Patent Application
20250194287
The disclosure relates to the technical field of solar cells, and more particularly, to a conductive contact structure of a solar cell, a solar module, and a solar cell.
In a solar cell, as shown in
The disclosure provides a conductive contact structure of a solar cell, a solar module, and a solar cell.
A conductive contact structure of a solar cell is provided, and the conductive contact structure of a solar cell includes:
the electrode includes a seed layer in contact with the semiconductor region;
y material, and includes at least one main component and at least one improved component, the at least one main component is one or more metals having an average refractive index lower than 2 and a wavelength in a range of 850-1200 nm, and the at least one improved component includes any one or more of Mo, Ni, Ti, W, Cr, Mn, Pd, Bi, Nb, Ta, Pa, Si, and V.
Optionally, the at least one main component includes any one or more of Al, Ag, Cu, and Mg.
Optionally, the at least one improved component further comprise a non-metallic composition.
Optionally, a content of the at least one main component is greater than 50 wt. % of the seed layer.
Optionally, the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Ni having a content less than or equal to 30 wt. % of the seed layer.
Optionally, the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is W having a content less than or equal to 30 wt. % of the seed layer.
Optionally, the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Ti having a content less than or equal to 30 wt. % of the seed layer.
Optionally, the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Mo having a content less than or equal to 30 wt. % of the seed layer.
Optionally, the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Cr having a content less than or equal to 30 wt. % of the seed layer.
Optionally, the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Si having a content less than or equal to 30 wt. % of the seed layer.
Optionally, the seed layer is formed on the substrate by physical vapor deposition manufacturing method, or screen printing manufacturing method, or chemical vapor deposition manufacturing method, or electroplating manufacturing method, or chemical plating manufacturing method.
Optionally, the electrode further includes a conductive layer disposed above the seed layer.
Optionally, the conductive layer includes any one or more of Cu, Ag, and Al.
Optionally, a passivation film is formed between the seed layer and the semiconductor region. The passivation film has an opening, and the seed layer is in contact with the semiconductor region through the opening.
Optionally, a transparent conductive oxide (TCO) thin film is further disposed between the seed layer and the passivation film, and the TCO thin film is in contact with the semiconductor region through the opening on the passivation film.
Optionally, the TCO thin film is an indium tin oxide or a zinc oxide-based thin film.
Optionally, the semiconductor region includes a tunnel oxide layer and doped polysilicon layer.
Optionally, a method for growing the conductive layer on the seed layer includes electroplating, physical vapor deposition, screen printing, or chemical plating.
Optionally, a protective layer covers the conductive layer.
Optionally, the protective layer is an Sn layer or an Ag layer.
Optionally, the protective layer is grown on the conductive layer by electroplating or chemical plating.
Optionally, the substrate is a silicon substrate.
Optionally, the seed layer is formed by stacking a plurality of sub-seed layers.
Optionally, contents of main components in the sub-seed layers stacked along a direction away from the substrate gradually decrease.
Optionally, a thickness of the seed layer is between 10 nm and 1000 nm.
Optionally, a thickness of the seed layer is between 30 nm and 300 nm.
Optionally, a thickness of the conductive layer is between 1 μm and 800 μm.
Optionally, a thickness of the conductive layer is between 1 μm and 100 μm.
The disclosure further provides a solar cell comprising the conductive contact structure.
The disclosure further provides a solar module comprising a plurality of solar cells that are electrically connected to each other.
To describe the technical solutions in the embodiments of the disclosure more clearly, the following briefly describes the accompanying drawings required for describing the embodiments of the disclosure. Obviously, the accompanying drawings in the following descriptions are merely some embodiments of the disclosure, and a person of ordinary skill in the art may further obtain other accompanying drawings according to the accompanying drawings without creative efforts.
The technical solutions of the disclosure are further described in detail below with reference to the accompanying drawings and specific implementations.
The accompanying drawings are merely schematic diagrams for exemplary descriptions, are not drawn to scale, and therefore are not intended to be construed as a limitation to the disclosure. To better illustrate the embodiments of the disclosure, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the size of an actual product. For a person skilled in the art, some well-known structures and descriptions thereof may be omitted in the accompanying drawings.
The same or similar components are denoted by the same or similar reference numerals in the accompanying drawings of the embodiments of the disclosure. In the description of the disclosure, it should be understood that, orientations or position relationships indicated by terms such as “up”, “down”, “left”, “right”, “inside”, and “outside” are orientations or position relationships shown based on the accompanying drawings, and are merely used for describing the disclosure and simplifying the description, but are not intended to indicate or imply that the apparatus or element should have a particular orientation or be constructed and operated in a particular orientation. Therefore, the terms used for describing the position relationships are merely used for exemplary descriptions, and cannot be constructed as a limitation to the disclosure. A person of ordinary skill in the art may understand specific meanings of the foregoing terms according to specific situations.
In the description of the disclosure, unless otherwise specified or defined, terms such as “connect” that indicates a connection relationship between components should be understood in a broad sense. For example, the connection may be a fixed connection, a detachable connection, or an integral connection; or the connection may be a mechanical connection or an electrical connection; or the connection may be a direct connection, an indirect connection through an intermediate, or internal communication between two components or an interaction relationship between two components. A person of ordinary skill in the art may understand specific meanings of the foregoing terms in the disclosure according to specific situations.
A conductive contact structure of a solar cell provided in an embodiment of the disclosure is shown in
A semiconductor region, and the semiconductor region is disposed on or in the substrate 1.
An electrode 100, is disposed in the semiconductor region.
The electrode includes a seed layer 2 in contact with the semiconductor region.
The seed layer 2 includes an alloy material, and includes at least one main component and at least one improved component. The at least one main component is one or more metals having an average refractive index lower than 2 and a wavelength in a range of 850-1200 nm (in some embodiments, any one or more of Al (aluminum), Ag (silver), Cu (copper), or Mg (magnesium)), and the at least one improved component includes any one or more of Mo (molybdenum), Ti (titanium), W (tungsten), Ni (nickel), Cr, Si, Mn, Pd, Bi, Nb, Ta, Pa, or V. In some embodiments, a content of the at least one main component in the seed layer is greater than 50%. In some embodiments, the at least one main component of the seed layer is Al, having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Ti having a content less than or equal to 30 wt. % of the seed layer, or the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is W having a content less than or equal to 30 wt. % of the seed layer, or the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Ti having a content less than or equal to 30 wt. % of the seed layer, or the at least one main component is Al having a content greater than or equal to 70 wt. % of the seed layer. The at least one improved component is Mo having a content less than or equal to 30 wt. % of the seed layer.
Ag paste is currently used as an electrode material in mass-produced crystalline silicon solar cells, and costs of Ag paste account for nearly 30% of costs of Non-silicon Cost of cells. Reducing an amount of Ag or not using the production technology of Ag can effectively reduce production costs of the solar cells. Cu is a desirable substitute for Ag. Compared with Ag, Cu has the following advantages as the conductive material, as shown in the following Table a:
It can be learned from the above Table a that Cu has relatively stable chemical properties, excellent ductility, and sufficiently low volume resistivity, and is available at low prices (close to 1/72 of a price of Ag), these excellent characteristics make Cu become an effective substitute for Ag. However, Cu has two important characteristics that limit the application in the solar cell. The first characteristic is that Cu has a too large diffusion coefficient.
The second characteristic is that defects of Cu have a large capture cross-section for a hole, which greatly reduces a bulk lifetime and reduces electrical performance of the solar cell. The impact of the Cu content on the bulk lifetime and the battery performance is shown in Table b below:
It can be learned from the Table b that with an increase in the Cu content, the bulk lifetime is greatly reduced, and the cell efficiency is also greatly reduced. Even if there are only 1E12/cm3 of Cu impurities, the cell efficiency is also reduced by 0.29%.
A method known to the inventors, Ni (nickel) is generally used as a barrier layer for diffusion of Cu, and also can well adhere to the substrate and the Cu electrode. The general process of the implementation is: preparing the coated substrate—opening a mould by laser—electroplating Ni—electroplating a Cu layer. However, during our research, it is found that Ni has a major defect as the barrier layer of Cu, that is, a relatively poor long-wavelength reflection effect, which reduces the light trapping effect of the cell and further reduces the conversion efficiency of the cell.
Comparison data of optical properties of the cell using Ni+Cu and Ag as electrode materials is shown in the following Table c:
It can be learned from the above Table c that a combination of Ni+Cu greatly reduces the short-circuit current density of the cell. The simulation results predict that the short-circuit current density is to be decreased by 0.75 mA/cm2, and the experimental result shows that the short-circuit current density is reduced by 1.36 mA/cm2, which is greater than that from theoretical prediction.
Trapping effects of the common metals are analyzed below.
At present, a silicon wafer thickness of the finished cell is about 150 μm, and photon having a wavelength greater than 850 nm can effectively penetrate the thickness. In addition, because a forbidden band width of Si is 1.12 eV, photon having a wavelength greater than 1200 nm is difficult to excite electron-hole pairs. Therefore, mainly 850-1200 nm bands are considered for the light trapping effect. The following Table d shows interface reflectivity of different metals and market prices found in February 2022.
It can be seen from the above Table d that interface reflectivity among different metals differ greatly. The four metals Ag/Al/Cu/Mg can obtain relatively ideal short-circuit current density results, and are used in the seed layer, so as to achieve the effective light trapping effect. Further analysis is as follows. Cu cannot be used as the seed layer because an important role of the seed layer is to block Cu. The chemical properties of Mg are excessively active, and therefore Mg is not a good choice. Ag is more expensive and is not a good choice either. Al is an ideal seed layer metal, which has an excellent back reflectivity effect, has relatively stable chemical properties, and has a low price that is only 1/223 of Ag and ⅓ of Cu.
However, pure Al used as the seed layer introduces another problem. The adhesion between Al and other metals is weak, the technology of using pure Al as the seed layer can cause product reliability not up to the standard, a case of alternating heat and cold or bending of the product or the stress of a solder joint in the component welding causes the Al to be separated from an external metal, resulting in falling and failure.
The bonding force between Al and Cu is poor, which easily causes fingers to fall in pieces. In order to resolve the problem, various improvement methods have been tried. For example, a contact area of the Al/substrate is increased, a sample is heated to promote intermetallic interdiffusion, a new material such as TiW is added between Al/Cu materials, and the like, and but the effect is not ideal. Finally, it is found that if the at least one improved component that can form good interconnection with Cu is added to the Al material as the seed layer, even additional annealing treatment is not required after Cu is electroplated. That is to say, desirable adhesion of the seed layer/electroplating layer has been formed, which greatly improves the adhesion of the electroplating layer, and eventually solves the problem.
The improved components such as Ni, Mo, Ti, W, Cr, Mn, Pd, Bi, Nb, Ta, Pa, Si, and V obviously enhance the adhesion.
Further, Ni, Mo, Ti, W, Cr, Mn, Pd, Bi, Nb, Ta, Pa, and Si have low reflectivity. If excessive materials are added, the optical performance will be reduced. Using W as an example, it is simply assumed that the property of the alloy material is an enhanced average value of the compositions, and the calculation results shown in the following Table e are obtained.
When the W content is 30%, a current loss is 0.36 mA/cm2, which causes a reduction in cell conversion efficiency by about 0.2%. Although the loss is relatively large, it is acceptable in terms of cost reduction brought about by replacement of Ag by Cu and the solution to the reliability problem. Therefore, it is considered that the at least one improved component less than or equal to 30 wt. % of the seed layer is a recommended value.
In some embodiments, the improved components in the seed layer is unevenly distributed, so that better performance can be obtained. The principle is as follows. The content of the improved component of a part close to the substrate is less than the content of the improved component of other part, which can enhance the reflection of the light, while a part in contact with the metal of the conductive layer contains a relatively more content of the improved component, to improve the bonding force with the metal of the conductive layer.
The following Table f shows comparison of welding tension of different electrode technologies.
It can be seen from the above Table f that the pure Al seed layer has relatively low finger tension and is much lower than that of a conventional Ag electrode, while the welding tension is improved after TiW are directly added between Al and Cu, but there are still shortcomings. In the disclosure, the solar cell made by the Al alloy seed layer has even higher welding tension than the conventional Ag electrode.
Al is used as the at least one main component to improve the adhesion between the seed layer and the Cu conductive layer and the light trapping effect of the solar cell. Table g lists data of the technical effects that can be brought by the combination of each single improved component and the at least one main component Al:
It can be learned from the above experimental data that Cr, Mn, Pd, Bi, Nb, Ta, Pa, Si, and V as improved components can also improve the adhesion between the seed layer and the Cu conductive layer and the light trapping effect of the solar cell. It should be emphasized that there are hundreds of combinations of any one or more of the at least one improved components Mo, Ni, Ti, W, Cr, Mn, Pd, Bi, Nb, Ta, Pa, Si, and V combined with Al, and it is impossible for us to provide experimental comparative data for all compositions. Therefore, on the premise that the experimental data of Ni, Mo, Ti, W, Cr, Mn, Pd, Bi, Nb, Ta, Pa, Si, and V as individual improved components are given in the specific implementation, it is obvious that other improved components combined with the at least one main component Al can also achieve the desired technical effect.
In some embodiments, a thickness of the seed layer is greater than or equal to 30 nm. It is found by experiments that the seed layer having the thickness of 30 nm is sufficient to prevent the diffusion of the Cu metal. For the thickness less than or equal to 300 nm, the main consideration is to control the cost. For example, the seed layer is made by physical vapor deposition. Even if Al is cheaper than other metals, the cost impact of the Al target material still cannot be ignored. Besides, a larger thickness of the seed layer leads to lower production capacity on the device side, which is not conducive to the promotion of mass production. Therefore, in the embodiments, the thickness of the seed layer is between 30 nm and 300 nm.
Further, in order to save the costs of the alloy target material and further limit the diffusion of Cu to the substrate, a transparent conductive oxide (TCO) layer may be added between the alloy seed layer and the substrate, and light in a long-wavelength band can pass through the TCO layer and can be effectively reflected at the interface of the alloy layer. In this way, ideal performance and reliability results can also be obtained.
In some embodiments, the seed layer is formed on the substrate by any of manufacturing methods such as the physical vapor deposition (comprising sputtering and evaporation), screen printing, chemical vapor deposition, electroplating, or chemical plating. In some embodiments, the seed layer is formed by stacking a plurality of sub-seed layers. In some embodiments, contents of main components in the sub-seed layers stacked along a direction facing away from the substrate gradually decrease. A high content of the at least one main component in the sub-seed layer at a small distance from the substrate can enhance the reflective effect, thereby improving the light-trapping effect of the solar cell. The sub-seed layer at a large distance from the substrate (closer to the conductive layer) has a high content of the at least one improved component and a relatively low content of the at least one main component, which can ensure the bonding force between the sub-seed layer and the conductive layer.
In some embodiments, the thickness of the seed layer is preferably between 10 nm and 1000 nm, and in some embodiments, the thickness of the seed layer is between 30 nm and 300 nm.
The electrode provided in this embodiment is shown in
In order to protect the conductive layer, in some embodiments, an upper portion of the conductive layer is covered with a protective layer 4. In some embodiments, the protective layer 4 is an Sn layer or an Ag layer. In some embodiments, The protective layer 4 is grown on the conductive layer 3 by electroplating or chemical plating.
As shown in
Based on the above, according to the disclosure, the seed layer is added between the conductive layer and the substrate. A material of the seed layer is an alloy material, and the at least one main component thereof is one or more metals having an average refractive index lower than 2 within the wavelength range of 850-1200 nm, and the at least one improved component is any one or more of Mo, Ni, Ti, W, Cr, Si, Mn, Pd, Bi, Nb, Ta, Pa, or V. The seed layer formed by fusing the at least one main component and the at least one improved component can be tightly bonded to the conductive layer and the substrate. In addition, a light trapping effect of the solar cell is enhanced.
An embodiment of the disclosure further provides a solar cell. The solar cell includes the above conductive contact structure.
An embodiment of the disclosure further provides a solar module, comprising a plurality of solar cells having the above conductive contact structure that are electrically connected to each other.
An embodiment of the disclosure further provides a solar power generation system, comprising a plurality of solar modules that are electrically connected to each other.
It should be noted that, the foregoing specific embodiments are merely exemplary embodiments of the disclosure and descriptions of the applied technical principles. A person skilled in the art may understand that various modifications, equivalent replacements, and changes may be made to the disclosure. However, such changes without departing from the spirit of the disclosure shall all fall within the protection scope of the disclosure. In addition, terms used in this specification and claims of this application are not limitative, but are merely used for convenience of description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210239253.9 | Mar 2022 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/000057 | 6/21/2022 | WO |
