shunt diodes, manufacturing discrete shunt diodes based on a semiconductor substrate, mounting discrete shunt diodes into recesses, contacting solar cells with shunt diodes with help Strongly switching tires (see. US patent US 5,616,185).

The disadvantages of the known manufacturing method include the low reproducibility of the manufacturing process due to the high probability of peeling (loss of adhesion) of metallization during the formation of metallization on the non-working side. In addition, when cutting into crystals on silicon single-crystal substrates, cracks form, and when connecting busbars by welding, the welding point breaks out with silicon, which leads, as a result, to a low yield of crystals after thermal cycling tests (thermal shock).

Disclosure of invention

The technical result of the claimed invention is:

- increasing the resistance of the SB to thermal shock, to the effects of mechanical and thermomechanical loads, increasing the manufacturability of the structure, increasing the active life of the SB of spacecraft, increasing the functionality by expanding the temperature range of operation and optimizing the design of the SB,

- simplification of the switching system, which is achieved by increasing the strength of the connection of shunt diodes and solar cells,

- increasing the reproducibility of the manufacturing process of SB spacecraft by optimizing the manufacturing technology of shunt diodes and SC SB, as well as switching buses connecting SC and shunt diodes, which are multilayer.

The technical result of the claimed invention is achieved by the fact that the solar battery of small spacecraft contains:

- panels with solar modules (SE) glued to them,

- shunt diode;

- switching buses welded to the front and back sides of the shunt diodes and connecting the front and back sides of the shunt diode with the SC, while the shunt diode is installed in a cutout in the corner of the SC,

in this case, the switching buses are multilayer, consisting of molybdenum foil, on both sides of which a layer of vanadium or titanium, a layer of nickel and a layer of silver are successively applied.

In a preferred embodiment, the thickness of the molybdenum foil is 8-12 microns, the total thickness of the layers of vanadium or titanium and nickel is 0.1-0.3 microns, the thickness of the silver layer is 2.7-6 microns.

A method of manufacturing a solar battery for small spacecraft includes:

- manufacture of solar cells (SC) based on a photovoltaic semiconductor substrate with a cutout in the corner under the shunt diodes,

- manufacture of shunt diodes based on a photoelectric semiconductor substrate,

- manufacture of commutation tires,

- welding of switching buses to the front and back sides of the shunt diodes,

- installation of shunt diodes in the cutout in the corner of the solar cell,

- connection of SC with shunt diodes using commutating

tires

at the same time, the switching buses are made of multilayer molybdenum foil, on both sides of which a layer of vanadium or titanium, a layer of nickel and a layer of silver are successively applied.

In a preferred embodiment, a vanadium or titanium layer, a nickel layer and a silver layer are successively applied on both sides to the prepared molybdenum foil by vacuum magnetron sputtering at a temperature of molybdenum foil of 110-130 ° C with preliminary ion bombardment, and a molybdenum foil with formed vanadium or titanium layers, Nickel and silver are annealed in vacuum at a temperature of 300-350 ° C.

Brief Description of the Drawings

The features and essence of the claimed invention are explained in the following detailed description, illustrated by the drawings, which show the following.

Figure 1 shows the SC with side mounted using a switching bus by a shunt diode.

Figure 2 schematically shows the layered structure of the switching

tires.

Figure 3 presents the algorithm of the method of manufacturing SB SC.

Figure 4 presents the values of internal mechanical stresses calculated from experimentally measured strains in the metal layers of the switching buses formed at different temperatures of the molybdenum foil.

Figure 4 on the graphs in parentheses indicates the optimal operating temperature range of the molybdenum foil during spraying. Figure 1 indicates the following:

1 - shunt diode;

2 - a switching bus connecting the front side of the shunt diode (1) with SC (4);

3 - a switching bus connecting the back side of the shunt diode (1) with SC (4);

4 - solar cell (SE);

Figure 2 indicates the following:

5 - prepared molybdenum foil;

6 - a layer of vanadium or titanium;

7 - nickel layer;

8 - a layer of silver.

The implementation and example implementation of the invention

The claimed method was used in the implementation of a group technology for manufacturing solar panels of spacecraft and consists of the following sequence of technological operations (see Fig. 3): solar cells are manufactured on the basis of a photovoltaic semiconductor substrate, shunt diodes are manufactured on the basis of a photovoltaic semiconductor substrate, the manufacture of switching buses , including the preparation of molybdenum foil and metallization of the prepared molybdenum foil by the method in vacuum magnetron sputtering on both sides with layers of vanadium, nickel and silver at a temperature of molybdenum foil 110-130 ° C with preliminary ion bombardment, then annealing the molybdenum foil with formed layers of vanadium or titanium, nickel and silver in vacuum at a temperature of 300-350 ° C weld the switching buses to the shunt diodes, test the shunt diodes for thermal cycling and thermal shock, connect the solar cells to the shunt diodes with the help of switching buses and carry out the output control l solar spacecraft.

The thickness of the molybdenum foil was selected based on the greatest pull-out force of the welded switching bus to the front and back sides of the shunt diode after thermal shock tests.

The separation force of the welded commutating bus from the shunt diode was determined as follows: molybdenum foil was prepared in several stages, after which the molybdenum foil was thinned to the following thicknesses: 6 ± 0.1 μm, 7.5 ± 0.1 μm, 10 ± 0.1 μm, 13 ± 0.1 μm. Then, on the prepared molybdenum foil by the method of vacuum magnetron sputtering, layers of vanadium, nickel and silver were applied on both sides at a molybdenum foil temperature of 110-130 ° C with preliminary ion bombardment.

After that, the molybdenum foil with the formed layers of vanadium or titanium, nickel and silver was annealed in vacuum at a temperature of 300-350 ° C and cutting of the busbars was made of molybdenum foil. After that, control welding of the switching buses to the front and back sides of the shunt diodes was performed and the effort of separation of the switching buses from the shunt diodes was controlled (see Table 1).

Table 1 The thickness of the molybdenum foil, ± 0.1 μm 6 7.5 10 13 The effort of separation of the switching bus from the shunt diode, g Front side 25-50 110-125 110-130 100-125 back side 25-50 > 150 > 150 <25

Then, tests were carried out on the thermal shock of the welded switching busbars to the shunt diodes, which consisted of 450 thermal shock cycles from a temperature of -180 ° C (liquid nitrogen vapor) to 120 ° C on specialized equipment. After that, the electrical parameters of the shunt diodes were measured, which showed a slight increase in forward voltage against the background of constant values of leakage currents and reverse voltage. Then, the effort of separation of the switching buses from the shunt diodes was controlled (see Table 2).

table 2 The thickness of the molybdenum foil, ± 0.1 μm 6 7.5 10 13 The effort of separation of the switching bus from the shunt diode, g Front side 25-50 100-125 > 125 100-125 back side 50-75 > 150 > 150 > 125

As a result of the tests, an increase in the separation force of all variants of the thickness of the switching buses from the shunt diodes was revealed with a slight change in the electrical characteristics of the shunt diodes. Based on table 2, it was found that the optimal thickness of the molybdenum foil is 10 ± 0.1 μm, since the maximum force of separation of the bus from the shunt diode is provided.

The temperature of the molybdenum foil during the technological operation of metal deposition was chosen based on the minimum stresses in the resulting structure (see figure 4). Internal stresses were determined as follows: single-cantilever microbalks were formed by magnetron sputtering of V-Ni-Ag metal films on prepared molybdenum foil with photolithography and plasma-chemical etching of metals. The obtained samples of single-console microbeams were examined using an Axio Imager Carl Zeiss optical microscope at a magnification of 6000x. We measured the dimensions of the beam structure and the direction of deformation. The shape of the deformation was determined by the deviation of the microbeams at various points of its length from the surface. After that, using mathematical processing according to the Stoney formula, the voltage values of the beams were calculated. The beam curvature was found by measuring the deviation of the shank of a single-console microbeam. The indicated modes were chosen based on considerations of the reproducibility of the technological process, which is ensured if the welding point does not break out when connecting busbars by welding (see Table 3).

Table 3 Temperature of molybdenum foil during metallization with vanadium, nickel and silver, ° C The yield of suitable shunt diodes for operations to control the welded joint according to the criterion of separation force,% 25 50-70 70 80-90 90 85-90 120 95-99 150 85-95 180 70-80

According to the proposed design and manufacturing method, SBs were produced for small-sized spacecraft, which included frameless shunt diodes of a triangular shape with a reverse voltage of 100 V and a direct current of 2 A and cascade photoconverters based on A ₃ B ₅ compounds.

Prior to the use of the claimed technical solution, silver switching buses were used, which were welded to the shunt diodes and solar cells. Testing of diodes showed low resistance to thermal shock (structure was destroyed after 10-15 thermal shock from -180 ° C to + 100 ° C), and the percentage of suitable diodes in electrical characteristics at the thermal cycling stage was not more than 70% of suitable diodes after assembly, and in the remaining 30% there was a destruction of the structure in the welding zone (interlayer destruction of the basic materials when exposed to elevated and lowered temperatures) while controlling the strength of the welded joint. The force of separation of metallization from the crystal was 50-100 g / mm ² , and after using this technical solution it was more than 150 g / mm ² , as a result of which the percentage of suitable diodes at the stage of thermal cycling increased to 85%.

Claims (7)

1. The solar battery for small spacecraft contains:
- panels with solar modules (SE) glued to them,
- shunt diode;
- switching buses welded to the front and back sides of the shunt diodes and connecting the front and back sides of the shunt diode with the SC, while the shunt diode is installed in a cutout in the corner of the SC,
characterized in that
switching buses are multilayer, consisting of molybdenum foil, on both sides of which a layer of vanadium or titanium, a layer of nickel and a layer of silver are successively applied. 2. The solar battery according to claim 1, characterized in that the thickness of the molybdenum foil is 8-12 microns. 3. The solar battery according to claim 2, characterized in that the total thickness of the layers of vanadium or titanium and nickel is 0.1-0.3 microns. 4. The solar battery according to claim 3, characterized in that the thickness of the silver layer is 2.7-6 microns. 5. A method of manufacturing a solar battery for small spacecraft, including:
- manufacture of solar cells (SC) based on a photovoltaic semiconductor substrate with a cutout in the corner under the shunt diodes,
- manufacture of shunt diodes based on a photoelectric semiconductor substrate,
- manufacture of commutation tires,
- welding of switching buses to the front and back sides of the shunt diodes,
- installation of shunt diodes in the cutout in the corner of the solar cell,
- connection of solar cells with shunt diodes using commutation buses,
characterized in that
the switching buses are made of multilayer molybdenum foil, on both sides of which a layer of vanadium or titanium, a layer of nickel and a layer of silver are successively applied. 6. The method according to claim 5, characterized in that the vanadium or titanium layer, the nickel layer and the silver layer are applied sequentially on both sides to the prepared molybdenum foil by vacuum magnetron sputtering at a molybdenum foil temperature of 110-130 ° C with preliminary ion bombardment. 7. The method according to claim 6, characterized in that the molybdenum foil with the formed layers of vanadium or titanium, nickel and silver is annealed in vacuum at a temperature of 300-350 ° C.

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