Flexible thin film solar cell and preparation method thereof

Abstract

The invention discloses a flexible thin film solar cell and a preparation method thereof, and the preparation method comprises the following steps: 1, carrying out the first bonding: taking an epitaxial layer with a supporting substrate, and manufacturing a first bonding metal layer on the surface of the epitaxial layer; a flexible substrate is taken, a second bonding metal layer is manufactured on the surface of the flexible substrate, and the first bonding metal layer and the second bonding metal layer are bonded to form a back electrode; step 2, secondary bonding: providing a temporary rigid substrate and a thermal stripping film, and bonding the temporary rigid substrate to the flexible substrate through the thermal stripping film; step 3, electrode manufacturing: stripping the supporting substrate, and then manufacturing a front electrode and an antireflection film on the surface of the epitaxial layer; and 4, manufacturing the flexible thin film solar cell: heating to strip the thermal stripping film and the temporary rigid substrate from the flexible substrate to obtain the flexible thin film solar cell. According to the invention, only two-time bonding is carried out in the battery manufacturing process, so that compared with three-time bonding in the prior art, the method is simpler, the production process is simplified, the production cost is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the field of solar cells, and in particular to a flexible thin-film solar cell and a preparation method thereof. Background Art

[0002] GaAs solar cells have always been a hot topic in research in various countries. They have high photoelectric conversion efficiency and excellent reliability, and are widely valued by people. GaAs solar cells are divided into rigid GaAs solar cells and flexible GaAs solar cells. Compared with rigid GaAs solar cells, flexible GaAs solar cells also have the advantages of being ultra-thin and bendable.

[0003] The conventional method of making flexible GaAs solar cells is:

[0004] (1) First bonding: firstly, an epitaxial layer is grown on a GaAs substrate, and then the GaAs substrate with the epitaxial layer is bonded to a first temporary substrate using a resin adhesive to perform the first bonding; the first temporary substrate is arranged on the back side of the epitaxial layer, and the GaAs substrate is arranged on the front side of the epitaxial layer;

[0005] (2) Second bonding: remove the GaAs substrate, make a front electrode on the front side of the epitaxial layer, and then use a resin glue to bond the front electrode to the second temporary substrate for a second bonding;

[0006] (3) Third bonding: remove the first temporary substrate on the back of the epitaxial layer, make a back electrode on the back of the epitaxial layer, and then bond a flexible substrate to the back electrode for the third bonding to obtain a flexible GaAs solar cell.

[0007] The conventional manufacturing process needs to go through three bonding steps, the preparation process is complicated, and the resin glue used in the temporary substrate bonding process needs to go through multiple acid and alkali solution soaking steps. The resin glue can easily lose viscosity during the preparation process, resulting in failure of the temporary substrate bonding. Summary of the invention

[0008] The purpose of the present invention is to solve the technical problems of complex preparation process and high cost of flexible gallium arsenide solar cells in the prior art.

[0009] In order to achieve the above object, the present invention provides a method for preparing a flexible thin-film solar cell, comprising the following steps:

[0010] Step 1, first bonding: take an epitaxial layer with a supporting substrate, and make a first bonding metal layer on the surface of the epitaxial layer; take a flexible substrate, and make a second bonding metal layer on the surface of the flexible substrate, and bond the first bonding metal layer and the second bonding metal layer to form a back electrode.

[0011] Step 2, second bonding: providing a temporary rigid substrate and a thermal release film, and bonding the temporary rigid substrate to the flexible substrate via the thermal release film.

[0012] Step 3, electrode production: peeling off the support substrate, and then producing a front electrode and an anti-reflection film on the surface of the epitaxial layer.

[0013] Step 4, manufacturing of flexible thin-film solar cells: heating to peel off the thermal peeling film and the temporary rigid substrate from the flexible substrate to obtain the flexible thin-film solar cell.

[0014] Optionally, in the above step 1, the epitaxial layer is a sacrificial layer, a contact layer, a window layer, an emitter region, a base region and a back field layer arranged in sequence; and the back field layer is close to the first bonding metal layer.

[0015] Optionally, the back field layer is made of aluminum gallium indium phosphide, and the first bonding metal layer is made of at least one of gold, platinum, copper, silver, aluminum, and palladium.

[0016] Optionally, a first transition layer is provided between the back field layer and the first bonding metal layer, and the first transition layer is made of at least one transition metal selected from titanium, chromium and nickel.

[0017] Optionally, in the above step 1, the flexible substrate is made of polyimide and / or polyethylene terephthalate, and the second bonding metal layer is made of at least one of gold, platinum, copper, silver, aluminum, and palladium.

[0018] Optionally, a second transition layer is provided between the flexible substrate and the second bonding metal layer, and the second transition layer is made of at least one transition metal selected from titanium, chromium and nickel.

[0019] Optionally, the supporting substrate is at least one of a silicon substrate, a gallium arsenide substrate, and an indium phosphide substrate.

[0020] Optionally, in the above step 4, the peeling temperature of the thermal peeling film is 200° C. to 250° C., and the thickness of the thermal peeling film is 80 μm to 100 μm.

[0021] The invention also provides a flexible thin-film solar cell prepared by the method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention provides a method for preparing a flexible thin-film solar cell. The flexible thin-film solar cell of the present invention is prepared by only performing two bonding steps during the process of manufacturing the cell, first bonding the epitaxial layer to the flexible substrate, and then bonding the flexible substrate to the temporary rigid substrate. Compared with the three-step bonding preparation method of the prior art, the preparation method of the present invention is simpler, simplifies the production process, reduces the production cost, and improves the production efficiency.

[0024] (2) The present invention uses a thermal release film for temporary substrate bonding. The thermal release film is not easy to lose adhesion during the preparation process, thereby ensuring the stability of the temporary substrate bonding and is suitable for all semiconductor flexible thin-film solar cells grown by vapor phase epitaxy.

[0025] (3) Since the physical and chemical properties of the back field layer and the first bonding metal layer are quite different, there may be a problem of unstable bonding. The present invention enhances the bonding stability between the back field layer and the first bonding metal layer by providing a first transition layer between the back field layer and the first bonding metal layer. The first transition layer is made of a transition metal, and its physical and chemical properties are between those of the back field layer and the first bonding metal layer. The first transition layer is provided between the back field layer and the first bonding metal layer to form a transition between the two, thereby enhancing the bonding stability between the back field layer and the first bonding metal layer.

[0026] Similarly, in the present invention, a second transition layer is disposed between the flexible substrate and the second bonding metal layer, and the bonding stability between the flexible substrate and the second bonding metal layer is enhanced by the second transition layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The following is a flow chart of the preparation of the flexible thin film solar cell of the present invention:

[0028] Wherein, A represents a cross-sectional view of the epitaxial layer with a supporting substrate in step 1 of embodiment 1;

[0029] B represents a cross-sectional view of a component formed after the flexible substrate is bonded in step 2 of embodiment 1;

[0030] C represents a cross-sectional view of a component formed after bonding of a temporary rigid substrate in step 3 of Example 1;

[0031] D represents a cross-sectional view of a component formed after the support substrate is peeled off in step 4 of Example 1;

[0032] E represents a cross-sectional view of a component formed after the front electrode is manufactured in step 5 of Example 1;

[0033] F represents a cross-sectional view of a component after the isolation groove is formed in step 6 of embodiment 1;

[0034] G represents a cross-sectional view of a component formed after the anti-reflection film is produced in step 7 of Example 1;

[0035] H represents a cross-sectional view of a component formed after the thermal release film is peeled off in step 8 of Example 1.

[0036] Figure 2 It is an enlarged schematic diagram of the epitaxial layer with the supporting substrate of the present invention.

[0037] Figure 3 It is a schematic structural diagram of the flexible thin-film solar cell of the present invention. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0039] like Figure 1 As shown, the present invention provides a method for preparing a flexible thin-film solar cell, comprising the following steps:

[0040] Step 1, such as Figure 1 As shown in A, an epitaxial layer 1 having a supporting substrate 2 is provided, and the supporting substrate 2 is arranged on the front side of the epitaxial layer 1; the epitaxial layer 1 having the supporting substrate 2 can be made by MOCVD equipment.

[0041] In some embodiments, Figure 2 As shown, Figure 2 yes Figure 1 When the flexible thin film solar cell is a single junction cell, the epitaxial layer 1 includes: an AlAs sacrificial layer 101 and a single cell functional layer, and the single cell functional layer includes a contact layer 102, a window layer 103, an emitter region 104, a base region 105 and a back field layer 106 arranged in sequence.

[0042] The AlAs sacrificial layer 101 is a layer close to the support substrate 2 and is used for subsequently peeling off the support substrate 2. When the AlAs sacrificial layer 101 is removed by etching, the AlAs sacrificial layer 101 and the support substrate 2 are peeled off from the contact layer 102 together, thereby achieving the purpose of peeling off the support substrate 2.

[0043] In some embodiments, when the flexible thin film solar cell is a multi-junction cell, for example, when the flexible thin film solar cell is a triple-junction cell, the epitaxial layer 1 includes an AlAs sacrificial layer 101, a top cell functional layer, a middle top tunnel junction, a middle cell functional layer, a middle bottom tunnel junction, and a bottom cell functional layer grown in sequence.

[0044] In the above-mentioned top cell functional layer, middle cell functional layer and bottom cell functional layer, each cell functional layer includes a contact layer, a window layer, an emitter region, a base region and a back field layer. That is, when the flexible thin film solar cell is a triple junction cell, the epitaxial layer is an AlAs sacrificial layer 101, a top cell contact layer, a top cell window layer, a top cell emitter region, a top cell base region, a top cell back field layer, a middle top tunnel junction, a middle cell contact layer, a middle cell window layer, a middle cell emitter region, a middle cell base region, a middle cell back field layer, a middle bottom tunnel junction, a bottom cell contact layer, a bottom cell window layer, a bottom cell emitter region, a bottom cell base region and a bottom cell back field layer arranged in sequence.

[0045] Step 2, bonding: make a first bonding metal layer on the back of the epitaxial layer 1; then Figure 1 As shown in B, a flexible substrate 4 is provided, a second bonding metal layer is made on the front side of the flexible substrate 4, the first bonding metal layer is directed toward the second bonding metal layer, and the two are bonded together to form a back electrode 3.

[0046] Then, if Figure 1 As shown in C, a temporary rigid substrate 6 is provided, and a thermal peeling film 5 is respectively adhered to the front side of the temporary rigid substrate 6 and the back side of the flexible substrate 4, and the temporary rigid substrate 6 is bonded to the back side of the flexible substrate 4 through the thermal peeling film 5.

[0047] In some embodiments, the flexible substrate 4 may be a polyimide substrate and / or a polyethylene terephthalate substrate.

[0048] In some embodiments, the temporary rigid substrate 6 may be a silicon wafer, a glass wafer, a sapphire wafer, etc., which has the same size as the epitaxial wafer.

[0049] Step 3, electrode preparation: Figure 1 As shown in D, the support substrate is peeled off. Figure 1 As shown in E, F, and G, a front electrode 7 and an anti-reflection film 9 are manufactured on the front side of the epitaxial layer 1.

[0050] The front electrode 7 and the anti-reflection film 9 can be prepared by using existing processes, which will not be described in detail here, but will be described in detail in the embodiments.

[0051] Step 4, flexible thin film solar cell production: Figure 1 As shown in H, the thermal peeling film 5 is heated to reach the peeling temperature, the viscosity of the thermal peeling film 5 fails, and the thermal peeling film 5 and the temporary rigid substrate 6 are peeled off from the back of the flexible substrate 4 to obtain the flexible thin film solar cell.

[0052] The thermal peeling film 5 used in the present invention has the property of being sticky when cold and non-sticky when hot, and is sticky at room temperature, but loses its stickiness after heating. Therefore, in the above step 2, the thermal peeling film 5 can bond (stick) the temporary rigid substrate 6 to the flexible substrate 4 at room temperature. In step 4, when the thermal peeling film 5 is heated to the peeling temperature, the stickiness of the thermal peeling film 5 is lost, so that it can be peeled off from the flexible substrate 4.

[0053] The present invention is described in detail below with reference to the embodiments.

[0054] Example 1

[0055] This embodiment provides a method for preparing a flexible thin-film solar cell, comprising the following steps:

[0056] Step 1, such as Figure 1 As shown in A, an epitaxial layer 1 is grown on a supporting substrate 2 by using a MOCVD device.

[0057] In this embodiment, the support substrate 2 is a gallium arsenide substrate. In other embodiments, the support substrate 2 may also be a silicon or indium phosphide substrate.

[0058] like Figure 2 As shown, in this embodiment, the flexible thin film solar cell is a single junction cell, and the epitaxial layer 1 is an AlAs sacrificial layer 101, a contact layer 102, a window layer 103, an emitter region 104, a base region 105, and a back field layer 106 arranged in sequence. The thickness of the AlAs sacrificial layer 101 is 20nm to 100nm.

[0059] Step 2: Use metal evaporation process to form a first bonding metal layer on the surface of the back field layer 106. Figure 1 As shown in B, a polyimide (PI) flexible substrate 4 is provided, and a second bonding metal layer is formed on the surface of the flexible substrate 4 by a metal evaporation process. The first bonding metal layer is facing the second bonding metal layer, and the two are relatively overlapped together to form a back electrode 3. The bonding temperature is between 200°C and 400°C, and the bonding pressure ranges from 5000mbar to 9000mbar.

[0060] In this embodiment, the first bonding metal layer and the second bonding metal layer are both made of gold. In other embodiments, the first bonding metal layer and the second bonding metal layer may also be made of platinum, copper, silver, aluminum, palladium or other materials.

[0061] Step 3: To ensure the stability of the flexible thin-film solar cell during the subsequent positive electrode manufacturing process, the flexible thin-film solar cell needs to be supported by a temporary rigid substrate. Figure 1As shown in C, a silicon temporary rigid substrate 6 is provided, a thermal release film 5 is attached to the front side of the silicon temporary rigid substrate 6 and the back side of the flexible substrate 4, and the temporary rigid substrate is bonded in a vacuum hot press so that the silicon temporary rigid substrate 6 is bonded to the back side of the flexible substrate 4. The bonding temperature does not exceed 100° C., and the bonding pressure is between 100 mbar and 500 mbar.

[0062] The thermal peeling film 5 has the property of being sticky when cold and non-sticky when hot. It is sticky at room temperature, becomes sticky after low temperature heating (below 100°C), and loses its stickiness after high temperature heating to the peeling temperature (above 200°C). Thus, in this step, the thermal peeling film 5 can bond (stick) the temporary rigid substrate 6 to the flexible substrate 4.

[0063] Step 4, such as Figure 2 and Figure 1 As shown in D, the battery after the treatment in step 3 is immersed in a hydrofluoric acid solution (HF solution, concentration 5%-20%), and the AlAs sacrificial layer 101 is etched away at 30-60°C, so that the supporting substrate 2 is peeled off from the contact layer 102. In this step, the HF solution is used to peel off the supporting substrate 2 because the HF solution has a high corrosion rate for the AlAs sacrificial layer 101, while the corrosion rate for the contact layer 102, the window layer 103, the emitter region 104, the base region 105, and the back field layer 106 is low, so that the use of the HF solution to etch the AlAs sacrificial layer 101 causes less damage to the battery.

[0064] Step 5, front electrode preparation: Figure 1 As shown in E, the battery after step 4 is ultrasonically cleaned in an alcohol-acetone solution for five minutes, then rinsed with deionized water and dried. A front electrode pattern is made on the front of the epitaxial layer 1 by a photolithography-development process, and then a front electrode 7 is prepared by a vacuum coating process, and then cleaned and dried by acetone, alcohol, and semiconductor cleaning solution in turn.

[0065] In this embodiment, the front electrode 7 is a gold layer, a germanium layer, a nickel layer, a gold layer, a silver layer, and a gold layer arranged in sequence, with a thickness of about 3 μm, and the thickness of the gold layer accounts for about 10%.

[0066] Step 6, such as Figure 1 As shown in E and F of FIG. 1 , an isolation region 10 is reserved on the front side of the epitaxial layer 1 for subsequent formation of an isolation groove 8. Photoresist is coated on the front side of the epitaxial layer 1, outside the isolation region 10, by means of photolithography, and then an etchant is used for etching, so that the epitaxial layer 1, the back electrode 3, and the flexible substrate 4 at the isolation region 10 form an isolation groove 8. The photoresist is then removed and cleaned with acetone alcohol.

[0067] The etchant used in this embodiment is composed of a variety of reagents. Specifically, the epitaxial layer 1 is first etched with phosphoric acid hydrogen peroxide and hydrochloric acid solution until the back electrode 3 is exposed, and then the back electrode 3 and the flexible substrate 4 are etched with HF solution.

[0068] Step 7, such as Figure 1 As shown in G, the battery after step 6 is placed in a vacuum evaporation device, and an anti-reflection film 9 is evaporated on the front of the epitaxial layer 1. The anti-reflection film 9 is a double-layer film composed of Ti3O5 and Al2O3. After the anti-reflection film 9 is evaporated, it is cleaned with acetone alcohol.

[0069] Step 8, such as Figure 1 As shown in F and H of FIG. 8 , a dicing machine is used to cut along the isolation groove 8, and the cut battery is placed on a hot plate for heating. The hot plate is heated to the peeling temperature of the thermal peeling film 5, 200° C., and maintained for five minutes. The thermal peeling film 5 will be automatically desorbed from the flexible thin film solar cell, and the result is as shown in FIG. Figure 3 The flexible thin film solar cell shown.

[0070] Example 2

[0071] This embodiment provides a method for preparing a flexible thin-film solar cell, which is different from the embodiment 1 in that, in step 2 of this embodiment, a first transition layer is provided between the back field layer 106 and the first bonding metal layer, and a second transition layer is provided between the flexible substrate 4 and the second bonding metal layer. Both the first transition layer and the second transition layer are made of transition metals such as titanium, chromium, and nickel.

[0072] Based on the description in Example 1, the first bonding metal layer and the second bonding metal layer are bonded to form the back electrode 3, so the first bonding metal layer and the second bonding metal layer are usually made of gold, platinum, copper, silver, aluminum, palladium and other materials. At this time, since the back field layer 106 is usually made of aluminum gallium indium phosphide, its physical and chemical properties are quite different from those of the first bonding metal layer, directly bonding the back field layer 106 with the first bonding metal layer may cause the problem of unstable bonding. Therefore, in this embodiment, a first transition layer is provided between the back field layer 106 and the first bonding metal layer. The first transition layer is made of transition metal materials such as titanium, chromium, nickel, etc., and its physical and chemical properties are between the back field layer 106 and the first bonding metal layer. A transition can be formed between the back field layer 106 and the first bonding metal layer, thereby enhancing the bonding between the back field layer 106 and the first bonding metal layer.

[0073] Similarly, the flexible substrate 4 is usually made of organic polymer materials, and its physical and chemical properties are quite different from those of the second bonding metal layer. In this embodiment, a second transition layer is provided between the flexible substrate 4 and the second bonding metal layer to enhance the bonding between the flexible substrate 4 and the second bonding metal layer.

[0074] In this embodiment, the first transition layer and the second transition layer can be prepared by metal evaporation process.

[0075] In summary, the present invention provides a method for preparing a flexible thin-film solar cell, which is simpler and improves production efficiency by only performing two bonding steps in the process of manufacturing the cell, compared with the three bonding steps in the prior art.

[0076] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for preparing a flexible thin-film solar cell, characterized in that: The following steps are involved: Step 1, first bonding: take an epitaxial layer with a supporting substrate, and form a first bonding metal layer on the surface of the epitaxial layer; take a flexible substrate, and form a second bonding metal layer on the surface of the flexible substrate, and bond the first bonding metal layer and the second bonding metal layer to form a back electrode; Step 2, second bonding: providing a temporary rigid substrate and a thermal release film, and bonding the temporary rigid substrate to the flexible substrate via the thermal release film; Step 3, electrode fabrication: peeling off the support substrate, and then fabricating a front electrode and an anti-reflection film on the surface of the epitaxial layer; Step 4, manufacturing of flexible thin-film solar cells: heating to peel off the thermal peeling film and the temporary rigid substrate from the flexible substrate to obtain the flexible thin-film solar cell.

2. The method for preparing a flexible thin film solar cell according to claim 1, characterized in that: In step 1, the epitaxial layer is a sacrificial layer, a contact layer, a window layer, an emitter region, a base region and a back field layer which are arranged in sequence; the back field layer is close to the first bonding metal layer.

3. The method for preparing a flexible thin film solar cell according to claim 2, characterized in that: The back field layer is made of aluminum gallium indium phosphide, and the first bonding metal layer is made of at least one of gold, platinum, copper, silver, aluminum, and palladium.

4. The method for preparing a flexible thin film solar cell according to claim 3, characterized in that: A first transition layer is provided between the back field layer and the first bonding metal layer, and the first transition layer is made of at least one transition metal selected from titanium, chromium and nickel.

5. The method for preparing a flexible thin film solar cell according to claim 1, characterized in that: In step 1, the flexible substrate is made of polyimide and / or polyethylene terephthalate, and the second bonding metal layer is made of at least one of gold, platinum, copper, silver, aluminum, and palladium.

6. The method for preparing a flexible thin film solar cell according to claim 5, characterized in that: A second transition layer is provided between the flexible substrate and the second bonding metal layer, and the second transition layer is made of at least one transition metal selected from titanium, chromium and nickel.

7. The method for preparing a flexible thin film solar cell according to claim 1, characterized in that: The support substrate is at least one of a silicon substrate, a gallium arsenide substrate, and an indium phosphide substrate.

8. The method for preparing a flexible thin film solar cell according to claim 1, characterized in that: In step 4, the peeling temperature of the thermal peeling film is 200°C to 250°C.

9. The method for preparing a flexible thin film solar cell according to claim 1, characterized in that: The thermal release film has a thickness of 80 μm to 100 μm.

10. A flexible thin film solar cell, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 9.

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