Stacked solar cell

Abstract

The application provides a laminated solar cell, which comprises a back electrode, a bottom cell, a top cell, a front electrode, and an inter-junction conductive layer located between the bottom cell and the top cell, wherein the inter-junction conductive layer comprises at least two layers of transparent conductive films, and the work functions of the different transparent conductive films are different. Compared with the prior art, the application can well match the energy levels of the two-side cells by improving the properties of the inter-junction conductive layer of the laminated cell, and make the transition of the energy band from the bottom cell to the top cell more continuous, thereby reducing the contact resistance with the two-side cells, helping to improve the carrier transmission, improving the FF of the cell, effectively improving the conversion efficiency of the cell, and having important significance for the development of the laminated cell and the photovoltaic industry.

Description

Technical Field

[0001] This invention relates to the field of photovoltaics, and more particularly to a tandem solar cell with low junction contact resistance. Background Technology

[0002] With the continuous advancement of silicon-based tandem solar cell technology, especially the development of heterojunction (HJT) technology, single-junction silicon-based cells have approached their theoretical limit (~29%). To further improve cell efficiency, tandem cell technology has gradually gained favor among developers. Among the top-layer cells in silicon-based heterojunction tandem solar cells, perovskite cells are considered the preferred material due to their high conversion efficiency, wide bandgap of the light-absorbing material, and good matching of current density and voltage with silicon-based cells. They have received extensive research in recent years.

[0003] In typical tandem solar cell designs, two-junction cells usually use thin films made of materials such as ITO and ZnO prepared by physical or chemical vapor deposition as the intermediate transparent conductive layer. The work function of these films is generally between 4.0 eV and 4.8 eV, which is relatively low. When they form contact with p-type polycrystalline silicon or hole transport layers, they will form a large potential barrier, thereby increasing the series resistance of the cell and reducing the conversion efficiency.

[0004] In view of this, it is necessary to provide an improved tandem solar cell to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a tandem solar cell with low junction contact resistance.

[0006] To solve one of the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A tandem solar cell includes a back electrode, a bottom cell, a top cell, a front electrode, and an interjunction conductive layer located between the bottom cell and the top cell. The interjunction conductive layer includes at least two transparent conductive films, and the different transparent conductive films have different work functions.

[0008] Furthermore, the work function of at least two layers of the transparent conductive film gradually increases from bottom to top, or the work function of at least two layers of the transparent conductive film gradually decreases from bottom to top.

[0009] Furthermore, the work function of the interjunction conductive layer ranges from 3.0 eV to 9.0 eV.

[0010] Furthermore, the transparent conductive film includes one or more of indium oxide doping, zinc oxide doping, transparent conductive oxide, or conductive polymer.

[0011] Furthermore, the doped indium oxide is doped with one or more of tin, titanium, cerium, tungsten, molybdenum, and hydrogen;

[0012] And / or, the doped zinc oxide is doped with one or more of aluminum, magnesium, boron, hydrogen, etc.;

[0013] And / or, the transparent conductive oxide includes one or more of indium tin oxide, indium tungsten oxide, tungsten oxide, titanium oxide, zinc oxide, and zirconium oxide;

[0014] And / or, the conductive polymer includes one or more of PEDOT:PSS and P3HT.

[0015] Furthermore, the thickness of the transparent conductive film is 5 nm to 200 nm.

[0016] Furthermore, the bottom layer battery is a silicon-based battery, the top layer battery is a perovskite battery, and the work function of at least two transparent conductive films gradually increases or decreases from bottom to top.

[0017] Furthermore, the silicon-based solar cell includes, from bottom to top, a back transparent conductive layer, a first doped amorphous silicon layer, a first intrinsic amorphous silicon layer, a crystalline silicon layer, a second intrinsic amorphous silicon layer, and a second doped amorphous silicon layer;

[0018] The perovskite solar cell includes, from bottom to top, a hole transport layer, a perovskite light-absorbing layer, an electron transport layer, and a top transparent conductive layer.

[0019] The work function of at least two of the transparent conductive films gradually increases from bottom to top.

[0020] Furthermore, the interjunction conductive layer comprises a lower transparent conductive film and an upper transparent conductive film, wherein the work function of the lower transparent conductive film is 3.5eV to 4.3eV, and the work function of the upper transparent conductive film is 4.9eV to 8.6eV.

[0021] Furthermore, the lower transparent conductive film is an ITO film or an aluminum-doped zinc oxide film; the upper transparent conductive film is an IWO film, a PEDOT:PSS film, or an IMO film.

[0022] The beneficial effects of this invention are as follows: Compared with the prior art, this invention improves the properties of the conductive layer between the junctions of the tandem cells, which can better match the energy levels of the cells on both sides and make the transition of the energy band from the bottom cell to the top cell more continuous, thereby reducing its contact resistance with the cells on both sides, which helps to improve carrier transport, increase the cell FF, and effectively improve the cell conversion efficiency. This is of great significance to the development of tandem cells and the photovoltaic industry. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the stacked solar cell of the present invention;

[0024] Figure 2 This is a flowchart illustrating the fabrication process of the tandem solar cell of the present invention.

[0025] Among them, 100-tandem solar cell, 1-back metal electrode, 2-bottom cell, 21-crystalline silicon layer, 22-first intrinsic amorphous silicon layer, 23-first doped amorphous silicon layer, 24-back transparent conductive layer, 25-second intrinsic crystalline silicon layer, 26-second doped amorphous silicon layer, 3-interjunction conductive layer, 31-lower transparent conductive film, 32-upper transparent conductive film, 4-top cell, 41-perovskite light-absorbing layer, 42-hole transport layer, 43-electron transport layer, 44-top transparent conductive layer, 5-front metal electrode. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0027] In the various illustrations of this invention, for ease of illustration, certain dimensions of structures or parts may be exaggerated relative to other structures or parts; therefore, only the basic structure of the subject matter of this invention is used to illustrate the invention.

[0028] Please refer to Figure 1 As shown, the tandem solar cell 100 of the present invention includes, from bottom to top, a back metal electrode 1, a bottom cell 2, an interjunction conductive layer 3, a top cell 4, and a front metal electrode 5.

[0029] The underlying battery 2 is a silicon-based battery, including but not limited to silicon heterojunction batteries, emitter batteries, PERC back passivated batteries, PERT batteries, IBC batteries, MWT batteries, or Top-con batteries.

[0030] Preferably, the silicon-based cell is a silicon heterojunction cell, which includes a crystalline silicon layer 21, a first intrinsic amorphous silicon layer 22, a first doped amorphous silicon layer 23, and a back transparent conductive layer 24 sequentially disposed on the back side of the crystalline silicon layer 21; and a second intrinsic crystalline silicon layer 25 and a second doped amorphous silicon layer 26 sequentially disposed on the front side of the crystalline silicon layer 21.

[0031] The crystalline silicon layer 21 can be an N-type or P-type crystalline silicon wafer with a thickness of 80μm to 300μm.

[0032] The thicknesses of the first intrinsic amorphous silicon layer 22 and the second intrinsic amorphous silicon layer 21 are 2nm to 60nm, which provides a good passivation effect on the crystalline silicon layer 21.

[0033] The first doped amorphous silicon layer 23 and the second doped amorphous silicon layer 26 have different doping types and can be interchanged, depending on the battery design. For example, the crystalline silicon layer 21 can be an N-type or P-type crystalline silicon wafer, the first doped amorphous silicon layer 23 is a P-type doped crystalline silicon layer, and the second doped amorphous silicon layer 26 is an N-type doped crystalline silicon layer; or, the first doped amorphous silicon layer 23 is an N-type doped crystalline silicon layer, and the second doped amorphous silicon layer 26 is a P-type doped crystalline silicon layer.

[0034] In this invention, the thicknesses of the first doped amorphous silicon layer 23 and the second doped amorphous silicon layer 26 are 5 nm to 250 nm, respectively, and the doping concentration is 1e. 18 ~1e 23 .

[0035] The thickness of the back transparent conductive layer 24 is 10nm to 500nm, and the material is a transparent conductive oxide or a conductive polymer. The transparent conductive oxide includes, but is not limited to, one or more of indium tin oxide, indium tungsten oxide, tungsten oxide, titanium oxide, zinc oxide, and zirconium oxide; the conductive polymer includes, but is not limited to, one or more of PEDOT:PSS, P3HT, etc.

[0036] The back transparent conductive layer 24 can be prepared using any method commonly used to prepare transparent conductive films, including but not limited to one or more of deposition methods such as chemical vapor deposition, magnetron sputtering deposition, reactive plasma deposition, spin coating, spray coating, or roll-to-roll printing.

[0037] The top-layer battery 4 is a perovskite battery, which can be a pin-type battery with the hole transport layer 42 on top, or a nip-type battery with the hole transport layer 42 on the bottom.

[0038] Taking a nip-type structure as an example, the perovskite solar cell includes a perovskite light-absorbing layer 41, a hole transport layer 42 disposed on the back side of the perovskite light-absorbing layer, an electron transport layer 43 and a top transparent conductive layer 44 disposed sequentially on the front side of the perovskite light-absorbing layer. In certain specific cases, the electron transport layer 43 may also be combined with the top transparent conductive layer 44 into one layer.

[0039] The perovskite light-absorbing layer 41 has a thickness of 80 nm to 2000 nm and the material has an ABX3 structure, wherein A is a monovalent cation including K. + Na + Cs + 、Rb +HN=CHNH3 + (represented as FA), CH3NH2 + One or more of (denoted as MA); B is a divalent cation, including Sn. 2+ Pb 2+ One or more of the following; X includes a halide anion, said halide ion including F - Cl - ,Br - and I - etc.; or other ions, such as O2 - O2 - One or more of them.

[0040] The perovskite light-absorbing layer 41 has a band gap of 1.2 eV to 2.2 eV and can be prepared by one or more methods such as thermal evaporation, spin coating, spray coating, or roll-to-roll printing.

[0041] The hole transport layer 42 refers to the film layer that collects and transports photogenerated holes in the perovskite light-absorbing layer 41. The material can be one or more of PEDOT:PSS, nickel oxide, molybdenum oxide, tungsten oxide, graphite, etc., with a thickness of 5 nm to 100 nm. The preparation method employs one or more of chemical vapor deposition, magnetron sputtering deposition, reactive plasma deposition, spin coating, spray coating, or roll-to-roll printing.

[0042] The electron transport layer 43 refers to the film layer that collects and transports photogenerated electrons from the perovskite light-absorbing layer 41. Its material can be one or more of lithium fluoride, titanium dioxide, zinc oxide, tin oxide, polyethyleneimine (PEI), fullerenes and their derivatives (PCBM), with a thickness of 5 nm to 100 nm. The preparation method employs one or more of chemical vapor deposition, magnetron sputtering deposition, reactive plasma deposition, spin coating, spray coating, or roll-to-roll printing.

[0043] The preparation method and materials of the top transparent conductive layer 44 are the same as those of the back transparent conductive layer 24 in the silicon-based battery, and will not be described again here.

[0044] It should be noted that the films in the upright and inverted structures are the same, the only difference being their vertical position, which will not be elaborated here.

[0045] The bottom battery 2 and the top battery 4 are stacked and connected in series. The interjunction conductive layer 3 is located between the bottom battery 2 and the top battery 4, and mainly serves to collect the current of the batteries on both sides and improve the interface contact.

[0046] In this invention, the interjunction conductive layer 3 includes at least two transparent conductive films. The different transparent conductive films have different work functions, which can well match the energy levels of the cells on both sides and make the transition of the energy band from the bottom cell 2 to the top cell 4 more continuous, which helps to improve carrier transport and increase the battery FF.

[0047] Preferably, the work function of at least two layers of the transparent conductive film gradually increases from bottom to top, that is, the at least two layers of the transparent conductive film are arranged in order of gradually increasing work function from bottom to top; or the work function of at least two layers of the transparent conductive film gradually decreases from bottom to top, that is, the at least two layers of the transparent conductive film are arranged in order of gradually decreasing work function from bottom to top; the energy levels are stepped, which has a high degree of matching with the energy levels of the batteries on both sides, and can reduce the contact resistance between the bottom battery 2 and the top battery 4, which can effectively improve the battery conversion efficiency, and has important significance for the development of tandem batteries and the photovoltaic industry.

[0048] The work function of the interjunction conductive layer 3 ranges from 3.0 eV to 9.0 eV, and the work function of the multilayer transparent conductive film is located in different intervals within this range.

[0049] Specifically, the transparent conductive film comprises indium oxide doped with, zinc oxide doped with, transparent conductive oxide, or conductive polymer. The indium oxide doped with one or more of tin, titanium, cerium, tungsten, molybdenum, and hydrogen; the zinc oxide doped with one or more of Al, Mg, B, and H; the transparent conductive oxide comprises one or more of indium tin oxide, indium tungsten oxide, tungsten oxide, titanium oxide, zinc oxide, and zirconium oxide; and the conductive polymer comprises one or more of PEDOT:PSS and P3HT. This invention achieves this by selecting different materials to match the increase or decrease of film layers.

[0050] The thickness of the single-layer transparent conductive film is between 5 nm and 200 nm, and it can be prepared by any method commonly used to prepare transparent conductive films, including but not limited to deposition methods, such as one or more of chemical vapor deposition, magnetron sputtering deposition, reactive plasma deposition, spin coating, spray coating, or roll-to-roll printing.

[0051] In one embodiment, the bottom cell 2 is a silicon-based cell, and the second doped amorphous silicon layer 26 is an N-type doped crystalline silicon layer; the top cell 4 is a perovskite cell, and the hole transport layer 42 is located on the back side of the perovskite light-absorbing layer 41, and the work function of at least two transparent conductive films gradually increases from bottom to top.

[0052] Taking the interjunction conductive layer 3 as an example of a two-layer structure, the work function of the lower transparent conductive film 31 is less than that of the upper transparent conductive film 32. For example, the work function of the lower transparent conductive film 31 is 3.5 eV to 4.3 eV, and it can be made of materials such as ITO film or aluminum-doped zinc oxide (ZnO:Al) film. The work function of the upper transparent conductive film 32 is 4.9 eV to 8.6 eV, and it can be made of materials such as IWO film, PEDOT:PSS film, or IMO (indium molybdenum doped oxide) film.

[0053] Please refer to Figure 2 As shown, the fabrication method of this tandem solar cell is as follows: An N-type monocrystalline silicon wafer with a thickness of approximately 130 nm and a resistivity of 0.5 Ω·cm to 5 Ω·cm is texturized to form a pyramidal textured surface; intrinsic amorphous silicon layers of 212 nm to 10 nm are deposited on both the front and back sides of the silicon wafer using PECVD; p-type doped amorphous silicon with a thickness of 5 nm to 20 nm is deposited on the back side; an n-type doped amorphous silicon layer 21 with a thickness of 5 nm to 20 nm is deposited on the front side; ITO is deposited on the back side as the back transparent conductive layer 24 with a thickness of 50 nm to 100 nm and a sheet resistance of 30 Ω / □ to 100 Ω / □; two interjunction transparent conductive films are deposited on the front side using PVD, with film thicknesses of 30 nm to 100 nm and sheet resistances of [missing information]. The sheet resistance is 50 Ω / □ to 150 Ω / □, respectively. Above the interjunction conductive layer 3, MoO3 is vacuum-deposited as a hole transport layer 42 with a thickness of 50 nm to 100 nm and a sheet resistance of 30 Ω / □ to 100 Ω / □. A perovskite light-absorbing layer 41, made of CH3NH2PbCl3, is then prepared on top of this layer using a spin-coating method. An electron transport layer 43 is then prepared on top of this layer using a PCBM thin film with a thickness of 5 nm to 20 nm. An ITO top transparent conductive layer 44, with a thickness of 50 nm to 100 nm and a sheet resistance of 30 Ω / □ to 100 Ω / □, is then deposited using PVD. Finally, the front metal electrode 5 and the back metal electrode 1 are prepared by screen printing silver grid lines.

[0054] Comparative Example 1: The only difference from the Example is that the interjunction conductive layer 3 is prepared using a single layer of ITO with a work function of 4.2eV to 4.7eV, prepared by magnetron sputtering, with a film thickness of 60nm to 140nm and a sheet resistance of 50Ω / □ to 200Ω / □.

[0055] The battery performance data of Example 1 and Comparative Example 1 are shown in the table below:

[0056] Comparative Example 1 1740.5 21.42 81.07 30.22 Example 1 1742.0 21.48 82.77 30.97

[0057] It can be seen that the interjunction conductive layer 3 uses a multilayer film structure, which greatly improves the FF of the battery and thus improves the battery efficiency. This indicates that the intermediate transparent conductive layer plays a role in regulating the contact between the two batteries.

[0058] In summary, compared with the prior art, the present invention improves the properties of the conductive layer 3 between the junctions of the tandem cells, which can better match the energy levels of the cells on both sides and make the transition of the energy band from the bottom cell 2 to the top cell 4 more continuous. This reduces the contact resistance between the cell and the cells on both sides, helps to improve carrier transport, increase the cell FF, and effectively improve the cell conversion efficiency. This is of great significance to the development of tandem cells and the photovoltaic industry.

[0059] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0060] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tandem solar cell, comprising a back electrode, a bottom cell, a top cell, and a front electrode, characterized in that, The underlying battery is a silicon-based battery, which includes a crystalline silicon layer, a second intrinsic amorphous silicon layer and a second doped amorphous silicon layer sequentially disposed on the front side of the crystalline silicon layer. The top-layer battery is a perovskite battery, which includes a hole transport layer, a perovskite light-absorbing layer, an electron transport layer, and a top transparent conductive layer arranged sequentially from bottom to top. The tandem solar cell further includes an interjunction conductive layer located between the bottom cell and the top cell. The interjunction conductive layer includes at least two transparent conductive films, each with a different work function. The interjunction conductive layer includes a lower transparent conductive film and an upper transparent conductive film. The lower transparent conductive film is in contact with the second doped amorphous silicon layer, and the upper transparent conductive film is in contact with the hole transport layer. The work function of the lower transparent conductive film is less than that of the upper transparent conductive film, and the work function of the upper transparent conductive film is 4.9 eV to 8.6 eV.

2. The tandem solar cell according to claim 1, characterized in that: The work function of at least two of the transparent conductive films gradually increases from bottom to top.

3. The tandem solar cell according to claim 1, characterized in that: The work function of the interjunction conductive layer ranges from 3.0 eV to 9.0 eV, and the work function of the multilayer transparent conductive film is located in different intervals within this range.

4. The tandem solar cell according to claim 1, characterized in that: The transparent conductive film includes one or more of indium oxide doped with indium oxide, zinc oxide doped with zinc oxide, transparent conductive oxide, or conductive polymer, and the conductive polymer includes one or more of PEDOT:PSS and P3HT.

5. The tandem solar cell according to claim 4, characterized in that: The doped indium oxide is doped with one or more of tin, titanium, cerium, tungsten, molybdenum, and hydrogen; And / or, the doped zinc oxide is doped with one or more of aluminum, magnesium, boron, and hydrogen; And / or, the transparent conductive oxide includes one or more of indium tin oxide, indium tungsten oxide, indium cerium oxide, tungsten oxide, titanium oxide, zinc oxide, and zirconium oxide.

6. The tandem solar cell according to claim 1, characterized in that: The thicknesses of the lower transparent conductive film and the upper transparent conductive film are 5 nm to 200 nm, respectively.

7. The tandem solar cell according to claim 1, characterized in that: The work function of the lower transparent conductive film is 3.5 eV to 4.3 eV.

8. The tandem solar cell according to claim 1, characterized in that: The silicon-based battery also includes a first intrinsic amorphous silicon layer, a first doped amorphous silicon layer, and a back transparent conductive layer sequentially disposed on the back side of the crystalline silicon layer.

9. The tandem solar cell according to claim 8, characterized in that: The crystalline silicon layer is an N-type crystalline silicon wafer. The first doped amorphous silicon layer and the second doped amorphous silicon layer have different doping types. The second doped amorphous silicon layer is an N-type doped crystalline silicon layer.

10. The tandem solar cell according to claim 1, characterized in that: The lower transparent conductive film is an ITO film or an aluminum-doped zinc oxide film; the upper transparent conductive film is an IWO film, or a PEDOT:PSS film, or an IMO film. And / or, the hole transport layer material is one or more of PEDOT:PSS, nickel oxide, molybdenum oxide, tungsten oxide, and graphite; And / or, the thickness of the hole transport layer is 5nm~100nm.

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