The invention concerns a method for fabricating a solar module having a plurality of solar cells, a sub-laminate for fabricating the solar module and a solar module.

Huang, J., Li, G., Yang, Y. : A Semi-transparent Plastic Solar Cell Fabricated by a Lamination Process, Adv. Mater., 20, 415-419 (2008) discloses a method for fabricating a plastic solar cell. The method comprises the steps of forming a laminate having a first carrier layer, a first electrode layer, a photoactive layer, a second electrode layer, and a transparent second carrier layer, the photoactive layer being disposed between the first and the second electrode layers, the first electrode layer being superimposed by the first carrier layer, and the second electrode layer being superimposed by the second carrier layer so that the first and the second carrier layers form outside surfaces of the laminate.

By the known method it is possible to produce a solar cell. A solar cell as such is not very effective. In order to increase the effectiveness it is generally known to combine a plurality of solar cells to form a solar module. In the solar module the solar cells are interconnected by electrically conducting paths.

The object underlying the present invention is to provide a method by which a solar module having a plurality of solar cells can be fabricated easily and at low cost. A further object of the invention is to provide a sub-laminate for fabricating the solar module as well as a solar module which can easily be manufactured at low cost.

This object is solved by the features of claims 1 , 15 and 22. Embodiments of the invention result from the features of claims 2 to 24, 1 6 to 21 and 23 to 25. According to a first aspect of the invention a method for fabricating a solar module having a plurality of solar cells is proposed, the method comprising:

Forming a laminate having a first carrier layer, a first electrode layer, a photoactive layer, a second electrode layer, and a transparent second carrier layer, the photoactive layer being disposed between the first and second electrode layers, the first electrode layer being superimposed by the first carrier layer, and the second electrode layer being superimposed by the second carrier layer so that the first and the second carrier layers form outside surfaces of the laminate, and manufacturing, after the step of forming the laminate, a first pattern of electrically isolating paths within the second electrode layer by means of a laser.

The proposed solar module may be in particular a thin-film solar module. The proposed solar module can be produced at low cost by a relative simple lamination process. The second electrode layer is superimposed by a transparent second carrier layer which forms an outside surface of the laminate. According to the invention, it is provided that a first pattern of isolating paths is formed within the second electrode layer after the laminate has been formed. Thereby, the

manufacture of the first structure can easily be carried out. The first structure can be easily aligned with a second pattern within the laminate which may be produced in one of the layers during the lamination process. By the proposed method a geometric fill factor of more than 90% and an power conversion efficiency of up to 5,3% for organic photoactive layers, and of up to 9,8% for perovskite photoactive layers can be achieved.

The term "transparent" is understood in the context of the present invention to be permeable for electromagnetic radiation, in particular light.

The second electrode layer is advantageously embodied to have a lower laser ablation threshold compared to the superimposed transparent second carrier layer and the underlying photoactive layer. This makes it possible to pattern or structure, respectively, the second electrode layer in particular by in-depth-resolved post patterning-technique while leaving the sandwiching second carrier layer and the photoactive layer essentially unaffected. By means of the laser the intercalated second electrode layer is destroyed along a predetermined path. It turned out that thereby electrically isolating paths may be produced, the electrically isolating properties of which are sufficient to manufacture a solar module.

In the context of the present invention the second electrode layer has a first electrical conductivity. The electrical isolating path has a second electrical conductivity which is lower than the first electrical conductivity. The first electrical conductivity of the second electrode is usually more than 1 .000 S/m, in particular more than 10.000 S/m. The second electrical conductivity of the isolating path is usually less than 1 .000 S/m, in particular less than 100 S/m.

According to an embodiment of the invention the second electrode layer is formed of a electrically conducting particle layer and an electrically conducting adhesive layer. The electrically conducting particle layer is advantageously in contact with the second carrier layer. The electrically conducting adhesive layer is

advantageously in contact with the electrically conducting particle layer. The electrically conducting particles are advantageously fixed by the electrically conducting adhesive layer.

According to an embodiment of the invention the electrically conducting adhesive layer is made of an adhesive which may be activated thermally, by pressure or radiation. The electrically conducting adhesive layer advantageously has an electrical conductivity of at least 3 S/m. The electrically conducting adhesive layer may comprise one or more of the following components:

poly(ethylenedioxythiophene) (= PEDOT):poly(styrenesulfonate) (= PSS) doped with a sugar, e. g. D-sorbitol or volemitol. The electrically conducting adhesive layer may also be formed by a resin doped with electrically conducting particles. The proposed adhesive makes it possible to manufacture the laminate by roll- lamination of two sub-laminates. According to a further embodiment of the invention the first electrode layer may be formed of one of the following materials: nanowires, indium tin oxide (= ITO), ITO/metal/ITO (= IMI), where the metal may be Ag, an Ag-Pd- or Ag-Ti-alloy, graphene, Ag-paste, highly conductive PEDOT:PSS, in particular combined with a metal grid.

The electrically conducting particles of the electrically conducting particle layer may be selected from the following group: nanowires, graphene, carbon

nanotubes, metal particles. The nanowires or the metal particles may be made of one of the following metals: Au, Ag, Cu. The first and/or the second carrier layer may be made of glass or a transparent polymer being selected from the following group: PET, PI, PEN.

According to a further embodiment of the invention the first electrode layer may be provided with a predetermined second pattern by means of a laser before the photoactive layer is deposited thereon. In a similar manner the photoactive layer may be provided with a predetermined third pattern by means of a laser before the first electrode is deposited thereon. According to a particular advantageous embodiment of the invention the laminate is fabricated by the following steps:

Forming a first sub-laminate having the first carrier layer, the first electrode layer, and the photoactive layer, the first electrode layer being disposed between the first carrier layer and the photoactive layer, forming a second sub-laminate having the transparent second carrier layer, the electrically conducting particle layer and the electrically conducting adhesive layer, the electrically conducting particle layer being disposed between the second carrier layer and the electrically conducting adhesive layer, superimposing the first sub-laminate and the second sub-laminate such that the first and the second carrier layers form the outside of the laminate, and exerting a pressure upon a stack of layers formed by the superimposed first and second sub-laminates thereby forming the laminate where the first and the second sub-laminates are glued by means of the electrically conducting adhesive layer.

The forming of the first and the second sub-laminate has the advantage that the processing of the second electrode can be decoupled from the rest of the fabrication process. This allows for easily switching between a manufacture of single cells, tandem cells or modules. Further, the second sub-laminate functions as a barrier, e. g. against moisture, and thus enables an encapsulation at the earliest possible stage of manufacture. The exerting of a pressure upon the stack of the layers may be advantageously carried out by a roll lamination process. Such process is simple and fast. An exact alignment of the first sub-laminate with the second sub-laminate is not necessary as the first pattern is formed after gluing the first with the second sub-laminate. According to a further embodiment of the invention the stack of layers is heated up to a temperature in the range of 50 °C to 150 °C during the step of exerting a pressure. Thereby a curing of the electrically conducting adhesive can be accelerated. Further, following the step of forming the first pattern within the second electrode, the laminate may be heated up to a temperature in the range of 50 °C to 150 °C.

According to a second aspect of the invention there is proposed a sub-laminate for fabricating a solar module comprising the following layers being superimposed in the order a) to c): a) A second carrier layer made of a transparent material, b) an electrically conducting particle layer, and

c) an electrically conducting adhesive layer.

The proposed sub-laminate is a product which may be combined with different kinds of further sub-laminates, e. g. by roll-lamination. The sub-laminate provides advantageously the electrically conducting particle layer which may be patterned by means of a laser when the sub-laminate forms part of a laminate. As the carrier layer is made of a transparent material a laser beam may pass through the transparent polymer without destroying it. By the laser beam there can be selectively destroyed the electrically conducting particle layer along predetermined paths or sections. The proposed sub-laminate may be used for fabricating solar modules, touch screens or the like. - The electrically conducting adhesive layer may be covered by a protective cover layer which may be peeled off before attaching the sub-laminate to another laminate. The protective cover layer may be made e. g. of waxed paper or the like.

According to an embodiment the electrically conducting adhesive layer may be made of an adhesive adapted to be activated thermally by pressure or radiation. The electrically conducting adhesive layer may have electrical conductivity of at least 3 S/m. Preferably, the electrically conducting adhesive layer has an electrical conductivity of at least 4 S/m. The electrically conducting adhesive layer may comprise one or more of the following components: PEDOT:PSS doped with a sugar, e. g. D-sorbitol or volemitol. The electrically conducting adhesive layer may also be formed of a resin doped with electrically conducting particles. The electrically conducting particles may be formed by Ag, Cu, Au or the like.

The electrically conducting particles of the electrically conducting particle layer may be selected from the following group: nanowires, graphene, carbon

nanotubes, metal particles. The nanowires or the metal particles are preferably made of one of the following metals: Au, Ag, Cu. According to a third aspect of the invention a solar module comprising the following layers being superimposed in the order a) to d) is proposed: a) A first carrier layer,

b) a first electrode layer,

c) a photoactive layer,

d) the sub-laminate according to the invention, the electrically conducting adhesive layer being in contact with the photoactive layer. The proposed solar module may be manufactured easily and at low cost. It provides a large geometrical fill factor of more than 90%. The solar cell is semitransparent and flexible. It is robust against environmental influences.

The first electrode layer may be formed of one of the following materials:

nanowires, ITO, I M I , graphene, Ag-paste, highly conductive PEDOT:PSS, in particular combined with a metal grid, metal particles. The nanowires or metal particles may be made of one of the following metals: Au, Ag, Cu.

According to a further embodiment of the invention the first and/or the second carrier layer may be made of glass or a transparent polymer being selected from the following group: PET, PI, PEN.

In the solar module the second electrode layer may be provided with a first pattern of isolating paths, the first electrode layer may be provided with a second pattern of electric isolating paths and the photoactive layer may be provided with a third pattern of electric isolating paths. By the electrically isolating paths there are produced a plurality of solar cells. The electrically isolating paths may be filled with a superimposed material to form connections between the solar cells and thereby to form the solar module.

Embodiments of the invention are described by reference to the accompanying figures. Fig. 1 a-g shows steps of a method for manufacturing a solar module,

Fig. 2 shows schematically a sectional view of the solar module according to Fig. 1 g,

Fig. 3a shows a cross-section scanning electron-microscopy (SEM) image of the solar module and Fig. 3b shows a top view of the layer of nanowires after a delimitation of the transparent first carrier layer.

Fig. 1 a shows a first and a second step of the method. A first carrier layer 1 , e. g. a transparent foil made of PET, is coated in a conventional manner with a first electrode layer 2, e. g. a transparent electrode made of an I Ml (= ITO/Metal /ITO) or of Indium tin oxide (= ITO)). The first electrode layer 2 is then provided by laser patterning with a second pattern A2 (second step).

On top of the first electrode layer 2 there is coated as a third step a layer made of ZnO nanoparticles. The layer had a thickness of around 30 nm. The layer 3a was dried at a temperature of 80 °C for five minutes. The aforementioned layer 3a forms an electron transfer layer (= ETL).

In a fourth step of the method there is coated a photoactive layer 3b on top of the ETL 3a (see Fig. 1 b). As photoactive layer 3b there was used a medium band gap conjugated polymer PBTZT-stat-BDTT-8 blended with phenyl-C61 -butyric acid methyl ester (PC[60]BM). In a fifth step of the method there is provided a third pattern A3 within the photoactive layer 3b by use of a laser. Steps one to five of the method result in a first sub-laminate S1 (see Fig. 1 c). - The ETL 3a is considered in this example to be a sub-layer of the photoactive layer 3b. The method further comprises the manufacture of a second sub-laminate S2. As a second carrier layer 6 there is used e. g. a foil made of transparent PET which is coated by a layer of nanowires 5, in particular Ag-nanowires (sixth step of the method). The layer of nanowires 5 was made of a water-based solution which was dried at around 100 °C for 3 to 5 minutes. The layer of nanowires 5 has a thickness in the range of 50 to 200 nm, preferably 80 to 120 nm. On top of the layer of nanowires 5 there is coated an electrically conducting adhesive layer 4 containing e. g. PEDOT:PSS and D-sorbitol which has an electrically conductivity of around 8,5 S/m (seventh step of the method).

In an eight step of the method the first sub-laminate S1 is then glued with the second sub-laminate S2 by a roll-lamination process as shown in Fig. 1 e. When forming the laminate L the electrically conducting adhesive layer 4 is pressed into the grooves formed by the third pattern A3 providing an electrical contact between the photoactive layer 3b and the electrically conducting particle layer, in particular between the ETL 3a and the layer of nanowires 5. The outside of the laminate L is formed by the carrier layers 1 and 6. The roll-lamination process is carried out at a temperature in the range of 60 °C to 150 °C. The laminate L is afterwards annealed at a temperature in the range of 60 °C to 150 °C for 10 minutes.

In a ninth step of the method there is manufactured a first pattern A1 within the layer of nanowires 5 by in-depth laser ablation. Thereby there is produced an isolating path within the first electrode layer 2 made of the layer of nanowires 5 and the layer of electrically conducting adhesive 4.

According to an alternative of the method the photoactive layer 3b may be made of perovskite. In this case a first carrier layer 1 made of PET or glass is spin-coated with an LT-NiO layer at a speed of 3.000 to 6.000 rpm and annealed at 140 °C for 5 to 15 minutes in air. A dimethylformamide (DMF)-perovskite precursor solution is made by adding Pbl ₂ and CH ₃ NH ₃ I powders with a molar ratio of approximately 1 :1 and a concentration of 40 wt% and 20 wt% to a vial and mixed with anhydrous DMF. The precursor solution is then stirred for 10 to 40 minutes at 40 to 70 °C and filtered with 0.45 μηπ PTFE syringe filter prior to deposition. The precursor solution is then spin-coated in an inert atmosphere at room temperature using 2.000 to 5.000 rpm for 10 to 40 seconds. During the last 5 seconds of the spin-coating process, the layer is treated with chlorobenzene drop-casting. The coated first carrier layer 1 is then dried on a hot plate at 80 °C to 120 °C for 5 to 15 minutes. After the deposition of the perovskite a compact 60 nm thick layer of PC ₆ oBM is spin-coated. A 2 wt% solution of PC ₆ oBM in chlorobenzene is then spin-coated. Afterwards a ZnO film forming the ETL 3a is spin-coated at 1 .000 to 4.000 rpm and annealed for 2 to 10 minutes at 60 °C to 120 °C. Polyethylenimine (= PEI) is spin-coated at 500 to 3.000 rpm and annealed at 60 °C to 120 °C for 2 to 10 minutes. - The connection with the second sub-laminate S2 is carried out at 40 to 70 °C in inert atmosphere by roll-lamination.

The proposed method for manufacturing solar modules with the laminated second electrode 4, 5 involves a depth-resolved post-patterning technique. The

manufacture is fully roll-to-roll compatible due to the high processing speed of the laser patterning approach (up to 4 m s ^"1 ) and solution processing of all functional layers. The method according to the invention includes layer coating and laser patterning, e. g. under ambient atmospheric conditions. Generally, in order to achieve electrical series interconnection between individual solar cells in a solar module, three patterns A1 to A3 are manufactured (see Fig. 2). There may be used a femtosecond-laser patterning with optimized ablation thresholds for each pattern A1 to A3 in order to achieve high spatial resolution and a high geometrical fill factor (= GFF). After electrical separation of the first electrode layer 2 by the second pattern A2, the ETL 3a as well as the photoactive layer 3b are

successively coated. During the fifth step the photoactive layer 3b and the ETL 3a are ablated to form the third pattern A3 by applying a laser fluence lower than the ablation threshold of the first electrode layer 2. In a separate process, the layer of nanowires 5 and the electrically conducting adhesive layer 4 are consecutively coated on the second carrier layer 6 to form the second sub-laminate S2, which is then assembled on top of the photoactive layer 3b of the first sub-laminate S1 by passing through a pre-heated roll-laminator. Afterwards the second electrode 4, 5 included in the fully laminated stack is patterned using depth-resolved laser patterning through the transparent second carrier layer 6. This step allows to selectively structure the second electrode 4, 5 and, by carefully tuning the laser fluence, neither damaging the second carrier layer 6 nor the photoactive layer 3b. This technique becomes viable as the second electrode layer, in particular the layer of nanowires 5, exhibits an ablation threshold lower than the value for the materials of which the second carrier layer 6 and the photoactive layer 3b are made. Fig. 2 shows schematically a cross section through a solar module according to the present invention. A first carrier layer 1 is e. g. made of a IMI-based flexible PET foil. The first electrode layer 2 is superimposed by a photoactive layer 3b. The photoactive layer 3b is connected by the electrically conducting adhesive layer 4 with the layer of nanowires 5. The layer of nanowires 5 is superimposed by the second carrier layer 6 which may be made of transparent PET.

The first pattern A1 , the second pattern A2 and the third pattern A3 can be provided within a narrow lateral area, the so-called "dead area" (see Fig. 2). Within the dead area a production of solar energy is not possible. The GFF which is in percent the total remaining area outside the dead areas can be set to values more than 90% by the proposed method.

Fig. 3a shows a cross-section scanning electron-microscopy image of the solar module. The layer of nanowires 5 appears as bright spots in the SEM image.

Fig. 3b shows a top view of the layer of nanowires 5. The nanowires form a mesh where the nanowires are in point or line contact. List of reference signs

1 first carrier layer

2 first electrode layer

3a ETL

3b photoactive layer

4 electrically conducting adhesive layer

5 layer of nanowires

6 second carrier layer

A1 first pattern

A2 second pattern

A3 third pattern

L laminate

51 first sub-laminate

52 second sub-laminate