CN118507599B - Flexible solar cell and preparation method thereof - Google Patents

Abstract

The invention discloses a flexible solar cell and a preparation method thereof, wherein a flexible substrate is adopted to replace a rigid substrate and two temporary substrates in the prior art to bond to prepare a double-smooth-surface solar cell, so that the volume and the weight of the solar cell are reduced, the weight ratio power is greatly improved, the space flexibility is increased, the application range is wide, a thermal stripping film with a fixing bracket is also introduced, the thermal stripping film with the fixing bracket can fix a semi-finished product, the surface of an epitaxial layer of the semi-finished product is flatly paved on the thermal stripping film, the flexible substrate is prevented from warping, the subsequent photoetching and evaporation process can be carried out on the surface of the other epitaxial layer of the semi-finished product, the manufacture of a front electrode and a back electrode is completed, and the problem that the conventional double-smooth-surface solar cell preparation process adopts the flexible substrate to grow is solved.

Description

A flexible solar cell and a method for preparing the same

Technical Field

The present invention belongs to the technical field of solar cells, and in particular relates to a flexible solar cell and a preparation method thereof.

Background Art

With the rapid development of my country's aerospace industry, GaAs solar cells are widely used in the aerospace field due to their high photoelectric conversion efficiency and good reliability. The inverted GaAs solar cells have greatly improved the photoelectric performance of GaAs space solar cells due to their good bandgap matching structure.

The double-sided inverted solar cell based on a rigid permanent substrate breaks the conventional practice of improving the weight-to-power ratio of traditional gallium arsenide solar cells only by improving the photoelectric conversion efficiency. It allows the solar cell to receive light on both sides and fully utilize the sunlight received by the cell at all angles. This not only greatly improves the electrical output power of the solar cell, but also avoids the back heating of traditional solar cell modules and the reduction in product service life.

Chinese patent CN201520745057.4 discloses making independent front cells and back cells on the front and back of the same rigid permanent substrate to absorb sunlight and increase the electrical output power of the cells. The detailed steps are as follows:

(1) Epitaxial growth:

MOCVD equipment is used to successively grow N-type GaAs buffer layer, GaInP etching stop layer, N-type GaAs cap layer, top cell GaInP, middle cell GaAs, bottom cell InGaAs and P-type InGaAs on GaAs substrate to produce epitaxial layer containing GaAs temporary substrate, as shown in the figure.

(2) Bonding layer production:

Take two epitaxial layers produced in step (1), clean and dry them, and evaporate Ti, Pt, and Au metal bonding layers on the P-type InGaAs with a total thickness of not less than 1 μm;

Take a double-sided polished Si substrate with a thickness of 200um, clean and dry it, and evaporate Ti, Pt, and Au metal bonding layers on its front and back surfaces with a total thickness of not less than 1um.

(3) Transfer and peeling of substrate:

The two sides of the Si substrate are bonded to the metal bonding layers of two epitaxial layers respectively to form a sandwich-type semi-finished product, and the upper and lower GaAs temporary substrates and the N-type GaAs buffer layer of the sandwich structure bonding piece are etched away with a mixture of ammonia and hydrogen peroxide to expose the GaInP cutoff layer.

(4) Making the upper electrode:

The GaInP cut-off layer is removed by etching with a mixed solution of hydrochloric acid and phosphoric acid, and after cleaning and drying, the upper electrodes of the positive and negative batteries are made by a photolithography process.

(5) Selective corrosion to make anti-reflection film:

The semi-finished product prepared in step (4) is selectively etched with a mixed solution of citric acid, hydrogen peroxide and water. After cleaning and drying, a TiO2/Si3N4/SiO2 multilayer anti-reflection film is evaporated on the front and back surfaces of the semi-finished product, with thicknesses of 50nm, 25nm and 95nm respectively.

(6) Annealing and making the lower electrode:

Anneal at 400℃ for 20min to make ohmic contact, then perform overlay etching to penetrate the metal bonding layer to complete the production of the lower electrode.

(7) Slicing and end surface processing complete the production of flip-chip solar cell chips:

Apply glue to protect the front and back sides, split the battery chip with a diamond blade or laser cutting method, remove the edges, retain the complete battery chip, and use a mixed solution of citric acid, hydrogen peroxide, and water to corrode the end faces, remove the glue and clean to complete the double-sided battery.

The above prior art has the following disadvantages:

(1) Heavy weight and large volume

Existing patents use a 200um thick Si permanent substrate as a rigid substrate, while the thickness of the epitaxial layer is only a few to a dozen um. Even if a double-sided growth method is used to grow multi-junction solar cells, the weight and volume of the rigid substrate still account for the vast majority of the solar cell as a whole, and also account for a large part of the cost of the cell, resulting in waste of materials and increased costs, which seriously limits the use value of solar cells in aerospace fields such as space stations, satellites, and long-stay UAVs.

(2) Rigid substrate cannot meet the needs of flexible material applications

In some application areas, such as smart wearable devices, foldable marching tents, buildings, and aircraft surfaces, when equipped with solar cells, rigid substrates are difficult to meet the application requirements in these scenarios.

(3) Wet etching to remove the substrate is costly

The method of removing the GaAs substrate by wet etching results in a waste of the original GaAs substrate. Especially when inverted double-sided solar multi-junction cells are grown, two GaAs substrates are used, which doubles the wasted substrate material and greatly increases the cost of solar cells.

Summary of the invention

The object of the present invention is to provide a flexible solar cell and a preparation method thereof, which adopts a permanent flexible substrate instead of a rigid substrate, has a small size, light weight and a wide range of applications.

To achieve the above object, the present invention provides the following technical solutions:

A method for preparing a flexible solar cell, comprising:

Providing two semiconductor substrates, wherein a reversely stacked epitaxial layer is grown on one surface of the semiconductor substrate;

Providing a flexible substrate, growing a first bonding layer and a second bonding layer on both side surfaces of the flexible substrate respectively, and growing a first bonding layer and a second bonding layer on one side surfaces of two epitaxial layers respectively;

Bonding two semiconductor substrates and a flexible substrate together through a first bonding layer and a second bonding layer to form a sandwich-type semi-finished product with the flexible substrate in the middle and epitaxial layers on both upper and lower sides;

The semiconductor substrate is removed, and the outermost layer of the epitaxial layer is an N-type contact layer;

A surface of an epitaxial layer of a semi-finished product with the semiconductor substrate removed is attached to a thermal stripping film with a fixed support, a gate line pattern is formed on another surface of the epitaxial layer of the semi-finished product, and then a front electrode is grown;

Selectively corrode the semi-finished product with the front electrode prepared on one side to remove the N-type contact layer except for the corresponding part of the front electrode;

forming an anti-reflection film on the selectively etched surface of the epitaxial layer;

The semi-finished product is etched using a first etching solution to expose the first bonding layer, and the exposed first bonding layer portion is used as a back electrode, thereby completing the production of a front electrode and a back electrode on the surface of an epitaxial layer of a battery;

Spin-coat photoresist on one side of the electrode for protection and remove the thermal stripping film;

Stick the side protected by the photoresist on a thermal stripping film with a fixed bracket, repeat the above steps to prepare the front electrode on the surface of another epitaxial layer of the battery, and etch to expose the second bonding layer to form the back electrode on the surface of another epitaxial layer;

The battery with prepared double-sided electrodes is annealed, coated with glue, diced, end-faced and de-bonded to complete the preparation of the double-sided battery.

Optionally, the process of forming the epitaxial layer structure includes:

A first cutoff layer, a sacrificial layer, a second cutoff layer, an N-type contact layer, a first window layer, a first emitter region, a first base region, a first tunnel junction, a second window layer, a second emitter region, a second base region, a second tunnel junction, a P-type buffer layer, a third window layer, a third emitter region, a third base region and a P-type contact layer are sequentially grown on a semiconductor substrate.

Optionally, removing the semiconductor substrate includes:

The semi-finished product is immersed in HF solution for 48 hours to etch and remove the sacrificial layers on the two epitaxial layers, the two semiconductor substrates are peeled off, and the first cutoff layer on the semiconductor substrate and the second cutoff layer on the epitaxial layer are etched and removed with hydrochloric acid solution.

Optionally, growing the first bonding layer and the second bonding layer on both side surfaces of the flexible substrate respectively, and growing the first bonding layer and the second bonding layer on one side surfaces of the two epitaxial layers respectively comprises:

Ti, Pt, and Au with thicknesses of 70 nm, 70 nm, and 800 nm, respectively, are deposited on both sides of the flexible substrate by electron beam evaporation to form a first bonding layer and a second bonding layer;

Ti, Pt and Au with thicknesses of 70 nm, 70 nm and 800 nm respectively are deposited on one side surface of the two epitaxial layers by electron beam evaporation to form a first bonding layer and a second bonding layer.

Optionally, growing the front electrode comprises:

Au, Ge, Ni and Au are deposited on the surface of the epitaxial layer by electron beam evaporation, with thicknesses of 100 nm, 80 nm, 100 nm and 500 nm respectively.

Optionally, forming an anti-reflection film on the upper and lower surfaces of the selectively etched semi-finished product includes:

By electron beam evaporation, any one of TiO2/Al2O3, TiO2/Si3N4 or TiO2/SiO2 is deposited on the surface of the epitaxial layer of the selectively etched semi-finished product. Each anti-reflection film has two layers of film with thicknesses of 30nm and 70nm.

Optionally, after one or both electrodes are made, the heat release film must be removed, and the semi-finished product is immersed in acetone and isopropyl acetone for 5 minutes each, and then rinsed and dried in a fast-drain spray rinse tank.

Optionally, the flexible substrate is a PET film or a PI film.

Optionally, the battery is coated with glue and subsequent processes include:

Stick a blue film on one side of the battery, and then stick a blue film on the other side after applying glue for protection. Remove the blue film on the side not coated with glue, apply glue for protection, and then perform slicing, end face etching, and glue removal. After completion, remove the blue film on the remaining side, and perform slicing, end face etching, and glue removal.

A flexible solar cell is prepared by any one of the above-mentioned methods for preparing a flexible solar cell.

After adopting the above scheme, the beneficial effects of the present invention are:

1. The present invention adopts a flexible substrate to replace the rigid substrate of the prior art. The flexible substrate is light in material and thin in thickness, which not only reduces the volume and weight of the solar cell, greatly improves the weight-to-power ratio, but also increases the spatial scalability. The flexible substrate can be bent into different angles and bonded to different supports. For example, it can be used for spacecraft solar cells, which can reduce the launch cost of the spacecraft and improve its carrying capacity.

2. After removing the semiconductor substrate, the release of epitaxial stress can easily cause the flexible substrate to warp, making it impossible to carry out subsequent lithography and evaporation processes. The present invention prepares the battery by symmetrically distributing the double-sided epitaxial layer on both sides of the flexible substrate. The directions of the epitaxial stress release are just opposite, which can offset each other and eliminate the warping caused by the epitaxial stress release to a certain extent.

However, the epitaxial layers on both sides of the flexible substrate will not be exactly the same, and the flexible substrate will still have an uncontrollable slight warping. The present invention introduces a thermal stripping film with a fixed bracket. The thermal stripping film with a fixed bracket can fix the semi-finished product, so that one epitaxial layer surface of the semi-finished product can be flattened on the thermal stripping film to prevent the flexible substrate from warping, so that subsequent lithography and evaporation processes can be performed on the other epitaxial layer surface of the semi-finished product to complete the preparation of the front electrode and the back electrode on the epitaxial layer surface, and then the same method is used to complete the preparation of the front electrode and the back electrode on the remaining epitaxial surface, thereby realizing the preparation of a flexible double-sided solar cell.

3. The sacrificial layer is corroded by HF solution, and the first cutoff layer on the semiconductor substrate prevents HF from further corroding the substrate. Then, the first cutoff layer is corroded and removed by hydrochloric acid solution to obtain a complete semiconductor substrate. No additional chemical mechanical polishing is required to improve the roughness and flatness of the semiconductor substrate surface. The substrate can be directly used for the next epitaxial layer growth, and the semiconductor substrate can be peeled off and reused. For inverted multi-junction double-sided structure solar cells, the production cost can be greatly saved and the double waste of substrate raw materials by wet etching can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of the present invention after an epitaxial layer is grown on a semiconductor substrate;

FIG2 is a schematic diagram of the structure of the present invention before bonding;

FIG3 is a schematic diagram of the structure of the present invention after evaporation of the bonding layer;

FIG4 is a schematic diagram of a structure in which bonding is completed according to the present invention;

FIG5 is a schematic diagram of the structure of the present invention after the semiconductor substrate is peeled off;

FIG6 is a schematic diagram of the structure of the semi-finished product of the present invention after being attached to a thermal release film and a front electrode is grown;

FIG7 is a schematic diagram of the structure of an anti-reflection film prepared according to the present invention;

FIG8 is a schematic diagram of the structure of the back electrode after preparation of the present invention;

FIG9 is a schematic diagram of the structure of a double-sided electrode prepared according to the present invention;

FIG10 is a top view of the fixing bracket of the present invention;

FIG. 11 is a flow chart of the preparation method of the present invention.

Description of labels:

1. Semiconductor substrate; 2. Epitaxial layer; 21. Sacrificial layer; 3. Flexible substrate; 4. First bonding layer; 5. Second bonding layer; 6. Thermal stripping film; 7. Front electrode; 8. Anti-reflection film; 9. Back electrode; 10. Fixed bracket.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

As shown in FIG. 11 , the present invention provides a method for preparing a flexible solar cell, comprising the following steps:

S1. Growth of epitaxial layer: providing two semiconductor substrates 1, wherein the semiconductor substrate 1 is a temporary substrate, and growing a reversely stacked epitaxial layer 2 on one surface of the semiconductor substrate 1 to form a flip-chip epitaxial structure. The specific structure can be referred to FIG1 ;

Optionally, the semiconductor substrate 1 is a GaAs substrate.

S2, evaporation bonding layer: providing a flexible substrate 3, growing a first bonding layer 4 and a second bonding layer 5 on both side surfaces of the flexible substrate 3, and growing a first bonding layer 4 and a second bonding layer 5 on one side surface of two epitaxial layers 2, respectively. The specific structure can be referred to FIG3 ;

Optionally, the flexible substrate 3 is a PET film or a PI film with a thickness of only tens of microns, preferably 50um, which reduces the volume and weight of the solar cell and increases the spatial scalability. The flexible substrate 3 can be bent into different angles and can be applied to more fields and has a wide range of applications.

Optionally, growing the first bonding layer 4 and the second bonding layer 5 on both side surfaces of the flexible substrate 3, and growing the first bonding layer 4 and the second bonding layer 5 on one side surfaces of the two epitaxial layers 2, respectively, specifically includes:

Ti, Pt and Au with thicknesses of 70 nm, 70 nm and 800 nm respectively are deposited on both side surfaces of the flexible substrate 3 by electron beam evaporation to form a first bonding layer 4 and a second bonding layer 5;

Ti, Pt and Au with thicknesses of 70 nm, 70 nm and 800 nm respectively are deposited on one surface of the two epitaxial layers 2 by electron beam evaporation to form a first bonding layer 4 and a second bonding layer 5 .

The first bonding layer 4 and the second bonding layer 5 are metal bonding layers, which are permanent bonds and can permanently bond the epitaxial layer 2 to the flexible substrate 3. They have a strong structure, a long service life, and a thin thickness, which can further reduce the volume and weight of the solar cell.

S3, bonding: bonding the two semiconductor substrates 1 and the flexible substrate 3 together through the first bonding layer 4 and the second bonding layer 5 to form a sandwich-type semi-finished product with the flexible substrate 3 in the center and the epitaxial layer 2 on both the upper and lower sides. For the specific structure, refer to FIG. 4 .

S4, stripping the substrate: removing the semiconductor substrate 1, the outermost layer of the epitaxial layer 2 is an N-type contact layer; the cross-sectional structure after removing the semiconductor substrate 1 is shown in FIG5.

S5. Making a single-sided front electrode: stick the surface of one epitaxial layer 2 of the semi-finished product with the semiconductor substrate 1 removed on a thermal stripping film 6 with a fixed bracket 10. The thermal stripping film 6 with the fixed bracket 10 can fix the semi-finished product to prevent the flexible substrate 3 from warping. Make a gate line pattern on the surface of the other epitaxial layer 2 of the semi-finished product, and then grow a front electrode 7. Refer to Figure 6 for the specific cross-sectional structure.

Optionally, the gate line pattern may be formed on the surface of another epitaxial layer 2 of the semi-finished product by adopting a photolithography process, performing photoresist coating, exposure, and development to form the gate line pattern.

Optionally, the front electrode 7 can be specifically grown by: depositing Au, Ge, Ni, and Au on the surfaces of the two epitaxial layers 2 by electron beam evaporation, with thicknesses of 100 nm, 80 nm, 100 nm, and 500 nm, respectively, to form the front electrode 7, and the specific cross-sectional structure is shown in FIG6. The front electrode 7 is a metal electrode.

Optionally, the top view of the fixing bracket 10 may refer to FIG. 10 , and may be a ring-shaped bracket matching the shape of the wafer, or may be other shapes capable of fixing and supporting the thermal peeling film 6 .

S6, selective etching: selectively etching the semi-finished product with the front electrode 7 prepared on one side to remove the N-type contact layer except for the corresponding part of the front electrode 7;

Optionally, before selective etching, a photolithography process is required to be used on the surface of the epitaxial layer 2 on which the front electrode 7 is prepared, and after photoresist coating, exposure, development, and overlay etching, the front electrode 7 is protected to prevent the front electrode 7 and the N-type contact layer at the corresponding part of the front electrode 7 from being corroded.

Optionally, the corrosion solution used in the selective corrosion may specifically be a solution of citric acid, hydrogen peroxide and water mixed in a volume ratio of 2:2:1.

S7, making an anti-reflection film: forming an anti-reflection film 8 on the selectively etched surface of the epitaxial layer 2. For a specific cross-sectional structure, refer to FIG. 7.

Optionally, the anti-reflection film 8 may be formed by:

By electron beam evaporation, any one of TiO2/Al2O3, TiO2/Si3N4 or TiO2/SiO2 is deposited on the surface of the selectively etched epitaxial layer 2, so that each anti-reflection film 8 has two layers of film with thicknesses of 30nm and 70nm.

S8. Making a single-sided back electrode: Use the first corrosion solution to etch the semi-finished product to expose the first bonding layer 4. The exposed portion of the first bonding layer 4 is used as the back electrode 9 to complete the production of the front electrode 7 and the back electrode 9 on the surface of the first epitaxial layer 2 of the battery. For the specific cross-sectional structure, please refer to Figure 8.

Optionally, before etching the semi-finished product with the first corrosive solution, a photolithography process is required to be performed on the surface of the epitaxial layer 2 to perform overlay etching after photoresist coating, exposure, development, and protection of the front electrode 7 and corresponding parts except the back electrode 9.

Optionally, the first corrosion solution may specifically be a mixed solution of phosphorus and hydrogen peroxide in a ratio of 1:2 and a hydrochloric acid solution.

S9, removing the thermal stripping film: spin-coating a photoresist on one side of the electrode for protection, placing it in an oven at 180° for 3 minutes, and removing the thermal stripping film 6 after taking it out;

S10. Make the front electrode and back electrode on the other side: stick the side protected by the photoresist on the thermal stripping film 6 with a fixed bracket 10, repeat steps S5-S8 to prepare the front electrode 7 on the surface of the other epitaxial layer 2 of the battery, and etch to expose the second bonding layer 5 to form the back electrode 9 on the surface of the other epitaxial layer 2. Refer to Figure 9 for the specific cross-sectional structure.

Optionally, after the front electrode 7 and the back electrode 9 on one side are made and the thermal stripping film 6 on the side is removed, the semi-finished product needs to be immersed in acetone and isopropyl acetone (IPA) for 5 minutes each, and then rinsed and dried in a quick drain spray rinsing tank (QDR) to keep the surface of the epitaxial layer 2 clean. Similarly, after the front electrode 7 and the back electrode 9 on the other side are made and the thermal stripping film on the other side is removed, the semi-finished product also needs to be immersed in acetone and isopropyl acetone (IPA) for 5 minutes each, and then rinsed and dried in a quick drain spray rinsing tank (QDR).

S11, completing the subsequent process: annealing, gluing, slicing, end face etching, and degumming the battery with the prepared double-sided electrodes to complete the preparation of the double-sided battery.

Optionally, annealing the battery with the prepared double-sided electrodes may be performed as follows:

The battery with double-sided electrodes was annealed in an alloy furnace at 350°C for 30 minutes to make a good ohmic contact.

Optionally, the battery with the prepared double-sided electrodes is coated with glue and the subsequent processes are specifically as follows:

A blue film is pasted on one side of the battery to prevent the flexible substrate 3 from warping, so that glue can be applied to the other side of the battery for protection. Then a blue film is also pasted on the battery, and the blue film on the side not coated with glue is removed for glue protection, and the battery is sliced as a whole. After completion, the blue film on the remaining side is removed, and the end face of the battery is corroded and glue is removed.

Optionally, the slicing may be performed as follows:

Use a diamond blade or laser to cut and remove the ineffective area on the outer ring of the battery, retaining the core area in the center of the battery.

Optionally, the end face etching and adhesive removal may be specifically performed as follows:

The cut cells are immersed in a second etching solution to remove residual particles on the end surfaces, and a single flexible solar bifacial cell with a complete pattern is obtained by removing the glue.

Optionally, the second corrosion solution may be a mixed solution of citric acid, hydrogen peroxide and water in a volume ratio of 2:2:1.

In the present application, a flexible substrate 3 is used to replace the rigid substrate of the prior art, such as Si, GaAs, sapphire, or SiC, and the thickness of the rigid substrate is above 200um. The flexible substrate 3 used in the present application can be any one of PET film and PI film (polyimide film), and its thickness can be only 50um, which not only reduces the volume and weight of the solar cell, greatly improves the weight-to-power ratio, but also increases the spatial scalability. The flexible substrate 3 can be bent into different angles and bonded to different supports. For example, it can be used for spacecraft solar cells, which can reduce the launch cost of the spacecraft and improve its carrying capacity.

Therefore, the flexible substrate 3 promotes the application of solar cells in various special fields and expands the application scope of solar cells in complex space environments and limited volume spaces, such as high-altitude airships, large near-space drones, new energy vehicles, smart wearable devices and other systems for real-time energy needs. In addition, the flexible substrate 3 is made of insulating material to ensure that the current of the battery will not crosstalk when bonding.

However, it is not easy to grow flexible substrates using flexible materials. The existing preparation processes mainly use two methods:

① Using the permanent bonding method, that is, the method used in the present invention, the flexible substrate can be a PI film or a PET film. However, since the thermal expansion coefficient of the flexible substrate does not match the epitaxy of the solar cell, after the substrate is corroded, the release of the epitaxial stress will inevitably lead to the warping of the semi-finished product, which will affect subsequent processes such as lithography.

② Use temporary bonding method: First, evaporate or electroplate copper on the surface of the solar cell, use copper as a flexible material and as the back electrode; second, apply temporary bonding glue and make temporary bonding with a temporary rigid substrate (GaAs, silicon or glass); third, remove the GaAs substrate with epitaxial growth by corrosion, evaporate metal by photolithography to make the front electrode, and evaporate anti-reflection film; then, debond and cut to complete the production of solar cell products. This process is complicated to make. With copper as a flexible material, on the one hand, the lattice constant and thermal expansion coefficient of copper do not match the epitaxy. After the GaAs substrate is corroded and removed, the epitaxial stress cannot be eliminated, which will cause the warping of the flexible substrate, and then the semi-finished product warping, making the subsequent photolithography process impossible; on the other hand, the presence of temporary bonding glue greatly limits the subsequent alloy annealing temperature, resulting in the inability to form a good ohmic contact, and the low success rate of debonding also restricts the production of solar cell products.

Therefore, in order to solve the above problems, the present invention prepares the battery by symmetrically distributing the double-sided epitaxial layer 2 on both sides of the flexible substrate 3 on the basis of permanent bonding. The directions of epitaxial stress release are just opposite and can offset each other, thereby eliminating the warping caused by epitaxial stress release to a certain extent.

However, the epitaxial layers 2 on both sides of the flexible substrate 3 will not be exactly the same, and the flexible substrate 3 will still have an uncontrollable slight warping. In this regard, the present invention introduces a thermal stripping film 6 with a fixed bracket 10. The thermal stripping film 6 with a fixed bracket 10 can fix the semi-finished product, so that the surface of one epitaxial layer 2 of the semi-finished product is flattened on the thermal stripping film 6 to prevent the flexible substrate 3 from warping, that is, to prevent the semi-finished product from warping, so that subsequent lithography and evaporation processes can be carried out on the surface of the other epitaxial layer 2 of the semi-finished product to complete the preparation of the front electrode 7 and the back electrode 9 on the surface of the epitaxial layer 2, and then use the same method to complete the preparation of the front electrode 7 and the back electrode 9 on the surface of the remaining epitaxial layer 2, so that the preparation of flexible double-sided solar cells can be realized. The operation is convenient, simple and practical, and solves the problem that the flexible substrate 3 is not easy to grow in the existing double-sided solar cell preparation process.

On the basis of the above embodiment, in another embodiment of the present application, the formation process of the epitaxial layer 2 structure includes:

An N-type buffer layer, a first cutoff layer, a sacrificial layer 21, a second cutoff layer, an N-type contact layer, a first window layer, a first emitter region, a first base region, a first tunnel junction, a second window layer, a second emitter region, a second base region, a second tunnel junction, a P-type buffer layer, a third window layer, a third emitter region, a third base region and a P-type contact layer are sequentially grown on a semiconductor substrate 1.

Among them, the N-type buffer layer is an N-type GaAs buffer layer, the P-type buffer layer is an AlGaAs buffer layer, the first cutoff layer and the second cutoff layer are both GaInP cutoff layers, the sacrificial layer 21 is an AlAs sacrificial layer 21, the N-type contact layer is an N-type GaAs contact layer, the P-type contact layer is a P-type InGaAs contact layer, the first window layer and the second window layer are AlInP window layers, the third window layer is an InGaAs window layer, the first emitter region is a GaInP emitter region, the second emitter region is a GaAs emitter region, the third emitter region is an InGaAs emitter region, the first base region is a GaInP base region, the second base region is a GaAs base region, the third base region is an InGaAs base region, the first tunnel junction and the second tunnel junction are both GaInP tunnel junctions, and the specific cross-sectional structure refers to Figure 1.

Since the preparation process of each layer structure in the epitaxial layer 2 is well known to those skilled in the art, it will not be described in detail in this application.

It should be noted that the present application also provides a process of removing the semiconductor substrate 1 in step S40, including:

The bonded semi-finished product is immersed in HF solution (hydrofluoric acid solution) to etch and remove the sacrificial layer 21 and the N-type buffer layer on the two epitaxial layers 2, and the two semiconductor substrates 1 are peeled off. The specific cross-sectional structure after peeling is shown in Figure 5. The first cut-off layer on the semiconductor substrate 1 and the second cut-off layer on the epitaxial layer 2 are then etched and removed with hydrochloric acid solution.

The sacrificial layer 21 is corroded by HF solution, and the first cutoff layer on the semiconductor substrate 1 prevents HF from further corroding the substrate. Then, the first cutoff layer is corroded and removed by hydrochloric acid solution to obtain a complete semiconductor substrate 1. No additional chemical mechanical polishing is required to improve the roughness and flatness of the surface of the semiconductor substrate 1. The semiconductor substrate 1 can be directly used for the next epitaxial layer 2 growth, thereby realizing the peeling and reuse of the semiconductor substrate 1. For solar cells with an inverted multi-junction double-sided structure, the production cost can be greatly saved, and the double waste of substrate raw materials caused by wet etching can be avoided.

Similarly, the second cutoff layer on the epitaxial layer 2 protects the core area of the epitaxial layer 2 . After the second cutoff layer is removed by etching with a hydrochloric acid solution, a photolithography process can be directly performed on the surface of the epitaxial layer 2 to manufacture the front electrode 7 .

Optionally, the semi-finished product is immersed in the HF solution for 48 hours.

Correspondingly, an embodiment of the present application further provides a flexible solar cell, which is prepared by the method for preparing a flexible solar cell described in any of the above embodiments.

In summary, the embodiment of the present application provides a flexible solar cell and a method for preparing the same, wherein a flexible substrate 3 is used to replace the rigid substrate of the prior art, which not only reduces the volume and weight of the solar cell, greatly improves the weight-to-power ratio, but also increases the spatial scalability, can be bent into different angles, and can be bonded to different supports, such as solar cells for spacecraft, which can reduce the launch cost of spacecraft and improve its carrying capacity. Therefore, the flexible substrate 3 promotes the application of solar cells in various special fields and expands the application scope of solar cells in complex space environments and limited volume spaces, such as the real-time energy needs of systems such as high-altitude airships, large near-space drones, new energy vehicles, and smart wearable devices.

Moreover, the prepared solar cells receive light on both sides, which can match the complex aerospace environment. There is no need for additional angle adjustment, which reduces energy consumption and can greatly meet the needs of long-term space travel.

In addition, the sacrificial layer 21 is corroded by HF solution, and the first cutoff layer on the semiconductor substrate 1 prevents HF from further corroding the substrate. Then, the first cutoff layer is corroded and removed by hydrochloric acid solution to obtain a complete semiconductor substrate 1. There is no need to perform additional chemical mechanical polishing to improve the roughness and flatness of the surface of the semiconductor substrate 1. The semiconductor substrate 1 can be directly used for the next growth of the epitaxial layer 2, thereby realizing the peeling and reuse of the semiconductor substrate 1. For solar cells with an inverted multi-junction double-sided structure, the production cost can be greatly saved, and the double waste of substrate raw materials caused by wet etching can be avoided.

It is worth noting that the thicknesses of the semiconductor substrate 1, epitaxial layer 2, flexible substrate 3, first bonding layer 4, second bonding layer 5, front electrode 7, back electrode 9, and anti-reflection film 8 shown in the drawings of the present application are only examples and do not represent their actual thicknesses. In addition, the actual proportions between the semiconductor substrate 1, epitaxial layer 2, flexible substrate 3, first bonding layer 4, second bonding layer 5, front electrode 7, back electrode 9, and anti-reflection film 8 are not as shown in the drawings, but are for reference only. The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other.

The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method for preparing a flexible solar cell, comprising: Providing two semiconductor substrates, wherein a reversely stacked epitaxial layer is grown on one surface of the semiconductor substrate, wherein the epitaxial layer comprises a first cutoff layer, a sacrificial layer, a second cutoff layer, and an N-type contact layer grown sequentially on the semiconductor substrate; Providing a flexible substrate, growing a first bonding layer and a second bonding layer on both side surfaces of the flexible substrate respectively, and growing a first bonding layer and a second bonding layer on one side surfaces of two epitaxial layers respectively; Bonding two semiconductor substrates and a flexible substrate together through a first bonding layer and a second bonding layer to form a sandwich-type semi-finished product with the flexible substrate in the middle and epitaxial layers on both upper and lower sides; The semiconductor substrate is removed, and the semi-finished product is immersed in an HF solution to remove the sacrificial layers on the two epitaxial layers by etching, and the two semiconductor substrates are peeled off, and the first cut-off layer on the semiconductor substrate and the second cut-off layer on the epitaxial layer are removed by etching with a hydrochloric acid solution. After the semiconductor substrate is removed, the outermost layer of the epitaxial layer is an N-type contact layer; The surface of one epitaxial layer of the semi-finished product with the semiconductor substrate removed is attached to a thermal stripping film with a fixed support, and a gate line pattern is made on the surface of the other epitaxial layer of the semi-finished product by photolithography, coating, exposure, and development, and then a front electrode is grown; Selectively corrode the semi-finished product with the front electrode prepared on one side to remove the N-type contact layer except for the corresponding part of the front electrode; forming an anti-reflection film on the selectively etched surface of the epitaxial layer; The semi-finished product is etched using a first etching solution to expose the first bonding layer, and the exposed first bonding layer portion is used as a back electrode, thereby completing the production of a front electrode and a back electrode on the surface of an epitaxial layer of a battery; Spin-coat photoresist on one side of the electrode for protection and remove the thermal stripping film; Stick the side protected by the photoresist on a thermal stripping film with a fixed bracket, repeat the above steps to prepare the front electrode on the surface of another epitaxial layer of the battery, and etch to expose the second bonding layer to form the back electrode on the surface of another epitaxial layer; The battery with prepared double-sided electrodes is annealed, coated with glue, diced, end-faced and de-bonded to complete the preparation of the double-sided battery. 2. The method for preparing a flexible solar cell according to claim 1, wherein the process of forming the epitaxial layer structure comprises: A first window layer, a first emitter region, a first base region, a first tunnel junction, a second window layer, a second emitter region, a second base region, a second tunnel junction, a P-type buffer layer, a third window layer, a third emitter region, a third base region and a P-type contact layer are sequentially grown on the N-type contact layer on the semiconductor substrate. 3. The method for preparing a flexible solar cell according to claim 1, wherein removing the semiconductor substrate comprises: The semi-finished product was immersed in the HF solution for 48 hours. 4. A method for preparing a flexible solar cell according to claim 1, characterized in that the first bonding layer and the second bonding layer are respectively grown on both side surfaces of the flexible substrate, and the first bonding layer and the second bonding layer are respectively grown on one side surface of the two epitaxial layers, comprising: Ti, Pt, and Au with thicknesses of 70 nm, 70 nm, and 800 nm, respectively, are deposited on both sides of the flexible substrate by electron beam evaporation to form a first bonding layer and a second bonding layer; Ti, Pt and Au with thicknesses of 70 nm, 70 nm and 800 nm respectively are deposited on one side surface of the two epitaxial layers by electron beam evaporation to form a first bonding layer and a second bonding layer. 5. The method for preparing a flexible solar cell according to claim 1, wherein growing the front electrode comprises: Au, Ge, Ni and Au are deposited on the surface of the epitaxial layer by electron beam evaporation, with thicknesses of 100 nm, 80 nm, 100 nm and 500 nm respectively. 6. The method for preparing a flexible solar cell according to claim 1, wherein forming an anti-reflection film on the upper and lower surfaces of the selectively etched semi-finished product comprises: _TiO2 / _Al2O3 , _TiO2 / _Si3N4 or _{TiO2 / SiO2} is deposited on the epitaxial layer surface of the selectively etched semi-finished product by _electron beam evaporation. Each anti-reflection film has two layers with thicknesses of 30nm and 70nm. 7. A method for preparing a flexible solar cell as described in claim 1, characterized in that after one side electrode or both sides of the electrode are made, the thermal release film must be removed, and the semi-finished product is immersed in acetone and isopropyl tone for 5 minutes each, and then rinsed and dried in a quick-drain spray rinse tank. 8. The method for preparing a flexible solar cell according to claim 1, wherein the flexible substrate is a PET film or a PI film. 9. A method for preparing a flexible solar cell according to claim 1, characterized in that the process of coating the cell with glue and subsequent processes comprises: Stick a blue film on one side of the battery, and then stick a blue film on the other side after applying glue for protection. Remove the blue film on the side not coated with glue, apply glue for protection, and then perform slicing, end face etching, and glue removal. After completion, remove the blue film on the remaining side, and perform slicing, end face etching, and glue removal. 10. A flexible solar cell, characterized in that it is prepared by the method for preparing a flexible solar cell according to any one of claims 1 to 9.