CN101471389B - Solar battery - Google Patents

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CN101471389B
CN101471389B CN 200710160548 CN200710160548A CN101471389B CN 101471389 B CN101471389 B CN 101471389B CN 200710160548 CN200710160548 CN 200710160548 CN 200710160548 A CN200710160548 A CN 200710160548A CN 101471389 B CN101471389 B CN 101471389B
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solar cell
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CN101471389A (en
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黄文瑞
林进章
戴国勋
黄建斯
吴钧闵
林正勋
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Giga Solar Materials Corp
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Guoshuo Science & Technology Industrial Co Ltd
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Abstract

The invention provides a solar battery comprising a base plate which comprises a p-n doping structure formed in the base plate, back material which is attached on the base plate, and comprises glass mixture, organic medium, aluminized material and additive, wherein the glass mixture comprises Al2O3, Bi2O5, B2O3, SiO2, PbO, Tl2O3 and ZnO, the content of aluminium powder in the material is 60-80%, the degree of purity is about 90-99.99%, the additive comprises stearic acid of C10-C24, whose content is smaller than 5%, the content of the organic medium is about 20-35%, and comprises 60-90%alcohol ether organic solvent, 10-20%cellulose resin and 1-5% advection agent, rheologic agent or thixotropic agent. The solar battery of the invention can improve the bending of the silicon base plate caused by stress.

Description

Solar cell
Technical field
The present invention provides a kind of solar cell (Solar Cell); Particularly relevant for through forming uniform al-si eutectic layer at silicon (wafer) back side; Reducing the structural stress that the slimming solar cell is produced, and then improve silicon substrate effectively because the buckling phenomenon that stress caused.
Background technology
In recent years, based on industrial high development, fossil energy is exhausted fast, causes environmental pollution to be on the rise.Therefore, alternative energy source all is devoted to develop for energy demand and environmental protection reason in countries in the world.Solar energy is available affluent resources as far as the mankind now, and having does not need cost of transportation, clean and the earth do not increased advantage such as heat load.Based on above-mentioned advantage, solar energy becomes one of clean renewable energy resources of tool potentiality to be exploited now.
Solar cell (solar cell) is to utilize photovoltaic effect (photovoltaic effect), converts solar energy the semiconductor subassembly of electric energy into, and any basically semi-conductive diode all can become electric energy with transform light energy.Solar cell produces electric energy and is based on photoconductive effect (photoconductive effect) and internal electric field two factors.Therefore, select the material of solar cell, must consider the photoconductive effect of its material and how produce internal electric field.
The height of solar cell properties is mainly judged with the conversion efficiency between the photoelectricity.And the factor that influences conversion efficiency comprises sunlight intensity, temperature; The resistance of material and the quality of matrix, defect concentration; Concentration, the degree of depth of pn knot; Surface light reflex rate size; Metal electrode live width, high, the contact resistance of line.So, must strict control just be able to make solar cell with high conversion efficiency to various aforesaid influencing factors.
Conversion efficiency and cost of manufacture are for make the major consideration of solar cell now.Solar battery product in the market is that the solar cell of raw material occupies majority in occupation rate of market with silicon.According to the crystal structure classification, can be divided into three kinds in monocrystalline solar cells, polycrystalline solar cell and armorphous solar cell etc.; With conversion efficiency, be main factor of evaluation still at present with the utilization rate of monocrystaline silicon solar cell, be approximately 24% conversion efficiency, polysilicon then takes second place, and is about 19%, and amorphous silicon then is about about 11%.Use other compound semiconductor to come as photoelectric conversion substrate, the GaAs of III-V family (GaAs) for example, conversion efficiency then can be up to more than 26%.
How improving its energy conversion efficiency, reduce silicon thickness, also is the main direction of solar battery technology development.About the problem of chip thickness, (except that letting cell thickness reduces to below the 37 μ m, its efficient also can reach 20% to the manufacturing process of a kind of laser sintered electrode capable of using on the prior art for Laser-Fired Contact, LFC) technology.Its step is greatly slightly: on the back of the body surface of solar cell, utilize the vapor deposition mode to make the aluminium film and form passivation layer (passivation layer), punch the aluminium film to form conductive junction point through laser.Laser sintering processes can solve the problem that original electric energy runs off effectively; And utilize laser sintered contact technology; Need not utilize little shadow, the etching technique of traditional and expensive in the passivation layer at the silicon crystal slate back side, to form hole (holes) pattern, to hold aluminium matter electrode.
In addition, also have a kind of prior art,, use the half tone of low warpage aluminium paste (coating at the battery wafer back side) and high mesh number instead, to reduce wafer fragmentation rate through the mode of adjustment traditional silk-screened; Improve its conversion efficiency in addition and with the LFC manufacturing process.
Yet LFC manufacturing process cost is too high relatively, and the performance that prior art is improved is still on the low side.If can effectively improve conversion efficiency of solar cell and improve the warpage issues that its thickness brings and be the task of top priority now.
Summary of the invention
In sum, the present invention provides a kind of and can effectively improve conversion efficiency of solar cell and the solar cell that improves the warpage issues that its thickness brings.
The object of the present invention is to provide the solar cell of a kind of high conversion efficiency, sheet.
The present invention also aims to provide a kind of required silk screen aluminium paste of method for printing screen volume production solar cell that utilizes.
The present invention also aims to provide a kind of the be warpage of improving the required silicon wafer of sheet solar cell, the unleaded and high efficiency method of raising conversion.
The present invention provides a kind of solar cell, comprising: substrate comprises the p-n doped structure that is formed in this substrate; Back Material, it is attached at said substrate, and this Back Material comprises glass mixture, organic media, contains aluminium material and additive.
The composition of the glass mixture that the present invention is above-mentioned comprises Al 2O 3, Bi 2O 5, B 2O 3, SiO 2, PbO, Tl 2O 3Or ZnO; Preferably, the composition of this glass mixture also contains Fe 2O 3, P 2O 5, MgO, Ga 2O 3, Li 2O, Na 2O, ZrO 2, AgO, Sc 2O 5, SrO, BaO, CaO, Pd, Pt, Rh etc. any one.
Wherein, this contain aluminium material comprise 60～80% and purity 90 to 99.99% between aluminium powder; Said additive comprises C 10～C 24Hard fatty acids, this C 10～C 24The content of hard fatty acids less than 5%; The content of said organic media is 20～35%, and above mass percent is that 100% benchmark measures with the quality of said Back Material.Comprise 60～90% pure ethers organic solvent or 10～20% celluosic resin in this organic media, this organic media preferably also comprises 1～5% advection agent, auxiliary rheological agents or thixotroping auxiliary agent etc.
Solar cell of the present invention, described glass mixture comprise at least two kinds of main glass and form, and these two kinds main glass are formed and comprised first glass ingredient and second glass ingredient.
Above-mentioned first glass ingredient is selected from one of following or its mixing: PbO-SiO 2-B 2O 3-Al 2O 3, SiO 2-PbO-B 2O 3-Al 2O 3-ZrO 2, Bi 2O 3-ZnO-SiO 2-B 2O 3-Al 2O 3, SiO 2-SrO-Bi 2O 3-B 2O 3-Al 2O 3, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3-TiO 2, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3, SiO 2-Bi 2O 3-B 2O 3-Al 2O 3-Tl-ZnO, PbO-B 2O 3-SiO 2, Bi 2O 3-SiO 2-ZnO-V 2O 5, Bi 2O 3-SiO 2-ZnO, Bi 2O 3-SiO 2-Al 2O 3, Bi 2O 3-SiO 2-V 2O 5, Bi 2O 3-SiO 2-B 2O 3-K 2O, Bi 2O 3-SiO 2-ZnO-B 2O 3-Li 2O-Na 2O-Nb 2O 5, PbO-SiO 2-ZnO-Al 2O 3, PbO-SiO 2-ZnO-Al 2O 3-Ta 2O 5, PbO-SiO 2-Al 2O 3-HfO 2-In 2O 3-Ga 2O 3, PbO-SiO 2-Al 2O 3-Ta 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-Sb 2O 5, PbO-SiO 2-Al 2O 3-ZrO 2, PbO-SiO 2-Al 2O 3-P 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-ZrO 2-Sb 2O 5, PbO-SiO 2-Al 2O 3-HfO 2, PbO-SiO 2-Ga 2O 3, SiO 2-ZrO 2-B 2O 3-ZnO-MgO-TiO 2-Na 2O-LiO 2-Bi 2O 3
Above-mentioned second glass ingredient is selected from one of following or its mixing: PbO-SiO 2-B 2O 3-Al 2O 3, SiO 2-PbO-B 2O 3-Al 2O 3-ZrO 2, Bi 2O 3-ZnO-SiO 2-B 2O 3-Al 2O 3, SiO 2-SrO-Bi 2O 3-B 2O 3-Al 2O 3, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3-TiO 2, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3, SiO 2-Bi 2O 3-B 2O 3-Al 2O 3-Tl-ZnO, PbO-B 2O 3-SiO 2, Bi 2O 3-SiO 2-ZnO-V 2O 5, Bi 2O 3-SiO 2-ZnO, Bi 2O 3-SiO 2-Al 2O 3, Bi 2O 3-SiO 2-V 2O 5, Bi 2O 3-SiO 2-B 2O 3-K 2O, Bi 2O 3-SiO 2-ZnO-B 2O 3-Li 2O-Na 2O-Nb 2O 5, PbO-SiO 2-ZnO-Al 2O 3, PbO-SiO 2-ZnO-Al 2O 3-Ta 2O 5, PbO-SiO 2-Al 2O 3-HfO 2-In 2O 3-Ga 2O 3, PbO-SiO 2-Al 2O 3-Ta 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-Sb 2O 5, PbO-SiO 2-Al 2O 3-ZrO 2, PbO-SiO 2-Al 2O 3-P 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-ZrO 2-Sb 2O 5, PbO-SiO 2-Al 2O 3-HfO 2, PbO-SiO 2-Ga 2O 3, SiO 2-ZrO2-B 2O 3-ZnO-MgO-TiO 2-Na 2O-LiO 2-Bi 2O 3
The objective of the invention is to improve the conversion efficiency and the warpage issues of solar cell.The present invention utilizes the aluminium back of the body (BSF) structure; Aluminium, glass and organic media at solar cell back doping special ratios composition; Via experiment confirm; This technology can effectively be improved the conversion efficiency of solar cell and increase rigidity to solve its warpage issues, so the usefulness that can effectively reduce the fragmentation rate on the manufacturing process and promote solar cell.In addition, the present invention only is the aluminium paste material of special ratios composition of mixing merely, can reach the effect that is superior to above-mentioned two kinds of prior aries, the fragmentation rate on reducing manufacturing process, also can reduce above-mentioned manufacturing cost, more can increase its conversion efficiency.
Description of drawings
Fig. 1: focusing ion microscope (FIB) figure of solar cell of the present invention;
Fig. 2: focusing ion microscope (FIB) the analysis result figure of the control group back side aluminium film of solar cell of the present invention;
Fig. 3: the sims analysis of solar cell of the present invention is sketch map as a result;
Wherein, recognize that represent respectively is embodiment 9-Si, control group-Si, embodiment 9-Al, and control group-Al from top to bottom from the datum mark of degree of depth 5000nm;
Fig. 4 A: the experiment parameter sketch map of the temperature of solar cell of the present invention and short circuit current;
Fig. 4 B: the experiment parameter sketch map of the temperature of solar cell of the present invention and withdrawal ratio;
Fig. 4 C: the experiment parameter sketch map of the temperature of solar cell of the present invention and open circuit voltage;
Fig. 4 D: the experiment parameter sketch map of the temperature of solar cell of the present invention and conversion efficiency;
Fig. 5 A: the experiment parameter sketch map of the temperature of solar cell of the present invention and short circuit current;
Fig. 5 B: the experiment parameter sketch map of the temperature of solar cell of the present invention and withdrawal ratio;
Fig. 5 C: the experiment parameter sketch map of the temperature of solar cell of the present invention and open circuit voltage;
Fig. 5 D: the experiment parameter sketch map of the temperature of solar cell of the present invention and conversion efficiency;
Fig. 6 A: the experiment parameter sketch map of the temperature of solar cell of the present invention and short circuit current;
Fig. 6 B: the experiment parameter sketch map of the temperature of solar cell of the present invention and withdrawal ratio;
Fig. 6 C: the experiment parameter sketch map of the temperature of solar cell of the present invention and open circuit voltage;
Fig. 6 D: the experiment parameter sketch map of the temperature of solar cell of the present invention and conversion efficiency.
Embodiment
Specify the present invention below in conjunction with accompanying drawing, but do not limit practical range of the present invention.
Some embodiments of the present invention are described in detail as follows.Yet except the embodiment that describes in detail, the present invention can extensively implement in other embodiment, and claim scope of the present invention is not limited to following embodiment, and its scope with claim is as the criterion.In addition, for clearer description being provided and being more readily understood the present invention, each several part is not drawn according to its relative size in the diagram, and incoherent detail section is not drawn fully yet, succinct in the hope of drawing.Please refer to accompanying drawing and icon, wherein show it only is for the preferred embodiments of the present invention are described, is not in order to restriction the present invention.
In miniaturization as thin as a wafer in the solar battery structure of silicon wafer; In order not make ultra thin silicon wafers produce distortion or warpage; The present invention finds after deliberation; Can form special substance or back of the body slurry in the silicon wafer back side to change structural stress, strengthen whole solar battery structure, the ability of improve conversion efficiency of solar cell, promoting anti-strain of structure or stress.And the present invention directly uses the back of the body slurry material that is formed at the solar battery chip back side, and this rete is able to effectively improve conversion efficiency and prevent deformation.For example, the main constituent of al-si eutectic layer material comprises aluminium powder, organic media, glass frit.
In an embodiment, through changing material or back of the body slurry and utilize the characteristic of glass frit to improve the deformation degree, and increase the conversion efficiency of solar cell, this is also contained by notion of the present invention.
Solar cell of the present invention comprises: substrate, for example silicon is used to make the solar energy monomer in wherein.The p-n doped structure that it comprises n-doped region and p-doped region is formed among the silicon.The al-si eutectic layer is to be formed at the silicon back side in order to improve the structural stress of sheet solar base plate.The material of back of the body slurry adopts the component ratio relation between aluminium powder, glass frit, organic media through research of the present invention and discovery, is able to slow down structural stress and prevents base plate deformation.
One of characteristic of the present invention is to utilize the plural glass ingredient that mixes to form above-mentioned back of the body slurry.
Above-mentioned back of the body slurry (aluminium paste) composition content of aluminium powder is about 60～80%; Purity is about 90 to 99.99%; Average grain diameter is about 1～20 μ m; Shape can be selected from sphere or like spherical, granular, bar-shaped, needle-like, column, squamous, spongy, tip-angled shape, radiussed, cellular, polygonal, sheet, strip, dendroid, fibrous and irregular shape etc., wherein any is more than shape; Organic media, content is about 20～35%, comprises pure ether solvent 60～90%, celluosic resin 10～20%, advection agent, auxiliary rheological agents or thixotroping auxiliary agent etc. 1～5%; Additive, for example, C 10～C 24Hard fatty acids, content is less than 5%; Glass frit, content is about below 5%, and the glass frit composition is as shown in the table.Above degree is mass percent.
Following is illustration, non-in order to limit the present invention.With the preferred embodiments of the present invention, select for use and select two or more composition mixing manufacture back of the body slurry in the many glass types of following tabular, look characteristic and do selection.
Figure 2007101605482A00800011
Other glass ingredient also can be selected for use, be not limited to above-mentioned as: Bi 2O 3-SiO 2-ZnO-V 2O 5, Bi 2O 3-SiO 2-ZnO, Bi 2O 3-SiO 2-Al 2O 3, Bi 2O 3-SiO 2-V 2O 5, Bi 2O 3-SiO 2-B 2O 3-K 2O, Bi 2O 3-SiO 2-ZnO-B 2O 3-Li 2O-Na 2O-Nb 2O 5, PbO-SiO 2-ZnO-Al 2O 3, PbO-SiO 2-ZnO-Al 2O 3-Ta 2O 5, PbO-SiO 2-Al 2O 3-HfO 2-In 2O 3-Ga 2O 3, PbO-SiO 2-Al 2O 3-Ta 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-Sb 2O 5, PbO-SiO 2-Al 2O 3-ZrO 2, PbO-SiO 2-Al 2O 3-P 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-ZrO 2-Sb 2O 5, PbO-SiO 2-Al 2O 3-HfO 2, PbO-SiO 2-Ga 2O 3, SiO 2-ZrO 2-B 2O 3-ZnO-MgO-TiO 2-Na 2O-LiO 2-Bi 2O 3
Many experimental datas by shown in the present learn that foundation back of the body slurry composition of the present invention and manufacture method can make the solar cell substrate angularity reduce and promote solar energy converting efficient.The present invention is able to through mixing heterogeneity glass and adding additive, change the coefficient of expansion under its room temperature through changing the mode of thermal coefficient of expansion and temperature relation, makes the coefficient of expansion approach silicon substrate.By the preferred embodiments of the present invention, mix back glass principal component and comprise Al 2O 3, Bi 2O 5, B 2O 3, SiO 2, PbO, Tl 2O or ZnO.Also contain Fe again, 2O 3, P 2O 5, MgO, Ga 2O 3, Li 2O, Na 2O, ZrO 2, AgO, Sc 2O 5, SrO, BaO, CaO, Pd, Pt, Rh etc. any one be preferred.In addition, be able to the reinforced aluminum back of the body (Back Surface Field), so and then increase conversion efficiency through back of the body slurry composition as suggested in the present invention.
Illustrative glass constituent (visible characteristic is selected wherein several kinds or whole):
Experimental group is respectively embodiment 1, embodiment 2, embodiment 3, embodiment 4, embodiment 5, embodiment 6, embodiment 7, embodiment 8, embodiment 9 and embodiment 10, and makes comparisons with control group.Observe short circuit current, open circuit voltage, fill factor, curve factor, warpage and the temperature of solar cell of the present invention and the relation of conversion efficiency and temperature.With monocrystalline silicon crystal face 100, its p-cake core resistivity is 1.2 Ao Mu-centimetre (ohm.cm).The size of chip is selected according to practical application.In preferred embodiment, when being of a size of (very little) at 5 o'clock as if its chip, its length of side is 125mm; If when it was of a size of (very little) at 6 o'clock, its length of side was 150mm or 156mm.And the thickness of silicon is 80～240 microns (micro-meter).Solar cell manufacturing of the present invention comprises the steps that so its non-pattern characteristics for avoiding fuzzy focus, only done a common property statement, and is non-in order to limit the present invention.Those skilled in the art need know, the illustrative back of the body slurry of the present invention institute, and non-limiting following described structure or the manufacturing process of being used for, it makes an embodiment.
In a preferred embodiment, the monocrystalline (10cm*10cm) of (very little) when its chip is selected size 4, the chip of about 180～210 μ m of thickness; The common property manufacturing step of general solar cell comprises: (1) forms suede structure (Texture); (2) phosphorous diffusion; (3) edge cuts and oxide layer are removed; (4) antireflection layer deposition; (5) silk screen printing, silk screen printing comprise front side silver paste, back silver aluminium paste and back side aluminium paste; (6) drying and sintering; (7) the I-V electrical characteristic is measured or the like, is described below.Yet, for fear of fuzzy the present invention, thus explanation omitted with the irrelevant step of the present invention, for example, HPM cleaning, tempering, H 2Steps such as SINTER.
(1) form suede structure (Texture): make the antireflection layer that one deck all has the texture structure, reduce the reflection of incident sunlight, if there is not this reflector, incident light 30% reflection loss of can having an appointment, this is quite serious as far as solar cell.The surface of its plane of illumination of solar cell all can stay the texture processing of big and small pyramid (pyramid) prior to the surface, lowers the probability that incident light just turns back through first reflection, and pyramidal size is several microns (μ m) approximately.
(2) phosphorous diffusion: the degree of depth of general n-type diffusion layer has only about 0.5 μ m, so p-n junction in fact is to be formed at the pyramidal surface of texture.The general POCl that uses 3Oxygen and nitrogen spread at the High temperature diffusion boiler tube, and the phosphorus atoms of generation gets in the silicon crystal lattice via the High temperature diffusion mode, form mixing of n-type.In order to form p-n junction, generally use diffusion method, doing the n-type phosphorous diffusion on the p-type silicon wafer.
(3) edge cuts and oxide layer are removed: the silicon wafer surface can produce layer of silicon dioxide layer (SiO 2).Generally can use hydrofluoric acid (HF) to remove surperficial formed silicon dioxide layer.Through after this process, but p-type wafer coating one deck n-type mixes thing, then via the processing of edge etching (edge etching), the isolated leakage current of laser cutting is removed or after sintering is accomplished, used at n-type layer edge, forms the structure of p-n junction.If it is complete inadequately that edge isolation (edge isolation) is handled, then the shunt resistance of solar cell (shuntresistance (Rsh)) thereby reduces the efficient of solar cell just can reduce.
(4) antireflection layer deposition: the general methods of using plasma (electricity slurry) gain chemical vapour deposition (CVD) (PECVD) of silicon wafer solar cell more; On solar cell wafer, plate one deck silicon nitride (SiNx) and form antireflection layer plated film (anti-reflection coating; ARC), can effectively reduce the incident light reflection, and have passivation (passivation) effect; And then the protection solar cell, also have functions such as anti-scratch, moisture-resistant gas.
(5) silk screen printing: utilize screen process press that front side silver paste, back silver aluminium paste and back side aluminium paste are applied in the solar cell wafer front and the back side respectively, form Metal Contact through high-temperature process.Aspect the silver electrode characteristic, need low series resistance, low metal coverage rate and with the good adhesion of antireflection layer.Front side silver paste metallic finger electrode (finger electrode) graph thinning can make solar battery front side irradiation area strengthen; Increase the light incident intensity; Can collect carrier effectively, make the current density that photovoltaic effect produced increase, cause the solar cell photoelectric transformation efficiency to promote.
At present general solar cell is mainly the BSF structure; Its characteristics are that back (non-irradiation face) makes the layer of aluminum electrode; Aluminium is diffused in the p-type semiconductor, form the p+ layer, this mode can increase the Voc value in the circuit; Produce the field effect of the aluminium back of the body, increase the conversion efficiency of solar cell.
Because the thermal coefficient of expansion of aluminum metal and silicon substrate has gap, when the thickness of solar cell reduces, cause the angularity of solar cell to improve, the too high difficulty with integration of the fragmentation rate on the solar module manufacturing process of increasing.So present control for low warpage belongs to the adjustment of constituent more, add the thermal coefficient of expansion of glass in the major control aluminium glue, so substantial connection is arranged with its selected glass additive composition.
And the back silver aluminium paste is the lead of binding two solar panels, and its characteristics are that high conductivity can be contacted the electric current that solar cell produced.The diffusion of suitable aluminium can form the p+ layer, and the open circuit voltage that increases solar cell is representing of aluminium back of the body field effect, thus BSF thickness of structure, uniformity, all can be relevant with open circuit voltage, conversion efficiency.Usually back side aluminium electrode layer is enough thick, and collocation sintering time and sintering temperature (Peak Firing) just have best open circuit voltage performance, and then promotes the conversion efficiency of solar cell.
(6) drying and sintering: baking temperature 200-300 ℃, drying time, dry purpose was to let the organic solvent of front side silver paste, back silver aluminium paste, aluminium paste volatilize less than 20 seconds.Sintering uses infrared ray to transmit stove (IRbelt) usually, and sintering time 2-3 minute, and the peak firing temperature of sintering (Peak Firing Temperature) is at 600-1000 ℃.The purpose of sintering be let front side silver paste, back silver aluminium paste, aluminium paste dispersant and organic media voloxidation and make it form the BSF layer.
(7) the I-V electrical characteristic is measured: last, and the voltage-current characteristic curve (IVCurve) of test solar cell, and the conversion efficiency of solar cell, short circuit current and open circuit voltage or the like characteristic.
Of the present invention focusing on can form special substance or back of the body slurry through the silicon wafer back side via discovering; For example; Aluminium paste is strengthened whole solar battery structure to change structural stress, the ability of improve conversion efficiency of solar cell, promoting anti-strain of structure or stress.
Table 1 is depicted as mix different aluminium powders and glass frit first glass composition A or second glass and forms B, does not add additive, and organic media comprises diethylene glycol butyl ether, ethyl cellulose, rilanit special; Percentage is: diethylene glycol butyl ether 85%, ethyl cellulose 13%, rilanit special 2%.Its angularity is about 0.25-0.35mm, 0.20-0.25mm.
Table 2 is depicted as solvent, the aluminium powder with table 1, but heats to mix and make it produce crystallization again or no longer crystallization for importing two kinds of different glass frits, no additive, and two kinds of glass mixed proportions can be joined shown in the table 2.The ratio of the doping ratio of the first glass A and the second glass B is between 1-9.Learn that by experimental data the conversion efficiency of control group can reach 14.13%.And experimental group is 1.5 o'clock in the glass ratio, obtains best conversion efficiency 14.07%.
Table 3 is depicted as rough solvent with table 2, about 95% aluminium powder, and the ratio ratio of the first glass A and the second glass B is about 1.5.Learn that by experimental data 905 ℃ of sintering temperatures, control group conversion efficiency are 13.97%, and experimental group can reach 14.13% conversion efficiency, is much better than control group.But along with variations in temperature, the open circuit voltage of the branch battery (cell) of embodiment 5 can be also lower than control group.
Adjust solid content shown in the table 4, the two kinds of glass that mix, and add oleic acid, the content of oleic acid is about below 1%.During 925 ℃ of sintering temperatures, conversion efficiency 13.41% of the present invention, angularity 0.20～0.25mm; Control group No.12 efficient 13.14%, angularity 0.60～0.75mm.905 ℃ of sintering temperatures, efficient 13.48% of the present invention, angularity 0.25～0.35mm; Control group No.13 efficient 13.21%, angularity 0.60～0.75mm.
With reference to Fig. 1, be focusing ion microscope (FIB) analysis result of embodiment 9 back side aluminium films.Can find out that from the regional A of the FIB analysis chart of embodiment 9 when sintering formed eutectic, aluminum shot shakeout earlier on silicon face, is diffused into the silicon substrate internal layer through flooding mechanism again, form the al-si eutectic layer.Yet the parameter that determines this eutectic layer has three: glass dust composition, aluminum shot size shape, the extra substance of aluminium paste.Via decision aluminum shot size shape, improve the al-si eutectic layer and form.The area that contacts with silicon when aluminum shot is many more, and in sintering process, these aluminum shots that touch silicon have higher ratio and diffuse into silicon layer, have also just increased the thickness of al-si eutectic layer.Therefore why can explain the aluminum shot shape when circle is transformed into ellipse, the reason that efficient can promote because of oval-shaped aluminum shot has more area contact silicon, forms thicker al-si eutectic layer.
In conduction partly, shown in Figure 2 is focusing ion microscope (FIB) analysis result of control group back side aluminium film in addition.The structure of control group has al-si eutectic layer preferably, but its efficient is not so good as embodiment 9, but its reason inference is an electric hole transmission course.The electricity hole moves to the al-si eutectic layer earlier via silicon layer, and then to the aluminium paste surface, the tightness of aluminum shot is a key factor during the course.Can know from Fig. 2, under unit are, the aluminum shot of control group comparatively sparse, the more cavity that distributes, the area that aluminum shot and aluminum shot are in contact with one another does not have embodiment more than 9, and this phenomenon makes the Path selection of transmission in electric hole less, and resistance value is bigger, and usefulness decreases.Yet improve the tightness of aluminum shot, but the aluminum shot of different-grain diameter mix each other, utilize short grained aluminum shot to clog the slit of bulky grain aluminum shot, can increase the tightness of aluminum shot, reach that resistance value reduces, high efficiency solar cell.
Fig. 3 is embodiment 9 and control group sims analysis.But conversion efficiency and minimum angularity can be superiorly selected in the invention of fractograph analysis knowledge capital thus.Can demonstrate the following points phenomenon in curve distribution:
1. aspect the slope of curve of aluminium, can find out two kinds of condition of different.What at first slope was bigger is to account for about the 100nm of skin depth approximately; Tend towards stability afterwards, this phenomenon is might be because between 0～100nm, also has residual aluminum shot on top layer; And the degree of depth demonstrates the exponential damping situation after 100nm; Expression has the aluminium of part to enter in the silicon with the diffusion form after this, and curve meets the diffusion formula
N＝αNo?exp(-βs)
α is the material factor, and β is a diffusion coefficient, and s is a diffusion depth, and No is the unit volume atomic quantity, and N is a unit volume diffusion quantity.
2. after aluminium was spread in degree of depth 3750nm, signal had vibration slightly, was illustrated within this degree of depth, and it is uneven that the diffusion concentration of aluminium distributes.
3. signal is tending towards smooth behind degree of depth 3500nm.
4. estimate embodiment 9 aluminium signals and can be tending towards 0 in the degree of depth 11.5 μ m, the aluminium signal of control group can be tending towards 0 in the degree of depth 10 μ m, is representing the al-si eutectic layer thickness of embodiment 9 also thicker than control group.So the BSF layer of embodiment 9 can be thicker, open circuit voltage can be than higher.
The experiment parameter of Fig. 4 A～Fig. 4 D series (comprising Fig. 4 A, Fig. 4 B, Fig. 4 C, Fig. 4 D), Fig. 5 A～Fig. 5 D series (comprising Fig. 5 A, Fig. 5 B, Fig. 5 C, Fig. 5 D), Fig. 6 A～Fig. 6 D series (comprising Fig. 6 A, Fig. 6 B, Fig. 6 C, Fig. 6 D) difference displays temperature and each sample such as short circuit current, temperature and withdrawal ratio, temperature and open circuit voltage, temperature and conversion efficiency.From Temperature Distribution, embodiment 7 is taller compared to control group with branch battery (cell) electrical characteristic of embodiment 8, and angularity is also smaller.Adjust the material solid content and, can reach the characteristic of high conversion efficiency and low warpage with two kinds of glass of this mixed.
The present invention from the above can promote solar energy converting efficient and angularity really.Angularity is to obtain through following formula:
δ = 3 ( α b - α a ) ( T f - T ) ( t b + t a ) d 2 4 t b 2 ( 4 + 6 t a / t b + 4 ( t a / t b ) 2 + ( E a / E b ) ( t a / t b ) 2 + ( E b / E a ) ( t b / t a ) )
δ is an angularity, t aBe the thickness of Si material, t bBe aluminium film thickness, T fBe the conversion temperature of aluminium, T is a room temperature, α aBe the coefficient of expansion of Si, α bBe the coefficient of expansion of aluminium, E aBe the elastic force modulus of Si, E bBe the elastic force modulus of aluminium, d is the length of cell.
In addition, the conversion temperature of aluminium is 577 ℃, and ambient temperature is 25 ℃, and the coefficient of expansion of silicon is 3.5ppm/K, and the coefficient of expansion of aluminium is 23ppm/K, and the coefficient of elasticity of silicon is about 110GPa, and the coefficient of elasticity of aluminium is about 70GPa.The factor that influences warpage in principle is only relevant with the thickness of the thickness of aluminium film and silicon substrate.In addition, have only the glass that mixes below 5% in the aluminium paste, and glass is at the about 0.4 μ m of the distribution of whole area (10cm*10cm).It below is four important parameters: the formula of short circuit current, open circuit voltage, fill factor, curve factor and conversion efficiency.
Short circuit current I Sc: I Sc=I o(e QV/kT-1)-I L
Open circuit voltage V Oc: V Oc = KT q Ln ( I L I o + 1 )
Fill factor, curve factor FF: FF = V Mp I Mp V Oc I Sc
Efficiency eta: η = V Mp I Mp P In = V Oc I Sc FF P In
The present invention explains as above that with preferred embodiment it is not in order to limit Patent right requirement scope of the present invention.Its scope of patent protection when look claim and etc. same domain and deciding.All those skilled in the art, in not breaking away from this patent spirit or scope, change of being done or retouching all belong to the equivalence of being accomplished under the disclosed spirit and change or design, and should be included in the claim scope.
Figure 2007101605482A00800031
[0086]?
Figure 2007101605482A00800041
[0088]?
Figure 2007101605482A00800051
[0090]?

Claims (10)

1. a solar cell is characterized in that, said solar cell comprises:
Substrate, it comprises the p-n doped structure that is formed in this substrate; And
Back Material, it is attached at this substrate, and said Back Material comprises glass mixture, organic media, contains aluminium material and additive;
Wherein the composition of this glass mixture comprises Ti 2O 3And Bi 2O 3Mixing.
2. solar cell as claimed in claim 1 is characterized in that wherein the composition of this glass mixture comprises Al 2O 3, B 2O 3, SiO 2, PbO, ZnO, Fe 2O 3, P 2O 5, MgO, Ga 2O 3, Li 2O, Na 2O, ZrO 2, AgO, Sc 2O 5, SrO, BaO, CaO, Pd, Pt, Rh be arbitrary.
3. solar cell as claimed in claim 1 is characterized in that, wherein this glass mixture comprises at least two kinds of main glass compositions, and wherein these two kinds main glass are formed and comprised first glass ingredient and second glass ingredient.
4. solar cell as claimed in claim 3 is characterized in that, wherein this first glass ingredient is selected from one of following or its mixing: PbO-SiO 2-B 2O 3-Al 2O 3, SiO 2-PbO-B 2O 3-Al 2O 3-ZrO 2, Bi 2O 3-ZnO-SiO 2-B 2O 3-Al 2O 3, SiO 2-SrO-Bi 2O 3-B 2O 3-Al 2O 3, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3-TiO 2, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3, SiO 2-Bi 2O 3-B 2O 3-Al 2O 3-Ti-ZnO, PbO-B 2O 3-SiO 2, Bi 2O 3-SiO 2-ZnO-V 2O 5, Bi 2O 3-SiO 2-ZnO, Bi 2O 3-SiO 2-Al 2O 3, Bi 2O 3-SiO 2-V 2O 5, Bi 2O 3-SiO 2-B 2O 3-K 2O, Bi 2O 3-SiO 2-ZnO-B 2O 3-Li 2O-Na 2O-Nb 2O 5, PbO-SiO 2-ZnO-Al 2O 3, PbO-SiO 2-ZnO-Al 2O 3-Ta 2O 5, PbO-SiO 2-Al 2O 3-HfO 2-In 2O 3-Ga 2O 3, PbO-SiO 2-Al 2O 3-Ta 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-Sb 2O 5, PbO-SiO 2-Al 2O 3-ZrO 2, PbO-SiO 2-Al 2O 3-P 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-ZrO 2-Sb 2O 5, PbO-SiO 2-Al 2O 3-HfO 2, PbO-SiO 2-Ga 2O 3, SiO 2-ZrO 2-B 2O 3-ZnO-MgO-TiO 2-Na 2O-LiO 2-Bi 2O 3
5. solar cell as claimed in claim 3 is characterized in that, wherein second glass ingredient is selected from one of following or its mixing: PbO-SiO 2-B 2O 3-Al 2O 3, SiO 2-PbO-B 2O 3-Al 2O 3-ZrO 2, Bi 2O 3-ZnO-SiO 2-B 2O 3-Al 2O 3, SiO 2-SrO-Bi 2O 3-B 2O 3-Al 2O 3, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3-TiO 2, SiO 2-PbO-ZnO-B 2O 3-Al 2O 3, SiO 2-Bi 2O 3-B 2O 3-Al 2O 3-Ti-ZnO, PbO-B 2O 3-SiO 2, Bi 2O 3-SiO 2-ZnO-V 2O 5, Bi 2O 3-SiO 2-ZnO, Bi 2O 3-SiO 2-Al 2O 3, Bi 2O 3-SiO 2-V 2O 5, Bi 2O 3-SiO 2-B 2O 3-K 2O, Bi 2O 3-SiO 2-ZnO-B 2O 3-Li 2O-Na 2O-Nb 2O 5, PbO-SiO 2-ZnO-Al 2O 3, PbO-SiO 2-ZnO-Al 2O 3-Ta 2O 5, PbO-SiO 2-Al 2O 3-HfO 2-In 2O 3-Ga 2O 3, PbO-SiO 2-Al 2O 3-HfO 2-In 2O 3-Ga 2O 3, PbO-SiO 2-ZnO-Al 2O 3-Ta 2O 5, PbO-SiO 2-Al 2O 3-Ta 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-Sb 2O 5, PbO-SiO 2-Al 2O 3-ZrO 2, PbO-SiO 2-Al 2O 3-P 2O 5-ZrO 2, PbO-SiO 2-Al 2O 3-B 2O 3-ZrO 2-Sb 2O 5, PbO-SiO 2-Al 2O 3-HfO 2, PbO-SiO 2-Ga 2O 3, SiO 2-ZrO 2-B 2O 3-ZnO-MgO-TiO 2-Na 2O-LiO 2-Bi 2O 3
6. solar cell as claimed in claim 1 is characterized in that, wherein, is 100% in the quality of this Back Material, and this contains aluminium material and comprises 60～80% aluminium powder, and purity is between 90 to 99.99%.
7. solar cell as claimed in claim 1 is characterized in that wherein this additive comprises C 10～C 24Hard fatty acids, be 100% in the quality of this Back Material, this C 10～C 24Hard fatty acids content less than 5%.
8. solar cell as claimed in claim 1 is characterized in that, wherein comprises organic media, is 100% in the quality of this Back Material, and the content of this organic media is 20～35%.
9. solar cell as claimed in claim 8 is characterized in that, wherein, is 100% in the quality of this Back Material, and this organic media comprises 60～90% pure ethers organic solvent or 10～20% celluosic resin.
10. solar cell as claimed in claim 8 is characterized in that, wherein, is 100% in the quality of this Back Material, and this organic media comprises 1～5% advection agent, auxiliary rheological agents or thixotroping auxiliary agent.
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