DE102011051307A1 - Process for the production of plated-through solar cells - Google Patents

Abstract

A method for producing a through-plated solar cell (70), comprising method steps of introducing (10; 30) contact holes (54) into a solar cell substrate (52), diffusing (14) dopant into the solar cell substrate (52) for the purpose of forming an emitter ( 82) on a front side of the solar cell substrate (52) and the application (18) of a dielectric coating (88) to a rear side of the solar cell substrate (52) for the purpose of passivating this rear side, during which dopant diffuses (14) into the solar cell substrate (52) for the purpose of forming an emitter (82) on the front side of the solar cell substrate (52) on at least a part of the rear side of the solar cell substrate (52) dopant is diffused into the solar cell substrate (52) (14) and in this way the emitter for Part on the back of the solar cell substrate (52) is formed (14) and in which the emitter from the back of the solar Ellensubstrats (52) is completely removed (16) before the dielectric coating (88) is applied to the back (18).

Description

The invention relates to a method for producing plated-through solar cells, often also referred to as metallization-wrap-through solar cells or short as MWT solar cells, according to the preamble of claim 1.

Solar cells usually have a large-area side, which is aligned with the incident light during operation of the solar cell. This page is referred to hereinafter as the front of the solar cell or of the solar cell substrate used for solar cell production. The opposite side of this front side is referred to below as the back of the solar cell, or the solar cell substrate. In conventional solar cell concepts, a large number of narrow contact fingers are arranged on the front side of the solar cell, which open into one or more busbars. These manifolds are usually designed to be significantly wider than the contact fingers to allow efficient Stromabtransport. The contact fingers, but especially the wider busbars shadow part of the front side of the solar cell from incident light, which results in a reduction of the generated current and thus the efficiency of the solar cell.

In plated-through solar cells, so-called MWT solar cells, these shading losses are reduced by electrically providing the solar cell with contact holes extending through the solar cell substrate and electrically electrically connecting the narrow contact fingers of the front side via these contact holes, which are often referred to as vias, with busbars arranged on the rear side of the solar cell be connected conductively.

This also has the advantage that both an emitter and a base of the solar cell can be contacted via the back. This allows a more cost-effective interconnection of the solar cells in the solar cell module.

In the manufacture of solar cells precautions must be taken to avoid short circuits between the emitter and the base of the solar cell. These provisions are commonly referred to as edge isolation. For this purpose, by means of laser beam evaporation on the front of the solar cell as close as possible to the edges of the solar cell running, circumferential trench is introduced. In the case of through-contacted solar cells, however, this is not sufficient, since emitter contacts as well as base contacts are located on the rear side and short circuits between these contacts must be prevented. This has hitherto been realized by means of complicated masking steps, in particular in the case of solar cells with passivated rear side, in which a back overcompensation of the emitter by means of, for example, aluminum is not readily possible.

On the Conference SiliconPV, which took place from 17 to 20 April 2011 in Freiburg, Germany, was, however, by Benjamin Thaidigsmann et al. a novel solar cell presented under the title "HIP-MWT: A simplified structure for metal wrap through solar cells with passivated rear surface" , This plated-through solar cell has a solar cell substrate and via holes extending through the solar cell substrate, in which a contact material is arranged. Contact fingers are arranged on a front side of the solar cell and extend over a contact hole or a plurality of contact holes in such a way that the contact material arranged in these contact holes is electrically conductively connected to one another by the respective contact finger. Each individual contact finger thus connects the contact material, which is arranged in those contact holes, over which it extends, electrically conductively with each other. This serves to conduct generated current from the contact fingers to the contact material in the contact holes and thus on the back of the solar cell. Emitter contacts are arranged on a rear side of the solar cell and extend in each case via a contact hole or a plurality of contact holes in such a way that the contact material arranged in these contact holes is electrically conductively connected to one another by the respective emitter contact. A back surface of the solar cell substrate is free of an emitter. On the back surface of the solar cell substrate, a dielectric coating is formed, which is arranged in sections between the emitter contacts and the back surface of the solar cell substrate, so that the emitter contacts are electrically insulated from a base of the solar cell by means of the dielectric coating.

The terms of the front side and the back side of the solar cell, or of the solar cell substrate, are to be understood in the manner explained above.

The emitter is formed by surface regions of the solar cell substrate in which emitter dopant is diffused.

The base of the solar cell is formed by non-emitter doped regions of the solar cell substrate. In these areas, the solar cell substrate is as it were in its initial state in which it has a basic doping opposite to the emitter doping. This basic funding is often referred to as volume distribution.

The terms base of the solar cell and base of the solar cell substrate usually designate the same thing.

Since the solar cell has no emitter on its back surface, it can be produced inexpensively. This is because masking steps to ensure electrical isolation of the emitter contacts from the base contacts are not required. In addition, can be dispensed with the above-described circumferential laser trenches on the front of the solar cell, which on the one hand reduces manufacturing costs, on the other hand can increase the efficiency of the solar cell, since no emitter surface is needed for the laser trenches and thus is available for the current generation. Since these laser processes for edge insulation can be omitted, there is also no danger of damaging the solar cell or the solar cell substrate in this case.

The dielectric coating may be formed by a layer or by a layer stack of several layers of different materials.

The dielectric coating formed on the rear surface of the solar cell substrate is preferably designed as a backside passivation, thus passivating recombination-active surface states on the back side of the solar cell substrate. This embodiment variant thus represents a cost-effectively producible plated-through solar cell, or MWT solar cell, with a passivated back. The solar cell substrate used is a silicon substrate.

Preferably, the dielectric coating is formed directly on the back surface of the solar cell substrate. This allows for efficient backside passivation.

In practice, it has been found useful to arrange the emitter of the solar cell in the contact holes and on the complete front side of the solar cell substrate. This enables high efficiencies of the solar cell.

On the back surface of the solar cell substrate, base contacts are disposed on the dielectric coating away from the emitter contacts. These extend locally through the dielectric coating and contact the base of the solar cell. Such local back contacts can have an advantageous effect on the efficiency of the solar cell.

To increase the efficiency of the solar cell, this can be provided on the front with a texture. This can be formed, for example, by means of a wet-chemical etching process.

Conveniently, the solar cell is provided on its front with an anti-reflection coating. This can for example consist of a silicon nitride coating. The arranged on the front of the solar cell contact fingers are preferably fired through the anti-reflection coating.

To realize the emitter-free back surface of the solar cell substrate Thaidigsmann et al. to coat, ie to mask the back surface of the solar cell substrate prior to emitter diffusion with a diffusion barrier. In this way, no dopant reaches the back surface of the solar cell substrate and this remains emitter-free. Although such masking steps are easier to perform than conventional through-contacted solar cells required masking steps for electrical insulation of the arranged on the back base and emitter contacts. This is due to the fact that a complete page is to be masked and not selected parts of it. However, such masking steps continue to be a significant expense in industrial manufacturing processes.

Against this background, the object of the present invention is to provide a cost-effective method for producing plated-through solar cells.

This object is achieved by a method having the features of claim 1.

Advantageous developments are the subject of dependent claims.

Definitions and definitions as well as other explanations made in connection with the description of the novel solar cell are also applicable to the method described below.

The method according to the invention for producing a plated-through solar cell provides for introducing contact holes into a solar cell substrate. Further, for the purpose of forming an emitter on a front side of the solar cell substrate, dopant is diffused into the solar cell substrate. In addition, a dielectric coating is formed on a back side of the solar cell substrate and thereby passivated this backside. The term of the passivation of the rear side is to be understood in the manner set forth above as a passivation of recombination-active surface states on the back side of the solar cell substrate. In the diffusion of dopant in the A solar cell substrate for the purpose of forming an emitter on the front side of the solar cell substrate is diffused on at least a part of the back surface of the solar cell substrate dopant into the solar cell substrate, and in this way, the emitter is partly formed on the back surface of the solar cell substrate. Before the dielectric coating is applied to the backside, the emitter is completely removed from the back side of the solar cell substrate. This means that as a result of the diffusion of the dopant into the solar cell substrate, emitter components located on the rear side of the solar cell substrate are completely removed before the dielectric coating is applied to the backside.

In the present case, any emitter or emitter components on the backside are to be understood as any doping on the back side of the solar cell substrate which is of the same doping type as the emitter and formed during the diffusion of dopant for the purpose of forming an emitter on the front side of the solar cell substrate. In this case, it does not matter whether the dopant diffused into the rear side of the solar cell substrate originates from a dopant source which has been arranged on the rear side of the solar cell substrate. For example, a dopant source for the emitter formation can be arranged exclusively on the front side of the solar cell substrate, however, transfer dopant from this dopant source into its gas phase and reach the rear side, where it diffuses into the solar cell substrate. Such a dopant entry into the back side of the solar cell substrate is also an emitter component formed on the back surface of the solar cell substrate.

Surprisingly, it has been found that emitter components located on the rear side of the solar cell substrate can be removed without any significant damage being caused to the emitter on the front side of the solar cell substrate. Such damage could, for example, take place by passing an etching medium used for removing the emitter from the rear side of the solar cell substrate to the front side of the solar cell substrate, in particular through the contact holes. Further, it has been found that the emitter components located on the back side of the solar cell substrate can be removed without damaging to a significant extent any optional emitter doping formed in the contact holes. In one embodiment variant of the method, damage to this emitter doping in the contact holes can even be completely ruled out. Complex masking of the back side of the solar cell substrate can therefore be dispensed with contrary to the previous concept.

Thus, with the method according to the invention, through-contacting solar cells, or MWT solar cells, can be manufactured with a passivated backside. In particular, with this method, the edge insulation can be ensured in conventional plated-through solar cells with passivated back. However, this is not possible with the above-described laser edge isolation method used in conventional plated-through solar cells for edge insulation alone.

Preferably, an emitter doping is formed in the contact holes. In this way, inter alia, the emitter area can be increased.

Advantageously, the dielectric coating is applied substantially to the entire backside of the solar cell substrate. This allows a substantial passivation of the back of the solar cell substrate. Ideally, the dielectric coating covers the entire back surface of the solar cell substrate except for those areas where a base contact locally contacts the back side of the solar cell substrate. Preferably, the dielectric coating is applied directly to the back of the solar cell substrate. For the purpose of passivating the rear side, a layer system which has a silicon oxide layer and / or a silicon nitride layer and / or an Al ₂ O ₃ layer and / or an amorphous silicon layer can be applied as the dielectric coating.

Preferably, the dielectric coating is applied such that it extends into the contact holes and at least partially lines the contact holes, wherein preferably at least half of a wall surface of the respective contact hole is covered by the dielectric coating. Ideally, the dielectric coating is applied such that it extends in the contact holes to the front of the solar cell substrate and thus completely covers the wall surface of the respective contact hole. This is particularly advantageous if it is dispensed with the formation of the emitter doping in the contact holes, since in the manner described local shorts can be at least partially avoided. If the emitter doping is formed in the contact holes, the described partial lining of the contact holes with dielectric coating material can also contribute to reducing or avoiding local short circuits which would otherwise reduce the efficiency of the finished solar cell in the event of damage or errors in the emitter doping.

Advantageously, the emitter is completely removed from the back of the solar cell substrate by means of wet chemical etching. Emitter components which have been formed in the course of the diffusion of dopant into the solar cell substrate for the purpose of forming an emitter on the back of the solar cell substrate, for example in the context of a diffusion from the gas phase such as a POCl ₃ diffusion, can be removed in this way at low cost. Appropriately, this is done by a one-sided etching of the solar cell substrate, namely the back of the solar cell substrate, in an etching solution. For this purpose, the solar cell substrate may be moved therethrough, for example, along the surface of the etching solution. In addition, however, all other methods for one-sided wet-chemical etching of the solar cell substrate, which is preferably a silicon solar cell substrate, can be used.

A variant of the method provides that the contact holes are introduced into the solar cell substrate before dopant is diffused into the solar cell substrate for the purpose of forming an emitter on the front side of the solar cell substrate. This makes it possible to form the emitter doping in the contact holes as part of the mentioned diffusion of dopant, so that no additional process step is required for this purpose. In practice, it has proven useful to realize the diffusion of dopant into the solar cell substrate for the purpose of forming the emitter by means of diffusion from the gas phase, for example by means of a POCl ₃ or BBr ₃ tube diffusion. If the emitter doping in the contact holes is formed simultaneously with the mentioned diffusion of dopant into the solar cell substrate, then it has proven useful for this purpose to diffuse emitter dopant into the entire wall surface of the contact holes.

In practice, it has proven in all embodiments of the method according to the invention to introduce the contact holes by means of laser beam evaporation in the solar cell substrate. In principle, however, the contact holes can also be introduced in a different way.

In another variant of the method, the contact holes are introduced after the complete removal of the emitter from the rear side of the solar cell substrate. This is done by locally using solar radiation, the solar cell substrate is evaporated in the presence of dopant-containing liquid. In this case, due to the local heat development by the laser radiation dopant from the dopant-containing liquid is diffused into wall surfaces of the contact holes. In this way, the emitter doping is formed in the contact holes. In principle, the dopant can also be provided in a different way than via the dopant-containing liquid, for example in the form of a dopant-containing gas mixture or dopant-containing solids or pastes. Therefore, instead of the dopant-containing liquid, it is generally possible to use any desired dopant source. However, the use of a dopant-containing liquid as dopant source has proven particularly useful. For example, in one embodiment of the method, the laser radiation can be guided in a liquid jet, which is formed from the liquid containing dopant.

With this variant of the method, it is possible to completely prevent the emitter doping formed in the contact holes, which is a component of the emitter, from being attacked during the removal of the emitter from the back, for example by capillary effects. Since the contact holes are applied only after the removal of the emitter from the back of the solar cell substrate, this is excluded.

In the method variant just described, the contact holes are preferably introduced into the solar cell substrate before the dielectric coating is applied to the rear side of the solar cell substrate for the purpose of passivating the rear side. Impairment of the dielectric coating due to the introduction of the contact holes can be avoided.

Advantageously, in the method according to the invention, contact fingers are formed on the front side of the solar cell substrate by printing on a metal-containing paste, the contact fingers extending over a contact hole or a plurality of contact holes. In principle, all printing methods known per se can be used, preferably screen printing methods.

After forming the dielectric coating on the back surface of the solar cell substrate, by printing a metal-containing paste, contact material can be introduced into the contact holes and emitter contacts formed on the back surface of the solar cell substrate. In turn, all printing methods known per se can be used, preferably screen printing methods. The emitter contacts can be designed geometrically in a variety of ways. For example, in the form of busbars, which are often referred to as busbars, they can be strip-shaped. Furthermore, it is possible to form the emitter contacts in the form of contact pads, which are often referred to as pads. Particularly preferred are in a common Pressure step introduced the contact material in the contact holes and formed the emitter contacts.

The metal-containing paste used is preferably a metal-containing paste with a low glass frit content. In this context, a proportion of glass frit is considered to be low if the paste can not be fired through the dielectric coating in conventional fire processes. Particularly preferred for the contact material and the emitter contacts a glass frit free, metal-containing paste is used. In this way, the risk of blasting the printed metal-containing paste through the dielectric coating, and thus the risk of short-circuiting, can be significantly reduced.

In a variant of the method, contact fingers are formed on the front side of the solar cell substrate by printing on a metal-containing paste. Furthermore, base contacts for contacting the base of the solar cell are formed on the back of the solar cell substrate by printing a metal-containing paste. The metal-containing paste introduced into the contact holes is then fired together with the metal-containing paste applied for the purpose of forming the contact fingers and together with the metal-containing paste applied for the purpose of forming the base contacts. This joint firing step enables cost-effective process management with minimized thermal stress. The printing of the metal-containing pastes is in each case preferably carried out by means of screen printing processes known per se. If the emitter contacts, as described above, are formed in a common printing step with the introduction of the contact material in the contact holes, they are also fired in the common firing step.

In principle, the contact material introduced into the contact holes and the emitter contacts can also be fired in a further firing step and thus separated from the contact fingers and / or the base contacts. In this case, first the contact fingers and / or the base contacts are printed and fired. Subsequently, by printing a metal-containing paste contact material is introduced into the contact holes and formed emitter contacts on the back. These are subsequently fired in a second, separate firing step.

The metal-containing pastes used to form the contact fingers, the base contacts, the emitter contacts, and to introduce the contact material are obviously not necessarily the same. In each case different metal-containing pastes can be used; For example, a glass frit-free metal-containing paste for forming the emitter contacts, an aluminum-containing paste for forming the base contacts and a silver and glass frit-containing paste for forming the contacts.

For the purpose of increasing the efficiency of the fabricated solar cell, it has been found useful to texture the solar cell substrate on its front side, preferably by means of a wet-chemical texture etching solution, before dopant is doped on the front side of the solar cell substrate for the purpose of forming an emitter.

Advantageously, an antireflection coating is applied to the front side of the solar cell substrate. This is preferably done prior to forming the contact fingers.

Particularly preferably, a silicon solar cell substrate, in particular a crystalline solar cell substrate, is used as the solar cell substrate.

Furthermore, the invention will be explained in more detail with reference to figures. Where appropriate, elements having the same effect here are given the same reference numbers. The invention is not limited to the embodiments shown in the figures - not even in terms of functional features. The previous description as well as the following description of the figures contain numerous features, which are reproduced in the dependent subclaims in part to several summarized. However, those features as well as all the other features disclosed above and in the following description of the figures will also be considered individually by the person skilled in the art and put together to form meaningful further combinations. In particular, these features can be combined individually and in any suitable combination with the method of the independent claim. Show it:

1 Through-contacted solar cell according to the prior art

2 Novel plated-through solar cell

3 A first embodiment of the method according to the invention

4 Another embodiment of the method according to the invention

1 shows a schematic partial sectional view of a plated-through solar cell 50 according to the prior art. This has a solar cell substrate 52 on, in which contact holes 54 are arranged, which through the solar cell substrate 52 pass through, and in which a contact material 56 is arranged. On a Front of the solar cell 50 are contact fingers 58 arranged, which each have a contact hole 54 or more contact holes 54 extend. On a back side of the solar cell substrate 52 , or the solar cell 50 , are emitter contacts 60 arranged. These contact an emitter 62 extending from the front of the solar cell 50 through the contact holes 54 extends to the back of the solar cell substrate. Thus, the emitter is located 62 partially on a back surface of the solar cell substrate 52 , A dielectric coating 68 For passivation of the back of the solar cell substrate may therefore at most parts of the back of the solar cell substrate 52 passivate.

The on the back of the solar cell substrate 52 arranged components of the emitter 62 serve to short-circuit the emitter contacts 60 and a base 66 of the solar cell substrate 52 as well as this base 66 avoid contact base contacts. For the realization of the back components of the emitter 62 it requires elaborate masking steps.

2 shows with a solar cell 70 An embodiment of the above-described, novel plated-through solar cell. This in turn has a solar cell substrate 52 which is embodied here as a silicon solar cell substrate. In the solar cell substrate 52 are in turn contact holes 54 arranged, which through the solar cell substrate 52 pass through and in which a glass frit free, metal-containing and fired paste 76 is arranged as contact material.

On a front side of the solar cell 70 are contact fingers 78 arranged, which each have a contact hole 54 or more contact holes 54 extend. In the second case, in this way, in the multiple contact holes 54 arranged contact material, in this case the glass frit-free, metal-containing and fired paste 76 electrically connected to each other. On a back of the solar cell 70 are emitter contacts 80 arranged, which each have at least one contact hole 54 extend such that in this at least one contact hole 54 arranged contact material 56 with the respective emitter contact 80 is electrically connected. An electrical conductive connection of several emitter contacts 80 can, especially if any emitter contact 80 itself in the manner described over only one contact hole 54 extends realized in the context of interconnection of various solar cells of a solar cell module.

Like the schematic partial sectional view of 2 shows is a back surface 72 of the solar cell substrate 52 free from an emitter 82 which is on a front side of the solar cell 70 is arranged and in the form of an emitter doping 84 in the contact holes 54 extends into it. Immediately on the back surface 72 of the solar cell substrate 52 is a dielectric coating 88 educated. This is in sections between the emitter contacts 80 and the back surface 72 of the solar cell substrate 52 arranged, resulting in an electrical insulation of the emitter contacts 80 opposite the base 66 the solar cell 70 causes. The emitter contacts 80 are directly on the dielectric coating 88 arranged.

Because of the back surface 72 of the solar cell substrate 70 free from the emitter 82 is, covers the dielectric coating 88 essentially the entire backside of the solar cell substrate 52 , Only in areas where basic contacts 90 locally through the dielectric coating 88 pass through and the back surface 72 of the solar cell substrate 52 this is not the case. As base contacts 90 screen-printed and fired aluminum-containing pastes are provided in the present embodiment. These form back side fields during the firing process 91 , so-called back surface fields, which in the representation of 2 are shown schematically.

How out 2 is visible, is the front of the solar cell substrate 52 , and thus the solar cell 70 , textured. In the present case, this texture was formed by means of a wet-chemical texture etching process. In principle, however, other texturing methods can also be used.

Further, on the front side of the solar cell substrate 52 , or the solar cell 70 , a silicon nitride layer 64 deposited as an antireflection layer. The contact fingers 78 are through the silicon nitride layer 64 by fired.

In the 2 illustrated embodiment of the novel plated-through solar cell can, as the inventors have recognized, be prepared inexpensively without masking steps. Thus, neither the masking steps for edge insulation typical of plated-through solar cells are required, nor is a masking step to ensure the emitter clearance of the back surface 72 , This will be possible because the back surface 72 free from the emitter 82 is. At the same time, a reliable electrical insulation of the emitter contacts 80 opposite the base 66 of the solar cell substrate 52 , or compared to the base contacts 90 , through the dielectric coating 88 guaranteed.

3 shows a schematic representation of a first embodiment of the inventive method. This can, as well as the embodiment of the 4 for the production of novel through-contacted solar cells, in particular those in 2 represented solar cell can be used.

The method according to the 3 provides that contact holes are first introduced into a solar cell substrate by means of laser beam evaporation 10 , This is followed by a texture etching 12 a front side of the solar cell substrate. In this case, any damage caused to the solar cell substrate during the laser beam evaporation can be partially removed.

In addition, an emitter diffusion, which is realized in the present embodiment by a gas phase diffusion, for example, a POCl ₃ - or a BBr ₃ -Röhrendiffusion. In this, the emitter is also formed on the back surface of the solar cell substrate. Because at the time of emitter diffusion 14 the contact holes are already introduced into the solar cell substrate, during the emitter diffusion 14 Emitter dopant also diffused in Wandungsflächen the contact holes. In the context of emitter diffusion 14 Thus, an emitter doping is formed in the contact holes, which is part of the emitter. As a result, therefore, during the emitter diffusion 14 formed on the entire surface of the solar cell substrate, an emitter.

This becomes in a subsequent etching step 16 completely removed from the back of the solar cell substrate 16 , This is done in the present embodiment by a one-sided, wet-chemical etching process. For example, the solar cell substrate may be moved along the surface of an etching solution through the etching solution with the back side of the solar cell substrate in contact with the etching solution. However, other unilateral etching methods may be used.

In addition, a dielectric coating is applied to the rear side of the solar cell substrate to passivate the rear side of the solar cell substrate 18 , This will be briefly referred to as backside passivation 18 designated.

This is followed by a silicon nitride deposition 20 on the front of the solar cell substrate. The deposited silicon nitride layer serves as an antireflection coating.

Furthermore, in a common screen printing step 22 Emitter contacts printed on the dielectric coating and screen printing paste introduced into the contact holes. The screen-printing paste used is a metal-containing paste without glass frit. In this way it is ensured that the dielectric coating is not fired in a subsequent firing step.

Furthermore, by screen printing of a metal-containing paste, in the case of a p-doped solar cell substrate, for example an aluminum-containing paste, base contacts are screen-printed 24 , The base contacts are applied to the dielectric coating and introduced into local openings in the dielectric coating. Such local openings in the dielectric coating can be formed, for example, by means of laser beam evaporation or local etching processes.

Furthermore, by screen printing 26 a metal-containing paste contact fingers applied to the front of the solar cell substrate. It closes a joint fire step 28 in which fired for the purpose of the formation of the emitter contacts, the base contacts and the contact fingers, metal-containing pastes fired and ohmic contacts are formed.

4 illustrates another embodiment of the method according to the invention. This differs from that of the 3 among other things, that the contact holes only after etching 16 of the emitter are introduced from the back into the solar cell substrate 30 , This is done by means of a so-called laser chemical process. Although the contact holes are in turn formed by laser beam evaporation, but this is done in the presence of a dopant-containing liquid. As a result of the local heating of the solar cell substrate in the context of the local laser beam evaporation of the solar cell substrate for the purpose of introducing the contact holes is doped locally in the contact holes dopant from the dopant-containing liquid in the wall surfaces of the contact holes. In this way, the emitter doping is formed in the contact holes, which as a result forms part of the entire emitter.

The introduction 30 the contact holes after etching 16 the emitter from the back ensures that when etching 16 the emitter does not damage the emitter doping in the contact holes.

In addition, those already close in connection with the 3 explained steps of backside passivation 18 and the silicon nitride deposition 20 at.

The metallization takes place by first analogously as in 3 Base contacts are screen printed 24 and contact fingers are printed by screen printing on the front side 26 , In contrast to the embodiment of 3 are the for the purpose of forming the contact finder of Base contacts screen printed 24 . 26 metal-containing pastes before screen printing 22 the emitter contacts fired 32 , Only then are the emitter contacts screen-printed and screen printing paste introduced into the contact holes 22 , The emitter contacts and the screen printing paste introduced into the contact holes then become an additional firing step 34 fired. Depending on the type of metal-containing pastes used for the various contacts, this may be advantageous in order to avoid a firing of the emitter contacts through the dielectric coating.

In the 4 on the silicon nitride deposition 20 The following method steps can in the embodiment 3, the there on the silicon nitride deposition 20 replace the following steps. Conversely, in the embodiment of the 3 on the silicon nitride deposition 20 following method steps in the embodiment of 4 the there on the silicon nitride deposition 20 replace the following steps.

LIST OF REFERENCE NUMBERS

10

Introduction of contact holes by means of laser

12

Texturätzen

14

emitter diffusion

16

Etch emitter from the back

18

Backside passivation by means of dielectric coating

20

Silicon nitride deposition on front side

22

Screen printing emitter contacts and applying screen printing paste in contact holes

24

Screen printing base contacts

26

Screen print contact fingers on front

28

To fire

30

Introduction of contact holes by means of laser in the presence of dopant-containing liquid and formation emitter doping in contact holes

32

Fire contact fingers and base contacts

34

Fire emitter contacts and screen printing paste in contact holes

50

solar cell

52

solar cell substrate

54

contact hole

56

Contact material

58

contact fingers

60

emitter contact

62

emitter

64

silicon nitride

66

Base

68

dielectric coating

70

solar cell

72

back surface

76

glass frit-free, metal-containing and fired paste

78

contact fingers

80

emitter contact

82

emitter

84

emitter doping

88

dielectric coating

90

base contact

91

Back surface field

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Conference SiliconPV, which took place from 17 to 20 April 2011 in Freiburg, Germany, was, however, by Benjamin Thaidigsmann et al. a novel solar cell presented under the title "HIP-MWT: A simplified structure for metal wrap through solar cells with passivated rear surface" [0006]
• Thaidigsmann et al. [0019]

Claims (12)

Method for producing a through-contacted solar cell ( 70 ) comprising the following steps: - introducing ( 10 ; 30 ) of contact holes ( 54 ) into a solar cell substrate ( 52 ); - Diffuse ( 14 ) of dopant into the solar cell substrate ( 52 ) for the purpose of forming an emitter ( 82 ) on a front side of the solar cell substrate ( 52 ); - application ( 18 ) a dielectric coating ( 88 ) on a back side of the solar cell substrate ( 52 ) for the purpose of passivation of this reverse side; characterized in that - in the diffusing ( 14 ) of dopant into the solar cell substrate ( 52 ) for the purpose of forming an emitter ( 82 ) on the front side of the solar cell substrate ( 52 ) on at least a part of the back side of the solar cell substrate ( 52 ) Dopant in the solar cell substrate ( 52 ) is diffused ( 14 ) and in this way the emitter partly on the back side of the solar cell substrate ( 52 ) is formed ( 14 ); The emitter from the back of the solar cell substrate ( 52 ) is completely removed ( 16 ) before the dielectric coating ( 88 ) is applied to the back ( 18 ). Method according to claim 1, characterized in that in the contact holes an emitter doping ( 84 ) is formed ( 30 ; 14 ). Method according to one of the preceding claims, characterized in that the dielectric coating ( 88 ) substantially on the entire back side of the solar cell substrate ( 52 ) is applied ( 18 ), preferably immediately. Method according to one of the preceding claims, characterized in that the emitter by means of wet chemical etching ( 16 ) completely from the back of the solar cell substrate ( 52 ) Will get removed ( 16 ). Method according to one of the preceding claims, characterized in that the contact holes ( 54 ) into the solar cell substrate ( 52 ) ( 10 ), before for the purpose of forming an emitter ( 82 ) on the front side of the solar cell substrate dopant in the solar cell substrate ( 52 ) is diffused ( 14 ). Method according to claim 5, characterized in that simultaneously with the diffusion ( 14 ) of dopant into the solar cell substrate ( 52 ) for the purpose of forming the emitter ( 82 ) the emitter doping ( 84 ) in the contact holes ( 54 ) is formed ( 14 ). Method according to one of claims 1 to 4, characterized in that after complete removal ( 16 ) of the emitter from the backside of the solar cell substrate ( 52 ) the contact holes ( 54 ) ( 30 ), in that the solar cell substrate is locally evaporated by means of laser radiation in the presence of a dopant source ( 30 ), and thereby by diffusion of dopant from the dopant source in the wall surfaces of the contact holes ( 54 ) the emitter doping ( 84 ) in the contact holes ( 54 ) is formed ( 30 ). A method according to claim 7, characterized in that a dopant-containing liquid is used as the dopant source ( 30 ). Method according to one of the preceding claims, characterized in that after forming ( 14 ; 30 ) of the dielectric coating ( 88 ) by printing a metal-containing paste ( 76 ) Contact material ( 76 ) into the contact holes ( 54 ) brought in ( 22 ) and emitter contacts ( 80 ) on the back of the solar cell substrate ( 52 ) be formed ( 22 ), preferably by screen printing ( 22 ) of the metal-containing paste ( 76 ). Method according to claim 9, characterized in that for the purpose of introducing ( 22 ) of contact material ( 76 ) into the contact holes ( 54 ) and for the purpose of training ( 22 ) of the emitter contacts ( 80 ) a metal-containing paste ( 76 ) is printed with a low glass frit content, preferably a glass frit-free metal-containing paste ( 76 ). Method according to one of claims 9 to 10, characterized in that - on the front side of the solar cell substrate ( 52 ) Contact fingers ( 78 ) be formed ( 26 ) by imprinting ( 26 ) of a metal-containing paste and / or - for contacting the base ( 66 ) of the solar cell ( 70 ) on the back of the solar cell substrate ( 52 ) Basic contacts ( 90 ) be formed ( 24 ) by imprinting ( 24 ) of a metal-containing paste and - in the contact holes ( 54 ) introduced metal-containing paste ( 76 ) together with the for the purpose of forming the contact fingers ( 78 ) ( 26 ) metal-containing paste and / or together with the for the purpose of forming the base contacts ( 90 ) ( 24 ) metal-containing paste is fired ( 28 ). Method according to one of claims 9 to 10, characterized in that - on the front side of the solar cell substrate ( 52 ) Contact fingers ( 78 ) be formed ( 26 ) by imprinting ( 26 ) of a metal-containing paste and / or - for contacting the base ( 66 ) of the solar cell ( 70 ) on the back of the solar cell substrate ( 52 ) Basic contacts ( 90 ) be formed ( 24 ) by imprinting ( 24 ) a metal-containing paste; - First, for the purpose of forming the contact fingers ( 78 ) printed ( 26 ) metal-containing paste and / or for the purpose of forming the base contacts ( 90 ) printed ( 24 ) metal-containing paste is fired ( 32 ) and - subsequently by imprinting ( 22 ) and firing ( 34 ) a metal-containing paste ( 76 ) Contact material ( 76 ) into the contact holes ( 54 ) brought in ( 22 ) and emitter contacts ( 80 ) on the back of the solar cell substrate ( 52 ) be formed.

Images