METHOD FOR FABRICATING A SOLAR CELL/MODULE HAVING A PERIODIC TEXTURE AND A SOLAR CELL/MODULE INCORPORATING SUCH TEXTURE.

FIELD OF THE INVENTION

The present invention relates in general to an improved thin film solar cell/ module having an improved texture on its solar glass substrate/superstrate, for the purpose of enhancing its capability to trap maximum amount of solar energy incident on it and in particular, to an improved method for fabricating a solar cell/module having a periodic texture, on its solar glass substrate/superstrate.

BACKGROUND OF THE INVENTION

It is traditionally known, that primarily, a solar cell module includes a plurality of inter-connected solar cells, for trapping maximum amount of solar energy, incident on it. In fact, the efficiency of a thin-film solar cell/module is significantly determined by its ability to capture maximum amount of incident solar light. Efforts are on over the years to maximize the light absorbing capacity of the absorber layers of a cell. For that purpose, the substrates or superstrates with a random texture are used to scatter the Incident light. Thereby, the optical path length of the light in the absorber layer is increased, and hence absorption of maximum possible light, is ensured.

A known method to produce such random texture comprises applying a wet-chemical etching process of the (TCO) front contact or (metal) back-contact. Another method involves a deposition process technology that results in layers with a random texture, such as LPCVD of the front TCO contact.

In all the aforesaid methods, the texture is random in nature and the textural parameters can not be changed easily and independently, as they are dependent on the type of material used and the process parameters. So, it becomes difficult to independently optimize the textural parameters for maximum light-trapping in a given solar cell layer stack design, according to the nature of the given production processes.
Accordingly, there was a long felt need to develop a solar cell/module having improved texture on its substrate/superstrate, such that the textural parameters can be changed easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy, incident on the solar cell/module.

The present invention meets the aforesaid need and also solves the disadvantages as narrated above.

OBJECTS OF THE INVENTION

It is a prime object of the present invention to provide a thin film solar cell/module having an improved periodic texture on its substrate/superstrate, such that the textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

It is a further object of the present invention to provide a method for fabricating an improved thin film solar cell/module having a periodic texture on its substrate/superstrate, such that the textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

It is a further object of the present invention to maximize the light trapping efficiency of the absorber cells, of a thin film solar cell/module.

It is a further object of the present invention to fabricate a sub-micron sized texture on a substrate/superstrate of a thin film solar cell/module, such that maximum trapping of the solar energy, incident on solar cell/module is ensured.

It is a further object of the present invention to provide a method for its application both on substrate or superstrate configuration of a thin film solar cell/module, on large areas, in a cost-effective and reproducible way.

It is yet another object of the present invention to provide a method for fabricating an improved periodic texture on the substrate/superstrate of a thin film solar cell/module, such that the textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

It is yet another object of the present invention to decrease the thickness of the absorber layer of the thin-film cell/module as far as practicable, thereby ensuring improvement in the productivity and reduction in module cost.
How the foregoing objects are met and the other aspects of the invention will be clear from the following description, which is purely for the sake of understanding and not by way of any sort of limitation.

SUMMARY OF THE INVENTION

The present invention also provides an improved thin film solar cell/ module including a plurality of inter-connected cells wherein there is provided an improved periodic texture on the substrate/superstrate of said cell/module, said texture being of sub-micron size and is adapted to be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

In accordance with a preferred embodiment of the thin film solar cell/module of the present invention:

-the thickness of the absorber layer of said thin-film cell/module is adjustable.

The present invention also provides a method for fabricating a thin film solar cell/module having a plurality of inter-connected cells including an optical mastering method, said method comprising:

a) locally illuminating a photo-resist layer, by applying a focused sub-micron-sized laser spot,

b) developing the photo-resist layer, resulting in the dissolution of the illuminated/non-illuminated resist, whereby the master substrate remains, with the mastered periodic texture in the remaining photo-resist,

c) sputtering said master with suitable metal seed layer,

d) growing a stamper on top of said metal seed layer by suitable technique,

e) removing said stamper from said master substrate, said stamper having a negative image of sub-micron size periodic texture on its surface,

f) applying said stamper to replicate the sub-micron size periodic texture onto solar cell substrate/superstrate, whereby textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

In accordance with preferred embodiments of the method as described aforesaid,

-said metal seed layer is a Ni seed layer.

-said stamper is a Ni stamper, grown on top of said seed layer by electroplating.

-said replication involves a UV-curing process.

-said replication process involves a thermal curing process.

The present invention also provides a method for fabricating a periodic texture on the substrate/superstrate of a thin film solar cell/module, said method comprising:

a) locally illuminating a photo-resist layer, by applying a focused sub-micron-sized laser spot,

b) developing the photo-resist layer, resulting in the dissolution of the illuminated/non-illuminated resist, whereby the master substrate remains, with the mastered penodic texture in the remaining photo-resist,

c) sputtering said master with suitable metal seed layer,

d) growing a stamper on top of said metal seed layer by suitable technique,

e) removing said stamper from said master substrate, said stamper having a negative image of sub-micron size periodic texture on its surface,

f) applying said stamper to replicate the sub-micron size periodic texture onto solar cell substrate/superstrate, whereby textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The nature and scope of the present invention will be better understood from the accompanying drawing, which is by way of illustration of preferred embodiment and not by way of any sort of limitation. In the accompanying drawing,
Figure 1 illustrates schematically, the process flow of the method in accordance with the present invention.

BRIEF DESCRIPTION OF THE INVENTION

The following describes, some preferred embodiments of the present invention which are purely for the sake of understanding and not by way of any sort of limitation.

As stated before, the present invention describes a method to create a well-defined periodic texture onto solar cell/module substrates/superstrates, in order to maximize the light-trapping efficiency of thin-film solar cells/modules.

From extensive research and simulations pursuant thereto, it has been deciphered that solar cell substrates with a carefully optimized periodic texture can result in higher solar cell efficiencies than by using substrates with a periodic texture. The present invention successfully puts into practice, the results deciphered from such research and simulation.

Basically, the method in accordance with the present invention, involves the formation of a sub-micron sized texture onto a stamper, as well as the replication of this texture, onto the solar cell substrate/superstrate. This has been schematically represented in the accompanying Figure 1. There are six fundamental steps involved, numerically represented by 1, 2, 3, 4, 5 and 6 in that order as follows:

1. Locally illuminating a photo-resist layer, by applying a focused sub-micron-sized laser spot.

2. Developing the photo-resist layer, resulting in the dissolution of the illuminated/non-illuminated resist, whereby the master substrate remains, with the mastered periodic texture in the remaining photo-resist.

3. Sputtering said master with suitable metal seed layer.

4. Growing a stamper on top of said metal seed layer by suitable technique.

5. Removing said stamper from said master substrate, said stamper having a negative image of sub-micron size periodic texture on its surface,

6. Applying said stamper to replicate the sub-micron size periodic texture onto solar cell substrate/superstrate.

So, the present invention describes a method to produce a periodic texture onto a solar cell substrate or superstrate, to improve light-trapping by the solar cell. The method in accordance with the present invention produces a well-defined periodic texture with sub-micrometer dimensions. The parameters of the texture can be varied and optimized in an independent way. This technical advancement was hitherto not achieved or conceived by the prior art techniques, involving applying random texture on substrate/superstrates, of thin film solar cells/modules for increasing the energy absorbing capacity of the absorber cells.

The method in accordance with the present invention can be applied both on substrate or superstrate configurations and on large areas in a cost-effective and reproducible way.

The method involves making the sub-micron sized periodic texture first, by using an optical mastering process. A photo-resist layer is locally illuminated by using a focused sub-micron-sized laser spot. After illumination the photo-resist layer is developed, resulting in the dissolution of the illuminated (or alternatively the non-illuminated) resist. After the development process, a so-called master substrate remains, with the mastered periodic texture in the remaining photo-resist. The master is sputtered with a Nl seed layer, and via electroplating, a Ni stamper is grown on top of this seed layer. The Ni stamper is subsequently removed from the master substrate, and bears a negative image of the periodic texture at its surface. This Ni stamper is used, in accordance with the present invention to replicate the periodic texture onto the solar cell substrate or superstrate. Preferably, the replication involves a UV-curing process e.g a photopolymer lacquer (such as an acrylic resin) or a sol-gel material. Alternatively, a thermal curing process is used.

The novel aspect of the present invention lies in the formation of the sub-micron sized periodic texture onto solar cell substrates/superstrates of thin film solar cells/modules, which is adapted to be optimized in a reproducible way. To be precise, the texture can be optimized independently of the materials used in the improved light-capturing in thin-film solar cells, thereby facilitating increase in the efficiency of the solar cell/ module. It also results in applying decreased thickness of the absorber layer of the thin-film cell, thereby ensuring improvement in the productivity and reduction in module cost.
The present invention has been described with reference to some preferred embodiments and drawing, purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described hereinbefore and claimed in the appended claims.

WE CLAIM

1. An improved thin film solar cell/ module including a plurality of inter-connected cells wherein there is provided an improved periodic texture on the substrate/superstrate of said cell/module, said texture being of sub-micron size and is adapted to be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

2. The improved thin film solar cell/module as claimed in claim 1 wherein the thickness of the absorber layer of said thin-film cell/module is adjustable.

3. A method for fabricating a thin film solar cell/module having a plurality of inter-connected cells including an optical mastering method, said method comprising:

a) locally illuminating a photo-resist layer, by applying a focused sub-micron-sized laser spot,

b) developing the photo-resist layer, resulting in the dissolution of the illuminated/non-illuminated resist, whereby the master substrate remainsi with the mastered periodic texture in the remaining photo-resist,

c) sputtering said master with suitable metal seed layer,

d) growing a stamper on top of said metal seed layer by suitable technique,

e) removing said stamper from said master substrate, said stamper having a negative image of sub-micron size periodic texture on its surface,

f) applying said stamper to replicate the sub-micron size periodic texture onto solar cell substrate/superstrate,

whereby textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy.

4. The method for fabricating a thin film solar cell/module as claimed in claim 3 wherein said metal seed layer is a Ni seed layer.

5. The method for fabricating a thin film solar cell/module as claimed in claims 3 to 4 wherein said stamper is a Ni stamper, grown on top of said seed layer by electroplating.

6. The method for fabricating a thin film solar cell/module as claimed in claims 3 to 5, wherein said replication involves a UV-curing process.

7. The method for fabricating a thin film solar cell/module as claimed in claims 3 to 5, wherein said replication process involves a thermal curing process.

8. A method for fabricating a periodic texture on the substrate/superstrate of a thin film solar cell/module, said method comprising:

a) locally illuminating a photo-resist layer, by applying a focused sub-micron-sized laser spot,

b) developing the photo-resist layer, resulting in the dissolution of the illuminated/non-illuminated resist, whereby the master substrate remains, with the mastered periodic texture in the remaining photo-resist,

c) sputtering said master with suitable metal seed layer,

d) growing a stamper on top of said metal seed layer by suitable technique,

e) removing said stamper from said master substrate, said stamper having a negative image of sub-micron size periodic texture on its surface,

f) applying said stamper to replicate the sub-micron size periodic texture onto solar cell substrate/superstrate, whereby textural parameters can be optimized easily and independently of the material and process parameters, for the sole purpose of ensuring, maximum absorption of solar energy,

9. The method for fabricating a periodic texture as claimed in claim 8, wherein
said metal seed layer is a Ni seed layer.

10. The method for fabricating a periodic texture as claimed in claim 8, wherein said stamper is a Ni stamper, grown on top of said seed layer by electroplating .