DE102007035068A1 - Method for manufacturing silicon solar cell with selective emitter, involves producing laminar emitter at emitter surface of solar cell substrate and applying corroding barrier on sub ranges of emitter surface - Google Patents

Abstract

The method involves producing laminar emitter (5) at an emitter surface of a solar cell substrate (13) and applying a corroding barrier on sub range (7) of the emitter surface. The emitter surface is corroded in the from of corroding barrier covering another sub range (9) of the emitter surface. The corroding barrier is removed and metallic contacts (17) are produced at the former sub range. The emitter surface produces the porous silicon layer and oxidizes the porous silicon layer. The laminar emitter is produced by phosphorus chloride oxide gas phase diffusion. An independent claim is also included for a silicon solar cell.

Description

The The present invention relates to a method of manufacturing a Silicon solar cell with a selective emitter and a corresponding one Solar cell.

One large part the present industrially produced solar cells is based on silicon, in particular crystalline silicon. This is the predominant Majority of these solar cells with a whole-area homogeneous emitter layer the front surface and / or at the back surface of the Provided solar cell substrate. Many of today's industrial produced silicon solar cells are the metal contacts by means of thick film pastes produced by screen printing. This is a metal particle-containing Paste printed locally on the front emitter and then in Fired the emitter to make good electrical contact with to form the emitter layer.

It Here it is known that it may be necessary, the emitter layer at least in the areas contacted by the metal contacts be provided with a high doping concentration in the region of the emitter surface, for a good ohm To get in touch.

A characteristic size for the assessment of quality or the over the cross section of the emitter layer integrated doping concentration of Emitters is the so-called sheet resistance. The bigger the Sheet resistance is, the smaller the doping concentration within the emitter layer and the smaller is usually the doping concentration at the surface of the emitter layer. It It has been found that with conventionally manufactured emitters a maximum, with screen-printing metallization techniques Contactable sheet resistance of emitters typically in the range from 50-60 Ohm per square lies. Usually can Emitter layers with higher film resistors and basically no longer reliably contacted with lower doping by means of thick film pastes become.

It is thus the use of industrially advantageous screen printing metallization techniques necessary, emitter layers with a high surface doping concentration to provide in the field of metal contacts. On the other hand however, it is known that such a high surface doping concentration strong recombination losses at the surface of the solar cell with it can bring. In particular, pairs of charge carriers caused by high-frequency (blue or UV) light generated very close to the front solar cell surface are rapidly recombining within this heavily doped emitter layer and can therefore no longer contributing to the solar cell current. This can be the IQE (Internal Quantum Efficiency) in the high-frequency light spectrum and thus reduce the total power supplied by the solar cell, which ultimately reduces the efficiency of the solar cell. One additional Effect of a high surface doping concentration may be a so-called band-gap narrowing that can lead to a reduced open clamping voltage.

Tries, these conflicting requirements for good contactability On the one hand, and to meet a high IQE on the other, led to Concept of the so-called selective emitter. In this are the Emitter areas directly below the metal contacts locally strong while intermediate areas provide a substantial have lower doping concentration.

In front especially on a laboratory scale have already been some methods for the production of selective emitter structures developed and tested. In one approach can be divided into two Process steps using a local masking layer, for the often dielectric Layers are used, a selective emitter structure through two separate diffusion processes are generated. However, this is true the need for a plurality of high-temperature diffusion processes, which can significantly increase the production cost. Alternatively, by local etching a previously homogeneously produced emitter layer a selective Emitter structure are generated.

Indeed Such manufacturing processes are often not compatible with currently industrially used further process steps, such as Screen printing metallization. Furthermore, problems can occur that the doping concentration in the individual emitter areas due to a non-uniform etching process locally is inhomogeneous.

Previous approaches for the production of silicon solar cells with selective emitter underneath Using two diffusion processes are usually technically complex and industrially hardly feasible due to their high costs. on the other hand is the generation of a selective emitter structure by local etching of the Emitters so far mainly succeeded only in the laboratory, whereby mainly procedures were tested, where an etching of the emitter was carried out after a metallization of the solar cells. These manufacturing processes resulted usually to a significant decrease in the efficiency of solar cells or were industrial hardly realizable.

It can therefore be considered as an object of the present invention a method for the production of a silicon solar cell with a selective emitter to propose, in which in particular the above-mentioned problems of the prior art can be at least partially overcome. In particular, a manufacturing method for a silicon solar cell with a selective emitter may be desired, which is compatible with other conventional, industrially established manufacturing steps, is inexpensive and allows the production of solar cells with high efficiency. Furthermore, there may be a need for a corresponding solar cell.

These Tasks and requirements can be fulfilled by a method and a solar cell according to the independent claims. advantageous embodiments are in the dependent claims specified.

According to one The first aspect of the present invention is a method for Finishing a silicon solar cell with a selective emitter presented, the method comprising the following steps: Generate a flat Emitters on an emitter surface a solar cell substrate; Applying an etching barrier to first portions the emitter surface; Etching the emitter surface in not from the etching barrier covered second portions of the emitter surface; Remove the etching barrier; and generating metal contacts at the first portions. The Process steps are preferably in the order given carried out.

The specified method according to the invention can be considered based on the idea that initially a Emitter on at least one surface of a solar cell substrate is made with a homogeneous doping concentration that is high enough is that they, for example, for a contact using the screen printing process suitable is. Preferably directly following this generation of the flat Emitters, that is, preferably before depositing a dielectric layer, for example as an antireflective or passivation layer and also preferably before the application of the metal contacts, first subregions the emitter surface through an etching barrier protected. Subsequently will not be protected Areas of the emitter surface etched and thus reduce the thickness of the emitter in these areas, so that in these second subregions an emitter with an increased sheet resistance Subsequently, will the etch barrier removed and the solar cell can be further processed in a conventional manner be, that is, It may possibly have a dielectric layer on the front surface as Antireflex or passivation layer are deposited, and after can about that Metal contacts applied, for example by screen printing become.

The presented method can bring a number of advantages. It can be a cost-effective, industrial easy to implement method for producing a selective emitter structure to be provided. Advantageously, for the individual Process steps technologies are used as they are already large-scale used and tested. For example, as an etching barrier an etch resistant Paint can be applied by screen printing and the subsequent etching can be carried out with the aid of conventional wet-chemical etching processes. The method advantageously dispenses with the use cost-intensive vacuum technologies.

There preferably exclusively Technologies are used, which already for a long time in solar cell production can be used, the technological risk in the implementation of the method are kept low. Chemicals usable for the etching step already use in the production of solar cells use. Suitable as an etching barrier Screen printing inks are already being used in the large-scale construction of circuit boards used. Thus, for the implementation of the process technologies, media used and Consumables and their disposal techniques known, complete developed and already in use.

There the method preferably also be realized in a manner can, in the case of a conventional Processing sequence for the production of silicon solar cells only a few, easily manageable process steps are added, the process is preferably easy in existing production facilities can be integrated by installing one or more additional modules.

following will be more details, possible Advantages and preferred embodiments the method according to the invention explained.

The Method can be used to fabricate any silicon solar cell be used. For example, solar cells based on single crystal or multicrystalline silicon wafers or alternatively also be made based on a crystalline or amorphous silicon thin film.

A selective emitter is formed at a surface of the solar cell substrate hereinafter referred to as "emitter surface." The "emitter surface" may preferably be the front side surface of the solar cell substrate facing the sun in use. Alternatively or additionally, an emitter may also be formed on a backside surface. Under a selective emitter in this case is a doped semiconductor Layer of a conductivity type (for example, n-type) opposite to the conductivity type of the base substrate (for example, p-type) understood, in which the doping concentration varies greatly across the emitter surface locally. For example, first subregions of the emitter, at which the front metallization is to be arranged later, can be heavily doped with a high surface doping concentration of, for example, more than 5 × 10 ¹⁹ cm ^-3 , resulting in a sheet resistance of, for example, less than 60 ohms per square, preferably less as 50 ohms per square, and more preferably less than 40 ohms per square in these emitter regions, whereas other intervening emitter regions may be substantially less doped, for example, with a surface doping concentration of less than 1 x 10 ¹⁹ cm ^-3 , resulting in a sheet resistance of For example, more than 60 ohms per square, preferably more than 70 ohms per square and more preferably more than 80 ohms per square leads. The heavily doped regions may later be electrically contacted well with metal contacts, whereas the lightly doped regions may have a higher IQE and a lower emitter saturation current.

As the first essential process step of the proposed method, a planar emitter is produced on the emitter surface of a solar cell substrate. Any method can be used for this purpose. For example, as described in greater detail below, the planar emitter can be diffused into the surface of the solar cell substrate by means of POCl ₃ gas phase diffusion by diffusing phosphorus from a hot gas phase. But it can also be used any other technologies, such as diffusing from a z. B. printed solid dopant source, depositing an additional separate emitter layer, spraying (spin-on) or spin-on of phosphorus-containing substances, implanting dopants in the surface of the solar cell substrate, etc. The parameters when creating the planar emitter are chosen so in that preferably an emitter sheet resistance of less than 60 ohms per square, preferably less than 50 ohms per square, and more preferably less than 40 ohms per square, is established.

Subsequently, will on first portions of the front surface of the solar cell substrate an etching barrier applied. You can do this various technologies are used. Preferably technologies are used which are easy to implement industrially are, such as the printing of a Dickfilmpaste means Screen printing, local spraying a curable solution by means of an inkjet process, the aerosol printing, the vapor deposition through a mask, etc.

As an etching barrier In this case, such a material is selected, which in the subsequent etching step from the etching medium used is not attacked, so that the etching barrier the underlying first Subareas of the emitter surface against the etching medium protect can.

Subsequently, the regions of the emitter surface of the solar cell substrate that are not protected by the etching barrier are etched with the aid of an etching medium. Various etching fluids which can attack and dissolve the material of the solar cell substrate on its front side can be used as the etching medium. As this material is usually silicon or, z. B. after an additional optional oxidation step, silica is, for example, gases or solutions containing hydrofluoric acid (HF) and / or nitric acid (HNO ₃ ), for example, into consideration.

The emitter surface is preferably etched down so much in the second subregions until in the remaining emitter layer a desired, high sheet resistance for example, more than 60 ohms per square, preferably more as 70 ohms per square and stronger preferably more than 80 ohms per square with lowered by wet-chemical etching Surface concentration of Dopants such. B. phosphorus sets. The sheet resistance of remaining emitter layer can be controlled during the etching process by For example, the thickness of the already de-etched layer is optically observed is, or the etching process can be interrupted at short notice to increase the sheet resistance measure, for example by means of a conventional 4-point measurement. To this Way, the etching process aborted upon reaching a predetermined threshold for the sheet resistance become. Alternatively, the duration of the etching process may be reached of a particular desired Sheet resistance can be determined by preliminary tests.

To the etching process the etching barrier will be restored from the substrate surface away. This is preferably done chemically, for example with the help a solution the the etching barrier attacks and releases.

Optionally, a further etching process can now follow, in which, for example, a phosphor glass produced in a POCl ₃ diffusion can be etched away, wherein in the same step, the second partial regions already etched in the previous etching step can be further etched or an oxide optionally produced there is etched away can be. The sheet resistance which definitively settles in the second subregions can thus be influenced by the first etching process described above and by this optional second etching process.

optional can now follow further process steps such as the creation a dielectric layer as an antireflection and / or passivation layer on the emitter surface of the solar cell substrate.

Then be Metal contacts on the first sections, the previous Process course temporarily through the etching barrier against etching of the Emitter layer protected were generated. Due to the high surface doping concentration or the low sheet resistance in these first sections can be a good ohmic Contact between the metal contacts and the silicon solar cell substrate be achieved. The metal contacts can be made with any technologies be generated. However, they are industrially easy to implement Technologies such as the screen printing of a metal particle-containing Thick film paste preferred.

According to one preferred embodiment the method after the deposition of the etching barrier the additional Step of creating a porous Silicon layer on the second not covered by the etching barrier Subareas of the emitter surface of the solar cell substrate. Preferably, this process step simultaneously with the step of etching the emitter surface in the not from the etching barrier covered second subsections. In other words can, rather than the emitter surface in the of the etching barrier unprotected Area etching, an etching process chosen to form an at least partially porous silicon layer leads. This can be done by the proper choice of a suitable etching solution and suitable Ätzrandbedingungen such as a suitable temperature, a suitable etching time, etc. can be achieved. The porous one Silicon layer can be generated with good spatial homogeneity and the thickness of the resulting silicon layer can be determined by suitable Choice of process parameters are affected.

According to one another embodiment becomes the previously produced porous Silicon layer subsequently oxidized. You can do this, for example, an oxidizing medium such as an acid or an ozone-containing, wet-chemical bath or other ozone-containing bath or -producing source. In this case should advantageously the etch barrier also be resistant to this oxidizing medium.

The Process parameters in oxidizing the porous silicon layer, for example Process duration, process temperature, oxidizing capacity of the medium used, etc., can so chosen be that whole porous Layer is oxidized on.

According to one another embodiment then the possibly previously oxidized porous silicon layer in one etched another process step and be removed in this way. By the surface of the Emitter layer is not simply etched flat in a single etching step but first a porous one Layer is generated, which is then oxidized and then etched away can a more homogeneous etching result be achieved. The porous one Silicon layer can also be alkaline without having been previously oxidized etched become.

According to one more another embodiment will the etching the oxidized porous Silicon layer performed after removing the etching barrier. there can be used advantageously that the oxidized porous silicon layer of etching media can not be attacked, the pure, non-oxidized silicon is not or hardly attack. Thus, according to this embodiment first in that of the etching barrier unprotected etched in the second subareas and a porous one Silicon layer produced and then oxidized; subsequently can the etch barrier be removed; Subsequently, the porous silicon layer in a further etching are removed, with appropriate choice of the etching medium previously from the etch barrier protected first parts of this process not or hardly attacked become. Advantageously, when generating the flat emitter phosphor glass also removed during this additional etching step become.

According to one another embodiment the thickness of the generated porous Silicon layer can be optically detected. The porous silicon layer has a different refractive index than solid silicon, so that it at thin porous silicon layers interference effects can occur. Depending on the thickness of the porous silicon layer can these, similar an antireflective layer, appear in different colors. Consequently can the thickness of the generated porous Silicon layer already during of the etching process due to the color of the porous Silicon layer estimated become. Because the porous Silicon layer in a subsequent etching step preferably completely removed which reduces the thickness of the emitter layer remaining thereunder in which solar cell substrate is reduced, can in this way Indirectly derived, how high the sheet resistance the remaining emitter layer after removal of the porous silicon layer will be. Alternatively could the thickness of the generated porous Silicon layer also be determined ellipsometrically.

According to a further embodiment, the step of etching the emitter surface, producing the porous silicon layer and / or oxidizing the porous silicon layer with a flüs sigen solution. It can z. B acidic solutions are used. For example, solutions of acids that attack silicon or silicon oxide, such as HF, HNO ₃ , H ₂ SO ₄ or combinations thereof, may be used. Among other things, the use of liquid etching solutions enables very homogeneous etching with a high etching capacity and / or etching rate.

According to a further embodiment, the generation of the flat emitter is carried out by means of a POCl ₃ gas phase diffusion or else by spray-on or spin-on, and the resulting phosphorus glass is not removed before the application of the etching barrier. The POCl ₃ gas phase diffusion is industrially well implemented and widely used. The resulting during the diffusion of phosphorus glass must be regularly removed after diffusion from the emitter surface again, before z. B. further antireflective or passivation layers are deposited. However, in the process presented, this phosphor glass etching does not have to be done directly after diffusion, where it would be an additional process step, but can be performed simultaneously with one of the later etching steps, for example, the etching step to remove the porous silicon layer after removal of the etch barrier , In this way, the processing effort and the associated costs can be reduced.

According to one another embodiment becomes the etch barrier applied by means of a paste containing plastic. A such paste can be highly viscous (thick), so they for example by means of conventional Screen printing technology locally on the first sections to be protected the emitter surface can be printed. Alternatively, the paste may be low viscosity be (thin), so that they are sprayed locally, for example, in the ink-jet process can be. The first viscous paste can subsequently for example, by heat treatment or cured by irradiation with UV light and so a property as a reliable etch barrier receive.

According to others embodiments can the etching barrier and / or the metal contacts are applied by screen printing. The screen printing technology is well tested industrially and with many Benefits connected. In addition, many are conventional Production equipment already screen printer and in this regard Know-how ready, making the equipment easy to implement of the presented method can be modified.

According to one Another aspect of the present invention is a silicon solar cell presented with a selective emitter. The solar cell includes: a solar cell substrate with a flat emitter on one as emitter surface serving front and / or back surface thereof, one Dielectric layer and emitter metal contacts on the emitter surface. Of the area Emitter has a higher surface doping concentration in the first subregions on as in adjacent second sections. In other words it is a selective emitter. The solar cell substrate has a greater thickness in the first partial areas than in the second partial areas Some areas. In other words, it is between the first and the second subregions a slight step, as for example when re-etching the Emitters during a manufacturing process, as described above arise can. The dielectric layer, for example of silicon nitride or silicon oxide, for example, as an antireflective and / or passivation layer essentially covers the entire emitter surface and is local between the emitter metal contacts and the solar cell substrate arranged. In other words, the dielectric layer separates the Emitter metal contacts at least partially from the surface of the Solar cell substrate, wherein the metal contacts the dielectric layer However, at least locally, it can penetrate to an electric Contact between the metal contacts and the solar cell substrate to enable.

The presented silicon solar cell can be with, among others Help produce the method described above in an advantageous manner. Due to the selective emitter, it has a high efficiency on. It is also advantageous that the good antireflection and passivation properties unavoidable dielectric layer of the solar cell under the emitter metal contacts is located so that the metal contacts are exposed and without prior Removal of a covering dielectric layer contacted or soldered can be.

following will have some potential properties and advantages of the manufacturing method and the solar cell according to embodiments of the present invention.

The Procedure allows the cost-effective application a selective emitter structure with an increase in efficiency the manufactured solar cells of about four percent relative, caused by an increase of Short-circuit current and / or open terminal voltage and / or fill factor the solar cell.

In addition to the increase in efficiency, a solar cell with selective emitter structure can offer even more advantages. In a standard solar cell with a homogeneous emitter, the alloying of the metal contacts can be a critical process step. The process window when setting the he required temperatures can be relatively small, since the layer resistances of the emitter of 50 to 60 ohms per square mean that it is already on the edge of the possible. In the case of a selective emitter structure, a higher doping can be selected among the metal contacts, that is to say in the first subregions, so that the window of possible process parameters becomes larger.

at the optimization of thick film pastes had to compromise so far between finger conductivity, Contact resistance and rheology (flow behavior) are received.

There good electrical contact easier with a selective emitter Thick film pastes can be made be optimized for other parameters, such as a higher finger conductivity and optimized flow behavior, which enables screen printing of finer fingers.

The Selective emitter structure can immediately make the use more cost effective Screen printing pastes allow, without the efficiency of the solar cells would be negatively affected.

moreover allows a selective emitter the wise application of procedures for Production of finer metal contacts. To reduce shading losses Is it possible, to make a metalgrid with finer fingers. Typical conventional Finger widths are in the range between 100 and 140 microns. Reduced the finger width is below 80 μm, Thus, the solar cell provides more power due to the lower shading through the metallization. The series resistance can be conventional However, solar cells increase because of the contact area between the metallization and the substrate surface is also reduced. In the case of the cell with selective emitter can the specific contact resistance due to the higher doping be reduced under the fingers, so that the overall series resistance not increased.

Around the process stability to ensure an additional Development of further measuring instruments for use in a production line, the presented manufacturing process implements, not required. Commercially available and already in solar cell construction used optical and electrical measuring devices are capable of, the To monitor process online. The process is very easy to control and also stable and variable.

Furthermore, it has been found that in solar cells produced according to the presented methods, the back etching in the regions not protected by the etching barrier can produce an emitter which has a favorable doping profile. Emitters in which a dopant source was brought into direct contact with the solar cell substrate surface for their production and the dopants were then diffused into the surface at high process temperatures have an extremely high doping concentration directly at the surface. This can in particular have a negative effect on the solar cell properties when illuminated with high-frequency (blue or UV) light. By etching back in the second subregions of the emitter surface, this very heavily doped superficial layer can be removed, which can have a positive effect on the IQE in the short-wave spectral range. It was found that the doping profile in the etched-back emitter is much flatter than in the case of emitters directly after diffusion, which have the same overall sheet resistance. For example, it has been found that a back-etched emitter having a sheet resistance of 60 ohms per square may have approximately similar properties with respect to IQE and / or emitter saturation current density J _0e as a conventional emitter having a sheet resistance of 100 ohms per square. Thus, in the presented methods, relatively low sheet resistances of, for example, 60 to 80 ohms per square can also be accepted in the second partial areas, which will lie between the metal contacts in the finished solar cell, without this having a negative effect on the IQE of the solar cell. At the same time, the total series resistances within the solar cell can be reduced with such low sheet resistances, which has an overall positive effect on the efficiency of the solar cell.

It It is noted that above in relation to individual embodiments features of the present invention in any manner be combined with each other. In particular, also features that are suitable for the manufacturing process have been described, with features of the solar cell according to the invention be combined.

The previously described and other aspects, features and advantages The present invention will become apparent from the following description specific embodiments with reference to the attached Drawings visible.

Brief description of the drawings

1 shows a cross section of a solar cell according to an embodiment of the present invention.

2 (a) - (g) shows a solar cell at various stages of a manufacturing process according to another embodiment of the present invention.

The Drawings are only schematic diagrams. Especially the thicknesses of the individual layers are not shown to scale. Same or similar Reference numerals in the drawings designate the same or similar Elements.

Detailed description of embodiments of the invention

1 shows a solar cell 1 with a p-type base 3 and an n-type areal selective emitter 5 , The emitter 5 has first sections 7 and intermediate second sections 9 where the thickness of the second subregions 9 smaller than that of the first subareas 7 and the sheet resistance of the second portions 9 is greater than that of the first subareas 7 , Between the first sections 7 and the second subareas 9 extends a small step 11 , Over the entire front surface of the solar cell substrate 13 that the base 3 and the emitter 5 includes, extends a dielectric layer 15 made of silicon nitride, which simultaneously serves as an antireflective layer and as surface passivation. Over the dielectric layer 15 are in the range of the first thicker parts 7 of the selective emitter 5 finger-shaped metal contacts 17 arranged, wherein the dielectric layer 15 between the metal contacts 17 and the surface of the solar cell substrate 13 is, however, partially penetrated by so-called "spikes", that of the metal contacts 17 towards the surface of the emitter 5 run to make an ohmic contact to this surface. At the back of the solar cell is a flat aluminum back contact 19 ,

With the help of 2 Now, a sequence of process steps for producing a solar cell according to an embodiment of the present invention will be described.

The starting point is a silicon wafer 21 , This may have been previously surface textured and cleaned (step (a)).

In the surface of the p-type wafer 21 , which for the most part is the basis 3 provides a flat emitter layer 5 with the help of a POCl ₃ gas phase diffusion at high temperatures of about 800 to 1000 ° C diffused. In this diffusion process forms on the surface of the emitter layer thus produced 5 a phosphorus glass layer 23 (Step (b)).

This is followed by the so-called edge insulation, in which the electrical connection between the emitter region generated on the front side 5 and the emitter region formed on the back side is separated. For this purpose, for example, provided with the emitter wafer 21 be exposed to an etch plasma at its edge, so that the emitter 5 is etched away containing the outermost layer of the wafer. Subsequently, an etch barrier 25 in the form of elongated fingers (in the figure perpendicular to the plane of the drawing) by means of screen printing on the phosphorus glass layer 23 printed. For this purpose, z. B. a screen printing paste from Peters Lackwerke (Germany) can be used with the name SD2052A1, which can form a layer of an organic plastic (step (c)).

After the material of the etching barrier 25 was cured thermally or by irradiation with UV light, the front surface of the solar cell substrate is exposed to an HF-HNO ₃ -H ₂ O solution. The etching solution initially etches into the non-etching barrier 25 protected areas the phosphorus glass layer 23 away and then grab the underlying emitter 5 on, taking a shift 27 made of porous silicon. As can be clearly seen in the enlarged section (A), the porous silicon layer extends 27 in the emitter layer 5 into (step (d)).

Subsequently, the generated porous silicon layer is oxidized in an acid containing nitric acid (HNO ₃ ) or sulfuric acid (H ₂ SO ₄ ).

After the etching barrier 25 For example, by dissolving ("stripping") in sulfuric acid, the remaining phosphorus glass layer is removed 23 and at the same time the generated oxidized porous silicon in the second partial areas 9 etched away in a hydrofluoric acid solution (HF + H ₂ O) (step (e)).

In this way was on the surface of the as a solar cell substrate 13 serving wafer 21 a selective emitter 5 with more heavily doped thick first sections 7 and weaker doped thin second portions 9 generated.

Subsequently, a dielectric layer serving as an antireflection layer and passivation layer is formed over the entire front surface 15 deposited, for example, in the PECVD (Plasma Enhanced Chemical Vapor Deposition) method (step (f)).

Finally, the heavily-doped first sub-areas 7 over the dielectric layer 15 Thick film metal contacts 17 printed by screen printing using a silver particle-containing thick film paste. On the back of the solar cell substrate is a flat back contact 29 printed using an aluminum particle-containing thick film paste. In a subsequent sintering step, the printed contacts are fired, with the front metal contacts 17 partly through the dielectric layer 15 "Eat through" and thus contact the underlying emitter 5 produce (step (g)).

Finally, it will pointed out that the terms "include", "exhibit" etc. the presence additional Do not exclude elements should. The term "one" also includes the presence of a plurality of elements or objects not out. Furthermore, can in addition to in the claims mentioned method steps further steps or necessary be advantageous to finalize the solar cell final. The Reference signs in the claims are only for better readability and should the scope of protection the claims restrict in any way.

Claims (13)

Method for manufacturing a silicon solar cell ( 1 ) with a selective emitter, the method comprising in the following order: generating a flat emitter ( 5 ) on an emitter surface of a solar cell substrate ( 13 ); Application of an etching barrier ( 25 ) on first subareas ( 7 ) the emitter surface; Etching the emitter surface in not by the etching barrier ( 25 ) covered second parts ( 9 ) the emitter surface; Removing the etching barrier ( 25 ); and producing metal contacts ( 17 ) in the first subareas ( 7 ). The method of claim 1, further comprising, after depositing the etch barrier: creating a porous silicon layer ( 27 ) at the second subregions not covered by the etching barrier ( 9 ) of the emitter surface. The method of claim 2, further comprising: oxidizing the porous silicon layer ( 27 ). The method of claim 2 or 3, further comprising etching the porous silicon layer ( 27 ). The method of claim 4, wherein the etching of the oxidized porous silicon layer ( 27 ) after removal of the etching barrier ( 25 ) is carried out. Method according to one of claims 2 to 5, the thickness of the produced porous silicon layer ( 27 ) is detected optically. Method according to one of claims 1 to 6, wherein at least one of the steps of the etching of the emitter surface, the production of the porous silicon layer ( 27 ) and oxidizing the porous silicon layer with a liquid solution. Method according to one of claims 1 to 7, wherein the generation of the planar emitter is carried out by means of a POCl ₃ gas phase diffusion and wherein the resulting phosphorus glass ( 23 ) is not removed prior to application of the etch barrier. Method according to one of claims 1 to 8, wherein the etching barrier is applied by means of a paste containing plastic. Method according to one of claims 1 to 9, wherein the etching barrier is applied by screen printing. Method according to one of claims 1 to 10, wherein the metal contacts be applied by screen printing. Silicon solar cell ( 1 ) with a selective emitter ( 5 ), wherein the silicon solar cell comprises: a solar cell substrate ( 13 ) with a flat emitter ( 5 at an emitter surface thereof; a dielectric layer ( 15 ); Emitter metal contacts ( 17 ) at the emitter surface; wherein the planar emitter ( 5 ) in the first subareas ( 7 ) has a higher surface doping concentration than in adjacent second subregions ( 9 ); wherein the solar cell substrate ( 21 ) in the first subsections ( 7 ) has a greater thickness than in the second subregions ( 9 ); and wherein the dielectric layer ( 15 ) covers substantially all of the emitter surface and is local between the emitter metal contacts ( 17 ) and the solar cell substrate ( 21 ) is arranged. Solar cell after. Claim 12, wherein the metal contacts ( 17 ) the dielectric layer ( 15 ) penetrate at least locally.