DE102012101359A1 - Method for producing solar cell, involves forming glass layer on partial region of weakly doped emitter and diffusing additional dopant into substrate locally in regions of substrate that are covered by glass layer by local heating - Google Patents

Abstract

A weakly doped emitter is formed (12) in regions of solar cell substrate that are covered by first glass layer by diffusion of dopant from glass layer into substrate using phosphorous oxychloride. The glass layer is removed (14) and a second glass layer containing dopant of first type is formed (16) on partial region of emitter and additional dopant of first type is diffused from the second glass layer into the substrate locally in regions of the substrate that are covered by the second glass layer by local heating (18). The strongly doped emitter regions are formed.

Description

The invention relates to a method for producing a solar cell with a selective emitter according to the preamble of claim 1 and a solar cell produced by this method.

It is known that the efficiency of solar cells can be improved by the formation of selective emitter structures. An interesting variant of the production of a selective emitter for industrial solar cell production is laser diffusion. This provides that initially a homogeneous, weakly doped and thus high-impedance emitter is formed on a solar cell substrate. Furthermore, the solar cell substrate is locally heated by means of laser radiation. In this way, on the one hand, the position of dopant already present in the solar cell substrate can be changed, for example, it can be driven deeper into the solar cell substrate and in this way the emitter profile can be changed locally. In addition, the ratio of electrically inactive dopant to electrically active dopant can be changed locally. On the other hand, it is possible to diffuse locally from a dopant source, which has already been used for the formation of the homogeneous, lightly doped emitter, by locally heating by means of the laser radiation additional dopant into the solar cell substrate. In this way, the dopant concentration can be increased locally.

The effects described make it possible to form locally heavily doped emitter regions which, together with the otherwise present weakly doped emitter, form the desired selective emitter. A method for forming a selective emitter by means of laser diffusion using a liquid-guided laser is among others US 2010/0213166 A1 known.

In practice, there are some limitations to laser diffusion which hinder the formation of an optimal selective emitter. For example, phosphorus or boron diffusions are designed to form a homogeneous emitter with an optimal emitter profile, more specifically emitter depth profile. For example, in tube diffusions, especially in POCl ₃ diffusions, driving steps are performed to reduce the surface concentration of the dopant in the solar cell substrate. Such driving steps, sometimes referred to as drive-in phases, are often carried out in an oxygen-containing atmosphere. This leads, in particular when using silicon solar cell substrates, to the growth of a silicon oxide layer at the interface between the solar cell substrate and the dopant-containing glass layer. The silicon oxide layer thus separates the surface of the solar cell substrate from the dopant-containing glass layer. During and after the formation of the silicon oxide layer, dopant from the dopant-containing glass layer and from the solar cell substrate diffuse into the silicon oxide layer so that it does not represent a pure silicon oxide layer. Depending on the process control, the silicon oxide layer is thinner or thicker and consequently more or less impedes the diffusion of additional dopant from the dopant-containing glass layer into the solar cell substrate during a subsequent local heating by means of laser radiation, ie during the subsequent laser diffusion. As a result of this obstruction of the laser diffusion, less dopant can be locally diffused into the solar cell substrate by laser diffusion than would be required for the formation of optimal heavily doped regions of the selective emitter. This results in increased contact resistance between the heavily doped emitter regions and disposed thereon metal contacts of the finished solar cell, which has a negative effect on the efficiency of the finished solar cell.

The present invention is therefore based on the object to provide an improved method for producing a solar cell with a selective emitter.

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

Advantageous developments are the subject of dependent claims.

The method according to the invention for producing a solar cell with a selective emitter provides that a first glass layer containing a dopant of the first type is formed on at least part of a surface of a solar cell substrate in areas of the solar cell substrate covered by the first glass layer by diffusion of first type dopant forming a lightly doped emitter into the solar cell substrate in the first glass layer and by locally heating selected regions of the solar cell substrate local additional dopant of the first type is diffused into the solar cell substrate to form heavily doped emitter regions.

Against this background, the basic idea of the invention is to remove the first glass layer before local inward diffusion of the additional dopant of the first type, prior to local heating of the selected regions of the solar cell substrate at least in the selected regions of the solar cell substrate, a second type dopant containing first glass layer form the surface of the solar cell substrate and by the local heating of the selected areas of the Solar cell substrate to diffuse the additional dopant from the second glass layer locally into the solar cell substrate and form in this way the heavily doped emitter regions.

In this way, the formation of the first glass layer and the diffusion of dopant from the first glass layer into the solar cell substrate may be performed for the purpose of forming the lightly doped emitter independently of the formation of the heavily doped emitter regions by means of local heating. For example, the first glass layer and its dopant content need not be designed so that enough dopant is available for the formation of heavily doped emitter regions during local heating. This results in advantageous freedom in the process and for the optimization of the selective emitter. In addition, an extended due to the formation of the second glass layer total residence time of the solar cell substrate in heated furnaces in individual cases can have a positive effect on the efficiency of solar cells made of crystalline silicon substrates.

The local heating of the selected regions is preferably carried out by means of laser radiation. As the dopant of the first type, either n-type dopant or p-type dopant may be used, especially phosphorus or boron.

As the solar cell substrate, a silicon substrate is preferably used.

For the purposes of the present invention, a weakly doped emitter is to be understood as meaning an emitter with a sheet resistance of 80 Ω / sq to 200 Ω / sq. Preferably, a lightly doped emitter is formed with a sheet resistance of 80 Ω / sq to 140 Ω / sq, and more preferably from 90 Ω / sq to 130 Ω / sq. In practice, in particular, lightly doped emitters having a surface charge carrier concentration of about 5 × 10 ¹⁹ cm ^-3 have proven to have a sheet resistance of about 100 Ω / sq. Heavily doped emitter regions in the sense of the present invention have a sheet resistance of less than 70 Ω / sq, preferably less than 60 Ω / sq.

As the first or second glass layer, a silicate glass layer is preferably formed, in particular a phosphorosilicate glass or a borosilicate glass layer.

The first glass layer may be removed by etching, preferably by wet chemical etching. In particular, hydrofluoric etching solutions have proven useful in this connection.

The second glass layer can be formed by means of a document step, as is usually carried out in the context of tube diffusion, for example POCl ₃ or BBr ₃ diffusion. Preferably, the second glass layer is formed by means of a POCl ₃ -Belegschrittes. The used POCl ₃ -Belegschritt is, as stated above, to a known first substep of POCl ₃ -Röhrendiffusionen which partially ₃ occupation rules is referred to as POCl. Advantageously, the POCl ₃ loading step is carried out in a diffusion oven. This allows a cost-effective process management, since no novel devices are required, but can be used on known and proven systems that are comparatively low cost available and operable. Instead of a POCl ₃ -Belegschrittes basically a BBr ₃ -Belegschritt be provided. The use of dopant sources other than POCl ₃ and BBr ₃ is possible.

The POCl ₃ loading step is preferably conducted at temperatures less than 790 ° C, more preferably at temperatures less than 770 ° C. Such low temperatures make it possible to largely reduce, ideally prevent diffusion of inactive phosphorus into the solar cell substrate. In practice, it has proven to be advantageous to carry out the POCl ₃ -Belegschritt at temperatures between 700 ° C and 750 ° C, have proven particularly useful temperatures between 725 ° C and 740 ° C.

An alternative embodiment variant provides that liquid containing a dopant of the first type is applied to the selected regions and dried for the purpose of forming the second glass layer. Preferably, this liquid is sprayed or spin coated, the latter being sometimes referred to as spinning. In particular, a one to twenty percent phosphoric acid has proven useful as a dopant containing the first type. Instead of the phosphoric acid, a dopant-containing liquid can be applied in a sol-gel process.

Another embodiment provides that the second glass layer is formed by means of a chemical vapor deposition (CVD), which preferably takes place in the continuous process at atmospheric pressure (APCVD). As dopant source for the formation of the second glass layer, in particular trimethyl phosphate or trimethyl phosphite, frequently referred to as TMP for short, have proven useful in this context.

Preferably, the chemical vapor deposition takes place at a temperature of less than 750 ° C. As stated above, restricting the temperatures may reduce and ideally prevent diffusion of inactive phosphorus into the silicon. If a plasma-driven deposition from the vapor phase (PECVD) is used, the deposition is preferably carried out at temperatures of less than 500 ° C.

In one embodiment variant of the method, a silicon substrate is used as the solar cell substrate. Furthermore, at least at times during the diffusion of dopant from the first glass layer into the solar cell substrate, a silicon oxide layer is formed directly on the at least part of the surface of the solar cell substrate. If the first glass layer was previously formed directly on the at least one part of the surface of the solar cell substrate, the silicon oxide layer is thus formed at the interface between the first glass layer and the at least one part of the surface of the solar cell substrate. During and after the formation of the silicon oxide layer, dopant of the first type diffuses out of the first glass layer and out of the solar cell substrate into the silicon oxide layer, so that it does not represent a pure silicon oxide layer. Furthermore, the silicon oxide layer is removed before local inward diffusion of the additional dopant of the first type. This preferably takes place together with the removal of the first glass layer. In this way, it can be prevented that the local in-diffusion of additional dopant from the second glass layer into the solar cell substrate is hindered by the silicon oxide layer.

The silicon oxide layer may be formed during a drive-in step, sometimes referred to as a drive-in phase, of the diffusion process of dopant from the first glass layer into the solar cell substrate. The driving step is usually carried out in a production of high-efficiency solar cells in an oxygen-containing atmosphere. In tube diffusion, driving steps, or driving phases, take place after the filling step. The allocation step is sometimes referred to as occupancy or simply occupancy.

Advantageously, the first glass layer is formed as part of a tube diffusion, preferably in the context of a POCl ₃ or BBr ₃ diffusion.

In practice, it has proven useful to provide at least the at least part of the surface of the solar cell substrate with a texture prior to forming the first glass layer. In this way, the light coupling can be increased in the finished solar cell.

The method according to the invention for producing a selective emitter is compatible with modern solar cell production methods, which provide a dielectric mirroring of the rear side of the solar cell substrate. Under the back side of the solar cell substrate is to be understood that the large-area side of the solar cell substrate, which is disposed facing away from the incident light during operation of the finished solar cell. The process according to the invention can be integrated cost-effectively into such solar cell production processes. In a preferred embodiment variant of the method described here, therefore, a layer stack of dielectric layers is applied to a rear side of the solar cell substrate.

Preferably, the second glass layer is formed directly on the surface of the solar cell substrate. In this way, it can be prevented that the diffusion of additional dopant of the first type from the second glass layer into the solar cell substrate is hindered by objects disposed between the second glass layer and the surface of the solar cell substrate.

With the method according to the invention improved solar cells can be produced.

The object mentioned at the outset, to provide an improved method for producing a solar cell with a selective emitter, is alternatively achieved by the alternative method described below:
In this alternative method of manufacturing a solar cell having a selective emitter, a first glass layer containing a dopant of the first type is formed on at least a part of a surface of a solar cell substrate. In areas of the solar cell substrate covered by the first glass layer, locally locally doped dopant of the first glass layer is diffused into the solar cell substrate by local heating of the solar cell substrate. In this way, heavily doped emitter regions are formed. After local heating of the solar cell substrate, a second glass layer containing a first type dopant is formed at least in those regions of the solar cell substrate in which lightly doped regions of the selective emitter are to be arranged. In regions of the solar cell substrate covered by the second glass layer, a lightly doped emitter is then formed by diffusion of dopant out of the second glass layer into the solar cell substrate, away from the heavily doped emitter regions.

In this alternative method, the formation of heavily doped emitter regions by means of locally heating the first glass layer, regardless of the formation of the lightly doped emitter respectively. Thus, for example, the second glass layer does not need to be designed such that, after the diffusion of dopant from the second glass layer, sufficient dopant is still available for subsequent laser diffusion. This results in advantageous freedom in the process and for the optimization of the selective emitter. The second glass layer and the diffusion of dopant into the solar cell substrate from the second glass layer can thus be optimally matched to the emitter depth profile to be formed away from the heavily doped regions.

Locally diffused dopant is driven deeper into the solar cell substrate during subsequent diffusion of dopant from the second glass layer. In this way, a deep emitter doping can be realized in heavily doped emitter regions. Such deep emitter doping, sometimes referred to as low emitters or deep emitter doping in short, reduces the risk of local short circuits forming in the heavily doped emitter regions after application of a metallization, which adversely affect the efficiency of the solar cell. In addition, a reduced contact resistance between the heavily doped regions of the solar cell substrate and metal contacts arranged thereon may result in the respective applications. Furthermore, it has been shown that in individual applications, there are improvements in contact passivation. In addition, some showed an improved homogeneity of the dopant concentration in the heavily doped emitter regions. This was the case in particular with textured solar cell substrates. This is presumably due to the fact that locally inwardly doped dopant from the first glass layer diffuses radially during the diffusion of dopant out of the second glass layer and inhomogeneities in the dopant concentration are thereby partially compensated.

The local heating of the selected regions is again preferably effected by means of laser radiation. As the dopant of the first type, either n-type dopant or p-type dopant may be used, especially phosphorus or boron.

As the solar cell substrate, in turn, a silicon substrate is preferably used.

The terms of the weakly doped emitter and the heavily doped emitter regions are to be understood in the sense explained above. The first or second glass layer is preferably a silicate glass layer, in particular a phosphosilicate glass layer or a borosilicate glass layer.

Preferably, the second glass layer is also formed on the heavily doped emitter regions. As a result, additional dopant from the second glass layer can be diffused there. In general, however, this is not significant since there is already considerably more dopant present than is additionally made available during the diffusion from the second glass layer.

The first glass layer can be formed by means of a document step, as is usually carried out in the context of tube diffusion, for example POCl ₃ or BBr ₃ diffusions. Preferably, the first glass layer is formed by means of a POCl ₃ -Belegschrittes. The partially as POCl ₃ occupation rules designated POCl ₃ -Belegschritt is advantageously carried out in a diffusion furnace. This allows a cost-effective process management, since it can be used on known and proven systems. Instead of a POCl ₃ -Belegschrittes in principle, a BBr ₃ -Belegschritt be provided. The use of dopant sources other than POCl ₃ and BBr ₃ is again possible.

The POCl ₃ loading step is preferably carried out at temperatures of less than 790 C, more preferably at temperatures of less than 770 ° C. Such low temperatures make it possible to largely reduce, ideally prevent diffusion of inactive phosphorus into the solar cell substrate. Electrically active phosphor is also diffused less quickly into the solar cell substrate. In practice, it has proven to be advantageous to carry out the POCl ₃ -blanking step at a temperature from a temperature range with a lower temperature range limit of 700 ° C and a temperature upper range limit of 750 ° C.

The POCl ₃ coating step is particularly preferably carried out such that a sheet resistance of about 400 Ω / sq is present in the region of the solar cell substrate covered by the first glass layer prior to local heating.

In another embodiment variant of the alternative method, for the purpose of forming the first glass layer, liquid containing a dopant of the first type can be applied to the at least one part of the surface of the solar cell substrate and dried. Preferably, this liquid is sprayed or spin coated. In particular, a one to twenty percent phosphoric acid has proven useful as a dopant containing the first type. Instead of the phosphoric acid, a dopant-containing liquid can be applied in a sol-gel process.

Another embodiment provides that the first glass layer is formed by means of a chemical vapor deposition (CVD). This is preferably done in a continuous process at atmospheric pressure (APCVD). As the dopant source for the formation of the second glass layer, in particular, the above-mentioned TMP has proven itself in this context.

Preferably, the chemical vapor deposition occurs at a temperature of less than 500 ° C. More preferably, the chemical vapor deposition is carried out in the continuous process at atmospheric pressure (APCVD).

Preferably, the first glass layer is removed prior to forming the second glass layer. This allows the greatest possible freedom in the process.

Alternatively, it is possible to purify the solar cell substrate in an aqueous hydrochloric acid solution before forming the second glass layer instead of removing the first glass layer.

Advantageously, prior to forming the second glass layer, the dopant diffused locally from the first glass layer into the solar cell substrate is driven deeper into the solar cell substrate. This is preferably done by heating the solar cell substrate in a nitrogen atmosphere, wherein the solar cell substrate is particularly preferably heated to a temperature of more than 800 ° C, in particular to 850 ° C. If the dopant diffused into the solar cell substrate from the first glass layer is driven too deeply into the solar cell substrate and / or driven too deep into the solar cell substrate as a result of strong oxidation during the diffusion of dopant from the second glass layer, then possibly the strongly doped emitter regions, the near-surface concentration of the dopant of the first type are so greatly reduced that this complicates the contacting of the heavily doped emitter regions. In these cases, the method first described above for the solution of the above-mentioned problem may be more suitable since there is no need for deeper driving in heavily doped emitter regions.

Advantageously, the second glass layer is formed as part of a tube diffusion, preferably a POCl ₃ or BBr ₃ diffusion.

In practice, it has proven useful at least in those areas in which the lightly doped emitter is formed to provide the surface of the solar cell substrate with a texture prior to forming the first glass layer. In this way, the light coupling can be increased in the finished solar cell.

The described alternative method for producing a selective emitter is also compatible with modern solar cell manufacturing processes which provide a dielectric mirroring of the back side of the solar cell substrate. In a preferred embodiment of the alternative method, therefore, a layer stack of dielectric layers is applied to a rear side of the solar cell substrate.

The described alternative method can also be used to produce improved solar cells.

Furthermore, the invention and the alternative method will be explained in more detail with reference to figures. Where appropriate, elements having equivalent effect are provided with like reference numerals. The invention is not limited to the embodiments illustrated in the figures - not even with respect to 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, these features, as well as all the other features disclosed above or in the following description of the figures, will also be considered individually by one skilled in the art and put together to meaningful further combinations. In particular, these features can be combined individually and in any suitable combination with the method and / or the solar cell of the independent claims. Show it:

1 A schematic diagram of a first embodiment of the method according to the invention

2 Schematic sectional views through a method according to 1 continuous solar cell substrate at different process times

3 Schematic representation of an embodiment of the alternative method

4 Schematic sectional view through a method according to 3 continuous solar cell substrate towards the end of the local heating of the solar cell substrate by means of laser radiation

1 shows a schematic diagram of a first embodiment of the inventive method. In this case, the solar cell substrate is first textured and cleaned in a conventional manner. This is followed by a POCl ₃ diffusion 12 at which a first Phosphor glass layer formed from the first phosphor glass layer dopant of a first type, in the present phosphorus, diffused into the solar cell substrate and in this way a lightly doped emitter 58 is trained 12 , As a solar cell substrate in the present case, a silicon substrate 50 used.

In the present embodiment, moreover, during a driving step, the POCl ₃ diffusion 12 a silicon oxide layer is formed directly on the surface of the silicon substrate. This can be omitted in another embodiment.

The first phosphorus glass layer is subsequently completely removed. In the present embodiment, this is done by a wet-chemical etching 14 the first phosphor glass layer. In the present case, the previously formed silicon oxide layer is removed together with the first phosphorus glass layer. Would during the POCl ₃ diffusion 12 no silicon oxide layer formed so eliminates their removal.

The following is a POCl ₃ -Belegschritt 16 on, by means of which surface on the entire lightly doped emitter, a second phosphorus glass layer 52 is trained 16 , The POCl ₃ assignment is advantageously carried out in the same tube diffusion furnace, in which already the POCl ₃ diffusion 12 was carried out. This is especially true when it comes to the POCl ₃ diffusion 12 Diffusion at low pressures, since such low-pressure diffusion allow high throughput. In a line production, however, is advantageously for the POCl ₃ assignment or the POCl ₃ -Belegschritt 16 another tube diffusion furnace or at least one further diffusion tube provided in the existing tube diffusion furnace. Such furnace or pipe separation for the various process steps increases the stability of the entire manufacturing process. The phosphor incorporation step 16 and thus the phosphorus occupancy takes place in the present embodiment at temperatures below 790 ° C, preferably at temperatures below 770 ° C and more preferably at temperatures between 725 ° C and 740 ° C.

In modifications of the in 1 In the embodiment shown, the second layer of phosphorus glass is formed by spraying or spinning and drying a phosphorus-containing liquid such as phosphoric acid or by means of chemical vapor deposition at atmospheric pressure (APCVD).

In the further course of the process, selected regions of the solar cell substrate are locally generated by means of laser radiation 54 heated 18 , By this local heating 18 the selected regions of the silicon substrate 50 becomes additional phosphorus from the second layer of phosphorus glass 52 into the silicon substrate 50 diffused. In this way, heavily doped emitter regions 60 educated 18 ,

2 illustrates in the schematic partial representation (a) of the solar cell substrate 50 towards the end of local heating 18 of the solar cell substrate 50 by means of schematically by arrows 54 indicated laser radiation. Additional phosphorus is already locally from the second layer of phosphorus glass 52 in the solar cell substrate 50 been diffused. As a result, the heavily doped emitter regions 60 in the means of laser radiation 54 heated areas already formed.

2 shows a solar cell substrate 50 which is only on the top with a texture 56 was provided. In principle, however, it is also possible to use a solar cell substrate, in particular a silicon substrate, which is provided with a texture on its entire surface.

After local heating 18 the selected areas by means of laser radiation 54 becomes the second phosphor glass layer 52 away 20 , In the present case, this again takes place by means of a wet-chemical etching 20 ,

In the following, a silicon nitride layer 61 on the silicon substrate 50 secluded 22 , This serves to passivate the surface of the silicon substrate 50 as well as an antireflection coating.

Subsequently, metal-containing pastes are applied by means of screen printing processes known per se 24 , this through the silicon nitride 61 round fired 24 and in this way front contacts 62 and back contacts 64 educated. In the present embodiment, for the purpose of forming the back contact 64 an aluminum-containing paste printed. During the firing 24 so can aluminum from the back contact 64 in the solar cell substrate 50 diffuse and at the back the weakly doped emitter 58 overcompensate. At the same time, a back field is created 66 , which is often referred to as a back surface field formed. In the schematic partial representation (b) of 2 containing the silicon substrate 50 after going through the process 1 and thus shows a finished solar cell, this is the back field 66 indicated by a dash-dotted line.

Finally, the front contacts 62 and the back contact 64 electrically isolated. This is done in the present embodiment by introducing separation trenches 68 by laser beam evaporation. This process is commonly called edge isolation 26 designated. Instead of the edge insulation 26 by laser beam evaporation, the Edges are electrically isolated by a wet chemical etching. Such an etching step preferably takes place before the removal of the second phosphor glass layer.

As already explained above, the method according to the invention can also be used in conjunction with a dielectric mirroring of the rear side of the solar cell substrate. In such cases, the type of back contact design is adjusted accordingly.

3 shows a schematic diagram of an embodiment of the alternative method for solving the above object. In this, the solar cell substrate, which is present through the silicon substrate 50 is formed, textured and cleaned in a conventional manner 10 , This is followed by a POCl ₃ loading step 32 by means of which on the entire surface of the silicon substrate 50 a first layer of phosphorus glass 72 is trained 32 , The POCl ₃ assignment 32 can be carried out in a tube diffusion furnace, for example, in the following manner: After loading the tube diffusion furnace with the silicon substrate 50 this is heated to an occupancy temperature of preferably 750 ° C and stabilizes this temperature. Furthermore, POCl ₃ , nitrogen as carrier gas and oxygen are introduced as process gases. Furthermore, over a period of 40 minutes at the above-mentioned coating temperature, the first phosphorus glass layer 72 educated.

In modifications of the in 3 In the embodiment shown, the first layer of phosphorus glass can be formed by spraying or spinning and drying a phosphorus-containing liquid such as phosphoric acid or by means of chemical vapor deposition at atmospheric pressure (APCVD). Such a trained first phosphorus glass layer covered, deviating from the illustration of 4 not necessarily the entire surface of the silicon substrate 50 ,

In the further course of the process, selected regions of the solar cell substrate 50 locally by means of laser radiation 54 heated 34 , By this local heating 34 Of the selected regions of the silicon substrate, phosphorus becomes the first phosphor glass layer 72 into the silicon substrate 50 diffused. In this way, heavily doped emitter regions 60 educated. 34 ,

4 schematically illustrates the solar cell substrate 50 towards the end of local heating 34 of the solar cell substrate 50 by means of schematically by arrows 54 indicated laser radiation. Phosphorus is already from the first phosphorus glass layer 72 in the solar cell substrate 50 been diffused. As a result, the heavily doped emitter regions 60 in the means of laser radiation 54 heated areas already formed. For the POCl ₃ assignment 32 became only the first layer of phosphorus glass 72 educated. An indiffusion of phosphorus from the first layer of phosphorus glass 72 into the silicon substrate 50 is within the POCl ₃ allocation 32 not to a practically relevant extent. Away from the heavily doped areas 60 has the silicon substrate 50 in the 4 state shown a sheet resistance of about 400 Ω / sq. This is not a weakly doped emitter in the present sense, which is why, in contrast to the representation of 2a) in 4 no weakly doped emitter is shown.

As well as 2 shows 4 a silicon substrate 50 which is only on the top with the texture 56 was provided. In principle, however, it is also possible to use a silicon substrate which is provided with a texture over its entire surface.

In the embodiment of 3 will after local heating 34 the selected areas by means of laser radiation 54 the first phosphorus glass layer 72 away 36 , In the present case, this again takes place by means of a wet-chemical etching 36 ,

Subsequently, a POCl ₃ diffusion 38 performed in which a second phosphor glass layer is formed. In addition, in the context of this POCl ₃ diffusion 38 Phosphorus from the second layer of phosphorus glass into the silicon substrate 50 diffused and formed in this way a lightly doped emitter 38 , During the diffusion of phosphorus from the second phosphorus glass layer to form the lightly doped emitter is also in the context of POCl ₃ diffusion 38 in the heavily doped emitter regions 60 already present phosphor deeper into the silicon substrate 50 driven. To this in the heavily doped emitter areas 60 present dopant even deeper into the silicon substrate 50 Initially recover, optionally, the silicon substrate 50 in a nitrogen atmosphere (N ₂ atmosphere) are heated 37 , This optional process step is shown in the illustration of 3 dashed lines reproduced.

The heating 37 of the silicon substrate 50 in the nitrogen atmosphere and the POCl ₃ diffusion 38 can be realized, for example, in a tube diffusion furnace as follows: First, the silicon substrate 50 heated in the nitrogen atmosphere, for example to 850 ° C, to that during local heating 34 of the silicon substrate 50 diffused phosphor deeper into the silicon substrate 50 collect. In addition, the silicon substrate is cooled to an exposure temperature of, for example, 815 ° C and at stabilized at this temperature. In addition, POCl ₃ , nitrogen as the carrier gas and oxygen are introduced as process gases for the formation of the second phosphor glass layer. Over an occupancy phase of 10 minutes, the second phosphorus glass layer is formed at the deposition temperature. Subsequently, phosphorus from the second phosphorus glass layer is diffused into the silicon substrate at the deposition temperature in a nitrogen atmosphere, and in this way, the lightly doped emitter is formed. Obviously, the POCl ₃ diffusion can also be carried out in other ways, in particular using different coating temperatures and diffusion times, and in this way between the heavily doped regions 60 the desired emitter profile or emitter depth profile desired for the respective application can be formed.

In the further course of the process, the second layer of phosphorus glass is removed 40 , In the present exemplary embodiment, this again takes place by means of a wet-chemical etching 40 ,

Analogous to the embodiment of the 1 Subsequently, a silicon nitride layer on the silicon substrate 50 secluded 22 , Subsequently, metal-containing pastes are again applied by means of screen printing processes known per se 24 , these are fired through the silicon nitride 24 and in the already related to 1 described in more detail front contacts and back contacts formed. In an analogous manner as in the embodiment of 1 Finally, an edge insulation takes place 26 ,

The result is a solar cell, which essentially corresponds to the schematic representation in FIG 2 B) equivalent. Only in the heavily doped emitter areas 60 For example, the dopant phosphorus is deeper into the silicon substrate 50 diffused.

As already explained above, the alternative method for achieving the object stated at the outset can also be used in conjunction with a dielectric mirroring of the rear side of the solar cell substrate. The type of back contact design is to be adjusted accordingly in such cases.

LIST OF REFERENCE NUMBERS

10

Texture and cleaning

12

POCl ₃ diffusion to form first phosphorus glass layer and lightly doped emitter

14

Etching first phosphorus glass layer and silicon oxide layer

16

POCl ₃ assignment for formation second phosphorus glass layer

18

local heating by means of laser radiation and formation of heavily doped emitter regions

20

Etching second layer of phosphorus glass

22

silicon nitride deposition

24

Screen printing contacts and firing

26

edge isolation

32

POCl ₃ assignment for the formation of the first phosphorus glass layer

34

local heating by means of laser radiation and formation of heavily doped emitter regions

36

Etching first phosphorus glass layer

37

Heating in N ₂ atmosphere to drive the phosphor in heavily doped emitter regions

38

POCl ₃ diffusion for formation second phosphorus glass layer and lightly doped emitter

40

Etching second phosphor glass layer

50

silicon substrate

52

second layer of phosphorus glass

54

laser radiation

56

texture

58

weakly doped emitter region

60

heavily doped emitter region

61

silicon nitride

62

front contact

64

back contact

66

Back surface field

68

separating trench

72

first phosphorus glass layer

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 patent literature

• US 2010/0213166 A1 [0003]

Claims (13)

Process for the production of a solar cell with a selective emitter ( 58 . 60 ) comprising the following steps: - training ( 12 ) of a first type dopant containing first glass layer on at least a part of a surface of a solar cell substrate ( 50 ), - training ( 12 ) of a lightly doped emitter ( 58 ) in areas of the solar cell substrate covered by the first glass layer ( 50 ) by indiffusion ( 50 ) of dopant of the first type from the first glass layer into the solar cell substrate ( 50 ), - local indiffusion ( 18 ) additional dopant of the first type into the solar cell substrate ( 50 ) by local heating ( 18 ) selected areas of the solar cell substrate ( 50 ) for the purpose of forming heavily doped emitter regions ( 60 ), characterized in that - the first glass layer before local diffusion ( 18 ) of the additional dopant of the first type is removed ( 14 ), - before local heating ( 18 ) of the selected regions of the solar cell substrate ( 50 ) at least in the selected regions of the solar cell substrate ( 50 ) containing a dopant first type, second glass layer ( 52 ) on the surface of the solar cell substrate ( 50 ) is formed ( 16 ) and - by local heating ( 18 ) of the selected regions of the solar cell substrate ( 50 ) the additional dopant from the second glass layer ( 52 ) locally into the solar cell substrate ( 50 ) and in this way the heavily doped emitter regions ( 60 ) be formed ( 18 ). Method according to claim 1, characterized in that the second glass layer ( 52 ) by means of a document step ( 16 ), preferably by means of a POCl ₃ -Belegschrittes ( 16 ) or a BBr ₃ loading step, is formed ( 16 ). Method according to claim 1, characterized in that the second glass layer ( 52 ) by means of a POCl ₃ loading step ( 16 ) and the POCl ₃ loading step ( 16 ) is carried out at temperatures of less than 790 ° C ( 16 ), preferably at temperatures less than 770 ° C. Method according to claim 1, characterized in that the second glass layer ( 52 ) by means of a POCl ₃ loading step ( 16 ) and the POCl ₃ loading step ( 16 ) is carried out at temperatures between 700 ° C and 750 ° C ( 16 ), preferably at temperatures between 725 ° C and 740 ° C. A method according to claim 1, characterized in that for the purpose of forming the second glass layer liquid containing a dopant of the first type is applied to the selected areas and dried. A method according to claim 1, characterized in that the second glass layer is formed by means of a chemical vapor deposition, which preferably takes place in a continuous process at atmospheric pressure. A method according to claim 6, characterized in that the chemical vapor deposition takes place at a temperature of less than 750 ° C. Method according to one of the preceding claims, characterized in that - as a solar cell substrate ( 50 ) a silicon substrate ( 50 ) is used, at least temporarily during the diffusion ( 12 ) of dopant from the first glass layer into the solar cell substrate ( 50 ) a silicon oxide layer directly on the at least part of the surface of the solar cell substrate ( 50 ) and - the silicon oxide layer before local diffusion ( 18 ) of the additional dopant of the first type is removed ( 14 ), preferably together with the first glass layer. Method according to one of the preceding claims, characterized in that the first glass layer in the context of tube diffusion ( 12 ), preferably a POCl ₃ or a BBr ₃ diffusion, is formed ( 12 ). Method according to one of the preceding claims, characterized in that at least the at least part of the surface of the solar cell substrate ( 50 ) before forming the first glass layer with a texture ( 56 ) ( 10 ). Method according to one of the preceding claims, characterized in that a layer stack of dielectric layers is applied to a rear side of the solar cell substrate. Method according to one of the preceding claims, characterized in that the second glass layer ( 52 ) directly on the surface of the solar cell substrate ( 50 ) is formed ( 16 ). Solar cell produced by the method according to one of the preceding claims.

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