WO2012103888A1

WO2012103888A1 - Method for producing a crystalline silicon solar cell avoiding unwanted metal deposits

Info

Publication number: WO2012103888A1
Application number: PCT/DE2012/100024
Authority: WO
Inventors: Werner Saule
Original assignee: Rena Gmbh
Priority date: 2011-02-03
Filing date: 2012-02-03
Publication date: 2012-08-09
Also published as: DE102011010306A1; TW201236188A

Abstract

The invention relates to a method for producing a crystalline silicon solar cell, wherein for the purpose of forming an emitter (52) on a first side of a silicon substrate (50) doping agent is diffused (10) into the silicon substrate, next a silicon nitride layer (56) is deposited (16) on the first side of the silicon substrate (50), next local openings (58) are introduced into the silicon nitride layer (56) on the first side of the silicon substrate (50), next metal contacts (60) are formed (20) in the openings (58) by means of plating (20), wherein before the deposition (16) of the silicon nitride layer (56) the emitter (52) is partially etched back (12) on the first side of the silicon substrate (50) and next before the deposition (16) of the silicon nitride layer (56) a silicon oxide layer (54) having a thickness of 1.0 nm to 10 nm is formed (14) on the first side of the silicon substrate (50).

Description

Process for producing a crystalline silicon solar cell while avoiding unwanted metal deposits

The invention relates to a process for preparing a crystalline silicon solar cell according to the preamble of claim 1. and a made by this method Solarzel ^¬ le.

From the international patent application WO 2008/039067 A2 it is known to wet-chemically oxidize the surface of a silicon substrate prior to the deposition of a silicon nitride layer as a dielectric layer. This serves to improve the surface passivation in solar cells with screen printed contacts. Another possibility for the formation of metal contacts for solar cells is locally form openings in the dielectric layers, which are arranged on a surface of a used Sili ^¬ ziumssubstrats. In these Öffnun ^¬ gen metal is deposited by plating in addition. It has been found that during plating, whether electroplating or electroless plating, metal is also partly deposited on unopened regions of the dielectric layer, for example on unopened regions of a silicon nitride layer. Such unwanted metal deposits are often referred to as "ghost deposits" or

They are therefore undesirable since they lead to additional shading losses and impair the efficiency of the solar cell. Against this background, the object of the present invention is to provide a method of the generic type with which the formation of ghosts - deposits can be avoided without reducing the efficiency of the finished solar cell.

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

Furthermore, the invention is based on the object to provide such a ^¬ larzelle formed by plating with contacts without ghost deposits are available.

This object is achieved by a solar cell having the ^features of claim 12.

Advantageous developments are each the subject of dependent subclaims.

The inventive method provides for the ren einzudiffundie- forming an emitter on a first side of a silicon ^¬ substrate dopant into the silicon substrate for the purpose from ^¬, subsequently deposit a silicon nitride layer at least on the first side of the silicon substrate, then locally on the first side of the silicon substrate Introduce openings in the silicon nitride layer and then form in the openings by means of plating metal contacts. Prior to depositing the silicon nitride layer, the emitter on the first side of the silicon substrate is partially etched back. Thereafter, but prior to depositing the silicon nitride layer, a silicon oxide layer ^¬ is formed with a thickness in the range of 1.0 nm to 10 nm on the first side of the silicon substrate.

It has been found that in this way ghost deposits can be avoided and thus solar cells with reduced shading losses can be produced. The formation of the emitter described is not notwendi ^¬ gerweise limited to the first side of the silicon substrate, but may also take place on other sites of the silicon substrate. The deposition of the silicon nitride layer, the formation of the silicon oxide ^¬ layer as well as the etching back of the emitter are also not necessarily limited to the first side of the silicon substrate. Under plating in the present sense, is a Elektroplattie- ren, which is sometimes also referred to as electro-deposition or electroplating, or means a electroless plating, which is sometimes referred to as chemical Me ^¬ tallabscheidung or electroless plating. A metal contact in the present sense is a contact formed from one or more metals or one or more metal alloys.

The openings are preferably introduced into the silicon nitride layer by means of laser ablation. Advantageously, ei ^¬ ne hydrogen-containing silicon nitride layer is deposited on the first side of the silicon substrate. In this way, in the course of solar cell production, hydrogen can be diffused from the silicon nitride layer to passivate defects into the silicon substrate. This is particularly advantageous when using multicrystalline silicon substrates. Due to the small thickness of the silicon oxide layer formed prior to the deposition of the silicon nitride layer, the diffusion of hydrogen from the silicon nitride layer into the silicon substrate is not hindered to a relevant extent by the silicon oxide layer.

Preferably, the metal contacts are formed in the openings by electroplating. In this embodiment the invention has a particularly advantageous effect, since ghost deposits occur to a greater extent in electroplating than in electroless plating. It has proven to be advantageous to zer etch back the emitter zen. Preferably, it is etched back in an etching solution comprising hydrofluoric acid and nitric acid or hydrofluoric acid and ozone. In an advantageous embodiment variant of the method, the etch-back of the emitter increases its layer ^resistance value by 10 Ω / sq to 50 Ω / sq. When using a mul ^¬ tikristallinen silicon substrate, a ceiling for whose sheet resistance value of 90 Ω has / sq proven in practice after the etching back of the emitter. Be monokri ^¬ stalline silicon substrates used, this can limit maximum ^¬ higher.

The silicon oxide layer is preferably formed by means of a wet-chemical oxidation. This can be done, for example, in a solution comprising ozone, hydrogen peroxide or nitric acid. Particularly preferably, the silicon oxide ^¬ layer is formed in an oxidation solution of deionized water and dissolved ozone therein.

In an alternative embodiment variant, the silicon oxide ^layer can be formed by means of a gas phase oxidation. Preferably, this takes place in an ozone-containing gas atmospheres ^¬ sphere. Advantageously, this is energetically excited, for example by irradiation of electromagnetic radiation, preferably of ultraviolet light.

In practice, it has been found useful to form the silicon oxide layer in a thickness in the range of 2 nm to 3 nm. Advantageously, in the silicon nitride layer is introduced into the openings, the silicon oxide layer is locally removed ^¬ ent. Again, this can be effected by means Laserabiation and particularly preferably in the same Laserabiationsschritt in which the openings are ^¬ into the silicon nitride layer.

According to a further development of the method, the openings are introduced into the silicon nitride layer by means of laser ablation and, in this case, emitter regions which are doped more heavily by laser diffusion are formed in regions of the openings. Under a La ^¬ serdiffusion is understood to mean that the silicon substrate by means of laser radiation which is already irradiated for Laserabiation, is locally heated so that it comes to a rearrangement of the dopant into the areas of the openings, an emitter profile is thus changed locally. Under such a rearrangement of dopant also falls the activation of electrically inactive dopant. By means of such a laser diffusion locally stronger doped emitter regions and thus a so-called selective emitter can be formed in regions of the openings.

In the practical implementation of the laser ablation have, both in conjunction with homogeneous and selective emitters, laser-induced chemical processes, sometimes referred to as laser chemical processing, proven; For example, a laser-induced chemical etching, which is sometimes referred to as laser chemical etching. Alternatively, the laser ablation can also be realized by means of laser beam evaporation, which, like the laser-induced chemical processes, enables laser diffusion for the purpose of forming a selective emitter. If a selective emitter is formed in the manner described, a stronger diffusion can be used to form the emitter on the first side of the silicon substrate. This facilitates on the one hand the process management on the other hand can be gettered in a greater diffusion of dopant into the silicon substrate impurities present bes ^¬ Ser, which has an advantageous effect ^¬ degree affects the the finished solar cell. For completeness, it should be mentioned that in the case of a selective emitter more do ^¬-oriented emitter regions may exceed the above-mentioned advantageous limits for emitter sheet resistance values off. Higher sheet resistance values in these areas can have an advantageous effect on the efficiency of manufactured solar cells.

Furthermore, the invention will be explained in more detail with reference to figures. Show it:

Figure 1 is a schematic representation of a first embodiment ^¬ example of the method ^{according to} the invention

Figure 2 is a schematic representation of a second embodiment ^¬ example of the method ^{according to} the invention Figure 1 shows an embodiment of the invention

Process. In this first dopant is diffused into a Sili ^¬ ziumsubstrat 50 and 10 formed an emitter 52 in this manner. In the present exemplary embodiment, the dopant is merely diffused into the upper side of the solar cell substrate 50. This can be done in a manner known per se, for example by diffusion of dopant from a top surface of the silicon substrate 50. th, dopant-containing solution. The dopant used is matched to the volume doping of the silicon substrate 50. In principle, both an n-doped and a p-doped emitter can be formed. Furthermore, it is fundamentally possible to diffuse dopant not only into the upper side of the silicon substrate, but into the entire surface. In this case would be appropriate level ^¬ measures must be taken to countries to prevent a short circuit between the emitter 52 and a subsequently applied back contact 62nd

In the further course of the process, the emitter 52 is partially etched back. In the present exemplary embodiment, this is carried out wet-chemically in a solution containing hydrofluoric acid and nitric acid.

In addition, the silicon substrate 50 is dipped for the purpose of forming ^¬ From 14 of a silicon oxide layer 54 in deionized What ^¬ ser, in which ozone is dissolved. In this way, a wet-chemical oxidation of the entire surface of the silicon substrate 50 takes place.

In addition, a hydrogen-containing silicon nitride layer is deposited 16. This is usually done by means of a chemical vapor deposition (CVD) deposition. The downwardly facing rear side of the silicon substrate 50 in the representation of FIG. 1 is kept free of the silicon nitride layer 56. This can be done for example, by the silicon substrates in pairs placed back to back in a used coating system or by the back print ^¬ te is placed on a boat to the plant, which is inserted into the ver ^¬ applied coating system. In the further course of the process, local openings 58 are introduced into the silicon nitride layer 56 on the first side of the silicon substrate 50, in the present exemplary embodiment thus on the upper side of the silicon substrate 50. This takes place in the illustrated exemplary embodiment by means of laser ablation. In this embodiment, the silicon oxide layer 54 is also locally removed in the openings 58.

Finally, front side contacts 60 are formed in the openings 58 by means of electroplates 20. In these han ^¬ it delt are metal contacts, which have, for example, nickel, and silver or nickel, copper and silver. In the context of the electroplating 20, the rear side contact 62 is additionally formed on the rear side of the silicon substrate 50. This therefore consists of the same material as the front ^¬ side contacts 60th

The illustration of a known process steps for forming of back panels, so-called back surface fields have been omitted in Figure 1 for reasons of clarity ^¬ friendliness. However, corresponding, known per se procedural ^¬ Rensch rode can be integrated easily.

In addition to the last method step of electroplating 20, the lowermost partial illustration in FIG. 1 also illustrates an exemplary embodiment of the solar cell according to the invention.

The embodiment of Figure 2 differs from that of Figure 1 in that the local introduction 28 of openings 58 in the silicon nitride layer 56 and a laser diffusion takes place 28. Here, in regions of the openings 58 more heavily doped emitter regions 64 are formed, which together with the remaining areas of the emitter 52 form a selective emitter. As in the case of the 1 of the game, the laser ablation, and in conjunction with the laser diffusion, can be realized by means of laser-induced chemical etching. Instead of a laserinduzier ^¬ th chemical etching can find reindeer using a Laserstrahlverdampfungsverfah-.

The bottom part shown in Figure 2 illustrates schematically ^¬ table next to the last step of Elektroplattie- Rens 20 also another embodiment of the invention the solar cell of invention.

Reference sign list

10 indiffusion dopant

12 etch etch emitter

14 forming silicon oxide layer

16 silicon nitride deposition

18 inserting openings

20 electroplating

28 introducing openings and laser diffusion

50 silicon substrate

52 emitters

54 silicon oxide layer

56 silicon nitride layer

58 opening

60 front side contact

62 back contact

64 more heavily doped emitter region

Claims

claims

A process for producing a crystalline silicon solar cell, in which

- for the purpose of forming an emitter (52) on a first side of a silicon substrate (50) dopant is diffused into the silicon substrate (50) (10);

- Subsequently, a silicon nitride layer (56) on the first ^¬ th side of the silicon substrate (50) is deposited (16);

- Subsequently, on the first side of the silicon substrate (50) locally openings (58) are introduced into the silicon nitride layer (56);

- subsequently in the openings (58) by means of plating

(20) metal contacts (60) are formed (20); characterized ,

that

- prior to depositing (16) the silicon nitride layer (56), the emitter (52) on the first side of the silicon substrate (50) is partially etched back (12);

- Before the deposition (16) of the silicon nitride ^¬ layer (56) on the first side of the silicon substrate (50) is subsequently formed a silicon oxide layer (54) having a thickness in the range of 1.0 nm to 10 nm (14).

2. The method according to claim 1,

characterized ,

that the metal contacts (60) in the openings (58) by means of

Electroplating (20) are formed (20).

3. Method according to one of the preceding claims,

characterized ,

that by the diffusion (10) of dopant into the Si a substrate (50), an emitter (52) with a sheet resistance value in the range of 50 Ω / sq to 70 Ω / sq is ^{ausgebil ¬} det.

4. Method according to one of the preceding claims,

characterized ,

that the emitter (52) is etched back wet-chemically (12).

5. Method according to one of the preceding claims,

characterized ,

in that the etch resistance (12) of the emitter (52) increases its sheet resistance value by 10 Ω / sq to 50 Ω / sq.

6. The method according to any one of the preceding claims,

characterized ,

the silicon oxide layer (54) is formed by means of a nasschemi ^¬ rule oxidation (14).

7. The method according to any one of the preceding claims,

characterized ,

the silicon oxide layer is formed by means of a gas phase oxidation.

8. The method according to any one of the preceding claims,

characterized ,

the silicon oxide layer (54) is formed in a thickness in the range of 2 nm to 3 nm (14).

9. The method according to any one of the preceding claims,

characterized ,

the silicon oxide layer (54) lo ^¬ kal is removed in the openings (58), preferably by means Laserabiation.

10. The method according to one of the preceding claims, d a d u r c h e c e n e c e n e,

a hydrogen-containing silicon nitride layer (56) is deposited (16).

11. The method according to any one of the preceding claims,

characterized ,

be that the openings (58) are introduced by means Laserabiation in the Sili ^¬ ziumnitridschicht (54) (28) while in the areas of the openings by laser diffusion (58) more heavily doped emitter regions (62) formed (28).

12. Solar cell produced by the method according to one of claims 1 to 11.