DE202016004837U1 - solar cell - Google Patents

Abstract

Solar cell (1), comprising a substrate (2), in particular a semiconductor substrate, which has a front side (3), a rear side (4) and at least one lateral edge (5), with a semiconductor contact layer (6) provided in the substrate (2) a first conductivity type, which extends at least over the front side (3) and one of the edges (5), and with a contact element (7), which is formed on the rear side (4) running close to the edge and which has a recombination shielding layer (8), which is designed to reduce and in particular prevent recombination with charge carriers of the semiconductor contact layer (6).

Description

FIELD OF THE INVENTION

The present invention relates to a solar cell.

TECHNICAL BACKGROUND

Solar cells have an emitter which is adjusted by targeted doping of the substrate of the solar cell.

In the formation of the emitter, which is diffused in the photovoltaic predominantly from the gas phase, a conductive doped layer is formed on all outer surfaces of the substrate or wafer. Alternatively, doping sources can also be applied to the wafer or the substrate.

During emitter formation, it is usually not possible to prevent part of the dopant from getting around the edge of the substrate and forming a so-called emitter grip. This can be done either already during the application of the doping source or at a subsequent high-temperature step. The emitter tip constitutes a conductive connection or a short circuit between a front side and a back side of the substrate, which leads to undesired recombination of charge carriers.

Thus, the solar cell can work effectively, it is therefore necessary to prevent this short circuit or remove it later.

The back of the solar cell is designed differently for different solar cell types. For example, aluminum BSF (BSF: back surface field) designates a solar cell design, wherein an aluminum layer is provided directly on the rear side of the semiconductor body. In the area of the layer boundary with silicon, an aluminum-silicon alloy is formed in the production during a fire process. Since aluminum is used as the p-dopant in silicon, a so-called back surface field (aluminum back-surface field or aluminum back-field) is formed by means of the recrystallized silicon with incorporated aluminum.

As another example, PERC (Passivated Emitter and Rear Cell) refers to a solar cell design in which the semiconductor body has a patterned passivation layer on the back side of the semiconductor body. This is intended to reduce recombination losses on the back side contact of the solar cell. The associated contact structure is arranged on the passivation layer and contacts the back surface of the semiconductor body in a local manner via the contact openings present in the passivation layer. Such a PERC solar cell is z. B. in the EN 20 2015 101 360 U1 described.

In the production of aluminum-BSF and PERC solar cells, an emitter embossment occurs at the lateral edges, in particular by a gas-phase emitter diffusion. A rear contact usually provided on the back side of the solar cells usually contains aluminum. At the edges of the solar cell thus metal-semiconductor contacts (Schottky contact) are formed, which lie directly on the emitter and handle can cause strong recombination. In order to prevent this, edge isolation is subsequently carried out in a wet-chemical etching bath, for example by means of hydrofluoric acid (HF) or nitric acid (HNO 3), the edge of the emitter being removed. However, the wet-chemical etching bath is costly in particular.

Another method for producing a solar cell while avoiding a short circuit without chemical etching is in DE 100 21 400 A1 described. Isolation is achieved here in a codiffusion by an Al-BSF formation between an n-doped emitter layer and a p-doped layer, so that a shunt is formed. Subsequently, the n-doped layer and the p-doped layer are each contacted from the outside. The disadvantage is that separate Kontaktierschritte are necessary here.

SUMMARY OF THE INVENTION

Against this background, the present invention has the object to provide an improved solar cell.

According to the invention, this object is achieved by a solar cell having the features of patent claim 1.

Accordingly, a solar cell is provided with a substrate having a front side, a rear side and at least one lateral edge, with a semiconductor contact layer of a first conductivity type provided in the substrate, which extends at least over the front side and one of the edges, and with a contact element, which is formed at the rear edge near the edge and which has a Rekombinationsabschirmschicht, which is adapted to reduce recombination with charge carriers of the semiconductor contact layer and in particular to prevent.

The idea on which the present invention is based is the strong recombination at the emitter handle by a circumferential one To prevent contact element on the back of the substrate, which has a recombination with charge carriers of the semiconductor contact layer-preventing formation. This is achieved in particular by the fact that the peripheral contact element provides a junction which permits no or at least only a very small recombination.

According to the invention, therefore, the edge insulation on the rear side is provided peripherally around the substrate surface or wafer surface via a contact element near the edge. In particular, in the case of a PERC solar cell in the region of the contact element, the passivating dielectric or the dielectric passivation layer is locally opened for this purpose. Advantageously, an insulation of the semiconductor contact layer is thus made possible simultaneously with the provision of the contact, which simplifies the production of the solar cell.

Another major advantage over an etched edge insulation is that according to the invention, the lateral edge of the substrate has a semiconductor contact layer, so that the lateral edge can also serve to generate electricity. In this way, advantageously, a short-circuit current of the solar cell and its efficiency can be improved. In particular, this effect is given when the edge is covered together with the front side with an antireflection layer, and thus also at the edge a good surface recombination speed is present.

Under a near-edge formation of the rotating contact element according to the invention is an education to understand, taking into account the manufacturing technology as close to the lateral edge of the substrate as possible, that is on the back as close to the edge runs.

Under a circumferential training in particular a closed circumferential training is to be understood, which is particularly adapted to the edge shape of the substrate.

Advantageous embodiments and further developments will become apparent from the other dependent claims and from the description with reference to the figures of the drawing.

According to a preferred embodiment, the circumferential contact element is designed to be electrically conductive. In this way, the contact element can advantageously be produced simultaneously with back contact, in particular by means of a screen printing process.

According to an advantageous embodiment, the circumferential contact element has a height of <100 μm growing out of the substrate. In particular, the height is <40 microns. In this way, small layer thicknesses of the contact element and thus a compact design of the solar cell are possible. Furthermore, the local molar ratio between the substrate and the material of the contact element can thus be adjusted.

Optionally or additionally, a minimum height of the revolving contact element can also be provided. For example, the circumferential contact element has a height of> 2 μm growing out of the substrate. In particular, the height is thus in a preferred embodiment between 2 microns and 40 microns.

According to a preferred embodiment, the peripheral contact element has a width in the range of 5 microns to 2 mm. Such a narrow formation provides for a local molar ratio between the material of the contact element and the substrate and / or the semiconductor contact layer, which advantageously favors the production of a formation preventing recombination with charge carriers of the semiconductor contact layer. The training can be carried out in particular in the course of a heat treatment or firing.

According to a preferred embodiment, the peripheral contact element extends at a distance in the range of 10 .mu.m to 3 mm from the edge. In particular, it runs continuously at this distance circumferentially along the edge. In this way, the largest possible area for back contact of the solar cell is advantageously provided in a region peripherally surrounded by the contact element.

According to one embodiment, a semiconductor contact layer of the first conductivity type is also provided on the rear side, from which the contact element is separated via the recombination preventing formation. The semiconductor contact layer provided on the rear side can either be provided under a passivation layer, in particular in the case of a PERC solar cell, and / or, in particular in the case of an Al-BSF solar cell, be provided in an intermediate region between a back contact or its aluminum back field and the contact element running around the edge , It may in particular be a remainder of the emitter handle.

According to an advantageous embodiment, the recombination preventing formation is formed as a doped region of a second conductivity type and has a transition to the Semiconductor contact layer of the first conductivity type. Advantageously avoided by the transition recombination.

According to one embodiment, the semiconductor contact layer of the first conductivity type is highly n-doped. The doped region of the second conductivity type is highly p-doped, so that the transition thus forms an n + / p + junction. Advantageously, the recombination, in particular without additional means, can be avoided in a very elegant manner.

In accordance with an advantageous embodiment, the semiconductor contact layer of the first conductivity type provided on the rear side is likewise highly n-doped. The p-doped region therefore has another junction which forms an n + / p + junction with the p-type semiconductor contact layer provided on the back side. In this way, recombination with the n-type semiconductor contact layer provided on the rear side is prevented at the rear side.

According to an advantageous embodiment, the separation is provided exclusively by the doped region of the second conductivity type. Advantageously, no additional measures for separation are necessary. The rear-side contact of the solar cell is preferably at least partially separated from the peripheral contact element, but locally provided bridges between the contact element and back contact are possible.

According to an advantageous embodiment, in addition to the doped region of the second conductivity type, the circumferential contact element is separated from the semiconductor contact layer of the first conductivity type provided on the rear side by a dielectric passivation layer. In particular, the passivation layer extends to the edge of the substrate and / or is locally opened in the region of the contact element in the form of a recess. Thus, the solar cell can be formed as a PERC solar cell, which advantageously increases their efficiency

According to an advantageous embodiment, the peripheral contact element contains a metal. According to a development, the metal comprises aluminum or an aluminum alloy. Advantageously, aluminum, which is the preferred p-dopant, for a comparatively inexpensive and easy to process, in particular by means of screen printing. On the other hand, aluminum is advantageously suitable for forming a rear field field or Al-BSF.

According to a preferred embodiment, the substrate contains silicon. The aluminum is at least partially provided with the silicon as aluminum-silicon alloy. The mixing takes place in particular in a fire process, if previously the aluminum in paste form, for example by screen printing, has been applied to the substrate. The formation of the aluminum-silicon alloy advantageously promotes the formation of an aluminum rear field or Al-BSF.

According to an advantageous development, an aluminum back side field is formed on an edge layer between the aluminum and the substrate, which forms the doped region of the second conductivity type. In particular, this is a p-doped region, preferably a highly p-doped region. In this way, a doped region of the second conductivity type can be produced in a particularly advantageous manner without additional manufacturing steps when the contact element is fired.

According to a preferred embodiment, an antireflection layer extending at least over the front and the edge is provided, which extends at the front side and the edge over the semiconductor contact layer of the first conductivity type. In this way, edge embracing of the antireflection layer can be advantageously exploited to improve the recombination shield through the doped region of the second conductivity type.

According to one embodiment, a rear-side contact of the solar cell is provided which has the contact element running around the edge of the edge. Preferably, the rear side contact and the contact element are formed as a continuous or common contact structure. If the rear-side contact comprises aluminum, a p-doped region in the form of a local aluminum rear-side field or back-surface field (BSF) can be formed at the edges of the rear side of the solar cell without additional effort. This results in an n + / p + junction, which does not permit strong recombination. In particular, this can be achieved by locally applied only a small volume, that is, in particular a small width and / or height of aluminum and thus the Rückseitenfeld- or BSF formation is favored.

In one embodiment, the backside contact is a printed contact structure. Unlike in the production of bifacial PERC solar cells, in which there is a local aluminum pressure in the form of fingers, it is here proposed to perform edge isolation via an edge-proximate or near-edge Al finger pressure circumferentially around the substrate or wafer surface. At PERC, the dielectric passivation layer would need to prepare for this fingerprint locally, in particular with a recess close to the edge, be opened.

The above embodiments and developments can, if appropriate, combine with each other as desired. Further possible refinements, developments and implementations of the invention also include combinations, not explicitly mentioned, of features of the invention described above or below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

CONTENT OF THE DRAWING

The present invention will be explained in more detail with reference to the exemplary embodiments indicated in the schematic figures of the drawing. It shows:

1 a schematic partial cross-sectional view in the region of the edge of a solar cell;

2 a schematic partial cross-sectional view of a solar cell according to another embodiment;

3 a schematic partial cross-sectional view of a solar cell according to yet another embodiment;

4 a rear view of a solar cell;

5 a rear view of a solar cell according to another embodiment;

6A -D process steps in the manufacture of a solar cell; and

7A -E process steps in manufacturing a solar cell according to another embodiment.

The accompanying figures of the drawing are intended to convey a further understanding of the embodiments of the invention. They illustrate embodiments and, together with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale to each other.

In the figures of the drawing are the same, functionally identical and same-acting elements, features and components - unless otherwise stated - each provided with the same reference numerals.

DESCRIPTION OF EMBODIMENTS

1 shows a schematic partial cross-sectional view in the region of the edge of a solar cell 1 ,

The solar cell 1 has a substrate 2 with a front side 3 , a back 4 and a side edge 5 on. Preferably, it is a silicon substrate 2 , in particular p-doped silicon substrate. The front 3 and the side edge 5 are with a semiconductor contact layer 6 , in particular an n-doped semiconductor contact layer provided. The semiconductor contact layer 6 extends over at least the entire front surface of the substrate 2 ,

At the back 4 the solar cell 1 is an electrically conductive contact element 7 intended. This has a recombination shielding layer 8th which is designed to recombine with charge carriers of the semiconductor contact layer 6 to avoid, preferably to prevent. The recombination shielding layer 8th is intended as a p-doped region.

In the illustrated embodiment, the contact element is 7 around an aluminum contact. The recombination shielding layer 8th is as aluminum back panel 13 formed, which represents a p-doped region.

In this way, between the semiconductor contact layer 6 and the aluminum back panel a transition 12 formed, which recombination with charge carriers of the semiconductor contact layer 6 prevented. In particular, the semiconductor contact layer 6 highly doped, so that together with a particular highly doped Al-BSF an n + / p + transition 12 is formed.

For example, it may be in the contact element 7 to act as part of a backside contact. In particular, the contact element 7 together with a rear side contact, not shown here 15 educated. Accordingly, the backside contacting 15 preferably a same material, in particular aluminum.

The contact element 7 is on the back 4 close to the edges running along the lateral edge 5 of the substrate 2 educated. It has one out of the substrate 2 growing height 9 which is smaller than 100 μm, preferably smaller than 40 μm.

A width of the contact element is between 5 microns and 2 mm. In this way, it is possible to provide locally only a small volume of aluminum and so in the production of the solar cell, in particular in producing the back contact, to favor the formation of a back field. In particular, this is realized in the form of pastes applied in paste form by the so-called firing. Here, the aluminum is melted, so that in contact areas with the substrate, an aluminum-silicon alloy is formed. This causes a boundary region between the aluminum-silicon alloy and the substrate 2 a doping of the silicon material of the substrate 2 takes place and thus an aluminum back panel is formed.

2 shows a schematic partial cross-sectional view of a solar cell 1 according to a further embodiment.

In addition to the semiconductor contact layer 6 Here's a look over the front 3 and the side edge 5 extending antireflection coating 11 provided, which is designed in particular as a silicon nitride layer (SiN _x ). The antireflection coating 11 extends, as does the semiconductor contact layer 6 , over the side edge 5 away to the contact element 7 , In this way, the efficiency of the solar cell becomes advantageous 1 increased, since the Kantenumgriff the emitter, ie the semiconductor contact layer 6 , and the antireflection coating 11 Here also for power generation and performance can be used. In this case, a Rekombinationsabschirmung by the p-doped region in the same manner as in relation to 1 described provided.

This is the solar cell shown here 1 around an aluminum back field or Al-BSF solar cell. Accordingly, the backside is apart from the area of the contact element 7 , over the entire surface with a back contact 15 made of aluminum. At the boundary layer between the backside contact 15 and the substrate 2 is a cross over the area of backside contact 15 extending aluminum back panel 16 educated.

3 shows a schematic partial cross-sectional view of a solar cell 1 according to yet another embodiment.

In contrast to the embodiment according to 2 this is a PERC solar cell. Accordingly, a passivation layer 10 at the back 4 intended. Between the passivation layer 10 and the substrate 2 is on the back of a large area an n-doped semiconductor contact layer 6 ' intended.

For the production of the contact element 7 is the passivation layer 10 in an area near the lateral edge 5 with a recess 17 Mistake. This can be produced in the production, for example by means of laser ablation.

The contact element 7 can in the production of the solar cell 1 , For example, in the form of an aluminum paste, on the passivation layer 10 applied and then fired. In the area of the recess 17 During firing, the contact element is formed 7 with the p-doped region in the form of a local aluminum back surface field 13 out.

Due to the fact that here in addition to the Emitterumgriff also on the back 4 a semiconductor contact layer 6 ' is provided, here is also an additional transition 14 to the backside semiconductor contact layer 6 intended. In particular, the semiconductor contact layer 6 ' also heavily doped, so that together with the particular highly doped Al-BSF an n + / p + transition 14 is formed.

4 shows a rear view of a solar cell 1 ,

The solar cell 1 is laterally through the side edge 5 limited. From the front not shown here via the side edge 5 encompassing is the semiconductor contact layer 6 intended.

A recombination shield is through the contact element 7 provided, which edges close to the edge on the back side shown here 4 is trained. The contact element 7 is in the embodiment shown here by a circumferential trench 18 from the backside contact 15 separated.

5 shows a rear view of a solar cell according to another embodiment.

In contrast to the embodiment according to 4 is the contact element 7 here from the back side contact 15 not cut off, but over in the ditch area 18 provided bridge sections 19 connected. For example, shows 3 the area of such a bridge section 19 in cross section, which is the contact element 7 continuous back contact 15 is recognizable.

The 6A -D show process steps in the manufacture of a solar cell.

6A shows the deployment substrate 2 , This is preferably a p-type silicon substrate.

6B shows the production of a semiconductor contact layer 6 in the form of a highly doped n + layer by emitter diffusion. For example, gas phase diffusion is performed with phosphorus oxychloride (POCl ₃ ) to produce a highly n-doped surface, ie, an n + layer.

6C shows a step of applying a backside contact 15 ,

Before applying the rear side contact, an antireflection layer (not shown here for clarity) can be used 11 be applied to the n + layer.

For example, the backside contact 15 in the form of a paste-like contact material 20 applied, preferably printed. For example, a screen printing process is used. The contact material is preferably aluminum.

Further, from the backside contact 15 separated the contact material 20 , in particular also in the form of aluminum paste 20 , For the production of the edge near the edge contact element 7 applied. This can also be printed, preferably simultaneously.

A screen-printing mask for producing such a solar cell has an embodiment which makes it possible to produce a contact element running around the edge of the edge. In particular, in one embodiment, a frame-like structure which can be positioned close to the edge for the edge region of a solar cell is provided on the screen-printing mask. According to one embodiment, the frame-like structure is preferably separated from the structure provided for the rear-side contacting, in particular at least partially or completely separated.

6D shows the from the state according to 6C by firing the backside contact 15 and the contact element 7 produced solar cell 1 ,

It is in particular a solar cell 1 according to 2 , wherein the antireflection coating 11 not shown here for clarity.

The 7A -E show process steps in manufacturing a solar cell according to another embodiment.

In the same way as the 6A and 6B show the 7A and 7B the provision of the substrate 2 and the production of a semiconductor contact layer 6 by emitter diffusion.

7C shows the application of a passivation layer 10 at the back 4 , where near-edge recesses 17 into the passivation layer 10 be introduced.

In one embodiment, in a central area of the back 4 between the near-edge recesses 17 further recesses are provided, which are not shown here for clarity.

7D shows the application of a paste-like contact material 20 , in particular an aluminum paste, for producing the rear-side contacting 15 , The contact material 20 extends over the recesses 17 time.

7E shows the from the state according to 7D by firing the backside contact 15 and the contact element 7 converted solar cell 1 ,

LIST OF REFERENCE NUMBERS

1

solar cell

2

substratum

3

front

4

back

5

edge

6

Semiconductor contact layer

6 '

Semiconductor contact layer

7

contact element

8th

Rekombinationsabschirmschicht

9

height

10

passivation

11

Antireflection coating

12

crossing

13

Aluminum back surface field

14

crossing

15

Back contact

16

Aluminum back surface field

17

recess

18

dig

19

bridge section

20

Contact material

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

• DE 202015101360 U1 [0007]
• DE 10021400 A1 [0009]

Claims (16)

Solar cell ( 1 ), with a substrate ( 2 ), in particular a semiconductor substrate, which has a front side ( 3 ), a back ( 4 ) and at least one lateral edge ( 5 ) with one in the substrate ( 2 ) semiconductor contact layer ( 6 ) of a first conductivity type, which at least over the front ( 3 ) and one of the edges ( 5 ) and with a contact element ( 7 ), which at the back ( 4 ) is formed circumferentially close to the edge and which a Rekombinationsabschirmschicht ( 8th ) which is designed to facilitate recombination with charge carriers of the semiconductor contact layer ( 6 ) and in particular to prevent it. Solar cell according to claim 1, characterized in that the contact element ( 7 ) is electrically conductive. Solar cell according to one of the preceding claims, characterized in that the contact element ( 7 ) relative to a surface of the substrate ( 2 ) growing height ( 9 ) of less than 100 microns, in particular less than 40 microns. Solar cell according to one of the preceding claims, characterized in that the contact element ( 7 ) has a lateral width in the range of 5 microns to 2 mm. Solar cell according to one of the preceding claims, characterized in that the contact element, preferably continuously, at a distance in the range of 10 microns to 3 mm to the edge ( 5 ) is arranged. Solar cell according to one of the preceding claims, characterized in that on the rear side ( 4 ) a semiconductor contact layer ( 6 ' ) of the first conductivity type, from which the contact element ( 4 ) via the recombination shielding layer ( 8th ) is disconnected. Solar cell according to one of the preceding claims, characterized in that the recombination screening layer ( 8th ) is formed as a doped region of a second conductivity type and a transition ( 12 ) to the semiconductor contact layer ( 6 ) of the first conductivity type. Solar cell according to one of the preceding claims, characterized in that the semiconductor contact layer ( 6 ) of the first conductivity type is highly n-doped, that the doped region of the second conductivity type is highly p-doped and that the transition ( 12 ) forms an n + / p + transition. Solar cell according to claim 8, characterized in that the at the back ( 4 ) provided semiconductor contact layer ( 6 ' ) of the first conductivity type is highly n-doped and that the p-doped region forms a further transition ( 14 ) having an n + / p + transition to the n-type semiconductor contact layer ( 6 ' ) trains. Solar cell according to one of claims 7 to 9, characterized in that the separation is provided exclusively by the doped region of the second conductivity type. Solar cell according to one of claims 7 to 10, characterized in that the peripheral contact element ( 7 ) in addition to the doped region of the second conductivity type through a dielectric passivation layer ( 10 ) from the one on the back ( 4 ) semiconductor contact layer ( 6 ' ) of the first conductivity type is separated. Solar cell according to one of the preceding claims, characterized in that the contact element ( 7 ) contains a metal, in particular aluminum or an aluminum alloy. Solar cell according to claim 12, characterized in that the substrate ( 2 ) is a semiconductor substrate and contains silicon and that the aluminum is provided at least partially mixed with the silicon as aluminum-silicon alloy. Solar cell according to claim 13, characterized in that at an edge layer between the aluminum and the substrate ( 2 ) an aluminum back panel ( 13 ) is formed, which forms the doped region of the second conductivity type. Solar cell according to one of the preceding claims, characterized in that at least over the front ( 3 ) and the edge ( 5 ) extending antireflection coating ( 11 ) is provided, which at the front ( 3 ) and the edge ( 5 ) over the semiconductor contact layer ( 6 ) of the first conductivity type. Solar cell according to one of the preceding claims, characterized in that a backside contact ( 15 ) of the solar cell ( 1 ) is provided, which the edge near the edge formed contact element ( 7 ) having.

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