METHOD FOR PRODUCING A THIN-FILM STACK THAT CAN BE DISBONDED FROM ITS SUBSTRATE

Abstract

A method for producing a thin-film solar cell on an initial substrate, the thin-film solar cell being removable from the initial substrate, the thin-film solar cell including a rear metal layer and a thin-film stack including a p-n junction, the method including depositing the rear metal layer on the initial substrate by sputtering; forming the thin-film stack on the rear metal layer, wherein the power, temperature and pressure used to deposit the rear metal layer are chosen so as to introduce shear stress into the rear metal layer in a controlled manner.

Claims

1. A method for producing a thin-film solar cell on an initial substrate, the thin-film solar cell being able to be disbonded from the initial substrate, the thin-film solar cell comprising a rear metal layer configured to form a rear electrical contact, a thin-film stack comprising a p-n junction, the method comprising: depositing the rear metal layer on the initial substrate by sputtering, and forming the thin-film stack on the rear metal layer; wherein a power, temperature and pressure used to deposit the rear metal layer are chosen so as to introduce shear stresses into the rear metal layer in a controlled manner.

2. The method for producing a thin-film solar cell on an initial substrate according to claim 1, wherein the rear metal layer is made of molybdenum.

3. The method for producing a thin-film solar cell on an initial substrate according to claim 1, wherein the power used to deposit the rear metal layer is comprised between 0.5 W/cm.sup.2 and 10 W/cm.sup.2.

4. The method for producing a thin-film solar cell on an initial substrate to claim 1, wherein the temperature used to deposit the rear metal layer is comprised between 25 C. and 200 C.

5. The method for producing a thin-film solar cell on an initial substrate according to claim 1, wherein the pressure used to deposit the rear metal layer is comprised between 1 Bar to 15 Bar.

6. The method for producing a thin-film solar cell on an initial substrate according to claim 5, wherein the initial substrate is made of glass.

7. The method for producing a thin-film solar cell on an initial substrate according to claim 1, further comprising a step during which the rear metal layer is disbonded from the initial substrate.

8. The method for producing a thin-film solar cell on an initial substrate according to claim 1, wherein the step of depositing the thin-film stack comprises the following sub-steps: depositing a first p-doped semiconductor; depositing an interface layer; depositing a second n-doped semiconductor.

9. The method for producing a thin-film solar cell on an initial substrate according to claim 1, wherein the first p-doped semiconductor is a CIGS alloy.

10. The method for producing a thin-film solar cell on an initial substrate according to claim 1, wherein the step of depositing the first semiconductor comprises: a step of depositing copper, indium, gallium by electrodeposition; a first step of annealing at 580 C.; a second step of annealing at 600 C.; a step of placing the whole assembly in a bath.

Description

BRIEF DESCRIPTION OF THE FIGS.

[0042] Other characteristics and advantages of the invention will become clear from reading the detailed description that follows, with reference to the appended figures, which illustrate: [0043] FIG. 1, a schematic representation of the steps of a method according to an embodiment of the invention, [0044] FIG. 2, a schematic representation in perspective of a solar cell obtained by a method according to an embodiment of the invention, [0045] FIGS. 3a to 3f, schematic representations explaining the different steps and the results of an adhesion test carried out on a layer of molybdenum.

[0046] For greater clarity, identical or similar elements are marked by identical reference signs in all of the figures.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0047] FIG. 1 represents the steps of a method for producing a solar cell on a substrate 1 according to an embodiment of the invention.

[0048] This method comprises a first step 101 of depositing a metal layer known as rear metal layer 2 on the substrate 1. The rear metal layer is preferably made of molybdenum. This rear metal layer 2 is deposited by sputtering. The parameters of depositing this rear metal layer will be detailed hereafter.

[0049] The method then comprises a step of forming a thin-film stack 7 comprising a p-n junction.

[0050] In this embodiment, this step of forming the thin-film stack 7 comprises a step 102 of depositing a first p-doped semiconductor 3 on the rear metal layer. This first p-doped semiconductor is preferably a CIGS alloy. To do so, the step 102 of depositing the first semiconductor preferably comprises firstly a step of depositing a layer of copper, then a layer of indium and finally a layer of gallium. These materials are preferably deposited by electrodeposition. The electrodeposition takes place in acid aqueous medium such that the bond between the rear metal layer and the initial substrate must withstand this acid aqueous medium. The step 102 then comprises a step of annealing at 580 C. under selenium atmosphere so as to cause a selenisation reaction, then a step of annealing at 600 C. under sulphur atmosphere so as to cause a sulphurisation reaction. The step 102 then comprises a step of passage in a bath containing KCN so as to remove all by-products produced during the selenisation and sulphurisation reactions. The steps of forming the first semiconductor 3 are thus very aggressive and the rear metal layer must remain fixed to the substrate during all of these steps.

[0051] In this embodiment, the step of forming the thin-film stack then comprises a step 103 of depositing a layer of cadmium sulphide CdS 4 on the first semiconductor 3, for example in a bath at 60 C.

[0052] In this embodiment, the step of forming the thin-film stack then comprises a step 104 of depositing transparent conductor oxide 5 which will make it possible to collect electrons from the p/n junction. This transparent conductor oxide 5 is preferably zinc oxide ZnO.

[0053] The method may also comprise a step 105 of forming front electrical contacts, as well as a step of discretisation of the future individual solar cells, and a step of forming electrical collectors.

[0054] The method according to this embodiment is particularly noteworthy in that during the step of depositing the rear metal layer by sputtering, the pressure, temperature and power used to deposit are chosen so as to create shear stresses in the rear metal layer 2. These shear stresses are going to make it possible to disbond easily the rear metal layer from the substrate. When the rear metal layer is made of molybdenum, in order to create sufficient shear stresses to disbond the rear metal layer: [0055] the power used to deposit the rear metal layer is preferably comprised between 0.5 W/cm.sup.2 and 10 W/cm.sup.2, and in a more preferential manner between 3 and 8 W/cm.sup.2, [0056] the temperature used to deposit the rear metal layer is preferably comprised between 25 C. and 200 C., and in a more preferential manner between 50 and 80 C., [0057] the pressure used to deposit the rear metal layer is preferably comprised between 1 Bar to 15 Bar, and in a more preferential manner between 1 and 5 Bar.

[0058] FIGS. 3a and 3b represent a disbondment test carried out on samples 12 obtained by a method according to the invention. Each sample 12 comprises: [0059] an initial substrate; [0060] a rear metal layer made of molybdenum of 500 nm.

[0061] The pressure used to deposit the rear metal layer has been modified so as to measure the adherence of the rear metal layer as a function of the pressure used to deposit this layer. The adhesion tests were carried out by applying a Scotch tape 11 at different locations of each sample 12 and by pulling it off sharply in the direction of the arrow 13. The results are represented in FIGS. 3c to 3f.

[0062] FIG. 3c represents the result of the test on a sample in which the rear metal layer has been deposited under a pressure of 1 Bar.

[0063] FIG. 3d represents the result of the test on a sample in which the rear metal layer has been deposited under a pressure of 3 Bar.

[0064] FIG. 3e represents the result of the test on a sample in which the rear metal layer has been deposited under a pressure of 5 Bar.

[0065] FIG. 3f represents the result of the test on a sample in which the rear metal layer has been deposited under a pressure of 7 Bar. As may be seen in these figures, the higher the deposition pressure, the more the rear metal layer disbonds easily, because the shear stresses in the rear metal layer increase with the pressure used to deposit this layer. Nevertheless, the pressure used to deposit the rear metal layer must not be too high, because the electrical resistance of the rear metal layer increases with the pressure used to deposit this layer. A compromise must thus be found so as to have a rear metal layer that disbonds easily but which has an electrical resistance that is not too high. The table below gives the values of the electrical resistance Rho of the rear metal layer of FIGS. 3c to 3f.

TABLE-US-00001 Deposition Rho pressure (Bar) (Ohms .Math. cm) Figure 3c 1 13.1 Figure 3d 3 13.4 Figure 3e 5 16.3 Figure 3f 7 18.3

[0066] Thus, a pressure used to deposit the rear metal layer between 1 Bar to 15 Bar, and preferably between 1 and 5 Bar enables a good compromise between a rear metal layer that disbonds easily and an electrical resistance of the layer that is not too high.

[0067] The method according to the invention thus makes it possible to produce a thin-film solar cell that can be disbonded from its initial substrate. This solar cell can thus then be disbonded from its initial substrate then re- bonded on the chosen substrate.

[0068] The method may then comprise a step 106 during which the thin-film solar cell is disbonded from the initial substrate 1 by raising a corner of the thin cell and by pulling on it. The rear metal layer then disbonds from the initial substrate 1. The method may then comprise a step 107 during which the thin-film solar cell may be re-bonded on a new substrate 8. This new substrate 8 may for example be a plastic, metal or textile film.

[0069] Naturally, the invention is not limited to the embodiments described with reference to the figures and variants could be envisaged without going beyond the scope of the invention. The thin-film stack could notably have a composition different to that described with reference to the figures, such that the steps of depositing the thin-film stack could be different to those described with reference to the figures.