DE102010006681A1 - Method for manufacturing tandem-junction photovoltaic cell of photovoltaic module to convert radiation energy in light into electrical power, involves exposing area of oxide layer to cleaning process that increases mirror layer adhesion - Google Patents

Abstract

The method involves providing a photoactive layer stack (3b) having an n-doped layer (33b), a p-doped layer (31b) and an intrinsic layer (32b). A back contact (4) having a transparent conductive oxide (TCO) layer (4a) and a mirror layer (4b) is applied on the photoactive layer stack, where the TCO layer is made of zinc oxide. A surface area of the TCO layer is exposed to a cleaning process e.g. ion sputtering process and ion etching process, before the mirror layer is applied on the TCO layer, where the cleaning process increases adhesion of the mirror layer on the TCO layer. An independent claim is also included for a photovoltaic cell comprising a photoactive layer stack.

Description

The invention relates to a photovoltaic cell, a photovoltaic module comprising a plurality of such photovoltaic cells, a method for producing such a photovoltaic cell and a method for producing a photovoltaic module comprising a plurality of photovoltaic cells.

Photovoltaic cells may be formed as so-called tandem junction photovoltaic cells, each having a photovoltaic cell comprising optically and electrically coupled in series substantially amorphous silicon and a photovoltaic cell comprising substantially microcrystalline silicon. Photovoltaic cells use the photovoltaic effect to convert radiant energy contained in light into electrical energy.

Photovoltaic modules typically comprise a plurality of photovoltaic cells electrically coupled to one another. In order to protect the individual photovoltaic cells from damage and environmental influences, they are arranged between two substrates, for example glass panes. The glass panes represent an encapsulation for the photovoltaic cells.

For electrical contacting of the photovoltaic cells usually find a front-side contact and a backside contact use, wherein the back contact can be composed of a plurality of layers. For adhesion of the individual layers of the rear side contact with one another usually finds an adhesion-promoting layer using, for example, has chromium. However, chromium has radiation-absorbing properties, which reduces the efficiency of such photovoltaic cells and photovoltaic modules.

It is desirable to provide a photovoltaic cell, a photovoltaic module and in each case methods for their production, which are characterized by increased efficiency and at the same time by a necessary adhesive strength.

These objects are achieved inter alia by a production method of a photovoltaic cell having the features of claim 1, a method of producing a photovoltaic module having the features of claim 10, a photovoltaic cell having the features of claim 11 and a photovoltaic module having the features of claim 15. Advantageous embodiments and preferred developments of the manufacturing method, the photovoltaic module and the photovoltaic cell are the subject of the dependent claims.

• – Bereitstellen zumindest eines photoaktiven Schichtstapels, der zumindest eine n-dotierte Schicht, eine p-dotierte Schicht und eine intrinsische Schicht aufweist,
• – Aufbringen eines Rückseitenkontakts auf dem photoaktiven Schichtstapel, der eine TCO-Schicht und eine Spiegelschicht umfasst, wobei
• – vor Aufbringen der Spiegelschicht auf der TCO-Schicht die Oberfläche der TCO-Schicht einem Reinigungsprozess unterzogen wird.

A method for producing a photovoltaic cell comprises in one embodiment the following method steps:

• Providing at least one photoactive layer stack comprising at least one n-doped layer, one p-doped layer and one intrinsic layer,
• - Applying a backside contact on the photoactive layer stack comprising a TCO layer and a mirror layer, wherein
• - Before applying the mirror layer on the TCO layer, the surface of the TCO layer is subjected to a cleaning process.

In the context of the present application, an intrinsic layer is to be understood as meaning a layer which is substantially undoped. Foreign substances, such as, for example, impurities in the layer, are not regarded as doping in the context of the application.

A TCO layer is in particular a layer comprising a transparent conductive oxide.

The cleaning process of the surface of the TCO layer advantageously increases the adhesion of the mirror layer deposited on the TCO layer, as a result of which deposition of the mirror layer directly on the TCO layer is possible. The use of an adhesion-promoting layer, for example of chromium, which can disadvantageously lead to a radiation absorption in this layer, is thus not necessary, as a result of which the optical properties are improved. For example, a high reflection effect of the backside contact is made possible, which advantageously increases the efficiency of such a photovoltaic cell.

By virtue of such a method, which comprises a cleaning process of the surface of the TCO layer, it is thus possible to produce a highly reflective and well adhering backside contact without requiring absorbent adhesion-promoting layers, such as, for example, chromium-containing layers. This leads to significantly higher efficiencies of up to 0.5% absolute.

In one embodiment, the cleaning process includes, inter alia, the use of an Ar plasma or other noble gas plasma. For example, the stoichiometry is influenced by means of an O ₂ plasma, an N-plasma or an Ar plasma, and the surface of the TCO layer is cleaned and activated.

In one embodiment, the cleaning process cleans and activates the surface of the TCO layer. As a result, the adhesion of the subsequently deposited on the TCO layer is advantageously Increased mirror layer, which makes the use of a chromium-containing layer as a primer layer superfluous.

In a further embodiment, the cleaning process of the TCO layer increases the adhesion of the subsequently applied mirror layer. In addition, the cleaning process preferably increases the reflectivity of the mirror layer.

In another embodiment, the cleaning process is an ion-assisted cleaning process.

Preferably, the TCO layer is deposited on the photoactive layer stack. Subsequently, the TCO surface is subjected to the ion-assisted cleaning process, whereby the surface of the TCO layer is cleaned and activated. Subsequently, the mirror layer is deposited on the cleaned surface of the TCO layer, which increases the adhesion of the deposited mirror layer by the cleaning process, whereby advantageously the use of an adhesion-promoting layer is not necessary.

In a further embodiment, the cleaning process is an ion sputtering process and / or an ion etching process.

For example, the ion sputtering process is carried out by means of a linear ion source in a vacuum. As a result, the necessary adhesive strength for the further process steps in the encapsulation process is advantageously ensured.

In another embodiment, the TCO layer is a zinc oxide layer (ZnO layer) deposited on the photoactive layer stack. Preferably, the mirror layer is a layer comprising silver or a silver alloy deposited on the TCO layer treated by the cleaning process. By way of example, the mirror layer comprises Mo, Al, Ti, TiO _x or other metals which have a high reflectivity.

In a further embodiment, the photoactive layer stack is provided on a further photoactive layer stack so that the further photoactive layer stack is arranged on the side of the photoactive layer stack opposite from the back side contact. Preferably, the further photoactive layer stack has at least one further n-doped layer, a further p-doped layer and a further intrinsic layer. Preferably, the further photoactive layer stack is arranged on a substrate.

In another embodiment, the photoactive layer stacks are encapsulated with a back cover to protect the layer stacks from damage and environmental influences. For example, for this purpose, find a cover made of glass, a multilayer film, a composite film of, for example, Tedlar, Al and PET (PET: polyethylene terephthalate) or the like, using EVA (EVA: ethylene vinyl acetate), PVB (PVB: Polyvenylbutyral) or a other thermoplastic is laminated.

Optionally, additional layers may be disposed between the back contact and the back cover. For example, a nickel vanadium layer can be used.

A method of manufacturing a photovoltaic module comprising a plurality of photovoltaic cells includes a common method of manufacturing the plurality of photovoltaic cells. The individual photovoltaic cells of the photovoltaic module are preferably produced in a so-called common composite.

In particular, the method for producing a photovoltaic module comprises the method steps explained for producing a photovoltaic cell, in particular any features and embodiments of the method for producing a photovoltaic cell, wherein the photovoltaic cells of the photovoltaic module are produced in a common method.

In one embodiment of the production method of the photovoltaic module, the individual layers of the photovoltaic cells are deposited over a large area on a common substrate, wherein after each deposition process, a structuring method is used to structure the large-area deposited layers in photovoltaic cells. The structuring methods preferably each comprise a laser structuring method.

For example, a front-side contact is deposited on the substrate and then patterned according to the intended photovoltaic cells. On the structured front side contact, the first and second photoactive layer stacks are deposited and patterned according to the photovoltaic cells predetermined by the structured TCO layer. The TCO layer of the rear-side contact is deposited on the layer stacks, the surface of the TCO layer being subjected to a cleaning process after application. Subsequently, the mirror layer is deposited on the aftertreated TCO layer. Optionally, a nickel vanadium layer can subsequently be deposited on the mirror layer. Subsequently, the layers of the Rear contact structured according to the given photovoltaic cells.

A photovoltaic cell according to the present application comprises at least a first photoactive layer stack comprising at least one n-doped layer, one p-doped layer and one intrinsic layer. On the n-doped layer of the second layer stack, a backside contact is arranged, which consists of a TCO layer and a mirror layer.

The back contact therefore has no, as commonly used adhesion promoting layer, for example, a chromium-containing layer on. Preferably, the back contact has a high reflectivity, whereby a high efficiency of the photovoltaic cell can be achieved. In particular, the absorption of radiation in the usually used adhesion-promoting layer is avoided by such a backside contact, which results in a significantly higher efficiency of up to 0.5% absolute with advantage.

In one embodiment, the backside contact does not include an adhesion promoting layer, thereby avoiding absorption losses in that layer.

In a further embodiment, the photovoltaic cell is a thin-film photovoltaic cell.

Thin-film photovoltaic cells represent a balanced and thus cost-effective variant of such photovoltaic cells with regard to their efficiency in the conversion of radiant energy into electrical energy and the production costs.

In a further embodiment, the photovoltaic cell comprises a further photoactive layer stack which has at least one further n-doped layer, a further p-doped layer and a further intrinsic layer, wherein the further layer stack is arranged on the side of the photoactive layer stack opposite from the rear contact ,

In one embodiment, the photovoltaic cell comprises a plurality of stacked layers, each having at least one n-doped layer, one p-doped layer and one intrinsic layer. Preferably, the photovoltaic cell comprises three stacked layers arranged one above the other.

In particular, the photovoltaic cell comprises any features and embodiments as well as any combination of features that are indicated with regard to the method for producing a photovoltaic cell.

A photovoltaic module according to the present application comprises a plurality of photovoltaic cells electrically coupled in series.

In particular, a photovoltaic module comprises any features and embodiments as well as any combination of features that are specified with regard to the photovoltaic cell and / or the method for producing a photovoltaic cell or a photovoltaic module.

In one embodiment, the photovoltaic module is designed as a frameless thin-film photovoltaic module.

The invention will be explained in more detail using exemplary embodiments with reference to the drawings. Further advantages, advantageous embodiments and developments of the invention will become apparent from the following in connection with the 1 to 3 described embodiments.

In the drawings show:

1a a schematic cross section of a photovoltaic cell according to an embodiment of the invention,

1b a schematic cross section of a photovoltaic cell according to another embodiment of the invention,

2 a schematic representation of a photovoltaic module according to an embodiment of the invention in a plan view, and

3 a flowchart for a method of manufacturing a photovoltaic cell according to an embodiment of the invention.

In the exemplary embodiments and figures, identical or identically acting components may each be provided with the same reference numerals. The illustrated elements and their proportions with each other are basically not to be regarded as true to scale, but individual elements, such as layers, cells, modules and areas, for better representability and / or better understanding exaggerated be shown thick or large.

1a shows a schematic representation of a photovoltaic cell 100 according to a first embodiment.

The photovoltaic cell 100 includes a substrate 1a on which a front side contact 2 out a transparent conductive oxide (TCO) is applied. On the front side contact 2 are preferably a first photoactive layer stack 3a and second photoactive layer stack 3b arranged, each in the finished photovoltaic cell 100 are suitable for light passing through the substrate 1a and the front side contact 2 falls to absorb to form pairs of electron holes and thereby generate an electric current.

On the second photoactive layer stack 3b is a backside contact 4 arranged. On the backside contact 4 is a cover 1b applied for encapsulation of the layer stack and the contacts. In particular, the cover protects 1b the layer stacks 3a . 3b and the contacts from damage and environmental influences.

The substrate 1a is set up, the first and second layer stack 3a . 3b to wear. The substrate 1a is especially transparent to radiation in the visible and infrared regions and has transparent properties in a wavelength range from 400 nm to 1100 nm. The substrate 1a includes, for example, glass, in particular low-iron flat glass, silicate glass or rolled glass.

The front side contact 2 comprises a transparent conductive oxide, for example zinc oxide or tin oxide. The substrate 1a and the front side contact 2 together have a transparency of greater than 80% in a wavelength range of 400 nm to 1100 nm.

The first photoactive layer stack 3a has a layer sequence formed from a p-doped layer 31a , an intrinsic, undoped layer 32a and an n-doped layer 33a on. Preferably, at least one layer of the first photoactive layer stack has 3a predominantly amorphous silicon. Particularly preferably, the intrinsic layer 32a predominantly amorphous silicon.

The second photoactive layer stack 3b has a layer sequence formed from a p-doped layer 31b , an intrinsic, undoped layer 32b and an n-doped layer 33b on. Preferably, at least one layer of the second photoactive layer stack has 3b predominantly microcrystalline silicon. At least the intrinsic layer is particularly preferred 32b predominantly microcrystalline silicon.

Due to the different absorption spectra of amorphous and microcrystalline silicon, a broad absorption spectrum and thus a high degree of efficiency can be achieved in such a so-called tandem cell.

For example, boron is used as the p-type dopant, while, for example, phosphorus is used as the n-type dopant.

The first photoactive layer stack 3a converts radiation in a wavelength up to about 700 nm more effectively into electrical energy and the second photoactive layer stack 3b converts radiation with a longer wavelength up to 1100 nm more effectively.

On the second photoactive layer stack 3b , in particular on the n-doped layer 33b , is the backside contact 4 arranged. The backside contact 4 consists of a TCO layer 4a and a mirror layer 4b , The TCO layer is, for example, a zinc oxide layer. The mirror layer is preferably a metallic layer comprising, for example, silver or a silver alloy.

The backside contact 4 has no, as commonly used adhesion promoting layer, for example, chromium, on. As a result, a radiation absorption in the adhesion promoter layer usually used can be avoided, so that the photovoltaic cell 100 has a higher efficiency of up to 0.5% absolute. At the same time has such a trained back contact 4 a high reflectivity. In particular, by such a backside contact 4 an effective multiple scattering in the photovoltaic cell 100 achieved.

The trained with such a backside contact photovoltaic cell 100 allows a highly reflective and well-adhering backside contact 4 without requiring the use of absorbent primer layers such as chromium-containing layers.

On the backside contact 4 may be provided for contacting the cell strips external current collector (not shown). External current collectors are, for example, metal strips, for example tinned copper strips, which are applied to the side of the back side contact facing away from the layer stacks. For example, the current collectors are applied by means of a soldering method or an adhesive method on the rear side contact. Due to the good adhesion of the backside contact 4 advantageously allows improved adhesion of the external current collector on the back contact.

The photovoltaic cell is preferred 100 a thin film silicon cell.

1b shows a further embodiment of a photovoltaic cell 100 , The photovoltaic cell 100 according to the 1b differs from the photovoltaic cell according to 1a only through additional layers between the backside contact 4 and the encapsulation 1b ,

On the backside contact 4 is a NiV layer 5 (Nickelvanadium layer) arranged. On the NiV layer 5 can be a protective layer 6 be arranged. The protective layer 6 is for example a PVB layer (polyvinyl butyral layer), by means of which the encapsulation 1b is laminated to the photovoltaic cell.

Incidentally, the embodiment of the 1b with the embodiment of 1a match.

2 shows a photovoltaic module 200 in that a plurality of photovoltaic cells 100 . 100a which are arranged side by side and electrically coupled in series.

The photovoltaic module 200 is designed, for example, as a flat element that is suitable for converting radiant energy into electrical energy.

The photovoltaic module is preferred 200 designed as a frameless thin-film solar module. Thin-film solar modules have photoactive layers of a thickness in the range of a few 10 nm to a few micrometers. Usually, the photoactive layers together with contact and optionally reflection layers are applied over a large area to a substrate, for example a glass substrate. With the aid of one or more structuring steps, a plurality of individual strip-shaped photovoltaic cells 100 . 100a formed, which are electrically connected in series. The width of the strip-shaped photovoltaic cells 100 . 100a , also called cell strips, is in the range of centimeters.

On the outer cell strips 100a usually pantographs are applied, via which the thin-film solar module is connected externally and the generated electrical power can be dissipated. Such current collectors are, for example, metallic bands which are applied to the outer cell strips by means of a soldering process or an adhesive process 100a are applied along the alignment of the cell strips. The outer cell strips 100a are preferably not used as a converter on the photovoltaic effect of the radiant energy contained in the light into electrical energy. The backside contact, which is characterized by improved adhesion promoting properties due to the surface treatment of the TCO layer, allows the current collectors to be mounted and attached to the backside contact without the use of additional chromium-containing primer layers.

To reinforce the solar module, a circumferential frame, for example made of aluminum, can be used. In photovoltaic modules without such a frame can be arranged on the side remote from the light side of the module to stabilize and support the carrying capacity of the module, a support element or more support elements. Before the application of the carrier element or the semiconductor layers of the photovoltaic module, in which, for example, the semiconductor layers are arranged between two glass substrates, completely deposited.

Subsequently, the solar module can be coupled to a substrate (not shown).

The photovoltaic cells 100 of the 2 essentially correspond to the photovoltaic cells 100 from the embodiments of the 1a and or 1b ,

Method steps for producing a photovoltaic module comprising a plurality of photovoltaic cells according to one of the embodiments of 1a and 1b are below with reference to 3 explained with reference to a flow chart.

step 301 involves providing a substrate on which a front side contact, for example a TCO layer, is preferably applied over the whole area. By means of a first structuring method, for example a laser structuring method, the TCO layer is patterned after application in accordance with the intended photovoltaic cells.

In step 302 For example, a first photoactive layer stack is deposited on the patterned front-side contact, the first photoactive layer stack comprising an n-doped layer, a p-doped layer, and an intrinsic, undoped layer. On the first layer stack, a second photoactive layer stack is deposited, which has an n-doped layer, a p-doped layer and an intrinsic layer.

The layers of the first photoactive layer stack preferably comprise optoelectrically active layers of predominantly amorphous silicon, wherein the first Layer stack is adapted to at least partially convert the energy of the incident during operation radiation into electrical energy (internal photoelectric effect). The second photoactive layer stack is optoelectrically active and preferably comprises predominantly microcrystalline silicon, wherein the second photoactive layer stack is arranged to at least partially convert the energy of the radiation incident during operation into electrical energy.

After depositing the first and the second photoactive layer stack, the layer stacks are structured by means of a second structuring method, for example a laser structuring method, corresponding to the photovoltaic cells predetermined by the structured TCO layer.

After structuring the first and the second photoactive layer stack into photovoltaic cells, a rear-side contact is applied to the second photoactive layer stack, which in the steps 303a to 303c he follows.

In step 303a For example, a TCO layer, for example a zinc oxide layer, is applied to the n-doped layer of the second layer stack. In particular, the zinc oxide layer is deposited on the second photoactive layer stack.

In step 303b the surface of the TCO layer is subjected to a cleaning process. The cleaning process is preferably an ion-assisted cleaning process, for example an ion sputtering process and / or an ion etching process. For example, the cleaning process is carried out by means of a linear ion source in a vacuum.

Preferably, the surface of the TCO layer is modified or excited by means of an Ar plasma, an N plasma, for example N ₂ ⁺ or N ⁺ plasma, or another noble gas plasma. In particular, methods are used in which the kinetic energy distribution of the ions applied to the substrate has its maximum approximately at the mean lattice-bonding energy of TCO.

The choice of the maximum of the energy distribution near the lattice-binding energy preferably allows the excitation of atoms deposited on the surface and can lead to the mobilization or to the removal of deposited species. Preferably, one chooses the maximum of the energy distribution so that higher energy ions of the plasma do not lead to damage to the surface or the underlying monolayers.

As a result of the cleaning process of the surface of the TCO layer, it is cleaned and activated, so that the adhesion and the reflectivity of the TCO layer are improved, in particular increased.

In step 303c For example, a mirror layer, for example a silver layer, is deposited on the cleaned surface of the TCO layer. The previous cleaning process of the TCO layer advantageously increases the adhesion of the silver layer deposited directly thereon, so that the use of a chromium-containing layer as an adhesion-promoting layer becomes superfluous, which advantageously increases the efficiency of the photovoltaic cell.

Subsequently, a nickel vanadium layer can optionally be applied to the mirror layer.

Subsequently, the layers of the rear-side contact are structured according to the given photovoltaic cells by means of a third structuring method, preferably a laser structuring method.

Subsequently, optional in step 304 additional layers are applied to the finished back contact. For example, a backside encapsulation, for example made of glass or a film composite by means of an EVA layer, a PVB layer or another thermoplastic, laminated on the back contact, whereby the photoactive layers can be protected from damage and environmental influences.

To produce a photovoltaic module comprising a plurality of photovoltaic cells, the individual photovoltaic cells of the module are produced in particular in a common method. The photovoltaic module produced in this way can then be coupled to a substrate.

The invention is not limited by the description with reference to the embodiments. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

LIST OF REFERENCE NUMBERS

1a

substratum

1b

encapsulation

2

Front contact

3a

first photoactive layer stack

3b

second photoactive layer stack

4

Back contact

4a

TCO layer

4b

mirror layer

5

NiV layer

6

protective layer

31a, b

p-doped layer

32a, b

intrinsic layer

33a, b

n-doped layer

100, 100a

photovoltaic cell

200

photovoltaic module

301-304

Process steps in the production of a photovoltaic module

Claims (17)

Method for producing a photovoltaic cell ( 100 ), comprising the following method steps: providing at least one photoactive layer stack ( 3b ), wherein the photoactive layer stack ( 3b ) at least one n-doped layer ( 33b ), a p-doped layer ( 31b ) and an intrinsic layer ( 32b ), - application of a backside contact ( 4 ) on the photoactive layer stack ( 3b ), which has a TCO layer ( 4a ) and a mirror layer ( 4b ), wherein - before applying the mirror layer ( 4b ) on the TCO layer ( 4a ) the surface of the TCO layer ( 4a ) is subjected to a cleaning process. The method of claim 1, wherein the cleaning process comprises the surface of the TCO layer ( 4a ) cleans and activates. Method according to one of the preceding claims, wherein the cleaning process, the adhesion of the mirror layer ( 4b ) on the TCO layer ( 4a ) elevated. Method according to one of the preceding claims, wherein the cleaning process, the reflectivity of the mirror layer ( 4b ) elevated. Method according to one of the preceding claims, wherein the cleaning process is an ion-assisted cleaning process. The method of claim 5, wherein the cleaning process of the surface of the TCO layer ( 4a ) is performed by means of an Ar plasma, an N-plasma or a noble gas plasma. Method according to one of the preceding claims 5 or 6, wherein the kinetic energy distribution of the ions deposited on the substrate has its maximum at the average lattice-binding energy of TCO. Method according to one of the preceding claims, wherein the cleaning process is an ion sputtering process. The method of claim 8, wherein the ion sputtering process is performed by means of a linear ion source in vacuum. Method according to one of the preceding claims, wherein the TCO layer ( 4a ) is a ZnO layer which is deposited on the photoactive layer stack ( 3b ) is deposited. Method according to one of the preceding claims, wherein the mirror layer ( 4b ) is a silver layer deposited on top of the TCO layer ( 4a ) is deposited. Method for producing a photovoltaic module ( 200 ) comprising a plurality of photovoltaic cells ( 100 ) produced in a common method according to any one of the preceding claims. Photovoltaic cell ( 100 ), comprising - at least one photoactive layer stack ( 3b ), wherein the photoactive layer stack ( 3b ) at least one n-doped layer ( 33b ), a p-doped layer ( 31b ) and an intrinsic layer ( 32b ), and - one on the n-doped layer ( 33b ) of the layer stack ( 3b ) arranged back contact ( 4 ), whereby the back contact ( 4 ) from a TCO layer ( 4a ) and a mirror layer ( 4b ) consists. A photovoltaic cell according to claim 13, wherein the backside contact ( 4 ) does not include an adhesion layer. Photovoltaic cell according to one of the preceding claims 13 or 14, wherein the photovoltaic cell ( 100 ) is a thin-film photovoltaic cell. Photovoltaic cell according to one of the preceding claims 13 to 15, which comprises a further photoactive layer stack ( 3a ) comprising at least one further n-doped layer ( 33a ), another p-doped layer ( 31a ) and another intrinsic layer ( 32a ), wherein the further layer stack ( 3a ) on the backside contact ( 4 ) opposite side of the photoactive layer stack ( 3b ) is arranged. Photovoltaic module ( 200 ) comprising a plurality of photovoltaic cells ( 100 ) according to one of claims 13 to 16, which are electrically coupled in series.

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