Crystalline silicon wafer and silicon ingot for preparing crystalline silicon photovoltaic cell and laminated photovoltaic cell

Abstract

The invention relates to the technical field of photovoltaic cells and materials thereof, and discloses a crystalline silicon wafer for preparing a crystalline silicon photovoltaic cell, a silicon ingot and a laminated photovoltaic cell. The crystal silicon wafer has one of the following characteristics: 1) the crystal silicon wafer is a lithium crystal silicon wafer of lithium-doped silicon; and 2) the crystal silicon wafer is an alloy crystal silicon wafer, the alloy crystal silicon wafer comprises a substrate, an alloy area containing silicon, tin and germanium alloy elements is locally prepared on the substrate, the alloy crystal silicon wafer is formed, and the alloy area of the alloy crystal silicon wafer comprises the following alloy elements in percentage by atomic number: 5-53% of silicon, 2-12% of tin and the balance of germanium. Compared with the prior art, the current output potential is improved, the photoelectric conversion efficiency is improved, lithium in the lithium crystal silicon wafer effectively passivates defects in crystalline silicon, the minority carrier lifetime of the crystalline silicon is prolonged, the mobility of the crystalline silicon is improved, a better lithium interface passivation effect is achieved, and the function of resisting the ultraviolet induced degradation effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cells and their materials technology, and more specifically, to a crystalline silicon wafer, silicon ingot, and tandem photovoltaic cell for preparing crystalline silicon photovoltaic cells. Background Technology

[0002] The first aspect of the background technology of this invention is the crystalline silicon photovoltaic cell base cell in tandem photovoltaic cells, as well as the related crystalline silicon wafers and ingots.

[0003] Crystalline silicon, especially monocrystalline silicon photovoltaic cells, are currently the most cost-effective photovoltaic cells, offering stable performance, mature technology, and satisfactory photoelectric conversion efficiency. Therefore, when attempting to develop perovskite tandem photovoltaic cells with higher photoelectric conversion efficiency and lower cost potential, to mitigate the risks of poor stability and environmental problems associated with heavy metals like lead in perovskite cells, tandem photovoltaic cells combining perovskite and crystalline silicon cells have been developed. In these tandem photovoltaic cells, the perovskite cell acts as the top cell absorbing short-wavelength light, while the crystalline silicon cell acts as the bottom cell absorbing long-wavelength light, thus achieving a higher photoelectric conversion efficiency.

[0004] However, the inherent bandgap and indirect bandgap absorption of crystalline silicon materials hinder the improvement of photoelectric conversion efficiency and the reduction of material costs in the tandem photovoltaic cells.

[0005] The specific analysis is as follows: The number of solar photons Q that a photovoltaic cell can absorb determines the short-circuit current density j of the photovoltaic cell's output. sc The upper limit of the band gap width E of photovoltaic cell materials g The open-circuit voltage V of the photovoltaic cell is determined. oc The upper limit of j sc With V oc The product of these two values ​​represents the upper limit of the photovoltaic cell's power density output. The ratio of this upper limit to the solar irradiance represents the upper limit of the photovoltaic cell's photoelectric conversion efficiency. That is;

[0006] in: η: Photovoltaic cell photoelectric conversion efficiency; E g (λ): The band gap width of the photoactive material in a photovoltaic cell. Different band gap widths correspond to different light absorption cutoff wavelengths. For crystalline silicon materials, E g =1.12ev; Q(λ): The number of photons per unit irradiated area and per unit wavelength interval; E(λ): Solar irradiance.

[0007] Single-junction photovoltaic cells with a fixed bandgap width cannot simultaneously achieve both high open-circuit voltage by utilizing short-wavelength irradiation and high short-circuit current density by absorbing long-wavelength irradiation in distributed spectral irradiation.

[0008] For example, for the surface solar spectrum of AM1.5, E g Photoactive materials with a wavelength of 1.4 eV can achieve the highest single-junction photoelectric conversion efficiency, with a corresponding absorption cutoff wavelength of 886 nm. To improve the photoelectric conversion efficiency of photovoltaic cells by utilizing both semiconductor materials with higher bandgap widths to obtain higher output voltages and semiconductor materials with lower bandgap widths to absorb more photons and obtain larger output current densities, a tandem photovoltaic cell composed of materials with different bandgap widths was designed. This fully absorbs and utilizes sunlight irradiation of different wavelengths, thereby improving the overall photoelectric conversion efficiency of the photovoltaic cell.

[0009] One drawback of existing technologies using crystalline silicon photovoltaic cells as the base cells in tandem photovoltaic systems is the limitation of the band gap width of crystalline silicon materials. Crystalline silicon has a band gap width of 1.12 eV and a cutoff absorption wavelength of 1107 nm. Therefore, it cannot absorb the two "humps" of light quanta in the AM1.5 spectrum, with center wavelengths of 1200 nm and 1600 nm, thus limiting further improvements in the cell's photoelectric conversion efficiency.

[0010] The second aspect of the background technology of this invention is the ultraviolet-induced degradation (UVID) effect commonly encountered in high-efficiency crystalline silicon photovoltaic cells.

[0011] High-efficiency crystalline silicon photovoltaic cells heavily rely on hydrogen passivation of the crystalline silicon interface, thus commonly exhibiting ultraviolet-induced degradation (UVID) effects. Secondary ion mass spectrometry (SIMS) analysis shows that ultraviolet light at a wavelength of 365 nm dissociates Si-H bonds, causing hydrogen atoms to migrate from the passivation interface of the cell and form permanent damage or metastable defects. Based on case studies, photovoltaic modules exhibiting UVID effects show a power loss of 1% after the first year, decreasing to 0.4% annually thereafter. It is estimated that over 25 years, under this effect alone, the conversion efficiency of the photovoltaic module will decrease by 10%. Summary of the Invention

[0012] I. Nouns and Terminology: The following terms and terms have the following meanings in this application: Crystalline silicon / crystalline silicon wafer: Doping level is 10 21 / cm 3 The following refers to crystalline silicon / crystalline silicon wafers. This includes polycrystalline silicon and monocrystalline silicon, and the crystalline silicon in this application specifically includes lithium-doped lithium crystalline silicon.

[0013] Lithium crystalline silicon: Lithium-doped crystalline silicon includes lithium crystalline silicon wafers and lithium crystalline silicon ingots.

[0014] Alloy crystalline silicon / Alloy crystalline silicon wafers: Crystalline silicon / crystalline silicon wafers containing alloy regions of silicon, tin, and germanium alloying elements.

[0015] First quantum photon hump and second quantum photon hump: See Figure 3 The first and second quantum humps refer to the areas of concentrated quantum density around the center wavelength of 1250 nm and around the center wavelength of 1600 nm, respectively, in the AM1.5 spectrum sunlight quantum distribution diagram by wavelength.

[0016] Tandem photovoltaic cells at both ends: A tandem photovoltaic cell in which the light path of the bottom cell and the top cell are connected in series and the circuit is connected in series.

[0017] Four-terminal tandem photovoltaic cells: A tandem photovoltaic cell is a type of photovoltaic cell in which the optical paths of the bottom and top cells are connected in series, while the circuitry is independent and separate.

[0018] Non-primary light-receiving surface: The side of the battery that receives less total radiation is commonly known as the back side. II. Summary of the Invention: This invention uses lithium to partially replace hydrogen for passivation of the battery interface. The chemical bond between lithium and silicon is more ionic, resulting in a higher bond energy. Furthermore, lithium has a significantly higher mass and radius than hydrogen, thus providing greater passivation stability. In addition, lithium can passivate various defects within the silicon crystal, which is beneficial for improving the minority carrier lifetime and carrier mobility of crystalline silicon materials.

[0020] The first objective of this invention is to extend the cutoff absorption wavelength of crystalline silicon. The measures taken are as follows: First, by doping lithium ions into the lattice gaps of the silicon crystal, the interatomic spacing of the crystalline silicon material is expanded, reducing the band gap width of the bottom-cell crystalline silicon material. Second, by using group IVA elements germanium and tin to form alloys with silicon, the interatomic spacing of silicon atoms is altered. This achieves the goal of extending the absorption of at least one of the two "humps" at the center wavelengths of 1250 nm and 1600 nm in the AM1.5 spectrum, converting them into photovoltaic output current. Simultaneously, a larger share of short-wavelength, high-energy photons is allocated to the perovskite top-cell for high-efficiency absorption and conversion to obtain a higher open-circuit voltage, thereby improving the overall photoelectric conversion efficiency of the tandem photovoltaic cell.

[0021] A second objective of this invention is to passivate the battery interface by partially replacing hydrogen with lithium, thereby achieving in-vivo defect passivation and reducing the risk of ultraviolet-induced degradation (UVID).

[0022] In a first aspect, the present invention provides a crystalline silicon wafer for preparing crystalline silicon photovoltaic cells, having one of the following characteristics: 1) The crystalline silicon wafer is a lithium-doped silicon lithium crystalline silicon wafer with a density lower than 1×10⁻⁶. 17 / cm 3 Concentrations of elemental lithium can effectively passivate defects in silicon crystals, improve minority carrier lifetime, and increase minority carrier mobility, but they cannot significantly alter the bandgap width of crystalline silicon, especially above 10⁻⁶. 20 / cm 3 High doping concentrations can easily introduce new defects into silicon crystals. Doping concentrations of 10... 17 / cm 3 ~10 20 / cm 3 When dealing with a range, there is an empirical formula: ΔE g ≈A(N Li ) 0.33 in: ΔE g : Change in bandgap width, ev; A: Coefficient, A≈5×10 -8 ev•cm 3 ; N: Doping concentration, atoms / cm³ 3 .

[0023] This empirical formula determines that the bandgap width of crystalline silicon can be altered when the lithium doping concentration falls within the following range. Simultaneously, interstitial lithium atoms can, to some extent, modulate the lattice strain, making the crystal structure more stable.

[0024] The concentration of elemental lithium in the lithium-ion silicon wafer is at least one of the following ranges: a) (1×10 16 / cm 3 )≤N Li ≤(1×10 17 / cm 3 ); b) (1×10 17 / cm 3 )<N Li ≤(1×10 18 / cm 3 ); c) (1×10 18 / cm 3 )<N Li≤(1×10 20 / cm 3 ); 2) The crystalline silicon wafer is an alloy crystalline silicon wafer. The alloy crystalline silicon wafer includes a substrate. The substrate is locally prepared with an alloy region including silicon, tin, and germanium alloy elements to form an alloy crystalline silicon wafer. The alloy element ratio range (atomic ratio) of the alloy region of the alloy crystalline silicon wafer is as follows: silicon 5%~53%, tin 2%~12%, germanium balance (optional: tin 2%, silicon 5%, germanium balance, tin 2%, silicon 15%, germanium balance, tin 2%, silicon 30%, germanium balance, tin 5%, silicon 2%, germanium balance, tin 5%, silicon 18%, germanium balance, tin 5%, silicon 52%, germanium balance, tin 12%, silicon 15%, germanium balance, tin 12%, silicon 30%, germanium balance, tin 12%, silicon 50%, germanium balance, etc.).

[0025] The beneficial effects of the above-mentioned invention are: 1) See Figure 4 , Figure 4 This diagram illustrates the relationship between photonic quantum density and sunlight wavelength in the 300nm~1800nm ​​range, using key data from the AM1.5 spectral irradiance standard provided by IEC 60904-3. Within the range of 350nm and the bottom cell absorption cutoff wavelength λc, the area enclosed by the curve and the x-axis reflects the maximum current density that the tandem photovoltaic cell can output under ideal conditions.

[0026] Current tandem photovoltaic (TPM) technology uses conventional crystalline silicon photovoltaic cells as the base cell. Crystalline silicon has an absorption cutoff wavelength λc of 1107 nm, therefore it cannot absorb the first quantum peak (around 1250 nm) and the second quantum peak (around 1600 nm), resulting in a significant loss of output current density. Figure 4 It can be seen that the area of ​​the first hump near the center wavelength of 1250nm accounts for about 15% of the total area in the 350nm~1350nm range, meaning that the current provided by the first photon hump accounts for about 15% of the total current. Similarly, the sum of the area of ​​the first hump near the center wavelength of 1250nm and the area of ​​the second hump near the center wavelength of 1600nm accounts for 27% of the total area in the 350nm~1800nm ​​range, meaning that the current provided by the first and second humps accounts for about 27% of the total current.

[0027] This invention reduces the bandgap width of lithium-ion crystalline silicon or alloy crystalline silicon by doping lithium into crystalline silicon or by preparing crystalline alloy regions of germanium, tin, and silicon. This allows the silicon to absorb the photon energy represented by the first hump area near the center wavelength of 1250 nm and the photon energy represented by the second hump area near the center wavelength of 1600 nm, and convert it into the output current of the bottom cell of the tandem photovoltaic cell.

[0028] Although reducing the bandgap width Eg of crystalline silicon will decrease the output voltage of the bottom cell, the gain brought by the photon energy represented by the first hump area near the center wavelength of 1250nm and the photon energy represented by the second hump area near the center wavelength of 1600nm will improve the overall photoelectric conversion efficiency of the tandem photovoltaic cell.

[0029] Taking a typical case of a tandem photovoltaic cell with the top and bottom cells connected in series to output the same current as an example, calculations show that if the cutoff wavelength λc of the monocrystalline silicon bottom cell is increased to 1350nm, increasing the absorption of the first photon peak current, the power output increases by 4% compared to using a monocrystalline silicon bottom cell with existing technology, and the overall photoelectric conversion efficiency of the tandem photovoltaic cell increases by more than 1 percentage point. Subsequent embodiments will further illustrate this.

[0030] 2) Lithium impurities can effectively passivate defects in crystalline silicon, improve the minority carrier lifetime and carrier mobility, all of which are beneficial to improving the performance of photovoltaic cells.

[0031] 3) Compared with the alloy scheme, the lithium-doped scheme requires less doping, saving rare elements germanium and tin. At the same time, the technology for doping and growing crystalline silicon is mature.

[0032] 4) The silicon, germanium and tin alloy can obtain a direct band gap or a quasi-direct band gap; the band gap and interatomic spacing can be adjusted respectively; the carrier mobility is high, which is beneficial to reduce the thickness of the silicon, germanium and tin alloy and reduce the amount of rare elements germanium and tin used.

[0033] The advantages of using lithium doping in combination with the preparation of germanium, tin, and silicon crystalline alloy regions are: 1) To improve the light absorption coefficient of germanium-tin-silicon crystal alloys and reduce the amount of rare elements germanium and tin used, it is necessary to convert indirect bandgap germanium-tin-silicon crystal alloys into direct bandgap germanium-tin-silicon crystal alloys. Based on simulation calculations of the bandgap of germanium-tin-silicon crystals, when the proportion of elemental tin reaches 50% or more, the germanium-tin-silicon crystal can be transformed into a direct bandgap material with a bandgap of 0.7 eV, suitable for absorbing the photon energy represented by the first hump area near the center wavelength of 1250 nm and the photon energy represented by the second hump area near the center wavelength of 1600 nm. However, due to the significant melting point difference between metallic tin and silicon / germanium, a high proportion of tin composition easily leads to segregation of the alloy composition. To solve this problem, a combination of lithium doping and techniques for forming elemental germanium-tin-silicon crystal alloys is used. The addition of lithium introduces tensile stress into the alloy beforehand, which is beneficial for obtaining a direct bandgap germanium-tin-silicon crystal alloy with the required bandgap width under the premise of a lower tin content.

[0034] 2) The second benefit of using lithium doping and the technology for preparing silicon, tin, and germanium alloy regions in combination is that the silicon lattice expansion brought about by lithium helps to reduce the degree of lattice mismatch between the silicon, tin, and germanium alloy regions and the silicon substrate, thereby reducing the risk of introducing lattice defects.

[0035] The silicon, tin, and germanium alloy regions of the alloy crystal silicon wafer can be obtained by methods such as molecular beam epitaxy; the lithium doping can be obtained by methods such as silicon single crystal ingot doping to prepare silicon wafers or diffusion doping.

[0036] Furthermore, introducing germanium (Ge) or tin (Sn) atoms into the silicon (Si) lattice forms SiGe alloys or more advanced GeSn and SiGeSn alloys. The atomic radii of Ge and Sn differ from those of Si, and their introduction alters the crystal's lattice constant, causing lattice strain (typically tensile strain). It also changes the interatomic potential field: because different elements have different electron orbital hybridization patterns, different alloy proportions directly perturb the crystal's band structure. The addition of Ge increases the energy of the conduction band bottom (located far from the Γ point) of silicon. Simultaneously, its effect on the valence band top (located at the Γ point) is relatively small, thus a relatively higher proportion is used. Tin (Sn), with its strong band structure modulation capability, is more conducive to the transformation of the crystal alloy material into a quasi-direct bandgap semiconductor at relatively low Sn compositions. Through appropriate additions of Ge or Sn, the energy of the conduction band bottom gradually increases until the conduction band energy at the Γ point becomes lower than at other positions. At this point, both the conduction band bottom and the valence band top are located at the Γ point in momentum space, facilitating the transformation of the crystal alloy material into a quasi-direct bandgap semiconductor. The addition of a small amount of silicon can improve the bonding ability between the alloy region and the silicon substrate, thereby improving the stability of the wafer.

[0037] During the preparation of elemental germanium, tin, and silicon crystalline alloys, defects (such as vacancies and dislocations) are generated in the crystal lattice due to atomic size mismatch in Si, Ge, and Sn alloys. These defects become "traps" for charge carriers and non-radiative recombination centers, severely reducing the photoelectric properties of the material. Lithium ions have high mobility and can move to defect sites, acting as passivators to reduce the trapping of charge carriers by defects, thereby improving the effective quality of the material.

[0038] The alloy layer contains lithium, which can originate from lithium doping in silicon alloys or from the diffusion of doped lithium from lithium-ion silicon wafers. Lithium can provide electrons, altering the Fermi level. The additional electrons provided by n-type doping fill the conduction band bottom, potentially fine-tuning the band structure through carrier effects or other complex many-body effects. This helps stabilize and enhance the direct bandgap characteristics introduced by alloying. Simultaneously, interstitial lithium atoms can expand the silicon lattice, buffering the lattice strain caused by alloying to some extent, thus making the crystal structure more stable.

[0039] Furthermore, the alloy region of the alloy crystalline silicon wafer contains elemental lithium, and the concentration of elemental lithium in the alloy region is at least one of the following ranges: a) (1×10 15 / cm 3 )≤N Li ≤(1×10 16 / cm 3 ); b) (1×10 16 / cm 3 )<N Li ≤(1×10 17 / cm 3 ); c) (1×10 17 / cm 3 )<N Li ≤(1×10 18 / cm 3 ).

[0040] Alternatively, the alloy crystalline silicon substrate is doped with elemental lithium, and the concentration of elemental lithium in the alloy crystalline silicon substrate is at least one of the following ranges: a) (1×10 16 / cm 3 )≤N Li ≤(1×10 17 / cm 3 ); b) (1×10 17 / cm 3 )<N Li ≤(1×10 18 / cm 3 ); c) (1×10 18 / cm 3 )<N Li ≤(1×10 20 / cm 3 ).

[0041] Its beneficial effect is that the combination of alloy crystal silicon wafers and lithium doping schemes helps to expand the window for obtaining direct band gaps in alloy silicon crystals, providing greater freedom of choice.

[0042] Furthermore, the thickness of the alloy region of the alloy crystal silicon wafer is 0.1μm~10μm (selectable as 0.1μm, 0.4μm, 0.7μm, 0.9μm, 1.2μm, 1.4μm, 1.8μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 2.9μm, 3.5μm, 4.7μm, 5.8μm, 6.6μm, 7.4μm, 8.3μm, 9.1μm, 10μm, etc.).

[0043] Its beneficial effect is that the alloy region of the aforementioned alloy crystal silicon wafer can obtain an alloy with a direct bandgap or a quasi-direct bandgap, which has a high light absorption coefficient and photoelectric conversion efficiency. Therefore, a thinner alloy layer can be used to achieve the purpose of saving materials and reducing manufacturing costs.

[0044] Secondly, the present invention provides a lithium crystalline silicon ingot for preparing the aforementioned crystalline silicon photovoltaic cell wafer, wherein the lithium crystalline silicon ingot is doped with the impurity element lithium, and the concentration of the impurity element lithium is at least within one of the following ranges: a) (1×10 16 / cm 3 )≤N Li ≤(1×10 17 / cm 3 ); b) (1×10 17 / cm 3 )<N Li ≤(1×10 18 / cm 3 ); c) (1×10 18 / cm 3 )<N Li ≤(1×10 20 / cm 3 ).

[0045] Thirdly, the present invention provides a tandem photovoltaic cell, wherein the bottom cell of the tandem photovoltaic cell is prepared using a lithium crystal silicon wafer as a substrate.

[0046] Fourthly, the present invention provides another type of tandem photovoltaic cell, wherein the bottom cell of the tandem photovoltaic cell is prepared by using the aforementioned alloy crystalline silicon wafers as substrates, wherein the alloy region of the alloy crystalline silicon wafer is located on the non-primary light-receiving surface of the tandem photovoltaic cell, and one electrode of the bottom cell of the tandem photovoltaic cell is led out from the alloy region of the alloy crystalline silicon wafer.

[0047] Preferably, the top cell of the tandem photovoltaic cell is a photovoltaic cell made of crystalline silicon material.

[0048] Preferably, the top cell of the tandem photovoltaic cell is a perovskite photovoltaic cell.

[0049] Its beneficial effects are: First, the lithium crystalline silicon base battery material and alloy crystalline silicon base battery material of the present invention have a bandgap width lower than that of conventional crystalline silicon photovoltaic cells. When combined with photovoltaic cells with a wider bandgap width to form a stacked photovoltaic cell, it can absorb photons in the photon density concentration regions near the center wavelength of 1250nm and near the center wavelength of 1600nm, thereby improving the photoelectric conversion efficiency of the battery.

[0050] Second, when the top cell of the tandem photovoltaic cell is a perovskite type photovoltaic cell, it is beneficial to obtain higher photoelectric conversion efficiency and reduce costs.

[0051] In summary, the beneficial effects of this invention are reflected in the following aspects: 1) It has the potential to increase current output by 11% to 27% compared to existing technologies; 2) Compared with existing perovskite / monocrystalline silicon tandem photovoltaic cells, the photoelectric conversion efficiency can be improved by 4.0%~6.7%.

[0052] 3) Crystalline silicon top cells are more stable than perovskite top cells and do not pose a risk of heavy metal lead pollution.

[0053] 4) Lithium impurities in lithium-ion silicon wafers can effectively passivate defects in crystalline silicon, improve the minority carrier lifetime of crystalline silicon, and increase the carrier mobility, which is beneficial to improving the performance of photovoltaic cells.

[0054] 5) The bottom cell made of lithium crystal silicon wafer of the present invention or the single-junction photovoltaic cell made of the bottom cell alone has a better lithium interface passivation effect and has the function of resisting ultraviolet-induced degradation (UVID). Attached Figure Description

[0055] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a schematic diagram of the structure of the first tandem photovoltaic cell in Embodiment 1 of the present invention. The bottom cell is a crystalline silicon photovoltaic cell, the crystalline silicon wafer is a lithium-ion crystalline silicon wafer, and the top cell is a perovskite photovoltaic cell.

[0057] Figure 2 This is a schematic diagram of the structure of the second tandem photovoltaic cell in Embodiment 2 of the present invention. The bottom cell is a crystalline silicon photovoltaic cell, with crystalline silicon, tin, and germanium alloy regions fabricated on the crystalline silicon wafer. The top cell is a perovskite photovoltaic cell.

[0058] Figure 3 This is a schematic diagram of the structure of the third tandem photovoltaic cell in Embodiment 3 of the present invention. The bottom cell is a crystalline silicon photovoltaic cell, with a crystalline silicon wafer having an alloy region of silicon, tin, and germanium in a crystalline state. The top cell is a conventional photovoltaic cell.

[0059] Figure 4 This diagram illustrates the relationship between photonic quantum density and sunlight wavelength in the 300nm~1800nm ​​range, based on key data from the AM1.5 spectral irradiance standard provided in IEC 60904-3. It also shows the relationship between wavelength 350nm and the bottom cell absorption cutoff wavelength λ. C Within the range, the area enclosed by the curve and the x-axis reflects the maximum current density that the tandem photovoltaic cell can output under ideal conditions.

[0060] Explanation of reference numerals in the attached figures: 1. Top cell; 2. Bottom cell; 3. Non-main light-receiving surface of tandem photovoltaic cell; 4. First quantum hump; 5. Second quantum hump; 6. Lithium crystal silicon wafer; 7. Alloy crystal silicon wafer; 71. Alloy region; 11. Top cell output terminal; 21. Bottom cell output terminal; 100. First tandem photovoltaic cell; 200. Second tandem photovoltaic cell; 300. Third tandem photovoltaic cell. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The apparatus of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0062] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0063] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0064] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0065] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0066] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0067] Example 1: See Figure 1 , Figure 4 A crystalline silicon wafer for preparing crystalline silicon photovoltaic cells, wherein the lithium crystalline silicon wafer 6 is doped with 1×10⁶ lithium-ion nanoparticles. 19 / cm 3 The lithium impurities in the lithium-ion silicon wafer 6 are obtained through a diffusion process or by cutting a corresponding lithium-doped silicon ingot, which is obtained by CZ farad processing. The bottom cell 2 of the crystalline silicon is prepared from the lithium-ion silicon wafer 6. Due to the expansion effect of the lithium impurities on the crystalline silicon lattice, the band gap of the lithium-ion silicon wafer 6 shrinks to 0.92 eV, and the light absorption wavelength limit is extended from 1107 nm in the prior art to 1350 nm. The top cell 1 of the first tandem photovoltaic cell 100 is a CsPbI3 perovskite photovoltaic cell with a light absorption wavelength limit of 743 nm. Figure 4 It is evident that the number of photons (represented by area) in the range of 300nm to the left of 743nm is equal to the number of photons in the range of 743nm to the right of 743nm, from 743nm to 1350nm. Therefore, the top cell 1 and the bottom cell 2 have the same output current under the AM1.5 spectrum. The bottom cell and the top cell are connected in series to produce the first tandem photovoltaic cell 100 with outputs at both ends.

[0068] The beneficial effects of this embodiment are: 1) By doping lithium into crystalline silicon to obtain lithium crystalline silicon, the absorption of the first photon peak 4 near the center wavelength of 1250nm in the AM1.5 spectrum of sunlight is extended. Therefore, the first tandem photovoltaic cell 100 of the present invention improves the photoelectric conversion efficiency by 6.6% compared with the existing perovskite / monocrystalline silicon tandem cell technology. 2) The lithium doping content is relatively low, the process is simple, and the cost is low; 3) Lithium helps passivate crystal defects, improves crystal minority carrier lifetime and carrier mobility; and helps suppress UV-induced decay effects.

[0069] Example 2: See Figure 2 , Figure 4 A crystalline silicon wafer for preparing crystalline silicon photovoltaic cells, wherein the lithium crystalline silicon wafer 6 is doped with 1×10⁶ lithium-ion nanoparticles. 17 / cm 3 In a lithium-ion silicon wafer 6, a 2 μm alloy region 71 containing 10% silicon, 5% tin, and the remainder germanium is prepared on one side using molecular beam epitaxy, forming an alloy crystal silicon wafer 7. Lithium, a rapidly diffusing impurity in the lithium-ion silicon wafer 6, readily diffuses from the silicon wafer 6 to the alloy region 71, assisting in expanding the lattice constant of the alloy region 71 and reducing lattice matching stress. Through the interstitial impurity lithium, the lattice expansion of the alloy region 71 reduces the bandgap width of the alloy region 71 material to 0.69 eV, resulting in the localized preparation of an alloy region 71 containing silicon, tin, and germanium alloy elements. This extends the light absorption wavelength limit of the alloy crystal silicon wafer 7 to 1800 nm, compared to the 1107 nm of existing crystalline silicon wafers.

[0070] A crystalline silicon bottom cell 2 is prepared from an alloy crystalline silicon wafer 7 with an alloy region 71 on one side.

[0071] The top cell 1 of the second tandem photovoltaic cell 200 is a MAPbI3 perovskite photovoltaic cell with a light absorption wavelength limit of 830nm. Figure 4 It is evident that the number of photons (represented by area) in the range of 300nm to the left of 830nm is equal to the number of photons in the range of 830nm to the right of 830nm, from 830nm to 1800nm. Therefore, the top cell 1 and the bottom cell 2 have the same output current under the AM1.5 spectrum. The bottom cell and the top cell are connected in series to form a second tandem photovoltaic cell 200 with outputs at both ends. The alloy region 71 of the alloy crystalline silicon wafer 7 is located on the non-primary light-receiving surface 3 of the second tandem photovoltaic cell 200, and one electrode of the bottom cell 2 is led out from the alloy region 71 of the alloy crystalline silicon wafer 7. The beneficial effects of this embodiment are: 1) By changing the composition ratio of alloy region 71, the absorption of the first photon peak 4 and the second photon peak 5 near the center wavelength of AM1.5 sunlight at 1250nm and 1600nm is extended. The second tandem photovoltaic cell 200 of the present invention improves the photoelectric conversion efficiency by 4.5% compared with the existing perovskite / monocrystalline silicon tandem photovoltaic cell technology. 2) The elemental ratios in the alloy region can be adjusted to change the band gap width and lattice constant, allowing for greater controllability.

[0072] 3) Lithium helps passivate defects in the crystal body and at the interface, improves the minority carrier lifetime and carrier mobility of the crystal, and helps suppress the UV-induced decay effect.

[0073] Example 3 See Figure 3 , Figure 4 A crystalline silicon wafer for preparing crystalline silicon photovoltaic cells, wherein the lithium crystalline silicon wafer 6 is doped with 1×10⁶ lithium-ion nanoparticles. 17 / cm 3 Lithium is used to form an alloy crystal silicon wafer 7. A 2μm alloy region 71 containing 8% silicon, 3% tin, and the remainder germanium is fabricated on one side of a lithium crystal silicon wafer 6 using molecular beam epitaxy. The bottom cell 2 of a third-layer photovoltaic cell 300 is fabricated using the alloy crystal silicon wafer 7 as a substrate, with the alloy region 71 located on the non-primary light-receiving surface 3 of the third-layer photovoltaic cell. The band gap of the alloy region 71 material is 0.69 eV, extending the light absorption wavelength limit of the bottom cell 2 from 1107 nm in the prior art to 1800 nm.

[0074] The lithium crystal silicon wafer 6 is obtained by cutting the corresponding crystal silicon ingot, which is obtained by CZ farading.

[0075] In Example 3, the top cell 1 of the third tandem photovoltaic cell 300 is a monocrystalline silicon photovoltaic cell. The band gap of the monocrystalline silicon material is 1.12 eV, and the light absorption wavelength limit of the material is 1107 nm. The top cell 1 and the bottom cell 2 have different output currents and voltages under AM1.5 spectrum. Therefore, this example is designed as a four-terminal output tandem photovoltaic cell. The output terminal of the bottom cell 2 is 21, and the output terminal of the top cell 1 is 11. The bottom cell 2 and the top cell 1 are electrically independent power sources.

[0076] The beneficial effects of this embodiment are: 1) By increasing the absorption of the first photon peak 4 near the center wavelength of 1250nm and the second photon peak 5 near the center wavelength of 1600nm in the AM1.5 spectrum of sunlight, the photoelectric conversion efficiency of the tandem photovoltaic cell of this invention is improved by 11% compared with the existing single-junction monocrystalline silicon photovoltaic cell; 2) Crystalline silicon top-mounted solar cells are stable, reliable, and environmentally friendly. 3) Lithium helps passivate defects in the crystal body and at the interface, improves the minority carrier lifetime and carrier mobility of the crystal, and helps suppress the UV-induced decay effect.

[0077] In summary, the technical solution provided by this invention has significant cost advantages and cost reduction potential, and can suppress the generation of ultraviolet-induced degradation effects. It is of great significance to the development of the industry.

[0078] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A crystalline silicon piece for the production of crystalline silicon photovoltaic cells, characterized in that: Characterized by one of the following: 1) the crystal silicon wafer is a lithium crystal silicon wafer, and the concentration of lithium in the lithium crystal silicon wafer is at least one of the following ranges: a) (1 x 10 16 / cm 3 ) ≤ N Li ≤ (1 x 10 17 / cm 3 ); b) (1 x 10 17 / cm 3 ) < N Li ≤ (1 x 10 18 / cm 3 ); c) (1 x 10 18 / cm 3 ) < N Li ≤ (1 x 10 20 / cm 3 ); 2) the crystal silicon wafer is an alloy crystal silicon wafer, and the alloy crystal silicon wafer comprises a substrate, and the substrate is locally prepared with an alloy region comprising alloy elements of silicon, tin, and germanium, forming an alloy crystal silicon wafer, and the proportion of alloy elements in the alloy region of the alloy crystal silicon wafer is, by atomic percentage, silicon 5% to 53%, tin 2% to 12%, and germanium the balance.

2. The crystalline silicon slice according to claim 1, characterized in that, The alloy region of the alloy crystal silicon wafer contains lithium, and the concentration of lithium in the alloy region is at least one of the following ranges: a) (1 x 10 15 / cm 3 ) ≤ N Li ≤ (1 x 10 16 / cm 3 ) b) (1 x 10 16 / cm 3 ) < N Li ≤ (1 x 10 17 / cm 3 ); c) (1 x 10 17 / cm 3 ) < N Li ≤ (1 x 10 18 / cm 3 ).

3. The crystalline silicon slice of claim 1 wherein, The substrate of the crystal silicon wafer is doped with lithium, and the concentration of lithium in the substrate of the crystal silicon wafer is at least one of the following ranges: a) (1 x 10 16 / cm 3 ) ≤ N Li ≤ (1 x 10 17 / cm 3 ); b) (1 x 10 17 / cm 3 ) < N Li ≤ (1 x 10 18 / cm 3 ); c) (1 x 10 18 / cm 3 ) < N Li ≤ (1 x 10 20 / cm 3 ).

4. A crystalline silicon slice according to claim 1 or claim 2 or claim 3 characterised in that, The thickness of the alloy region of the alloy crystal silicon wafer is 0.1 μm to 10 μm.

5. A lithium crystalline silicon ingot for producing the crystalline silicon sheet according to any one of claims 1 to 4, the crystalline silicon sheet being a lithium crystalline silicon sheet, characterized in that, The lithium crystal silicon ingot is doped with impurity lithium, and the concentration of impurity lithium is at least one of the following ranges: a) (1 x 10 16 / cm 3 ) ≤ N Li ≤ (1 x 10 17 / cm 3 ); b) (1 x 10 17 / cm 3 ) < N Li ≤ (1 x 10 18 / cm 3 ); c) (1 x 10 18 / cm 3 ) < N Li ≤ (1 x 10 20 / cm 3 ).

6. A stacked photovoltaic cell characterized by, The bottom cell of the stacked photovoltaic cell is prepared from the crystal silicon wafer of claim 1, and the crystal silicon wafer is a lithium crystal silicon wafer.

7. A stacked photovoltaic cell, characterized by, The bottom cell of the stacked photovoltaic cell is prepared from the crystal silicon wafer of any one of claims 1 to 4, and the crystal silicon wafer is an alloy crystal silicon wafer, wherein the alloy region of the alloy crystal silicon wafer is located at the non-main light-receiving surface of the stacked photovoltaic cell, and one electrode of the bottom cell of the stacked photovoltaic cell is led out from the alloy region of the alloy crystal silicon wafer.

8. The tandem photovoltaic cell of claim 6 or claim 7, wherein, The top cell of the stacked photovoltaic cell is a photovoltaic cell of a crystal silicon material.

9. The tandem photovoltaic cell of claim 6 or claim 7, wherein, The top cell of the stacked photovoltaic cell is a photovoltaic cell of a perovskite material.

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