CN104835882B - Inverted high-efficiency flexible gallium arsenide solar cell and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of solar cells, and specifically discloses a flip-chip high-efficiency flexible gallium arsenide solar cell, which includes an inverted epitaxial layer, the light-receiving surface is located on the upper part, an upper electrode is arranged on the light-receiving surface, and the lower part of the epitaxial layer is sequentially arranged. There are metallized layers and copper-molybdenum-copper flexible substrates. The copper-molybdenum-copper flexible substrates are copper- ^molybdenum -copper three-layer composite materials. The molybdenum layer is 10-20 microns, and the top layer copper is 10-20 microns; the epitaxial layer is an inverted growth structure in the epitaxial wafer. The invention also discloses the preparation method of the battery: bonding the epitaxial wafer and the copper-molybdenum-copper flexible substrate; corroding the peeling layer by the corrosive solution, peeling off the substrate and the buffer layer to expose the light-receiving surface; making an upper electrode above the light-receiving surface, reducing Reflective film. The flip-chip high-efficiency flexible gallium arsenide solar cell of the present invention has the advantages of thin thickness, good flexibility, good heat dissipation, high efficiency, firmness and reliability, and long service life.

Description

A flip-chip high-efficiency flexible gallium arsenide solar cell and its preparation method

technical field

The invention relates to the technical field of solar cells.

Background technique

Gallium arsenide solar cell is a solar cell based on gallium arsenide (GaAs), and its development has a history of more than 40 years. Eg=1.43eV of GaAs material, it is theoretically estimated that the efficiency of GaAs single-junction solar cells can reach 27%. Since the 1980s, GaAs solar cell technology has experienced from LPE to MOCVD, from homoepitaxial to heteroepitaxial , several stages of development from single-junction to multi-junction laminated structures, its development speed is accelerating, and its efficiency is also improving. At present, the highest efficiency in the laboratory has reached 50% (data from IBM Corporation), and the conversion rate of industrial production can reach 30% %above. In the photovoltaic power generation industry, silicon-based photovoltaic cells such as monocrystalline silicon and polycrystalline silicon, which account for more than 94% of the total output, have the highest conversion efficiency of 24.7% in the laboratory, and the conversion efficiency of industrial-scale production is only 18%. %, and the photoelectric conversion efficiency of gallium arsenide solar cells is much higher than that of traditional crystalline silicon materials, and will become the mainstream of the market in some specific occasions (such as aviation, aerospace, wearable devices, etc.).

Single-junction GaAs cells can only absorb sunlight of a specific spectrum, and multi-junction GaAs cells made of Group III and V materials with different band gaps can selectively absorb and convert different subfields of the solar spectrum according to the size of the gap. , can greatly improve the photoelectric conversion efficiency of solar cells. Theoretical calculations show that the limit efficiency of double-junction GaAs solar cells is 30%, the limit efficiency of triple-junction GaAs solar cells is 38%, and the limit efficiency of four-junction GaAs solar cells is 41%.

Compared with silicon-based solar cells, GaAs solar cells have higher photoelectric conversion efficiency, stronger radiation resistance and better high temperature resistance, and are widely used in the field of space energy, such as my country's Shenba spacecraft and The "Tiangong-1" aircraft used triple-junction gallium arsenide solar cells with a conversion efficiency of 26.8%.

GaAs is a direct transition material, while Si is an indirect transition material. In the visible light range, the light absorption coefficient of GaAs material is much higher than that of Si material. Also absorbing 95% of sunlight, GaAs solar cells only need a thickness of 5-10 μm, while Si solar cells need to be greater than 150 μm. Therefore, GaAs solar cells can be made into a thin film type, and the mass can be greatly reduced. However, due to the small thermal conductivity of the substrate material Ge or GaAs of gallium arsenide solar cells, the heat generated inside the chip cannot be dissipated in time during use, which reduces the efficiency of the cell; at the same time, the thickness of the Ge or GaAs substrate is large and the flexibility is poor. It is extremely fragile and inconvenient to use, which limits its actual conversion efficiency and application. If gallium arsenide solar cells can be made into flexible thin-film solar cells, flexible thin-film solar cells can provide electricity for people in various fields of production and life with the help of flexible and portable features, and have broad application prospects.

Copper-molybdenum-copper (CMC) packaging material is a flat composite material with a sandwich structure. It uses pure molybdenum as the core material and is covered with pure copper or dispersion-strengthened copper on both sides. This material has adjustable thermal expansion coefficient, high thermal conductivity, and excellent high temperature resistance, and has been widely used in electronic packaging. Copper-molybdenum-copper materials belong to metal-based flat layered composite electronic packaging materials. The structure of this type of electronic packaging composite material is laminated, generally divided into three layers, the middle layer is a low-expansion material layer, and the two sides are high-conductivity and thermal-conduction material layers .

Contents of the invention

The technical problem to be solved by the present invention is to provide a flip-chip high-efficiency flexible gallium arsenide solar cell and its preparation method with thin thickness, good flexibility, good heat dissipation, high efficiency, firmness and reliability.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a flip-chip high-efficiency flexible gallium arsenide solar cell, which includes an inverted epitaxial layer, that is, the light-receiving surface of the epitaxial layer is located on the upper part; the light-receiving surface is provided with an upper An electrode, a metallization layer and a copper-molybdenum-copper flexible substrate are sequentially arranged below the epitaxial layer, and the copper-molybdenum-copper flexible substrate is a copper-molybdenum-copper three-layer composite material, including bottom copper, middle layer molybdenum and top layer copper; The epitaxial layer is taken from the following epitaxial wafer: the epitaxial wafer includes a substrate, a buffer layer, a peeling layer, and an epitaxial layer from bottom to top. .

Further, the thermal expansion coefficient of the copper-molybdenum-copper flexible substrate is (6-7) X10 ^-6 /°C, including 10-20 microns of bottom copper, 10-20 microns of molybdenum in the middle layer, and 10-20 microns of copper in the top layer.

Further, the peeling layer is N-In _x Ga _(1-x) P, 0<x<1.

Further, an anti-reflection film is also provided on the light-receiving surface of the reversed epitaxial layer.

Further, the antireflection film is composed of an upper silicon dioxide film and a lower titanium dioxide film, the thickness of the silicon dioxide film is 90±10 nm, and the thickness of the titanium dioxide film is 60±10 nm.

Further, the metallization layer is a titanium layer, a silver layer, and a gold layer sequentially from bottom to top.

Preferably, the thicknesses of the titanium layer, the silver layer, and the gold layer are 100 nm, 1000 nm, and 60 nm, respectively.

A method for preparing a flip-chip high-efficiency flexible gallium arsenide solar cell as described above, comprising the following steps,

Step 1. Bonding of the epitaxial wafer and the copper-molybdenum-copper flexible substrate: cleaning the bonding part of the P-side of the epitaxial wafer and the copper-molybdenum-copper flexible substrate, growing a metallized layer on the P-side of the epitaxial wafer, and bonding the metallized layer to the copper-molybdenum-copper flexible substrate The wafers are aligned and pressed, and finally put into the wafer bonding equipment, heated and pressurized to complete the bonding, and the bonded wafers are obtained;

Step 2, removing the peeling layer of the obtained bonding sheet with an etching solution, thereby peeling off the substrate and the buffer layer to expose the light-receiving surface;

Step 3, making an upper electrode above the light-receiving surface.

Further, it also includes step 4, growing an anti-reflection film on the light-receiving surface.

Further, the metallization layer is successively a titanium layer, a silver layer, and a gold layer from bottom to top, and their thicknesses are 100nm, 1000nm, and 60nm respectively, and the gold layer of the metallization layer is aligned with the copper-molybdenum-copper flexible substrate , Compress.

Further, when cleaning in step 1, the epitaxial wafer and the copper-molybdenum-copper flexible substrate are sequentially cleaned by acetone, isopropanol, deionized water, a mixed solution of HCl and H ₂ O with a volume ratio of 1:1, and deionized water; , the bonding temperature is 300-500 degrees, the time is 60-120 minutes, and the pressure is 2-5kg/cm ² .

Further, in step 2, the peeling layer is N-In _x Ga _(1-x) P, 0<x<1, and the etching solution is a mixed solution of HCl and H ₃ PO ₄ with a volume ratio of 3:2.

The beneficial effect of adopting the above technical solution is that: the present invention uses CMC with high flexibility as the base material of the solar cell, which reduces the thickness of the cell, effectively reduces the weight of the cell, and greatly improves the flexibility of the cell. The scope of application is greatly increased, and the use is more convenient.

The electrical and thermal conductivity of CMC is much higher than that of Ge or GaAs substrates in traditional technology, which improves the heat dissipation performance of the substrate. At the same time, its thermal expansion coefficient is controlled at (6~7) X10 ^-6 /°C, which is similar to that of Ge and GaAs materials. , which can ensure that the surface of the solar cell will not be split due to temperature changes during production and use, prolonging the service life of the battery.

At the same time, using CMC, compared with the traditional bonding process, it is not necessary to use expensive Au material as the bonding metal, but choose cheap Ag material for bonding, which greatly reduces the process cost and improves the yield.

The present invention adopts TiO ₂ and SiO ₂ materials as the anti-reflection film, which can obtain a good anti-reflection effect in the range of 400nm-1200nm, effectively reduce the reflectivity of the battery surface, make the short-circuit current gain the highest, and improve product efficiency.

Description of drawings

Fig. 1 is a structural schematic diagram of a flip-chip high-efficiency flexible gallium arsenide solar cell of the present invention;

2 is a schematic structural view of the upper electrode of a flip-chip high-efficiency flexible triple-junction GaAs solar cell in Example 1 of the present invention;

3 is a surface reflectance curve of a flip-chip high-efficiency flexible triple-junction GaAs solar cell in Example 1 of the present invention;

4 is a schematic structural view of a copper-molybdenum-copper flexible substrate of the present invention;

1. Anti-reflection film; 2. Upper electrode; 3. Epitaxial layer; 4. Metallized layer; 5. Copper-molybdenum-copper flexible substrate.

detailed description

The invention aims to solve the technical problems of poor heat dissipation, reduced battery efficiency and inconvenient use of gallium arsenide solar cells in the known technology due to the disadvantages of substrate materials such as Ge or GaAs with small thermal conductivity, large thickness, poor flexibility, and fragility. , using copper-molybdenum-copper (CMC) flexible substrate with high flexibility as the base material of solar cells can reduce the thickness of the battery, effectively reduce the weight of the battery, greatly improve the flexibility of the battery, and has the advantages of convenient use and wide application range. The advantages of long battery life and high efficiency.

In the present invention, the copper-molybdenum-copper flexible substrate 5 is a three-layer composite material. Referring to FIG. 4, it preferably includes 10-20 microns of bottom copper, 10-20 microns of molybdenum in the middle layer, and 10-20 microns of copper in the top layer. The coefficient of thermal expansion is (6-7) X10 ^-6 /°C. The copper-molybdenum-copper flexible substrate 5 in the present invention can be purchased from Yongfu Trading Co., Ltd., Japan.

The epitaxial layer 3 in the gallium arsenide cell epitaxial wafer in the present invention can be a two-junction, three-junction, four-junction or more junction gallium arsenide solar cell structure, which can be selected as required and does not affect the implementation of the present invention.

Taking a triple-junction gallium arsenide solar cell with an inverted structure as an example, a buffer layer, a peeling layer, and an epitaxial layer 3 are respectively grown upward along the substrate, wherein the structure of the epitaxial layer 3 is grown upside down, and N ⁺⁺ - InGaAs contact layer, top cell, middle cell, bottom cell and P ⁺⁺ -GaAs contact layer. The top battery and the middle battery, and the middle battery and the bottom battery are respectively provided with tunnel junction structures to communicate with each other. The epitaxial wafer and the copper-molybdenum-copper flexible substrate 5 are bonded, and the substrate surface of the epitaxial wafer is coated with a metallization layer, aligned with the CMC, and then heated and pressurized in the wafer bonding equipment to complete the bonding of the entire wafer . Select a suitable etching solution to etch and remove the peeling layer, so that the substrate and buffer layer are peeled off to expose the light-receiving surface. Then, according to different processes, the upper electrode 2 and the anti-reflection film 1 are grown on different regions of the light-receiving surface of the epitaxial wafer.

Finally, the CMC-bonded epitaxial wafer can be cut into multiple battery chips as required, and the battery chips can be directly connected in series and parallel with bonding wires so that they can output the required voltage and current.

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

Example 1

A flip-chip high-efficiency flexible gallium arsenide solar cell, see Figure 1, the upper part is the light-receiving surface, which includes an anti-reflection film 1 (anti-reflection layer), an upper electrode 2, an inverted epitaxial layer 3, and a metallization layer from top to bottom. 1. CMC flexible substrate, the material, thickness and composition of each layer are shown in Table 1 below, and the reverse epitaxial layer 3 is the second to the nineteenth layer in Table 1.

Table 1

The method for manufacturing the above-mentioned flip-chip high-efficiency flexible GaAs solar cell uses a triple-junction GaAs solar cell epitaxial wafer with a thickness of 355um±5um, including a substrate, a buffer layer, a lift-off layer, and an epitaxial layer 3 grown upside down. Its structure As shown in Table 2, the epitaxial layer 3 grown in an inverted structure is the third layer to the 20th layer in Table 2.

Table 2

The preparation process goes through the following steps in turn:

1. Substrate transfer.

Wash the epitaxial wafer and the CMC flexible substrate in acetone for 3 minutes, put them in isopropanol for 3 minutes, rinse them with deionized water for 3 minutes, remove the oil on the surface of the epitaxial wafer, and then put in HCl:H ₂ O=1: 1 solution for 1 minute, then rinse with deionized water for 3 minutes to remove the oxide layer on the surface.

Put the epitaxial wafer with a clean surface into the automatic evaporation evaporation table, load the material in the crucible of the equipment, and sequentially evaporate Ti, 1000nm Ag and 60nm Au on the P surface of the epitaxial wafer with a thickness of 100nm. Take out the epitaxial wafer, tightly press and align its evaporation surface and the CMC flexible substrate face to face, and put it into the wafer bonder for bonding. The temperature is 300-500 degrees, the time is 60-120 minutes, and the pressure is 2-5kg/cm ² .

2. Substrate corrosion stripping

After bonding, the wafer thins the substrate to a certain thickness, about 100um. Then use HCl:H ₃ PO ₄ =3:2 (volume ratio) etching solution to remove the InGaP peeling layer. After peeling off, the epitaxial wafer was taken out and washed with flowing deionized water for 3 minutes, and the surface of the wafer was blown dry with a nitrogen gun.

3. Metallization process

After removing the InGaP peeling layer with an etching solution, put the epitaxial wafer into the coating machine, evenly coat the RZJ-390 photoresist on the light-receiving surface, and bake it on a hot plate at 100 degrees for 1 minute, according to the graph in Figure 2 Make a photolithographic plate, and use a photolithography machine to photolithography the light-receiving surface. The photolithography time is 5-8s. Then put the photolithographic epitaxial wafer into the developer solution for 40-60s and develop it in the flowing deionized water. Clean for 3 minutes, blow dry the surface of the chip with a nitrogen gun, put it on a hot plate at 120 degrees and bake for 1 minute, use NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:30 etching solution, etch for 90s Finally, wash in flowing deionized water for 3 minutes, and remove the photoresist on the surface of the light-receiving surface with acetone.

Put the corroded epitaxial wafer into the coating machine, evenly coat the photoresist on the light-receiving surface, put it on a hot plate at 150 degrees and bake for 2 minutes, make a photoresist plate according to the figure in Figure 2, and pass it through the photolithography machine Perform photolithography on the light-receiving surface, the photolithography time is 5-9s, and then place the photolithographic epitaxial wafer on a hot plate at 100 degrees to bake for 1 minute, put it in the developing solution for 40-60s and develop it in the flowing Rinse in deionized water for 3 minutes, and dry the surface of the slide with a nitrogen gun. Etching cleans the impurities in the grid grooves on the light-receiving surface of the epitaxial wafer.

Put the epitaxial wafer into the automatic evaporation evaporation table, load the crucible and tungsten boat of the equipment, and sequentially evaporate AuGeNi with a thickness of 150nm, Ag with a thickness of 5000nm and Au with a thickness of 100nm on the light-receiving surface of the epitaxial wafer. After the vapor deposition is completed, the epitaxial wafer is taken out and soaked in acetone for 15 minutes, and ultrasonicated for 1 minute. Then rinse with flowing deionized water for 3 minutes, and dry the surface of the sheet with a nitrogen gun. After removing the photoresist, a metal electrode in the shape of Figure 2 is formed on the light-receiving surface of the epitaxial wafer.

4. Mesa corrosion

Put the epitaxial wafer with the evaporated electrode into the coating machine, evenly coat RZJ-390 photoresist on the light-receiving surface, put it on a hot plate at 100 degrees and bake for 1 minute, and light the light-receiving surface through the photolithography machine. The photolithography time is 7-10s, and then put the photolithographic epitaxial wafer into the developer solution for 40-60s, and then wash it in the flowing deionized water for 3 minutes, dry the surface of the wafer with a nitrogen gun, and put it on the Bake on a hot plate at 120 degrees for 2 minutes, etch with an etching solution for 10 minutes, wash in flowing deionized water for 3 minutes, and dry the surface of the chip with a nitrogen gun. After etching the mesas, the epiwafer is diced into battery chips.

5. Anti-reflection film 1 coating process

Put the corroded battery on the evaporation plate in the evaporation table, put TiO ₂ and SiO ₂ into the crucible respectively, close the vacuum chamber door, and operate the vacuum on the evaporation table with a degree of vacuum greater than 1.0E-4Pa. TiO ₂ of 60 nm and SiO ₂ of 90 nm were evaporated to complete the evaporation of the antireflection film 1 . The reflectance test on the surface of the battery shows a very good anti-reflection effect as shown in Figure 3.

6. Wire bonding

Use bonding wires to connect in series and parallel directly on the battery chip.

Claims (8)

1. a kind of upside-down mounting high-efficiency soft gallium arsenide solar cell it is characterised in that: include the epitaxial layer (3) that inverts, that is, epitaxial layer sensitive surface is located at top；Described sensitive surface is provided with Top electrode (2), the lower section of described epitaxial layer (3) is sequentially provided with metal layer (4) and copper-molybdenum copper flexible base board (5), described copper-molybdenum copper flexible base board (5) is copper-molybdenum copper 3-layer composite material, including bottom copper, intermediate layer molybdenum and top layer copper；Described epitaxial layer (3) pipettes from following epitaxial wafers: described epitaxial wafer includes substrate, cushion, peel ply, epitaxial layer (3) from bottom to top, and this epitaxial layer (3) is in be inverted growth structure in epitaxial wafer, and that is, sensitive surface is located at peel ply one side；

The thermal coefficient of expansion of described copper-molybdenum copper flexible base board (5) is (6～7) x10^-6/ DEG C, including 10～20 microns of bottom copper, 10～20 microns of intermediate layer molybdenum, 10～20 microns of top layer copper；

Described metal layer (4) is followed successively by titanium layer, silver layer, layer gold from bottom to top.

2. a kind of upside-down mounting high-efficiency soft gallium arsenide solar cell according to claim 1 is it is characterised in that described peel ply is n-in_xga_(1-x)P, wherein 0 < x < 1.

3. a kind of upside-down mounting high-efficiency soft gallium arsenide solar cell according to claim 1, it is characterized in that, it is additionally provided with antireflective coating (1) on epitaxial layer (3) sensitive surface inverting, described antireflective coating (1) is made up of the silica membrane on upper strata and the titanium deoxid film of lower floor, described silica-film thickness is 90 ± 10nm, and described titanium deoxid film thickness is 60 ± 10nm.

4. a kind of method preparing upside-down mounting high-efficiency soft gallium arsenide solar cell as claimed in claim 1 is it is characterised in that comprise the steps,

Step one, epitaxial wafer and copper-molybdenum copper flexible base board (5) bonding: the bonding position of cleaning epitaxial wafer p face and copper-molybdenum copper flexible base board (5), look unfamiliar long metal layer (4) in epitaxial wafer p, metal layer (4) is aligned, compresses with copper-molybdenum copper flexible substrate, it is finally putting in bonding chip equipment, heat, pressurizeing completes to be bonded, and obtains bonding pad；

Step 2, gained bonding pad corrosive liquid is removed peel ply, thus substrate and cushion are peeled off, expose sensitive surface；

Step 3, making Top electrode (2) above sensitive surface.

5. a kind of method preparing upside-down mounting high-efficiency soft gallium arsenide solar cell according to claim 4 is it is characterised in that also include,

Step 4, growth antireflective coating (1) on sensitive surface.

6. a kind of method preparing upside-down mounting high-efficiency soft gallium arsenide solar cell according to claim 4, it is characterized in that, described metal layer (4) is followed successively by titanium layer, silver layer, layer gold from bottom to top, its thickness is respectively 100nm, 1000nm, 60nm, and the layer gold of described metal layer (4) is aligned, compresses with copper-molybdenum copper flexible substrate.

7. a kind of method preparing upside-down mounting high-efficiency soft gallium arsenide solar cell according to claim 4 is it is characterised in that when step one is cleaned, epitaxial wafer and copper-molybdenum copper flexible base board (5) sequentially pass through acetone, isopropanol, deionized water, hcl and h₂O volume ratio is the mixed solution of 1:1, deionized water cleaning；During bonding, 300～500 degree of bonding temperature, 60～120 minutes time, pressure 2～5kg/cm².

8. a kind of method preparing upside-down mounting high-efficiency soft gallium arsenide solar cell according to claim 4 is it is characterised in that in step 2, peel ply is n-in_xga_(1-x)P, 0 < x < 1, corrosive liquid is hcl and h₃po₄Volume ratio is the mixed solution of 3:2.