CN101315953A

CN101315953A - Back electrode suitable for thin solar cell and production method thereof

Info

Publication number: CN101315953A
Application number: CNA2007100414045A
Authority: CN
Inventors: 郭里辉
Original assignee: TAIYUAN GREEN ENERGY CO Ltd SHANGHAI JIAOTONG UNIV
Current assignee: TAIYUAN GREEN ENERGY CO Ltd SHANGHAI JIAOTONG UNIV
Priority date: 2007-05-29
Filing date: 2007-05-29
Publication date: 2008-12-03

Abstract

The invention relates to a solar cell back electrode structure and a corresponding manufacture method, which provides a solution to a phenomenon that the solar cell is severely bent or even cracked owing to a back surface aluminium electrode. The solar cell back electrode structure is characterized in that a front surface structure of the solar cell of the invention is identical to the front surface structure of the solar cell of conventional crystalline silicon; the different aspects lie in the back surface electrode structure and corresponding manufacture method. A basic concept thereof is that the two functions of a conventional back surface aluminium electrode are separated, namely, the function of providing a back electric field and the function of providing a back surface electrode of low resistance are separated from each other. The back electrode structure can be also a non-grid shaped geometrical figure which is connected with a back main electrode such as a net-shaped electrode, etc. The solar cell back electrode structure and the corresponding manufacture method of the invention have the advantages that the phenomenon that the solar cell is severely bent or even cracked owing to a back surface aluminium electrode can be overcome; simultaneously, the back electric field and the electric performance of the back electrode necessary to the solar cell of the P-typed silicon substrate can be still remained.

Description

A kind of back electrode of suitable thin solar cell and manufacture method

Technical field

The present invention relates to solar energy is directly changed into the solar battery structure and the relative production technology of electric energy, particularly at the back electrode structure and the manufacture method of monocrystalline silicon, polycrystalline silicon solar cell.This structure and relevant manufacture method are specially adapted to adopt than the thin silicon sheet in producing crystalline silicon (monocrystalline silicon, polysilicon) solar cell and produce solar cell.

Background technology

On present solar cell market, monocrystalline, polycrystalline silicon solar cell have occupied the market share more than 90%.This class solar cell normally with so-called screen printing electrode technology, be produced on the monocrystalline or polycrystalline silicon substrate that is called as silicon chip.

Shown in Fig. 1 is the structural representation of the front surface (being the sunlight plane of incidence) of conventional crystal-silicon solar cell.It comprises the front surface 100 of solar cell (also being silicon substrate), front gate line electrode 120, positive main electrode 130.Wherein, front gate line electrode 120 and positive main electrode 130 can be used silk screen print method, at the silicon substrate front surface that processes, form by printing and sintering metal slurry (as silver paste).

Shown in Fig. 2 is the structural representation on the back of the body surface (being the non-sunlight plane of incidence) of corresponding conventional crystal-silicon solar cell.It comprises the back of the body surface 101 of solar cell (also being silicon substrate), back side aluminium electrode 104, back silver main electrode 105.The weldability of necessity when wherein, back silver main electrode 105 provides solar panel to become assembly.Back side aluminium electrode 104 and back silver main electrode 105 can be used silk screen print method, on the silica-based backboard surface that processes, form by printing and sintering metal slurry (as silver paste, aluminum slurry).

Shown in Fig. 3 is a kind of common the changing form of Fig. 2.Only be that with Fig. 2 institute difference back silver main electrode 105 is not made up of continuous electrode strip, but form by interrupted electrode strip.To describe as its typical back electrode with Fig. 2 in this explanation.

Shown in Fig. 4 is respectively the generalized section of A-A position and B-B position among Fig. 1.Wherein the A-A position is the profile without gate line electrode 120, and B-B is the profile through gate line electrode 120.

Fig. 1, Fig. 2, solar cell shown in Figure 3 are just, back electrode normally forms by following processing sequence and condition.Earlier, the silver paste printing is formed positive gate electrode 120 and positive main electrode 130 with silk screen printing in the silicon substrate front 100 that processes, under 100 ℃～200 ℃ condition with its oven dry; At the back side 101 of solar cell, back silver main electrode 105 is printed again, and it is dried under 100 ℃～200 ℃ condition with silk screen printing; Thereafter, also with silk screen printing back side aluminium electrode 104 is printed, its print thickness is generally 20 μ m～40 μ m, covers almost whole back of solar cell 101.The silicon substrate that prints all electrodes is carried out sintering by a body of heater with specified temp distribution, and its sintering temperature reaches as high as 750 ℃～950 ℃.Through this necessary sintering, solar cell just, backplate can reliably form.

Usually make solar cell with so-called P type silicon substrate.Adopt the preparation method of above-mentioned back side aluminium electrode 104 the aluminium atom can be diffused into the silicon substrate back side 101 under sintering temperature, for P type silicon substrate solar cell provides essential what is called " back of the body electric field ".On the other hand, certain thickness back side aluminium electrode 104 also is can obtain a lower back electrode resistance in order to satisfy, and makes solar cell reach due photoelectric conversion efficiency.

By back side aluminium electrode 104 electric charges collected, that in silicon substrate, produce, move to back silver main electrode 105 by back side aluminium electrode 104, export to the external loading of solar cell by back silver main electrode 105.

Yet, for the continuous cost that reduces crystal-silicon solar cell, the continuous attenuation of the thickness of the used silicon substrate of solar cell, this makes that the solar cell of being made bends, even occurs cracked through behind above-mentioned 750 ℃～950 ℃ high temperature sintering.The main cause that causes this phenomenon is that the coefficient of expansion of back side aluminium electrode 104 slurries and silicon substrate has very big difference, the aluminum slurry of thicker (20 μ m～40 μ m) covers the silicon substrate back side 101, behind high temperature (750 ℃～950 ℃), 101 the very big stress of generation in the back side aluminium electrode 104 and the silicon substrate back side cause the serious bending of solar cell piece and cracked.

The present invention is directed to this problem, a kind of solar cell back electrode structure and relevant manufacture method have been proposed, thereby can overcome because the serious crooked and even cracked phenomenon of the solar cell that back side aluminium electrode 104 is caused, the electrical property that still keeps simultaneously P type silicon substrate solar cell necessary " back of the body electric field " and required back electrode.

Do not see disclosed document and report related to the present invention.

Summary of the invention

The Facad structure of the solar cell that the present invention had is identical with the Facad structure of conventional crystal-silicon solar cell, and as shown in Figure 1, difference is its backplate structure and relevant manufacture method.It is conceived substantially is that two functional separations with the above-mentioned back side aluminium electrode 104 of routine come, and being about to provides the function of " back of the body electric field " and and provide the functional separation of low resistance backplate.

Shown in Fig. 5 is the backplate structure of crystal-silicon solar cell of the present invention, and Fig. 6 is respectively the generalized section of C-C position and D-D position among Fig. 5.Wherein the C-C position is the profile without back side gate line electrode 108, and D-D is the profile through back side gate line electrode 108.

As shown in Figure 5 and Figure 6, on the back side 101 of silicon substrate, the aluminium lamination 106 of layer thickness back of the body aluminium electrode 104 thickness (20 μ m～40 μ m) in Fig. 2～Fig. 4 is arranged, its thickness can be the hundreds of dust

To several microns (μ m).The thickness of this aluminium lamination is as long as can guarantee that abundant aluminium atom (750 ℃～950 ℃) under sintering temperature diffuses into the silicon substrate back side 101, gets final product for P type silicon substrate solar cell provides necessary " back of the body electric field ".Because the thickness of aluminium lamination is very little, can greatly reduces because the stress that the coefficient of expansion difference of aluminium lamination 106 and silicon substrate is caused, thereby can reduce the bending of solar cell piece behind the sintering and the probability of fragment effectively.

Yet, because aluminium lamination 106 is thinner, will have bigger resistance as back electrode, this can make the decreased performance of solar cell.For this reason, the present invention is on aluminium lamination 106, and introducing has certain geometric backplate, increases the charge-trapping ability of back side main electrode, to remedy owing to the thin loss owing to the excessive battery performance that causes of self-resistance that is brought of aluminium lamination 106.Fig. 5 and Fig. 6 have provided a kind of structure of possible backplate.Back electrode is made up of back of the body gate-shaped electrode 108 and back of the body main electrode 107.Because back of the body gate-shaped electrode has been arranged, make the electric charge that solar cell produced in back of the body aluminium electrode 106, after less distance of motion, can be captured by palisade back electrode 108, be transferred to back of the body main electrode 107.Adopt thicker palisade back electrode of thickness 108 and back of the body main electrode 107, to obtain low battery electrode resistance.And palisade back electrode 108 will adopt relative low making temperature with back of the body main electrode 107, can avoid silicon substrate is produced bigger stress.Though the resistance of thin back of the body aluminium electrode 106 is higher relatively, because back of the body gate-shaped electrode 108 has been arranged, electric charge move distance therein shortens, and can eliminate or reduce the solar cell performance decrease that higher self-resistance caused of thin back of the body aluminium electrode 106.So, just realized providing " back of the body electric field ", and mainly provide electric charge output required low resistance electrode by palisade back electrode 108 and back of the body main electrode 107 by thin back of the body aluminium electrode 106.

In order to increase electrically contacting between back electrode (107 and 108) and the aluminium lamination 106, can on aluminium lamination 106, cover the thin silver layer of one deck, and carry out sintering by sintering furnace with aluminium lamination 106 and front electrode.

For fear of making

back electrode

107 and 108 stress of being introduced, its making will be finished under relatively low substrate temperature, such as being lower than 300 ℃.

What Fig. 5 provided only is an object lesson of back electrode structure, its structure also can be non-palisade with the geometric figure that links to each other of back of the body main electrode 107, as mesh electrode etc.

Description of drawings

Front (the being the sunlight plane of incidence) schematic diagram of the conventional crystal-silicon solar cell of Fig. 1 tradition;

A kind of schematic rear view of the conventional crystal-silicon solar cell of Fig. 2 tradition;

The another kind of schematic rear view of the conventional crystal-silicon solar cell of Fig. 3 tradition;

The cross-sectional view of the conventional crystal-silicon solar cell of Fig. 4 tradition;

A kind of schematic rear view of the solar cell that Fig. 5 the present invention proposes;

The generalized section at a kind of back side of the solar cell that Fig. 6 the present invention proposes.

Embodiment

As an example, the present invention illustrates following implementation method:

1. adopt P-type silicon substrate.Silicon substrate is carried out the matte processing and the cleaning of solar cell;

2. silicon substrate is spread (expansion phosphorus) technology, obtain a PN junction in the front of silicon substrate (being the sunlight plane of incidence);

3. remove the PN junction that the silicon substrate periphery forms with the method for etching or cutting, make the positive and negative two sides of silicon substrate that electrical short not take place;

4. at the anti-reflection layer of the front of individual silicon substrate deposition one deck, as silicon nitride or titanium dioxide film;

5. with silk screen printing silver paste is printed on the front of silicon substrate, on the promptly anti-reflection layer, forms positive gate electrode and positive main electrode, under 100 ℃～200 ℃ condition with its oven dry;

6. at the whole back side of silicon substrate, with silk screen printing or spraying or other physics, chemical method, deposit a layer thickness less than 5 microns (μ m) greater than 0.05 micron aluminium lamination;

7. as an option, can be with silk screen printing or spraying or other physics, chemical method on aluminium lamination, deposit a layer thickness less than 5 microns (μ m) greater than 0.1 micron silver layer;

8. silicon substrate is sent into the body of heater with specified temp distribution and carried out sintering, its sintering temperature reaches as high as 7509. ℃～950 ℃.

10. with silk screen printing or spraying method, the low-temperature silver slurry is formed on the back side of silicon substrate with the pattern of gate-shaped electrode and main electrode, promptly on the aluminium lamination (or the aluminium lamination that has silver layer to cover).By it is carried out the baking that temperature is not higher than 300 ℃, form good solar cell back electrode.

Finish with of the crystal-silicon solar cell making of P-type silicon as substrate.

Claims

Claim of the present invention is as follows: 1. crystal-silicon solar cell, it is characterized in that: the back electrode of solar cell evenly covers the back side of silicon substrate by a kind of metal level (being called lower electrode) and the another kind of metal level (being called upper electrode) that has certain pattern on this layer is formed jointly.Upper electrode covers on the lower electrode.
2. in claim 1., in its upper electrode pattern, have two parallel ribbon patterns at least, as the back of the body main electrode of solar cell output, and other parts of electrode pattern are netted or the palisade pattern, and with back of the body main electrode be UNICOM.
3. in claim 1., crystal-silicon solar cell is made by so-called P-type silicon substrate.Can be the monocrystalline silicon silicon substrate, the also polycrystalline silicon substrate of making of casting method.
4. in claim 1., described lower electrode, its thickness are 0.05 micron to 10 microns, evenly cover the back side of silicon substrate, but it covers the edge that does not exceed silicon substrate.
5. to claim 1. and the described lower electrode of claim 4., can be formed (as aluminium lamination), also can be formed,, be covered one deck silver again as covering layer of aluminum earlier by two-layer or multiple layer metal by a kind of metal level.
6. in claim 1. and claim 2., upper electrode adopts argent as electrode material, and its thickness is 1 micron to 40 microns, and it covers the edge that does not exceed described lower electrode.
7. to claim 1., claim 4. and the described lower electrode of claim 5., can aluminium paste (or silver is starched behind the first aluminium paste) be printed on the silicon substrate back side with silk screen printing, also the way of available spraying is sprayed on the silicon substrate back side with aluminium paste (or behind the first aluminium paste silver slurry), and also the method for available sputter is deposited on the silicon substrate back side with aluminium film (or behind the first aluminium film silverskin).By 700 ℃ to 1000 ℃ sintering, form described lower electrode then.
8. to claim 1., claim 2. and the described upper electrode of claim 6., can the low-temperature silver slurry be printed on above the described lower electrode with silk screen printing, also the way of available spraying is sprayed on the low-temperature silver slurry above the described lower electrode, by 100 ℃ to 500 ℃ baking, form described upper electrode then.
9. to claim 1., claim 2. and the described upper electrode of claim 6., also the method for available sputter is deposited on silverskin above the described lower electrode, forms described upper electrode.