A crystalline silicon sheet, silicon ingot and stacked photovoltaic cell for preparing a crystalline silicon photovoltaic cell

Abstract

The application relates to the technical field of photovoltaic cells and materials thereof, and discloses a crystal silicon wafer for preparing a crystal 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 doped with lithium; and 2) the crystal silicon wafer is an alloy crystal silicon wafer, the alloy crystal silicon wafer comprises a base sheet, and the base sheet is locally prepared with an alloy region comprising alloy elements of silicon, tin and germanium to form the alloy crystal silicon wafer; and the proportion of the alloy elements in the alloy region of the alloy crystal silicon wafer is 5%-53% of silicon, 2%-12% of tin and the rest of germanium in terms of atomic percentage. Compared with the prior art, the application has the potential to improve current output and photoelectric conversion efficiency, lithium in the lithium crystal silicon wafer effectively passivates defects in the crystal silicon, the minority carrier lifetime and mobility of the crystal silicon are improved, the lithium interface passivation effect is better, and the application has the function of resisting ultraviolet-induced decay effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic cells and materials thereof, in particular to a crystalline silicon wafer for preparing a crystalline silicon photovoltaic cell, a silicon ingot and a laminated photovoltaic cell. BACKGROUND

[0002] The first item of the background of the present application is a crystalline silicon photovoltaic cell bottom cell in a laminated photovoltaic cell, and related crystalline silicon wafer and ingot.

[0003] Crystalline silicon, especially monocrystalline silicon photovoltaic cells, are currently the most cost-effective photovoltaic cells, which are stable in performance, mature in process, and have satisfactory photoelectric conversion efficiency. Therefore, when people try to develop perovskite laminated photovoltaic cells with higher photoelectric conversion efficiency and lower cost potential, in order to reduce the risk of poor stability of perovskite cells, environmental problems of heavy metal lead, etc., a laminated photovoltaic cell is developed by combining perovskite cells with crystalline silicon cells, in which the perovskite cell is used as a top cell to absorb short-wave light, and the crystalline silicon cell is used as a bottom cell to absorb long-wave light, so as to obtain higher photoelectric conversion efficiency of the laminated photovoltaic cell.

[0004] However, the inherent disadvantages of the band gap width and indirect band gap absorption of crystalline silicon material hinder the improvement of the photoelectric conversion efficiency of the laminated photovoltaic cell and the reduction of the material cost.

[0005] Specific analysis is as follows:

[0006] The number of sunlight photons Q that can be absorbed by a photovoltaic cell determines the upper limit of the short-circuit current density j sc of the photovoltaic cell, the band gap width E g of the photovoltaic cell material determines the upper limit of the open-circuit voltage V oc of the photovoltaic cell, and the product of j sc and V oc is the upper limit of the electric power density output of the photovoltaic cell. The ratio of the upper limit of the electric power density of the photovoltaic cell to the irradiance of sunlight is the upper limit of the photoelectric conversion efficiency of the photovoltaic cell. That is;

[0007]

[0008] Wherein:

[0009] η: photoelectric conversion efficiency of the photovoltaic cell;

[0010] E g (λ): band gap width of the photoactive material of the photovoltaic cell, different band gap widths correspond to different light absorption cut-off wavelengths, for crystalline silicon material, E g =1.12ev;

[0011] Q(λ): number of photons per unit area of irradiation per unit wavelength interval;

[0012] E(λ): solar irradiance.

[0013] Single-junction photovoltaic cells with fixed bandgap width cannot simultaneously take advantage of both short-wavelength light irradiation for higher open-circuit voltage and long-wavelength light absorption for higher short-circuit current density in distributed spectrum irradiation.

[0014] For example, for the AM1.5 ground sunlight spectrum, E g =1.4ev of photoactive material can obtain the highest single-junction photoelectric conversion efficiency, which corresponds to an absorption cutoff wavelength of 886nm. In order to take advantage of both higher bandgap width semiconductor materials for higher output voltage and lower bandgap width semiconductor materials for more light quantum absorption for larger output current density to improve the photoelectric conversion efficiency of the photovoltaic cell, a stacked photovoltaic cell composed of different bandgap width materials is designed to fully absorb and utilize sunlight irradiation of different wavelengths, thereby improving the overall photoelectric conversion efficiency of the photovoltaic cell.

[0015] One of the deficiencies of the prior art of using crystalline silicon photovoltaic cells as the bottom cell of the stacked photovoltaic cell is the limitation of the bandgap width of crystalline silicon material. The bandgap width of crystalline silicon material is 1.12ev, and its cutoff absorption wavelength is 1107nm, so it cannot absorb the light quanta of the two "hump" peaks in the AM1.5 spectrum with central wavelengths of 1200nm and 1600nm, which limits the further improvement of the photoelectric conversion efficiency of the cell.

[0016] The second background technology of the present application is the UV-induced degradation (UVID) effect commonly encountered by high-efficiency crystalline silicon photovoltaic cells.

[0017] High-efficiency crystalline silicon photovoltaic cells rely heavily on the passivation of hydrogen elements on the crystalline silicon interface, so the UV-induced degradation (UVID) effect is common. Secondary ion mass spectrometry (SIMS) analysis shows that ultraviolet light with a wavelength of 365nm can dissociate Si-H bonds, causing hydrogen atoms to migrate from the passivated interface of the cell and form permanent damage or form metastable defects. According to case observations, photovoltaic modules with the UV-induced degradation (UVID) effect have a power loss of 1% in the first year, and then 0.4% per year. It is estimated that only under this effect, the conversion efficiency of the photovoltaic module will be degraded by 10% in 25 years. SUMMARY

[0018] I. Nouns and Terms:

[0019] The following nouns and terms have the following meanings in this application document:

[0020] Crystalline silicon / crystalline silicon wafer:

[0021] Doping amount of 10 21 / cm 3 The following crystal silicon / crystal silicon wafer. Including polycrystalline silicon and monocrystalline silicon, the crystal silicon in this application also includes lithium-doped lithium crystal silicon.

[0022] Lithium crystal silicon:

[0023] Lithium-doped crystal silicon, including lithium crystal silicon wafer and lithium crystal silicon ingot.

[0024] Alloy crystal silicon / alloy crystal silicon wafer:

[0025] Crystal silicon / crystal silicon wafer containing silicon, tin, germanium alloy element alloy region.

[0026] First and second light quantum hump:

[0027] Referring to Figure 3 , the first and second light quantum hump, respectively, in the AM1.5 light spectrum sunlight light quantum wavelength distribution diagram, due to atmospheric absorption, the light quantum density concentration area near the center wavelength 1250nm and the light quantum density concentration area near the center wavelength 1600nm.

[0028] Two-end laminated photovoltaic cell:

[0029] The laminated photovoltaic cell with the light path of the bottom cell and the top cell in series and the circuit in series.

[0030] Four-terminal laminated photovoltaic cell:

[0031] The laminated photovoltaic cell with the light path of the bottom cell and the top cell in series and the circuit in independent and separate state.

[0032] Non-main light receiving surface:

[0033] The side of the cell that receives less total irradiance, commonly known as the back side. II. Summary of the invention:

[0035] The present application replaces part of the hydrogen element with lithium element to passivate the cell interface. The chemical bond between lithium and silicon tends to be ionic bond, so it has higher bond energy. At the same time, the mass and radius of lithium element are much higher than that of hydrogen element, so the stability of passivation is also higher than that of hydrogen element. In addition, lithium element can also passivate various defects inside silicon crystal, which is beneficial to improve the minority carrier lifetime and carrier mobility of crystalline silicon material.

[0036] The first object of the present invention is to extend the cut-off absorption wavelength of the crystalline silicon material, the measures taken are, first, to dope lithium ions into the interstitial space of the silicon crystal lattice to expand the atomic spacing of the crystalline silicon material, and to reduce the band gap width of the bottom cell crystalline silicon material, second, to form an alloy with the IV A group element germanium and the element tin and the element silicon to change the atomic spacing of the silicon atoms, to expand the light quantum of at least one of the two "hump" wavelengths of 1250nm and 1600nm in the center of the AM1.5 light spectrum, and to convert it into photovoltaic output current, while allocating more shares of short-wavelength high-energy light quanta to the perovskite top cell for efficient absorption conversion to obtain higher open-circuit voltage, and to achieve the purpose of improving the photoelectric conversion efficiency of the stacked photovoltaic cell as a whole.

[0037] The second object of the present invention is to replace hydrogen elements with partial lithium elements to passivate the cell interface and achieve in-diffusion passivation. Reduce the risk of ultraviolet-induced degradation (UVID).

[0038] In the first aspect, the present invention provides a crystalline silicon wafer for preparing a crystalline silicon photovoltaic cell, which has one of the following characteristics:

[0039] 1) The crystalline silicon wafer is a lithium-doped silicon lithium crystalline silicon wafer, with an element lithium doping concentration less than 1×10 17 / cm 3 , which can effectively passivate defects in the silicon crystal, improve minority carrier lifetime, and improve minority carrier mobility, but cannot significantly change the band gap width of the crystalline silicon, and doping concentrations exceeding 10 20 / cm 3 may easily cause new defects in the silicon crystal. When the doping concentration is in the range of 10 17 / cm 3 ~10 20 / cm 3 , there is an empirical formula:

[0040] ΔE g ≈A(N Li ) 0.33

[0041] Wherein:

[0042] ΔE g : change in band gap width, ev;

[0043] A: coefficient, A≈5×10 -8 ev•cm 3 ;

[0044] N: doping concentration, atoms / cm 3 .

[0045] By the empirical formula, it can be determined that when the lithium doping concentration is in the following range, the band gap width of the crystalline silicon can be changed. At the same time, the lithium atoms in the interstitial state can adjust the lattice strain to some extent, making the crystal structure more stable.

[0046] The concentration of elemental lithium in the lithium crystalline silicon wafer is at least in one of the following ranges:

[0047] a) (1 x 10 16 / cm 3 ) ≤ N Li ≤ (1 x 10 17 / cm 3 );

[0048] b) (1 x 10 17 / cm 3 ) < N Li ≤ (1 x 10 18 / cm 3 );

[0049] c) (1 x 10 18 / cm 3 ) < N Li ≤ (1 x 10 20 / cm 3 );

[0050] 2) The crystalline silicon wafer is an alloy crystalline silicon wafer, the alloy crystalline 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 crystalline silicon wafer, and the proportion (atomic number proportion) of the alloy elements in the alloy region of the alloy crystalline silicon wafer ranges from 5% to 53% of silicon, 2% to 12% of tin, and the rest of germanium (optionally 2% of tin, 5% of silicon, the rest of germanium, 2% of tin, 15% of silicon, the rest of germanium, 2% of tin, 30% of silicon, the rest of germanium, 2% of tin, 18% of silicon, the rest of germanium, 5% of tin, 52% of silicon, the rest of germanium, 5% of tin, 15% of silicon, the rest of germanium, 5% of tin, 30% of silicon, the rest of germanium, 5% of tin, 50% of silicon, the rest of germanium, etc.).

[0051] The beneficial effects of the above invention content are:

[0052] 1) Referring to Figure 4 , Figure 4 is a schematic diagram of the relationship between the light quantum density and the sunlight wavelength in the range of 300 nm to 1800 nm, which is drawn by means of the key data of the AM1.5 light spectrum irradiation standard given by IEC 60904-3, and the area enclosed by the curve and the x-axis in the range of 350 nm and the bottom cell absorption cutoff wavelength λc reflects the maximum current density that can be output by the stacked photovoltaic cell under ideal conditions.

[0053] The existing stacked photovoltaic cell technology uses a conventional crystalline silicon photovoltaic cell as the bottom cell. The absorption cut-off wavelength of crystalline silicon is 1107 nm, so it cannot absorb the light quanta of the first light quantum peak near the center wavelength of 1250 nm and the second light quantum peak near the center wavelength of 1600 nm, thus losing a large amount of output current density. Figure 4 It can be seen that the first peak area near the center wavelength of 1250 nm accounts for about 15% of the total area in the range of 350 nm to 1350 nm, i.e. the current provided by the first light quantum peak accounts for about 15% of the total current; similarly, the sum of the first peak area near the center wavelength of 1250 nm and the second peak area near the center wavelength of 1600 nm accounts for 27% of the total area in the range of 350 nm to 1800 nm, i.e. the current provided by the first peak and the second peak accounts for about 27% of the total current.

[0054] The present application reduces the band gap width of the lithium-doped crystalline silicon or the alloyed crystalline silicon by doping lithium in the crystalline silicon or preparing an elemental germanium, tin and silicon alloy region, so that the light quanta represented by the first peak area near the center wavelength of 1250 nm and the second peak area near the center wavelength of 1600 nm can be absorbed and converted into the output current of the bottom cell of the stacked photovoltaic cell.

[0055] Although reducing the band gap width Eg of the crystalline silicon reduces the output voltage of the bottom cell, the gain brought by the absorption of the light quanta represented by the first peak area near the center wavelength of 1250 nm and the second peak area near the center wavelength of 1600 nm will improve the photoelectric conversion efficiency of the total stacked photovoltaic cell.

[0056] Taking the general case of a two-end stacked photovoltaic cell with the top cell and the bottom cell connected in series and outputting the same current as an example, it is calculated that if the cut-off wavelength λc of the single-crystal silicon bottom cell is increased to 1350 nm to increase the absorption of the first light quantum peak current, the electrical energy output is increased by 4% compared with the single-crystal silicon bottom cell using the existing technology, and the total stacked photovoltaic cell photoelectric conversion efficiency is improved by more than 1%. Subsequent examples will continue to illustrate this.

[0057] 2) The impurity lithium can effectively passivate the defects in the crystalline silicon body, improve the minority carrier lifetime of the crystalline silicon, and improve the mobility of the carriers, which are all beneficial to improving the performance of the photovoltaic cell.

[0058] 3) Compared with the alloy scheme, the lithium-doped scheme has a smaller doping amount, saving the rare elements germanium and tin. At the same time, the technology of doping and growing crystalline silicon is mature.

[0059] 4) The silicon, germanium, tin alloy can obtain direct band gap or quasi-direct band gap; the band gap and interatomic distance can be adjusted respectively; the carrier mobility is high, which is beneficial to thinning the thickness of silicon, germanium, tin alloy and reducing the use amount of rare elements germanium and tin.

[0060] The advantages of using lithium doping and preparing germanium, tin, silicon crystal alloy region in combination are:

[0061] 1) In order to improve the light absorption coefficient of germanium, tin, silicon crystal alloy and reduce the use amount of rare elements germanium and tin, it is necessary to convert the indirect band gap germanium, tin, silicon crystal alloy into a direct band gap germanium, tin, silicon crystal alloy. According to the simulation calculation of the band gap of germanium, tin, silicon crystal, when the proportion of tin element is more than 50%, the germanium, tin, silicon crystal can be converted into a direct band gap material with a band gap of 0.7ev, which is suitable for absorbing the light quantum energy represented by the first hump area near the center wavelength of 1250nm and the light quantum energy represented by the second hump area near the center wavelength of 1600nm. However, due to the large difference in melting point between metal tin and silicon and germanium, a large proportion of tin component is easy to cause segregation of alloy composition. In order to solve this problem, the combination of lithium doping and the technical means of forming germanium, tin, silicon crystal alloy is used. The addition of lithium introduces tensile stress in the alloy, which is beneficial to obtain a direct band gap germanium, tin, silicon crystal alloy with the required band gap width under the premise of a lower tin component.

[0062] 2) The second benefit of the combined use of lithium doping and the preparation of silicon, tin, germanium element alloy region technical measures is that the silicon lattice expansion brought by lithium is beneficial to reduce the lattice mismatch degree between the silicon, tin, germanium element alloy region and the silicon substrate, and reduce the risk of introducing lattice defects.

[0063] The alloy crystal silicon wafer can be obtained by molecular beam epitaxy and other methods; the doping of lithium element can be obtained by silicon single crystal ingot doping, silicon wafer preparation or diffusion doping and other methods.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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:

[0068] a) (1×10 15 / cm 3 )≤N Li ≤(1×10 16 / cm 3 );

[0069] b) (1×10 16 / cm3 )<N Li ≤(1×10 17 / cm 3 );

[0070] c)(1×10 17 / cm 3 )<N Li ≤(1×10 18 / cm 3 )。

[0071] Alternatively, the alloyed crystalline silicon wafer substrate is doped with elemental lithium, and the concentration of the elemental lithium in the alloyed crystalline silicon wafer substrate is at least one of the following ranges:

[0072] a)(1×10 16 / cm 3 )≤N Li ≤(1×10 17 / cm 3 );

[0073] b)(1×10 17 / cm 3 )<N Li ≤(1×10 18 / cm 3 );

[0074] c)(1×10 18 / cm 3 )<N Li ≤(1×10 20 / cm 3 )。

[0075] The beneficial effect is that the alloyed crystalline silicon wafer in combination with the lithium doping scheme is beneficial to expand the window of alloyed silicon crystals to obtain direct bandgap, and has greater freedom of choice.

[0076] Further, the thickness of the alloyed region of the alloyed crystalline silicon wafer is 0.1 μm to 10 μm (optionally 0.1 μm, 0.4 μm, 0.7 μm, 0.9 μm, 1.2 μm, 1.4 μm, 1.8 μm, 2.1 μm, 2.3 μm, 2.5 μm, 2.7 μm, 2.9 μm, 3.5 μm, 4.7 μm, 5.8 μm, 6.6 μm, 7.4 μm, 8.3 μm, 9.1 μm, 10 μm, etc.).

[0077] The beneficial effect is that the alloyed region of the alloyed crystalline silicon wafer in the aforementioned proportion can obtain alloyed crystals with direct bandgap or quasi-direct bandgap, and has higher light absorption coefficient and photoelectric conversion efficiency, so that a thinner alloy layer can be used to achieve the purpose of saving materials and preparation cost.

[0078] In a second aspect, the present application provides a lithium crystal silicon ingot for preparing the crystal silicon sheet of the aforementioned crystal silicon photovoltaic cell, wherein the lithium crystal silicon ingot is doped with the impurity element lithium, and the concentration of the impurity element lithium is at least in one of the following ranges:

[0079] a) (1 x 10 16 / cm 3 ) ≤ N Li ≤ (1 x 10 17 / cm 3 ) ;

[0080] b) (1 x 10 17 / cm 3 ) < N Li ≤ (1 x 10 18 / cm 3 ) ;

[0081] c) (1 x 10 18 / cm 3 ) < N Li ≤ (1 x 10 20 / cm 3 ).

[0082] In a third aspect, the present application provides a laminated photovoltaic cell, wherein the bottom cell of the laminated photovoltaic cell is prepared by using the lithium crystal silicon sheet as a substrate.

[0083] In a fourth aspect, the present application provides another laminated photovoltaic cell, wherein the bottom cell of the laminated photovoltaic cell is prepared by using the aforementioned alloy crystal silicon sheet as a substrate, wherein the alloy region of the alloy crystal silicon sheet is located at the non-main light-receiving surface of the laminated photovoltaic cell, and one electrode of the bottom cell of the laminated photovoltaic cell is led out by the alloy region of the alloy crystal silicon sheet.

[0084] Preferably, the top cell of the laminated photovoltaic cell is a photovoltaic cell of a crystalline silicon material.

[0085] Preferably, the top cell of the laminated photovoltaic cell is a photovoltaic cell of a perovskite material.

[0086] The beneficial effects are as follows:

[0087] First, the lithium crystal silicon bottom cell material and the alloy crystal silicon bottom cell material of the present application have a lower band gap than the conventional crystal silicon photovoltaic cell, and when combined with a photovoltaic cell with a wider band gap to form a laminated photovoltaic cell, the photovoltaic cell can absorb light quanta in the light quantum density concentration region near the central wavelength of 1250 nm and the light quantum density concentration region near the central wavelength of 1600 nm, thereby improving the photoelectric conversion efficiency of the cell.

[0088] Second, when the top cell of the stacked photovoltaic cell is a perovskite type photovoltaic cell, it is beneficial to obtain higher photoelectric conversion efficiency and reduce cost.

[0089] In summary, the beneficial effects of the present application are reflected in the following aspects:

[0090] 1) 11% ~ 27% current output potential higher than prior art;

[0091] 2) 4.0% ~ 6.7% higher photoelectric conversion efficiency than prior art perovskite / single crystal silicon stacked photovoltaic cell.

[0092] 3) The top cell of the crystal silicon is more stable than the perovskite top cell, and there is no risk of heavy metal lead pollution.

[0093] 4) The impurity lithium in the lithium crystal silicon wafer can effectively passivate the defects in the crystal silicon, improve the minority carrier lifetime of the crystal silicon, and improve the carrier mobility, which is beneficial to improve the performance of the photovoltaic cell.

[0094] 5) The bottom cell composed of the lithium crystal silicon wafer or the single junction photovoltaic cell composed of the bottom cell alone has better lithium interface passivation effect and has the function of resisting ultraviolet induced decay effect (UVID). BRIEF DESCRIPTION OF DRAWINGS

[0095] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0096] Figure 1 For example 1 of the present application, the structure diagram of the first stacked photovoltaic cell. The bottom cell is a crystal silicon type photovoltaic cell, the crystal silicon wafer is a lithium crystal silicon wafer, and the top cell is a perovskite type photovoltaic cell.

[0097] Figure 2 For example 2 of the present application, the structure diagram of the second stacked photovoltaic cell. The bottom cell is a crystal silicon type photovoltaic cell, the crystal silicon wafer is prepared with an alloy region of silicon, tin and germanium in crystal state, and the top cell is a perovskite type photovoltaic cell.

[0098] Figure 3 For example 3 of the present application, the structure diagram of the third stacked photovoltaic cell. The bottom cell is a crystal silicon type photovoltaic cell, the crystal silicon wafer is prepared with an alloy region of silicon, tin and germanium in crystal state, and the top cell is a prior art photovoltaic cell.

[0099] Figure 4is a schematic diagram of the relationship between the light quantum density and the sunlight wavelength in the range of 300nm-1800nm, made with the aid of the key data of the AM1.5 light spectrum irradiation standard given in IEC 60904-3, in the range of wavelength 350nm and the bottom cell absorption cut-off wavelength λ C 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.

[0100] BRIEF DESCRIPTION OF DRAWINGS

[0101] 1, top cell; 2, bottom cell; 3, non-main light-receiving surface of the tandem photovoltaic cell; 4, first light quantum hump; 5, second light quantum hump; 6, lithium crystal silicon wafer; 7, alloy crystal silicon wafer; 71, alloy region; 11, top cell output end; 21, bottom cell output end; 100, first tandem photovoltaic cell; 200, second tandem photovoltaic cell; 300, third tandem photovoltaic cell. DETAILED DESCRIPTION

[0102] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the drawings of the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The devices of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0103] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0104] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0105] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0106] In addition, if the terms "first", "second" and the like appear, they are only used for differentiation description, and cannot be understood as indicating or implying relative importance.

[0107] It should be noted that the features in the embodiments of the present application can be combined with each other without conflict.

[0108] Embodiment 1:

[0109] Referring to Figure 1 , Figure 4 , a crystalline silicon wafer for preparing a crystalline silicon photovoltaic cell, the lithium-doped crystalline silicon wafer 6 is doped with 1×10 19 / cm 3 of lithium, the impurity lithium of the lithium-doped crystalline silicon wafer 6 is obtained through a diffusion process, or is obtained by cutting a corresponding lithium-doped crystalline silicon ingot, and the lithium-doped crystalline silicon ingot is obtained by the CZ method. The bottom cell 2 of the crystalline silicon prepared from the lithium-doped crystalline silicon wafer 6 is caused to have a band gap width of 0.92 ev due to the expansion effect of the impurity lithium on the crystalline silicon lattice, and the light absorption wavelength limit is extended to 1350 nm from 1107 nm of the prior art. The top cell 1 of the first stacked photovoltaic cell 100 is a CsPbI3 perovskite photovoltaic cell, and the light absorption wavelength limit is 743 nm. The light absorption wavelength limit of the bottom cell 2 is 1350 nm, and the light absorption wavelength limit of the top cell 1 is 743 nm. It can be seen that the number of light quanta (represented by the area) in the range of 300 nm to 743 nm to the left of 743 nm is equal to the number of light quanta in the range of 743 nm to 1350 nm to the right of 743 nm. 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 output the first stacked photovoltaic cell 100 at both ends. Figure 4

[0110] The beneficial effects of the present embodiment are as follows:

[0111] 1) By doping lithium in crystalline silicon to obtain lithium-doped crystalline silicon, the absorption of the first light quantum peak 4 of the light quantum near the center wavelength 1250 nm of the AM1.5 spectrum sunlight is expanded, and therefore the photoelectric conversion efficiency of the first stacked photovoltaic cell 100 of the present application is improved by 6.6% compared with the prior art perovskite / single-crystal silicon stacked cell technology;

[0112] 2) The amount of lithium doping is small, the process is simple, and the cost is low;

[0113] 3) Lithium helps to passivate crystal defects, improve crystal minority carrier lifetime and carrier mobility, and is conducive to inhibiting the ultraviolet-induced degradation effect.

[0114] Embodiment 2:

[0115] Referring to Figure 2 , Figure 4 , a crystalline silicon wafer for preparing a crystalline silicon photovoltaic cell, the lithium-doped crystalline silicon wafer 6 is doped with 1×10 17 / cm 3 ​The lithium in the lithium crystal silicon wafer 6 is a fast diffusing impurity, which is easy to diffuse from the lithium crystal silicon wafer 6 to the alloy region 71, and helps to expand the lattice constant of the alloy region 71, and reduce the lattice matching stress. With the expansion of the lattice of the alloy region 71 by the interstitial impurity lithium, the band gap width of the material of the alloy region 71 is reduced to 0.69 ev, which brings the benefit that the light absorption wavelength limit of the alloy region 71 locally prepared with the alloy elements of silicon, tin and germanium is extended from 1107 nm of the prior art crystal silicon wafer to 1800 nm, and the alloy crystal silicon wafer 7 is formed.

[0116] The crystal silicon bottom cell 2 is prepared from the alloy crystal silicon wafer 7 with the alloy region 71 prepared on one side.

[0117] The top cell 1 of the second stacked photovoltaic cell 200 is a MAPbI3 perovskite photovoltaic cell, and the light absorption wavelength limit is 830 nm. The bottom cell 2 is prepared from the alloy crystal silicon wafer 7 with the alloy region 71 prepared on one side. Figure 4 As can be seen, the number of light quanta (represented by the area) in the range of 300 nm to 830 nm to the left of 830 nm is equal to the number of light quanta in the range of 830 nm to 1800 nm to the right of 830 nm. Therefore, the top cell 1 and the bottom cell 2 output the same current under the AM1.5 spectrum. The bottom cell and the top cell are connected in series to output the second stacked photovoltaic cell 200 at both ends. The alloy region 71 of the alloy crystal silicon wafer 7 is located at the non-main light receiving surface 3 of the stacked photovoltaic cell of the second stacked photovoltaic cell 200, and one electrode of the bottom cell 2 of the stacked photovoltaic cell is led out by the alloy region 71 of the alloy crystal silicon wafer 7.

[0118] The beneficial effects of the present embodiment are:

[0119] 1) By changing the composition ratio of the alloy region 71, the absorption of the first light quantum camel hump 4 and the second light quantum camel hump 5 near the center wavelength 1250 nm and near 1600 nm of the AM1.5 spectrum sunlight is expanded, and the photoelectric conversion efficiency of the second stacked photovoltaic cell 200 of the present application is improved by 4.5% compared with the prior art perovskite / single crystal silicon stacked photovoltaic cell technology;

[0120] 2) The element ratio of the alloy region can adjust the band gap width and the lattice constant, and the control degree of freedom is large.

[0121] 3) Lithium helps to passivate the defects in the crystal and at the interface, and improves the minority carrier lifetime and the carrier mobility of the crystal; it is also helpful to suppress the ultraviolet-induced degradation effect.

[0122] Embodiment 3

[0123] Reference is made to Figure 3 , Figure 4A crystal silicon wafer for preparing a crystal silicon photovoltaic cell, the lithium crystal silicon wafer 6 is doped with 1×10 17 / cm 3 A 2μm alloy region 71 containing 8% silicon, 3% tin and the rest germanium is prepared on one side of the lithium crystal silicon wafer 6 by a molecular beam epitaxy process to form an alloy crystal silicon wafer 7. The alloy region 71 side is located on the non-main light receiving surface 3 of the third stacked photovoltaic cell. The band gap width of the material of the alloy region 71 is 0.69ev, which extends the light absorption wavelength limit of the bottom cell 2 to 1800nm from 1107nm of the prior art.

[0124] The lithium crystal silicon wafer 6 is obtained by cutting a corresponding crystal silicon ingot, which is obtained by the CZ method.

[0125] The top cell 1 of the third stacked photovoltaic cell 300 in Example 3 is a single crystal silicon photovoltaic cell, the band gap width of the single crystal silicon material is 1.12ev, and the light absorption wavelength limit of the material is 1107nm. The output current and voltage of the top cell 1 and the bottom cell 2 under the AM1.5 spectrum are different, so this embodiment is designed as a four-terminal output stacked 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 independent power sources in an electrical manner.

[0126] The beneficial effects of this embodiment are:

[0127] 1) The absorption of the first light quantum peak 4 near the center wavelength 1250nm of the AM1.5 spectrum sunlight and the second light quantum peak 5 near the center wavelength 1600nm is increased, and the light-to-electricity conversion efficiency of the stacked photovoltaic cell of the present application is improved by 11% compared with the prior art single-junction single crystal silicon photovoltaic cell;

[0128] 2) The crystal silicon top cell is stable and reliable in operation and environmentally friendly;

[0129] 3) Lithium helps to passivate the defects in the crystal and at the interface, improve the minority carrier lifetime and carrier mobility, and inhibit the UV-induced degradation effect.

[0130] In summary, the technical solution provided by the present application has significant cost advantages and cost reduction potential, and can inhibit the generation of the UV-induced degradation effect. It has great significance for the development of the industry.

[0131] The above examples are only preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A crystalline silicon piece for the production of crystalline silicon photovoltaic cells, characterized in that: The crystal silicon wafer is an alloy crystal silicon wafer, which comprises a substrate, and the substrate is locally prepared with an alloy region comprising alloy elements of silicon, tin and germanium, and the alloy crystal silicon wafer is formed, and the proportion of the alloy elements in the alloy region of the alloy crystal silicon wafer is as follows in terms of 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 elemental lithium, and the concentration of the elemental lithium in the alloy region is at least in 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 elemental lithium, and the concentration of the elemental lithium in the substrate of the crystal silicon wafer is at least in 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 stacked photovoltaic cell, characterized by, The bottom cell of the stacked photovoltaic cell is prepared from the crystal silicon wafer as claimed in claim 1, and the crystal silicon wafer is a lithium crystal silicon wafer.

6. A stacked photovoltaic cell characterized by, The bottom cell of the stacked photovoltaic cell is prepared from the crystal silicon wafer as claimed in 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 a 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.

7. The tandem photovoltaic cell of claim 5 or claim 6, wherein, The top cell of the stacked photovoltaic cell is a photovoltaic cell of a crystal silicon material.

8. The tandem photovoltaic cell of claim 5 or claim 6, wherein, The top cell of the stacked photovoltaic cell is a photovoltaic cell of a perovskite material.

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