DE102010037319B4 - Solar cell with improved backside metallization layer - Google Patents

Abstract

A solar cell (1) having a backside and a backside metallization layer (12) and the backside metallization layer (12) comprises nanoparticles (2) in the form of carbon nanofibers or in the form of carbon nanotubes or in the form of functionalized carbon nanotubes and fibers the diameter of the nanoparticles (2) is greater than or equal to 1 nm and less than or equal to 10 μm, and wherein the length of the nanoparticles (2) is greater than 1 μm.

Description

A silicon solar cell comprises a silicon layer which has two differently doped regions on its top and bottom. In each case on the top and the bottom of a metallization layer is applied, which serves for contacting the electrical connection contacts. The back metallization layer is usually applied in the form of a paste containing aluminum particles, and then heated in a firing step so strongly that aluminum and silicon form a diffusion bond. Another object of the metallization layer is to increase the mechanical stability of the solar cell. Due to the low ductility of the silicon and its small thickness of 100 to 200 microns, this solar cell is very susceptible to breakage. Since a solar cell is subjected to high stresses during its production, due to mechanical loads, as well as during its operation, by temperature fluctuations of up to 80 Kelvin in the course of the day, a metallization layer is desired, which can absorb and compensate for these stresses.

It is generally known to provide stabilizing layers with fibers. These fibers can absorb stresses and absorb the forces acting on them. However, this procedure is not possible for the metallization layer of a solar cell since the starting material of the metallization layer is applied to the solar cell in liquid or pasty form (metallization paste) by means of a (screen) printing process. Here, conventional fibers would clog the screen structure / print structure and prevent uniform coating with metallization material. Likewise, incorporation of non-conductive fibers would degrade the electrical properties of the metallization layer.

The US 2007/0221270 A1 relates to a screen printing paste and a solar cell in which an electrode structure has been produced from this screen printing paste. The screen printing paste comprises carbon nanoparticles which have a diameter of less than 1 μm. From the US 2010/0003781 A1 Furthermore, a thin-film solar cell with a transparent front electrode structure is known. The front electrode structure has carbon nanotubes.

• a) Fähigkeit zur Aufnahme von mechanischen Kräften, die bei der Herstellung, Verarbeitung und Betrieb der Solarzelle auftreten, ohne die Flexibilität der Solarzelle negativ zu beeinflussen;
• b) Gute Haftung zwischen Metallisierungsschicht und Solarzellen-Halbleiteroberfläche, um eine Delamination von Metallisierungsschicht und Halbleiter bei Herstellung, Verarbeitung und Betrieb der Solarzelle zu verhindern;
• c) Gute elektrische Querleitfähigkeit in der Metallisierungsschicht sowie guter Kontaktwiderstand zwischen Metallisierungsschicht und Halbleiter;
• d) Das Ausgangsmaterial der Metallisierungsschicht ist für die Verarbeitung mittels eines (Sieb-)Druckverfahrens geeignet.

The object of the invention is therefore to present a solar cell with a back-side metallization layer, which has the following properties:

• a) ability to absorb mechanical forces that occur during the manufacture, processing and operation of the solar cell, without negatively affecting the flexibility of the solar cell;
• b) Good adhesion between metallization layer and solar cell semiconductor surface to prevent delamination of metallization layer and semiconductor during manufacture, processing and operation of the solar cell;
• c) Good lateral electrical conductivity in the metallization layer and good contact resistance between metallization layer and semiconductor;
• d) The starting material of the metallization layer is suitable for processing by means of a (screen) printing process.

In this case, the solar cell comprises a silicon layer, a front side coating on the front side facing the sun, and a rear side metallization layer on the rear side facing away from the sun.

In addition to the screen printing method, other deposition methods can be used such. Dispensing, laser transfer printing, pad printing, inkjet printing, aerosol printing, etc.

According to the invention, the backside metallization layer contains structural materials in the form of nanoparticles in the form of carbon nanofibers or in the form of carbon nanotubes or in the form of functionalized carbon nanotubes and fibers, the diameter of the nanoparticles being greater than or equal to 1 nm and less than or equal to 10 μm, and wherein the length of the nanoparticles is greater than 1 μm.

This addition increases the strength of the metallization layer, since the nanoparticles absorb mechanical forces and thus reinforce the silicon layer. In addition, the adhesion of the metallization layer to the silicon layer is improved.

Due to their properties, the mentioned nanoparticles are suitable for use as structural material for this application. They have a high strength, are electrically conductive, so that the conductivity of the metallization layer is not impaired and can happen due to their small size and the usual Siebschablonen or printer nozzles. Furthermore, it is possible to bind further chemical compounds to the nanoparticles by means of a so-called functionalization, and thus to introduce them into the metallization layer.

A preferred embodiment is characterized in that the proportion of nanoparticulate structural material in the backside metallization layer does not exceed 30 percent by weight.

A possible embodiment is based 1 explained.

1 shows the schematic cross section through a solar cell 1 , This is shown simplified as a system of three layers, wherein the thickness of the individual layers and the ratio of layer thickness to the extent of the solar cell are not shown to scale.

The topmost layer forms the front side coating 13 , This is simplified here shown as a homogeneous layer. In practice, however, it is structured in order to ensure the highest possible incidence of light on the silicon layer.

The middle layer with the largest thickness is the silicon layer 11 , This is the electricity generating element of a solar cell and consists of two differently doped silicon layers. When the light is generated between its top and bottom, a voltage gradient and thus a current flow. The task to dissipate this power take over the front side coating 13 and the backside metallization layer 12 ,

On the bottom follows the backside metallization layer 12 , This is formed by a flat layer, which consists largely of aluminum. in the Rückseitenmetallisierungsschicht is homogeneously distributed, a plurality of nanoparticles 2 which are randomly aligned.

LIST OF REFERENCE NUMBERS

1

solar cell

11

silicon layer

12

Rückseitenmetallisierungsschicht

13

Front coating

2

nanoparticles

Claims (2)

Solar cell ( 1 ), which have a backside and a backside metallization layer ( 12 ) and the backside metallization layer ( 12 ) Structural materials in the form of nanoparticles ( 2 ) in the form of carbon nanofibers or in the form of carbon nanotubes or in the form of functionalized carbon nanotubes and fibers, the diameter of the nanoparticles ( 2 ) is greater than or equal to 1 nm and less than or equal to 10 μm, and wherein the length of the nanoparticles ( 2 ) is greater than 1 micron. Solar cell ( 1 ) according to claim 1, characterized in that the proportion of structural material in the form of nanoparticles ( 2 ) in the backside metallization layer ( 12 ) Does not exceed 30% by weight.

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