CN103849937A - Texturing method of solar cell wafer - Google Patents

Texturing method of solar cell wafer Download PDF

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CN103849937A
CN103849937A CN201310488489.7A CN201310488489A CN103849937A CN 103849937 A CN103849937 A CN 103849937A CN 201310488489 A CN201310488489 A CN 201310488489A CN 103849937 A CN103849937 A CN 103849937A
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substrate
surface treatment
solar cell
wet
solar batteries
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CN103849937B (en
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尹起燦
郭将荣
金起弘
金鍊起
李秉喆
崔锺亨
韩奭奎
洪定义
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Han Hua Chemical Co Ltd
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Hanwha Chemical Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Condensed Matter Physics & Semiconductors (AREA)
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  • Photovoltaic Devices (AREA)
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Abstract

The invention relates to a texturing method of a solar cell wafer. In dependence on the texturing method, the solar cell wafer is subjected to a first wet etching process, a reactive ion etching process and a second wet etching process, and a pyramid structure is formed on the surface of the wafer. By employing the pyramid structure, the optical reflectivity is reduced, and therefore the light absorption efficiency of a solar cell is improved. According to the invention, the kind and the directionality of the crystallization is not restricted, and the mono-like multi wafer can be effectively subjected to a surface treatment, and therefore the efficiency of the solar cell is improved.

Description

The surface treatment method of substrate used for solar batteries
Technical field
The present invention relates to a kind of surface treatment method of substrate used for solar batteries.More specifically, relate to a kind of kind of trellis that can not be subject to substrate or the restriction of quality and effectively carry out the surface treatment method of the substrate used for solar batteries of surface structuration.
Background technology
In recent years, expect the exhaustion of the existing energy such as oil or coal, the substitute energy that substitutes these energy is more and more received publicity.Wherein, solar cell, as a kind of battery of future generation that utilizes the direct semiconductor element that is electric energy by solar energy converting, is attracted attention by people.Solar cell is divided into silicon solar cell (silicon solar cell), compound semiconductor solar cell (compound semiconductor solar cell) and these several large types of laminated solar battery (tandem solar cell).
On the other hand, the silicon class solar cell of the most of solar cell of the conduct of batch production now, use silicon as semiconductor substrate, and silicon is as indirect band-to-band transition semi-conductor (indirect interband transition semiconductor), because the light only with the band-gap energy that is greater than silicon could produce electron-hole pair, so the specific absorption of light is on the low side.Therefore, silicon class solar cell makes more than 30% light of injecting inside solar energy battery from the silicon wafer surface reflection as substrate, and therefore the efficiency of solar cell will reduce.
In order to reduce this optical loss, in silicon solar cell, use surface treatment (texturing) method.Surface treatment method is in order to make maximum luminous energy be inhaled into wafer substrate inside, on the silicon substrate surface of silicon solar cell, form concavo-convex, to improve surfaceness.Start light and arrive and collide on the pyramid wall of inclination, a part is absorbed, and a part reflects back, and now, makes the light returning continue to collide on other gold tower walls, to increase absorbing amount.So, Pyramid structure increases absorbing amount, and result can improve battery efficiency.Therefore,, if manufacture silicon solar cell substrate by surface treatment method, just can realize the raising of minimizing, carrier collection effect and the light binding effect of internal reflection by solar cell of the surface reflection of solar cell.
As surface treatment method, the wet type surface treatment of useful acidity or basic solution and these two kinds of modes of dry type surface treatment with reactive ion gas substantially.In wet type surface treatment, use basic solution or acidic solution, basic solution is suitable for single-crystal wafer, and acidic solution is suitable for the surface treatment of polycrystalline wafers.And dry type surface treatment is used reactive ion gas, and is suitable for polycrystalline wafers.
On the other hand, have recently a kind of class single crystal substrate to be in the middle of exploitation for the manufacture of the method for solar cell, the method due to technique simply, once can manufacture in a large number and there is high price competitiveness.
For described class silicon single crystal, for example, No. 20100193031st, U.S.'s publication, in No. 0748884 grade of European patent, the method for utilizing crystal seed (seed) to make class monocrystalline silicon growing is disclosed.
Because class silicon single crystal is according to growth method, together with single-crystal region is all included in polycrystalline, so be difficult to All Ranges to carry out equably surface treatment.Therefore, for by class silicon single crystal for solar cell, be necessary that photoabsorption to making substrate becomes maximized surface treatment method and studies.
Summary of the invention
For addressing the above problem, the object of the present invention is to provide a kind ofly for substrate used for solar batteries, especially for class single crystal substrate, be not subject to the kind of crystallization and the restriction of directivity and effectively carry out surface-treated method.
For achieving the above object, the invention provides a kind of surface treatment method of substrate used for solar batteries, comprise the following steps: to carry out the first Wet-type etching for substrate used for solar batteries; Carry out reactive ion etching (reactive ion etching); And carry out the second Wet-type etching.
According to the present invention, can effectively carry out surface treatment to substrate used for solar batteries, thereby reduce reflectance, increase absorptivity, and then manufacture high efficiency solar cell.
And, be not subject to be divided into according to crystallinity the restriction of the kind of different types of class single crystal substrate, and only just can carry out equably surface treatment by a kind of method, therefore can simplify technique, minimizing expense.
Brief description of the drawings
Fig. 1 is for electron microscope, amplifies the photo of 5000 times of shootings by carrying out wet type surface-treated result for single crystal substrate and polycrystalline substrate.
Fig. 2 is the figure that shows the substrate of multiple quality.
Fig. 3, for microscope, will carry out respectively the photo of surface-treated result bust shot to class single crystal substrate with basic solution and acidic solution.
Fig. 4, for by scanning electronic microscope, amplifies the photo of 70000 times of shootings by the surface that proceeds to reactive ion etching operation substrate afterwards in described embodiment 1.
Fig. 5, for by scanning electronic microscope, amplifies the photo of 5000 times of shootings by the surface that proceeds to reactive ion etching operation and the second Wet-type etching operation substrate afterwards in described embodiment 1.
Fig. 6 shows the chart that carries out the reflectance of surface treatment substrate before and carry out the reflectance of process of surface treatment substrate afterwards in described embodiment 1 and comparative example 1.
Embodiment
Surface treatment method of the present invention, comprises the following steps:
Carry out the first Wet-type etching for substrate used for solar batteries;
Carry out reactive ion etching (reactive ion etching); And
Carry out the second Wet-type etching.
With first, second term such as grade, various textural elements are described in the present invention, the application target of described term is only to distinguish a textural element and other textural elements.
And the term using is in this manual just in order to illustrate exemplary embodiments, its intention does not lie in restriction the present invention.Unless the statement of odd number has the clearly different meanings in context, comprise plural number.In this manual, " comprise ", the term such as " having " or " having " is the existence of wanting to specify feature, numeral, step, textural element or these factor combinations implemented, should not be construed as and get rid of in advance one or the existence of more than one other features or numeral, step, textural element or these factor combinations or additional possibility.
And, in the present invention, in the time relating to each layer or key element and be formed at each layer or key element it " on " or " above ", represent that each layer or key element are directly formed on each layer or key element, or represent other layers or key element can further be formed between each layer, on subject or base material.
The present invention can carry out numerous variations, can have variform, specific embodiment is shown below, and is elaborated.But this is not to provide in order to limit the invention to disclosed specific modality, but is understood to include all changes, equivalent and the sub in thought of the present invention and technical scope.
The surface treatment method of the substrate used for solar batteries that below, present invention will be described in detail with reference to the accompanying.
Technology acuracy adopting when required substrate is according to purity, prepared substrate in semi-conductor used for solar batteries etc., in quality with there is in price very large difference.Required underlying condition have make impurity the minimized high purity of concentration, make the minimized high-quality of crystal defect and the low price that can produce in batches etc., these conditions are the most important parts that determine the batch production of solar cell.According to this trend, the substrate of exploitation has the class single crystal substrate (mono-like multi wafer, MLM wafer) simultaneously with monocrystalline and these two kinds of forms of polycrystalline recently.
Class single crystal substrate combines the advantage of monocrystalline and polycrystalline, utilizes polycrystalline ingot growth method etc. to produce.Can use the heat exchange method (HEMHeat Exchange Method) of one of conventional polycrystalline ingot growth method to prepare single crystal rod, and for the production of high efficiency solar cell.Polycrystalline ingot growth method, because technique is simple, once can be produced in a large number, therefore has the characteristic that price competitiveness is high, recently for as substrate used for solar batteries and in the middle of developing.
On the other hand, in order to improve the photoabsorption of solar cell, substrate surface is carried out to making herbs into wool processing (texturing, also referred to as " surface structure " or " surface treatment ") operation.If process and manufacture solar cell substrate by making herbs into wool, just can realize the surface reflection of solar cell minimizing, carrier collection effect raising and pass through the light binding effect of the internal reflection of solar cell.
Single crystal substrate refers to that entirety has the substrate of the single crystallization of consistent crystal orientation, and for described single crystal substrate, with the basic solution such as NaOH or KOH, the anisotropic etching that substrate surface is carried out to making herbs into wool (texturing) is effective.
On the contrary, the crystalline substrate of the crystallization that polycrystalline substrate refers to multiple random orientations in the main body of substrate, for described polycrystalline substrate, different because of crystallization direction, utilize the isotropic etching Billy of acid solution more effective with the etching of alkali.
Fig. 1 is for by scanning electronic microscope, amplifies the photo of 5000 times of shootings by single crystal substrate and polycrystalline substrate are carried out to wet type surface-treated result.
In Fig. 1, left photo is for to carry out wet type surface-treated photo with basic solution to single crystal substrate, and right photograph is for carrying out wet type surface-treated photo with acidic solution to polycrystalline substrate.With reference to Fig. 1, single crystal substrate and polycrystalline substrate be according to the feature of crystallization, form difference separately, but in single substrate, show uniform etch morphology.
But, class single crystal substrate is divided into substrate that substrate, single-crystal region and the polycrystalline of 100% monocrystalline mix and the substrate of 100% polycrystalline according to growth method and condition, substantially single-crystal region and polycrystalline are all included, are therefore difficult to all regions to carry out equably surface treatment.
Fig. 2 is the figure of the substrate of the multiple quality of demonstration (grade).
Known with reference to Fig. 2, be from left to right the substrate of the multiple quality such as class single crystal substrate (MLM wafer grade A, B) and 100% polycrystalline substrate (Multi wafer) that mixes of 100% single crystal substrate (Mono wafer), single-crystal region and polycrystalline.
In general, class single crystal substrate can be divided into three kinds of ranks according to the shared ratio in monocrystalline (mono) district, the shared ratio in single-crystal region be more than 90% for A level, more than 70% is B level, more than 25% is C level.
In general, the class single crystal substrate of A level, almost identical with single-crystal wafer, therefore can carry out etching with basic solution.But lower than the substrate of A level, the substrate of B level or C level, owing to comprising respectively multiple single-crystal region and polycrystalline, while therefore processing with alkalescence or acidic solution, is difficult to realize best making herbs into wool.
Fig. 3 will carry out respectively the photo of surface-treated result bust shot with microscope to class single crystal substrate with basic solution and acidic solution.In Fig. 3, left photo is for to carry out surface-treated photo with basic solution to class single crystal substrate, and right photograph is for carrying out surface-treated photo with acidic solution to class single crystal substrate.
As class single crystal substrate carried out to surface structure with basic solution, because the crystallization direction of single-crystal region is identical, therefore can etch the micro-pyramid structure with antiradar reflectivity, but polycrystalline is due to crystallization direction difference, therefore demonstrates the etch morphology different from monocrystalline.Because of the inhomogeneous surface structure of this monocrystalline and polycrystalline, as the left photo of Fig. 3, can see the maple leaf phenomenon occurring as maple leaf shape.Because this phenomenon can become reduction commodity value, be therefore not suitable for.
On the contrary, in the time carrying out surface structure with acidic solution, be not subject to crystallization direction restriction and form randomly shaped gold tower (random pyramid) with identical etching speed, therefore as the right photograph of Fig. 3, do not occur maple leaf shape (maple-shape).But, carry out the substrate of surface structure by acidic solution, than the substrate that carries out surface structure by basic solution, show higher reflectance.Therefore also improper by the surface structureization of acidic solution.
According to surface treatment method of the present invention, can not be subject to substrate surface the crystalline network such as single-crystal region or polycrystalline restriction and carry out surface structure.Therefore can realize uniform surface structure, and can solve according to crystalline network and show that the phenomenon of different surface structures produces the problem of maple leaf shape (maple-shape), and can prevent from thus causing because of the generation of maple leaf shape (maple-shape) reduction of commodity value.And, because processing step is simple, therefore have advantages of and can reduce process time and expense.
According to surface treatment method of the present invention, can be class single crystal substrate as the substrate used for solar batteries of surface treatment object.As mentioned above, described class single crystal substrate can be substrate or the polycrystalline substrate that single crystal substrate, single-crystal region and polycrystalline mix, and can be the substrate of multiple rank.According to surface treatment method of the present invention, can not be subject to the kind of substrate or the restriction of rank and be applicable in technique.Therefore, even if use the relatively low rudimentary substrate of price, also can obtain the surface treatment result that is equivalent to the substrate that uses senior rank, therefore can significantly reduce productive expense.
According to one embodiment of the invention, described substrate used for solar batteries can be for example the substrate being made up of the silicon of p-type electric-conducting type.In the time that described substrate used for solar batteries has p-type electric-conducting type, contain the trivalent element impurity such as boron (B), gallium or indium.
Or described substrate used for solar batteries can be served as reasons as the substrate of the silicon formation of N-shaped conductivity-type.In the time that described positive substrate used for solar batteries has N-shaped conduction type, can contain the pentad impurity such as phosphorus (P), arsenic (As), antimony (Sb).
To above-mentioned substrate used for solar batteries, first carry out the first Wet-type etching (wet etching).
By described the first Wet-type etching, can realize simultaneously and remove cutting damage (sawing damage removal) and the first making herbs into wool (texturing).Described removal cutting damage is to remove the defect producing because of the cutting of substrate, and removes the operation that is formed on lip-deep oxide film.
According to one embodiment of the invention, described the first Wet-type etching uses acid (acid) solution.
More specifically, the acid solution using in described the first Wet-type etching operation comprises HF, HNO 3and H 2o, volume ratio is about 1:2～4:1～3, preferably, is about 1:3:2.
And, in the time carrying out described the first Wet-type etching, can, under temperature is about the condition of 5～10 DEG C, in described solution, flood substrate approximately 1～5 minute, preferably flood approximately 1～2 minute.
According to one embodiment of the invention, carrying out after above-mentioned the first Wet-type etching operation, can further use deionized water (DI water) to clean for the first time (rinse), in carrying out with basic solutions such as KOH and operation, clean for the second time and HF cleans with deionized water (DI water), and carry out matting for the third time with deionized water (DI water).
By carrying out above-mentioned the first Wet-type etching, can remove the cutting damage of substrate, and being about 2～10 μ m by height of formation on etched substrate surface for the first time, preferably be about the concaveconvex structure of 3～5 μ m.
Then, carry out reactive ion etching (reactive ion etching, RIE) operation for the substrate that completes described the first Wet-type etching operation.
Described reactive ion etching operation, can be by carrying out plasma to etching gas, makes it activation for strong response behaviour, and make the surface of itself and substrate collide and implement.Can use F as described etching gas 2, SF 6, CF 4be gas, Cl in fluorine 2be gas and O Deng chlorine 2deng in a kind of or two or more.
According to one embodiment of the invention, in described reactive ion etching operation, in order to adjust etch morphology, in described etching gas, can comprise O 2.By comprise O in described etching gas 2, do not formed and playing the oxide film of mask effect by the side of ion bombardment, and do not formed film by the bottom of ion bombardment, regulate etch morphology thereby can pass through the only phenomenon of etching bottom.
According to one embodiment of the invention, can use Cl 2, SF 6and O 2carry out etching work procedure as described etching gas.
More specifically, in chamber, configure after described substrate, by etching gas injecting chamber.Then, apply the electric power of prescribed level to being arranged on two electrodes between described substrate, thereby the space between two electrodes produces the plasma based on described etching gas.The plasma generating has hyperergic free radical (radical) and ion (ion).Accelerate the plasma so generating, the surface of itself and substrate is collided.Thus, by the combination of physical impact and chemical reaction, can on the surface of described substrate, form multiple concaveconvex structures.
In described reactive ion etching operation, collide on substrate than the more high-octane ion of general plasma etching, this is because form the negative potential higher than ground-electrode on electrode.
By above-mentioned reactive ion etching operation, described substrate surface is carried out to the second making herbs into wool processing, to form pyramid structure on the surface of described substrate.
Described pyramid structure reduces the luminous reflectance factor of substrate surface, thereby improves the efficiency of light absorption of solar cell.Described pyramid structure can, by controlling the processing condition of reactive ion etching operation,, by etching gas, pressure, temperature, electrode height or power, be formed as variform and size.
According to one embodiment of the invention, in described pyramid structure, depth-width ratio is about 0.75～1.1.And, in the scope that maintains described ratio, can there is height and the width of several nanometers to hundreds of nanometers.For example, described pyramidal width is about 100～300nm, is highly about 150～350nm.According to the present invention, above-mentioned the first Wet-type etching operation of proceed step by step and reactive ion etching operation, thereby can not be subject to substrate crystalline texture restriction and form from the teeth outwards uniform pyramid structure.Thus, can reduce the light quantity from surface reflection, thereby realize low reflectance.
But, may produce and impact the surface damage causing because of the plasma of described reactive ion etching operation.If do not remove surface damage, because of the raising of surperficial recombination velocity, current value can reduce, and is difficult to expect thus the increase of battery conversion efficiency.That is, by reactive ion etching operation, reflectance step-down, and then can increase photoabsorption, but due to the surface damage meanwhile producing, the disappearance of electron-hole pair also can be accelerated, and therefore can not obtain the effect that increases photoabsorption.This can become the reason of low Voc and FF.
And, if the pyramid structure generating by described reactive ion etching operation maintains to obtain too sharp-pointed (needle), there is high electric leakage (leakage current) in pyramidal upper layer part branch.
Therefore,, in order to maintain low reflectance and to remove electrical surface damage, after described reactive ion etching operation, implement to remove surface damage (damage removal etching, DRE) operation.
Described removal surface damage operation is in order to remove the surface damage that produces in reactive ion etching operation, if but carry out too much described removal surface damage operation, etched surfaces too much, and then remove the pyramid forming by reactive ion etching operation, thereby can not obtain low reflectance.Therefore, described removal surface damage operation is necessary to remove and pass through O in can maintaining the pyramid structure forming by reactive ion etching operation 2the oxide film producing and effectively remove under the top condition of surface damage and carry out.
According to surface treatment method of the present invention, carry out the second Wet-type etching operation as described removal surface damage operation.More specifically, described the second Wet-type etching operation use comprises volume ratio and is about 1:13～17:15～19, is preferably HF, the HNO of 1:15:17 3and H 2the acid solution of O carries out.By removing surface damage operation with above-mentioned condition, can surface not by too much etched condition under, both maintained the pyramid structure forming by reactive ion etching operation, and maintain the depth-width ratio of described pyramid structure, and the top section that makes pyramid structure becomes soft (smoothly), thereby raising reflectance, and prevent electric leakage.And, in the formation operation of follow-up anti-reflective film, can effectively carry out the deposition (deposition) of anti-reflective film, and can obtain by synergy therewith the effect that reflectance further improves.According to one embodiment of the invention, by implementing described removal surface damage operation, can make reflectance ratio carry out further improving approximately 1～3% before described removal surface damage operation.
Now, the technological temperature of the second Wet-type etching operation is normal temperature, for example, be about 20～30 DEG C, can flood for approximately 10～60 seconds, preferably floods for approximately 20～50 seconds.
According to one embodiment of the invention, described the second Wet-type etching operation can be carried out as follows: be to carry out approximately 0.009～0.035% of described the second Wet-type etching operation substrate weight before by the etch quantity of described the second Wet-type etching operation.
Carry out surface-treated substrate with above-mentioned surface treatment method of the present invention, can show approximately 9～12% surface albedo.
For the substrate through above-mentioned process of surface treatment, follow-up can be according to the general manufacture method of solar cell, form emitter layer, anti-reflective film, electrode and backplate above, thereby obtain high efficiency solar cell.
More specifically, form emitter layer on the top of surface treated described substrate used for solar batteries.The impurity contrary with described substrate that can adulterate in described emitter layer, to form P-N knot (P-N junction).According to one embodiment of the invention, described emitter layer is the shallow emitter layer of approximately 100～500nm thickness, applicable to high efficiency solar cell.
And according to one embodiment of the invention, described emitter layer can have the surface resistivity that photoelectric transformation efficiency is high, for example about surface resistivity of 85～100 Ω/sq.
Then, form anti-reflective film on the top of described emitter layer.
Described anti-reflective film can pass through vacuum deposition method, chemical Vapor deposition process, rotary coating, silk screen printing or spraying and form, but and is not limited by it.And described anti-reflective film can have for example silicon nitride film, hydrogeneous silicon nitride film, silicon oxide film, silicon oxynitride film, MgF 2, ZnS, TiO 2and CeO 2in any monofilm or combine the multi-layer film structure of plural film, but and limited by it.According to one embodiment of the invention, described anti-reflective film is the silicon nitride film with approximately 2.0～2.2 specific refractory power, can be formed as the approximately thickness of 75～85nm.
Then, after silk screen printing silver (Ag) slurry, can heat-treat and form electrode above, and heat-treat formation backplate after the back up aluminium paste of substrate, thereby manufacture solar cell.When described aluminium (Al) slurry is heat-treated, aluminium is by the back side diffusion of substrate, thereby in the boundary surface of electrode and substrate, forms back of the body electric field (Back Surface field) layer overleaf.If form back of the body electric field layer, can prevent that current carrier from moving to the back side of substrate and carrying out combination again, if prevent the combination again of current carrier, open circuit voltage rises, thereby can improve the efficiency of solar cell.
With reference to embodiments of the invention, further describe the present invention below.But these embodiment are only that the present invention proposes in order to illustrate, and interest field of the present invention does not depend on these embodiment.
< embodiment >
embodiment 1
Prepare the p-type class single crystal substrate (MLM wafer, Grade B) doped with iii group element impurity.Comprising HF, the HNO that volume ratio is 1:3:2 3and H 2in the solution of O, be under 7 DEG C of conditions, to flood 1 point of 30 second of substrate in temperature, to carry out the first Wet-type etching, thereby remove cutting damage and the first making herbs into wool processing simultaneously.By described the first making herbs into wool processing, reach 3～5 μ m from surperficial etched thickness.
Then, use Cl as etching gas 2/ SF 6/ O 2implement reactive ion etching operation.The pyramid structure generating by described reactive ion etching operation, its height (Height) and the ratio H/W of width (width) are distributed in 0.75～1.1 scope.
Comprising HF, the HNO that volume ratio is 1:15:17 3and H 2in the solution of O, be under the condition of 25 DEG C, to flood 30 seconds of substrate in temperature, to carry out the second Wet-type etching, after this etching, compared with before carrying out this etching, substrate weight reduces 0.025%, now completes surface treatment.
By using POCL 3diffusing procedure, Doping Phosphorus (P), forms and has the emitter layer of 85 Ω/sq resistance.On described emitter layer, form the two-layer silicon nitride film with 2.0～2.2 scope specific refractory poweres with PECVD equipment, its total thickness is 85nm.
Carry out overleaf silk screen printing with Al paste, and under the temperature condition lower than 200 DEG C, carry out after drying process, form electrode above with the width of 70 μ m sizes with Ag paste, and under the temperature condition lower than 200 DEG C, carry out after drying process, in the belt firing furnaces of 940 DEG C (belt firing furnace), carry out sintering formation electrode and backplate above.
comparative example 1
Except not carrying out reactive ion etching operation, use the method identical with described embodiment 1 to manufacture solar cell.
< experimental example >
the evaluation of surface treatment result
Fig. 4, for by scanning electronic microscope, amplifies the photo of 70000 times of shootings by the surface that proceeds to reactive ion etching operation substrate afterwards in described embodiment 1.
Fig. 5, for by scanning electronic microscope, amplifies the photo of 5000 times of shootings by the surface that proceeds to reactive ion etching operation and the second Wet-type etching operation substrate afterwards in described embodiment 1.
Fig. 6 shows the chart that carries out the reflectance of surface treatment substrate before and carry out the reflectance of process of surface treatment substrate afterwards in described embodiment 1 and comparative example 1.
the electric property evaluation of solar cell
According to ASTM G-173-03, under AM1.5 illumination condition, adopt at (the Hanwha Solarone limited of Chinese Han Hua New Energy Corporation, HSOL) photovoltaic tester (solar tester), be the electric property that H.a.l.m cetis PV-products is determined at the solar cell of manufacturing in described embodiment 1 and comparative example 1, and the results are shown in following table 1.In following table 1, Isc represents in the time that impedance is low, the electric current flowing through for 0 time by the maximum current that transmits corresponding to the solar cell of short circuit condition or when the both end voltage of a solar cell, the electric current that per unit area flows through is Jsc, Voc is in the time that electric current is 0, be formed on the voltage at solar cell two ends, the peak voltage that expression can obtain from solar cell, shunting resistance Rsh refers to the resistance of certain circuit that is connected in parallel, low shunting resistance can cause electric leakage, thereby reduces electric current and voltage.Series resistance Rs is the resistance working by series connection (series) between the electrode of the upper and lower of solar cell, flows through this resistance by the electric current of emtting electrode and base stage, is defined as Rs by vertical resistor composition, and the large parameter of impact being subject to is FF.For the quality of solar cell, FF[%] be most important yardstick, packing factor (Fill Factor, FF) by relatively peak power and the theoretical(horse)power by open circuit voltage and short-circuit current output calculate, Eta[%] expression efficiency, be to show the most important factor of solar cell properties, be defined as exporting the ratio of energy and the energy of injecting from the sun.
[table 1]
Figure BDA0000397635190000141
From the result of upper table 1, adopt the solar cell of the Substrate manufacture of implementing surface treatment method of the present invention, to compare and only adopt Wet-type etching to carry out surface-treated substrate, its electric property is improved.

Claims (9)

1. a surface treatment method for substrate used for solar batteries, comprises the following steps:
Carry out the first Wet-type etching for substrate used for solar batteries;
Carry out reactive ion etching; And
Carry out the second Wet-type etching.
2. the surface treatment method of substrate used for solar batteries according to claim 1 wherein, by described the first Wet-type etching, is removed cutting damage and the first making herbs into wool processing simultaneously.
3. the surface treatment method of substrate used for solar batteries according to claim 1, wherein, in the time carrying out described the first Wet-type etching, uses and comprises HF, the HNO that volume ratio is 1:2～4:1～3 3and H 2the solution of O.
4. the surface treatment method of substrate used for solar batteries according to claim 1, wherein carries out the second making herbs into wool processing by described reactive ion etching, to form pyramid structure on the surface of described substrate.
5. the surface treatment method of substrate used for solar batteries according to claim 1, wherein, in the time carrying out described reactive ion etching, uses and comprises Cl 2, SF 6and O 2gas.
6. the surface treatment method of substrate used for solar batteries according to claim 4, the depth-width ratio of wherein said pyramid structure is 0.75～1.1.
7. the surface treatment method of substrate used for solar batteries according to claim 1, wherein, in the time carrying out described the second Wet-type etching, uses and comprises HF, the HNO that volume ratio is 1:13～17:15～19 3and H 2the solution of O.
8. the surface treatment method of substrate used for solar batteries according to claim 1, wherein said the second Wet-type etching, is to carry out for 10～60 seconds under the condition of 20～30 DEG C in temperature.
9. the surface treatment method of substrate used for solar batteries according to claim 1, wherein said substrate used for solar batteries is the kind single crystal substrate being selected from substrate and the polycrystalline substrate that single crystal substrate, single-crystal region and polycrystalline mix.
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