Patent Publication Number: US-2023155538-A1

Title: Method for making photovoltaic slats for photovoltaic blinds

Description:
The present invention relates to a method for making a photovoltaic slat for a photovoltaic blind, in particular for a blind of the Venetian type. 
     As known, a photovoltaic blind is an apparatus suitable for closing an opening on a facade of a building (typically a window) and generating electricity from solar radiation which passes through the opening. 
     Such photovoltaic blinds comprise a traditional Venetian blind comprising a plurality of photovoltaic slats, normally made of plastic or metallic material, on which are later fixed photovoltaic cells of the crystalline silicon type. 
     At this point it is useful to specify that the term “photovoltaic slat” is understood to reference in a fully general manner any slat that comprises solar cells. 
     The photovoltaic cells are then connected to each other by means of additional wiring which needs to be arranged in the window structure in such a way to not interfere with the movement of the blind. 
     US 2018/0195766 discloses photovoltaic slats for photovoltaic blinds wherein solar cells modules having solar cells are attached to the convex curved surface of a pre-existing conventional slat. 
     US 2007/0175599 discloses photovoltaic slats for photovoltaic blinds wherein conventional solar cells are mounted within recesses which are previously provided in a slat made of extruded plastic. 
     Although functional, the known photovoltaic slats have limitations, especially regarding handling, speed of production and features such as flexibility and form factor. The complete fabrication process involves several separate steps to prepare and process cells and circuit assemblies before a photovoltaic slat is complete. Using crystalline silicon technology, individual cells must be sorted and wired together and assembled into the photovoltaic circuit, which must be carefully placed and positioned prior to the lamination process and final assembly. The complexity of this manufacturing process strongly influences the market price of the device. 
     Furthermore, the size of such assembly tends to be too large to retrofit conventional windows. 
     The aim of the present invention is to solve the technical problem described above, obviate the drawbacks and overcome the limitations of the background art, by providing a method for making a photovoltaic slat that is simpler, quicker and more cost-effective with respect to the prior art. 
     Within the scope of this aim, an object of the present invention is to provide a method for making a photovoltaic slat that makes it possible to make photovoltaic slats which have a more compact structure with dimensions which can be smaller than the prior art. 
     Another object of the present invention is to provide photovoltaic slats which are more flexible and versatile in their design with respect to the prior art. 
     Moreover, an object of the present invention is to provide photovoltaic slats having an assembly that is easier with respect to the prior art. 
     Another object of the present invention is to provide an alternative to known solutions. 
     A further object of the present invention is to provide photovoltaic slats that require less maintenance. 
     This aim, these objects and others which will become better apparent hereinafter are achieved by a method according to claim  1 . 
    
    
     
       Further characteristics and advantages will become better apparent from the description of some preferred but not exclusive embodiments of a method for making a photovoltaic slat, illustrated by way of non-limiting examples with the aid of the accompanying drawings, wherein: 
         FIG.  1    is a top view of a first possible embodiment of a photovoltaic sheet according to the invention; 
         FIG.  2    is an enlarged detail of the photovoltaic sheet of  FIG.  1   , wherein the cut axis is depicted; 
         FIG.  3    is a top view of a second possible embodiment of a photovoltaic sheet according to the invention; 
         FIG.  4    is an enlarged detail of the photovoltaic sheet of  FIG.  2   , wherein the cut axis is depicted; 
         FIGS.  5 A- 5 D and  6 A- 6 B  show a series of different possible configurations of the electrical contact areas and of the through holes in a photovoltaic strip of a photovoltaic sheet according to the invention; 
         FIG.  6 C  is a vertical cross-section of part of the photovoltaic sheet of  FIG.  6 B ; 
         FIG.  7    is a schematic representation of the structure of a portion of a photovoltaic sheet, which forms a photovoltaic slat, according to a first way for carrying out the method according to the invention; 
         FIG.  8    is a vertical cross-section of part of the portion of  FIG.  7   ; 
         FIG.  9    is a perspective view of a first possible embodiment of a photovoltaic slat, according to the invention; 
         FIG.  10    is a schematic representation of the structure of a portion of a photovoltaic sheet, which forms a photovoltaic slat, according to a second way for carrying out the method according to the invention; 
         FIG.  11    is a vertical cross-section of part of the portion of  FIG.  10   ; 
         FIG.  12    is a perspective view of a second possible embodiment of a photovoltaic slat, according to the invention; 
         FIG.  13    is a perspective view of a further possible embodiment of a photovoltaic slat according to the invention, in connection with the connection elements; 
         FIGS.  14 A,  14 B, and  14 C  are cross-sectional side views of a blind comprising photovoltaic slats according to the invention, with the slats rotated in different positions; 
         FIG.  15    is a schematic front view of the blind of  FIGS.  14 A- 14 C , arranged in a window. 
     
    
    
     With reference to the cited figures, the method for making a photovoltaic slat  31  for a photovoltaic blind  30 , according to the invention, comprises the steps of (preferably in order): 
     a. providing a photovoltaic sheet  10 ,  10 ′ comprising at least one photovoltaic strip  2 , each photovoltaic strip  2  comprising at least one string  3  of thin film solar cells  40  monolithically connected to each other in series;
 
b. cutting out a portion of the photovoltaic sheet  10 ,  10 ′ in the shape of a slat  31  suitable for a blind  30 , said portion comprising the photovoltaic string  3 ;
 
c. providing in said portion of the photovoltaic sheet  10 ,  10 ′ (and preferably within the photovoltaic string  3  comprised in said portion) at least two through holes  39  suitable for being passed through by connection elements  12   a  for connecting a plurality of slats  31  into a blind  30 .
 
     Regarding the step a., the term “photovoltaic sheet” is understood to reference a sheet comprising a deposition of a plurality of active layers (comprising junction layers  44 ,  45  made of well-known semiconductors of p-type and n-type) which form a plurality of solar cells  40 . 
     With particular reference to  FIGS.  7 - 8  and  10 - 11   , the photovoltaic sheet  10 ,  10 ′ in turn comprises: a substrate  41 , at least one insulating layer  42  arranged on the substrate  41 , a back contact layer  43  arranged on the at least one insulating layer  42 , a plurality of junction layers  44 ,  45  arranged on the back contact layer  43  and at least a front contact layer  46  arranged on the plurality of junction layers  44 ,  45 . 
     Preferably, the substrate  41  is a flexible substrate and even more preferably is metallic, for instance made of aluminum (Al) or stainless steel (SS) or titanium (Ti) or magnesium (Mg). 
     The insulating layer  42  is preferably made of oxides of silicon (SiOx) or alumina (Al2O3) or polyamide and it is interposed between the substrate  41  and the overlying layers (i.e. the back contact layer  43 ,  44 , the junction layers  44 ,  45  and the front contact layer  46 ) which are active, so as to avoid electrical contact between the substrate  41  and the overlying active layers  43 ,  44 ,  45 ,  46 . 
     Optionally, the photovoltaic sheet  10  further comprises a second insulating layer (not illustrated), arranged on the other side of the substrate  41  (i.e. the substrate&#39;s surface that lies opposite with respect to the surface on which the above mentioned back contact layer  43  and the junction layers  44 ,  45  are deposited), in order to prevent possible short-circuits when the photovoltaic slats  31  are in contact, for example during the raising or the lowering of the blind  30 . 
     The back contact layer  43  is preferably a back metal contact layer, and even more preferably is made of molybdenum (Mo), deposited on the insulating layer  42 . 
     The junction layers  44 ,  45  are preferably made of well-known semiconductors of p-type and n-type so to realize p-n junctions. 
     The at least one front contact layer  46  preferably comprises a transparent conducting oxide layer (TCO), such as a layer of aluminum doped zinc oxide (ZnO:Al), for collecting and transporting the photo-generated charge carriers. 
     Optionally, the at least one front contact layer  46  is provided with a metal contact grid  47 , for example arranged above the transparent conducting oxide layer, to transport the electric current more efficiently. 
     Optionally, a polyethylene terephthalate (PET) or ethylene-vinyl acetate (EVA) or any other plastic foil laminating the photovoltaic sheet is arranged above the at least one front contact layer  46  to provide protection from possible damage or contaminants during handling and processing. 
     The photovoltaic sheet  10 ,  10 ′ further comprises interconnection grooves  51 ,  52 ,  53  (or scribing steps) which define in the photovoltaic sheet  131  a plurality of thin film solar cells  40 , monolithically connected to each other in series. 
     Various different structures of thin film solar cells monolithically connected to each other in series are well-known in the photovoltaic technologies field. The skilled person can thus provide a photovoltaic sheet  10 ,  10 ′ comprising interconnection grooves  51 ,  52 ,  53  which define in the photovoltaic sheet  10 ,  10 ′ a plurality of thin film solar cells  40 , monolithically connected to each other in series, according to the invention. 
     In some embodiments the plurality of thin film solar cells  40  comprises single-junction thin film solar cells  40  monolithically connected, in other embodiments the plurality of thin film solar cells  40  comprises multi junction thin film solar cells monolithically connected. 
     In the illustrated and non-limiting examples, in particular with reference to the single-junction CIGS solar cell structure visible in  FIGS.  7 ,  8 ,  10  and  11   , the junction layers  44 ,  45  comprise:
         a first junction layer  44 , namely an absorber layer, made of a semiconductor of the p-type, preferably a deposition of Cu(In,Ga)Se2, deposited on the back metal contact layer  43 , and   a second junction layer  45 , namely a buffer layer, made of a semiconductor of the n-type, preferably a layer of cadmium sulfide CdS, deposited on the absorber layer  44 .       

     In certain embodiments (not shown), between the junction layers  44 ,  45  and the at least one front contact layer  46  (e.g. between the buffer layer  45  and the transparent conducting oxide layer) an intrinsic zinc oxide (i-ZnO) layer is further provided to protect the underlying junction layer  45  from sputter damage in the subsequent step of the fabrication process, wherein the least one front contact layer  46  (e.g. a transparent conducting oxide (TCO) is sputtered on top of the intrinsic zinc oxide (i-ZnO) layer. 
     A possible configuration of the interconnection grooves  51 ,  52 ,  53  is shown in the figures, still related to the non-limiting example of the single-junction CIGS solar cell structure. In greater detail, in this example, the interconnection grooves  51 ,  52 ,  53  comprise:
         first interconnection grooves  51  extending through the back contact layer  43  and which are filled by the first junction layer  44  (i.e. the absorber layer);   second interconnection grooves  52  extending through the first junction layer  44  (i.e. the absorber layer) and the second junction layer  45  (i.e. the buffer layer) and filled by the front contact layer  46  (i.e. the transparent conducting oxide layer);   third interconnection grooves  53  extending through the front contact layer  46  (i.e. the transparent conducting oxide layer), the second junction layer  45  and the first junction layer  44  and remaining empty (i.e. unfilled with further material).       

     As can be understood by looking at the figures, the first interconnection grooves  51  are substantially parallel and not coincident with respect to the second interconnection grooves  52  which, in turn, are substantially parallel and not coincident with respect to the third interconnection grooves  53 ; in other words the grooves  51 ,  52 ,  53  have a certain offset. 
     In this way, the first junction layer  44  extends into the first grooves  51  and is in contact with the insulating layer  42 , and the front contact layer  46  extends into the second grooves  52  and is in contact with the back contact layer  43 . 
     Preferably, the interconnection grooves  51 ,  52 ,  53  are provided by laser scribing. Alternatively, other patterning techniques for forming the interconnection grooves  51 ,  52 ,  53  can be used, for instance: silk screening with resist masks, etching with positive or negative photoresists, mechanical scribing, electrical discharge scribing. 
     Accordingly, in the preferred way for carrying out the method, the step a. of providing a photovoltaic sheet  10 ,  10 ′ in turn comprises the steps of: 
     a1. providing a substrate  41 ;
 
a2. Applying (e.g. depositing) on said substrate  41  at least one insulating layer  42 , one back contact layer  43 , a plurality of junction layers  44 ,  45  and a front contact layer  46 , so as to form a photovoltaic sheet  10 ,  10 ′ and providing, within said back contact layer  43 , within said plurality of junction layers  44 ,  45  and within said front contact layer  46 , interconnection grooves  51 ,  52 ,  53 , so as to define in the photovoltaic sheet  10 ,  10 ′ at least one photovoltaic strip  2  comprising at least one string  3  of thin film solar cells  40  monolithically connected to each other in series.
 
     Preferably, in the step a2. at least a back contact layer, at least two junction layers and at least a front contact layer, such as a transparent conducting oxide layer (TCO), are deposited, in such a way that the junction layers define the required single p-n (or p-i-n) junctions or multi p-n (or p-i-n) junctions. 
     In greater detail, in one possible embodiment, wherein the single thin film solar cells  40  are CIGS single-junction solar cells, the step a2., in turn, comprises the following steps:
         depositing or gluing at least one insulating layer  42  on the substrate  41  (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   depositing a back contact layer  43  on the insulating layer  42  (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   cutting the back contact layer  43  so as to provide first interconnection grooves  51 , for example by laser scribing or by any other patterning techniques already mentioned (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   depositing a first junction layer  44 , namely an absorber layer made of a semiconductor of the p-type, on the back metal contact layer  43  in such a way that the absorber layer  44  fills the first interconnection grooves  51  (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   depositing a second junction layer  45 , namely a buffer layer made of a semiconductor of the n-type, on the first junction layer  44  (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   cutting the second junction layer  45  and the first junction layer  44 , so as to provide second interconnection grooves  52 , for example by laser scribing or by any other patterning techniques (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   depositing a front contact layer  46 , namely a transparent conducting oxide layer, on the second junction layer  45  in such a way that the front contact layer  46  fills the second interconnection grooves  52  (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 );   cutting the front contact layer  46 , the second junction layer  45  and the first junction layer  44 , so as to provide third interconnection grooves  53 , for example by laser scribing or by any other patterning techniques (in one single step performed for all the sheet  10  for every strip  2  which is comprised in the sheet  10 ).       

     As to the photovoltaic strip  2 , the term “photovoltaic strip” is understood to reference a line of solar cells (i.e. a series of solar cells aligned along a longitudinal axis). In some embodiments, each photovoltaic strip  2  consists of a continuous single string  3  of thin film solar cells  40  monolithically connected to each other in series. 
     In other embodiments, each photovoltaic strip  2  comprises a continuous line of strings  3  (each string being a string  3  of thin film solar cells  40  monolithically connected to each other in series). 
     In other embodiments, each photovoltaic strip  2  comprises:
         a plurality of strings  3  of thin film solar cells  40  monolithically connected to each other in series, which are aligned along a respective longitudinal axis, and   working areas  9 B of the photovoltaic sheet which are interposed between the strings  3 .       

     In other words, in these last embodiments, within each photovoltaic strip  2 , the strings  3  are separated by a working area  9 B of the photovoltaic sheet  10 . 
     The working areas  9 A,  9 B are portions of the photovoltaic sheet  10  which are not active, in the sense that they are not meant to generate photovoltaic power. In practice, the working areas  9 A,  9 B are not provided with solar cells monolithically connected with the solar cells  49  comprised within the strings  3  (e.g. in the working areas there are no solar cells since no solar cells are defined in the layers of the photovoltaic sheet  10  during the step a. of providing a photovoltaic sheet  10 , or, alternatively, in the working areas  9 A,  9 B there are solar cells which are isolated from the solar cells  40  comprised in the strings  3  for instance by means of isolation grooves). 
     Preferably, the strings  3  are defined by isolation grooves, provided in the photovoltaic sheet  10 ,  10 ′, which in practice delimit the strings  3 . 
     In practice, in some embodiments the method comprises a preliminary step of providing one or more working areas  9 A,  9 B in the photovoltaic sheet  10  by providing one or more isolation grooves  62 ,  63  which isolate said isolated areas from the solar cells  40 . These working areas separate each string  3  from the next string  3  of the same strip  2  and/or each strip  2  from the next strip of the same sheet  10 . 
     In the preferred embodiments, such isolation grooves extend at least through the back contact layer  43 , the junction layers  44 ,  45  and the front contact layer  46 . 
     In other words, the photovoltaic sheet  10 ,  10 ′ comprises an array (or matrix) of strings  3  of solar cells  40 , wherein each said string  3  constitutes an independent photovoltaic device, and wherein said strings  3  are aligned in one or more lines referred to as photovoltaic strips  2 . 
     In some embodiments, such as the embodiment depicted in  FIGS.  1  and  2   , the photovoltaic sheet  10  comprises a plurality of parallel photovoltaic strips  2  which are separated by a working area  9 A of the photovoltaic sheet  10 . 
     In the step b. of cutting out, a portion of the photovoltaic sheet  10 ,  10 ′ comprising one or more of the strings  3  is cut out of the sheet  10 ,  10 ′. This portion has the shape of a slat  31  suitable for a blind  30  in the sense that a skilled person can choose any suitable shape and size depending on the blind  30  the slat is intended for. 
     In the preferred embodiments, the slat  31  is a slat  31  for a blind  30  of the Venetian type. 
     In the illustrated examples, a rectangular portion is cut, in other embodiments the portion of the photovoltaic sheet  10  is cut to have different shapes, for example: rectangular with tapered ends, or oval, or trapezoidal, etc. 
     As will be made clearer hereinafter, the cut portion (i.e. the slat  31 ) may be further shaped by means of a bending step. 
     Preferably, in the step b. of cutting out, at least a transversal cut  91  and at least a longitudinal cut  92  are provided in the photovoltaic sheet  10 ,  10 ′ so as to include in the slat  31  at least an entire string  3 . 
     In the embodiments wherein the photovoltaic sheet  10  comprises a plurality of parallel photovoltaic strips  2  which are separated by working areas  9 A, the longitudinal cut  92  is provided through said working area  9 A. 
     In the embodiments wherein each photovoltaic strip  2  comprises a series of strings  3  which are separated by working areas  9 B, the transversal cut  91  is provided through one of said working areas  9 B. 
     In the example shown in  FIG.  2   , a transversal cut  91  is provided in the working area  9 B between two strings  3  and a longitudinal cut  92  is provided in a working area  9 A between two strips  2  so as to cut off a portion of the photovoltaic sheet  10  which includes an entire string  3 . 
     In the example shown in  FIG.  4   , a transversal cut  91  is provided between two strings  3  (on an electrical contact area  14 , at the border between two solar cells  40 ) and a longitudinal cut  92  is provided in an inactive area between two strips  2 , as to cut off a portion of the photovoltaic sheet  10  which includes an entire string  3 . 
     In other embodiments, at least a transversal cut  91  and at least a longitudinal cut  92  are provided in the photovoltaic sheet  10  so as to include in the slat  31  a plurality of strings  3 . 
     In the step c. of providing at least two through holes  39  in the cut portion (i.e. in the slat  31 ), two or more through holes  39  are provided in said cut portion. These through holes  39  are suitable for being passed through by connection elements  12   a  in the sense that they have a shape and size that allow the insertion of a predetermined connection element  12   a.    
     The skilled person can choose any connection element suitable for connecting a plurality of slats  31  into a blind  30  depending on the blind  30  the slat is intended for. 
     For example, the connection elements  12   a  can be connection elements for a mechanical connection, such as cords, wires and the like. As will be made clearer hereinafter, the connection elements  12   a  will also provide electrical connection between the slats  31 . 
     In the preferred embodiments, wherein the slat  31  is intended for a blind of the Venetian type, the connection elements  12   a ,  12   b  comprise strips or cords which, in the blind  30 , will be configured to pull or push the slats  31  so as to make them translate along a first axis and/or to rotate (preferably simultaneously) around second axes (see for instance  FIGS.  14 A- 14 C ). 
     Preferably, the method further comprises, before said step b. of cutting out, the step of: 
     b1. providing, in said portion of photovoltaic sheet  10  to be cut out, two electrical contact areas  14  configured to allow the electrical contact between the thin film solar cells  40  of said string  3  and said connection elements  12   a , so as to make it possible to electrically connect the slat  31  with another slat  31  via the connection elements  12   a.    
     Then, the resulting slat  31  will be connectable to at least two connection elements  12   a  of a photovoltaic blind  30  in an operative configuration wherein each of the connection elements  12   a  passes through a respective through hole  39  and can be electrically connected to a respective electrical contact area  14  so as to be electrically connected to the solar cells  40  of the string  3  (as shown for instance in  FIG.  13   ). 
     Preferably, the electrical connection between each connection element  12   a  and the respective electrical contact area  14  is carried out by means of an electrical connection structure  38 , such as a conductive flat ribbon  38  (e.g. a copper-based ribbon) or the like, in an assembly step, carried out after the step c., consisting in:
         inserting at least two connection elements  12   a  into respective through holes  39 , and   electrically connecting each connection element  12   a  to the solar cells  40  by means of an electrical connection structure  38  which connects each connection element  12   a  to a respective electrical contact area  14 .       

     At this point it is helpful to specify that the connection elements  12   a  do not necessarily pass through every through hole  39 : in some embodiments there are more than two through holes  39  and only some of them are engaged by the connection elements  12   a  (see for instance  FIG.  13   ). 
     In order to ensure the electrical connection, the connection elements  12   a ,  12   b  preferably comprise electrically conductive material (for example conductive textiles) and are configured to electrically and mechanically connect the photovoltaic slats  31 : in other words, the connection elements  12   a ,  12   b  provide the mechanical connection together with the electrical connection of the photovoltaic slats  31 . 
     In some embodiments (as shown in  FIGS.  7  and  8   ), the electrical contact area  14  is provided by depositing on at least one solar cell  40  a layer of conductive material  48  which shields the solar cell  40  from solar radiation so as to make said solar cell  40  an inactive solar cell  40 ′. 
     In other embodiments, the electrical contact area  14  is provided by fixing an electrically conductive adhesive on at least one solar cell  40  (preferably on the front contact layer  46 ). 
     In yet another embodiment, the electrical contact area  14  is provided by performing a welding (e.g. laser welding or electrical welding) or a fusion on at least one of said solar cells  40  so as to fuse active layers therein (i.e. to merge the back contact layer  43 , the junction layers  44 ,  45  and a front contact layer  46 ) and to make them become a permanently, electrically-conductive metalized alloy, thereby forming a conductive path between the front contact  46  and the back contact  43  layers. 
     In practice, the electrical contact areas  14  are configured to allow the photovoltaic generated current to flow from the active solar cells  40  to the connection elements  12   a , via the connection structure  38 , and vice-versa. 
     Obviously at least two electrical contact areas  14  are comprised in the portion that is cut to form the slat  31 , so that two connection elements  12   a ,  12   b  can be respectively connected to two points of the slat  31  between which a voltage ΔV is generated. 
     Each electrical contact area  14  can extend on the surface of one or more solar cells  40  that are adjacent (as shown in  FIGS.  5 A- 5 D ) and optionally also on a working area  9 B (as depicted in  FIGS.  6 A- 6 B ). 
     In the configuration shown in  FIGS.  6 A- 6 B  the electrical contact area  14  is preferably provided by applying a layer of conductive material  48  or an electrically conductive adhesive or the like. Optionally, as depicted in  FIG.  6 C , before applying the layer of conductive material  48  (or the electrically conductive adhesive or the like), on the working area  9 B between two strings  3  a dielectric layer  481  is applied (i.e. a layer of dielectric material such as a polyamide-based material, polyamide film, poly(methyl methacrylate) PMMA, silicon oxide etc.) in order to avoid short-circuits. The layer of conductive material  48  (or the electrically conductive adhesive or the like) will thus cover the dielectric layer  481 . 
     The through hole  39 , in turn, can be provided in an electrical contact area  14 , or in a solar cell  40  which is adjacent to at least an electrical contact area  14 , or in a solar cell  40 ,  40 ′ which is placed between two electrical contact areas  14 . 
     In the embodiment of  FIG.  5 A , a through hole  39  is provided in an active solar cell  40  which is adjacent to a solar cell  40  whereon an electrical contact area  14  is provided. 
     In the embodiment of  FIG.  5 B , an electrical contact area  14  is provided on two consecutive solar cells  40  and a through hole  39  is provided in one of these two consecutive solar cells  40 . 
     In the embodiment of  FIG.  5 C , an electrical contact area  14  is provided on a single solar cell  40  in which a through hole  39  is also provided. 
     In the embodiment of  FIG.  5 D , an electrical contact area  14  is provided on three consecutive solar cells  40  and a through hole  39  is provided in the central cell  40  of these three consecutive solar cells  40 . 
     In some embodiments, such as the ones of  FIGS.  6 A- 6 B , in the step b. of providing through holes  39 , a through hole  39  is provided in a working area  9 B between two strings  3 . 
     In the embodiment of  FIG.  6 A , an electrical contact area  14  is provided which extends on a solar cell  40  placed at the end of a string  3  and on an adjacent working area  14  in which a through hole  39  is provided; in this embodiment, in the step of cutting out, a transversal cut  91  is performed in the photovoltaic sheet  10  so as to include in the slat  31  the whole contact area  14 , the through hole  39  and the string  3 . 
     In the embodiment of  FIG.  6 B , an electrical contact area  14  is provided which extends on a solar cell  40  placed at the end of a string  3  and on an adjacent working area  14  and also on a solar cell of the next string  3  of the photovoltaic strip  2 ; a through hole  39  is provided in said working area  14  between the two strings  3 . In this embodiment, the electrical contact area  14  electrically connects the two illustrated strings  3 ; in the step of cutting out, both of the two strings  3  on which the electrical contact area  14  extends will be included in the slat  31 , together with the through hole  39 . 
     In a particular embodiment shown in  FIGS.  10 - 11   , before the step b. of providing through holes  39 , the method comprises a step of providing in a solar cell  40  a close-pattern isolation groove  61  so as to define an inactive area of the solar cell  40 ; and in the step b. of providing through holes  39 , the through hole  39  is provided in said inactive area of the solar cell  40 . 
     In greater detail, said close-pattern isolation groove  61  surrounds the through hole  39  and extends at least through the front contact layer  46 , the plurality of junction layers  44 ,  45  and the back contact layer  43 , so as to define an inactive area of the thin film solar cell  40  surrounding the through hole  39 . The inactive area is, in practice, electrically isolated from the rest of the solar cell  40 . 
     Preferably, the method further comprises, before the step b. of cutting out, a step of providing at one or more edges of the at least a photovoltaic strip  2  one or more peripheral isolation grooves  62  so as to define one or more peripheral inactive areas  33  of the photovoltaic strip  2 . 
     In greater detail, each isolation groove  62  extends at least through the front contact layer  46 , the plurality of junction layers  44 ,  45  and the back contact layer  43 , so as to define a peripheral inactive area that is electrically isolated from the rest of the string  3 . 
     Optionally the method further comprises a step of bending at least a portion of the slat  31 . 
     Preferably, the slat  31  is bent at said peripheral inactive area  33  (i.e. at least part of the peripheral inactive area  33  is bent), for example in the manner shown in  FIGS.  9  and  12    wherein the inactive areas  33  are bowed downwards. 
     In general, the isolation grooves  61 ,  62  make it possible to make cuts, holes and mechanical treatments in general while avoiding any short-circuit or damage to the active solar cells  40 . 
     All the above mentioned isolation grooves  61 ,  62  can be provided by any known patterning techniques, such as: laser scribing, silk screening with resist masks, etching with positive or negative photoresists, mechanical scribing, electrical discharge scribing. 
     Optionally, in the assembly steps the slats  31  can be connected, in addition to the connecting elements  12   a  which pass through the through holes  39 , also by means of second connection elements,  12 B which, for example, can be coupled to the peripheral inactive areas  33  and which are configured to make the slats rotate (preferably simultaneously) around an axis, as shown in  FIGS.  14 A- 14 C , so as to build a blind of the Venetian type such as the one that in  FIG.  15    is depicted in a window. 
     In the embodiments shown in  FIG.  13    and  FIGS.  14 A- 14 C , the photovoltaic slats  31  are assembled into a photovoltaic blind which comprises two first connection elements  12   a  (i.e. conductive lifting cords), each one of which is electrically connected with two second connection elements  12   b  (i.e. conductive orientation cords). The electrical connection between the first connection elements  12   a  and the second connection elements  12   b  is realized, in a known way, inside the bottom rail. 
     In practice, in the photovoltaic blind  30 , the charge carriers under bias voltage ΔV move from photovoltaic slats  31  towards the connection elements  12   b  and  12   a  and then can be transmitted to an electronic device and/or to a battery pack or an inverter which converts the variable direct current output into a synchronized alternating current that can be fed into a building&#39;s electrical grid. 
     In a different possible embodiment, the first connection elements  12   a  are electrically connected with the photovoltaic slats  31  and the second connection elements  12   b  are not. In yet another possible embodiment, the second connection elements  12   b  are electrically connected with the photovoltaic slats  31  and the first connection elements  12   a  are not. 
     Advantageously, the photovoltaic slats  31  can be provided with a plurality of through holes  39 , placed at different distances, and then it is possible to electrically connect only some thin film solar cells  40  with respective connection elements  12   a ,  12   b , and so it is possible to choose the voltage ΔV of the photovoltaic slats  31 , since the voltage ΔV depends on the number of thin film solar cells  40  connected in series, and therefore depends on the distance of the electrical contact areas  14  to which the connection elements  12   a ,  12   b  are connected. In that way, the connection elements  12   a ,  12   b  can be selectively arranged at different distances so as to allow customized working voltages such as 12V, 24V, 36V, 48V, etc., depending on the size of the blind  30 . 
       FIG.  13    shows an example of a photovoltaic slat  31  wherein three first connection elements  12   a  (i.e. three lifting cords) pass through three respective through holes  39  and can each be selectively electrically connected with one or two respective second connection elements  12   b  (i.e. orientation cords) and preferably with one (or two) second connection element (or elements)  12   b.    
     In this example, in practice, there are three possible voltages V 1 , V 2 , V 3 , selectable by selectively connecting two first connection elements  12   a  with two respective second connection elements  12   b.    
     It should be noted that by connecting the connection elements  12   a    12   b  to different electrical contact areas  14  it is possible to provide different voltages V 1 , V 2 . V 3 . 
     In one embodiment of the present invention, ultrasonic welding is used to reduce the thermal stress in the previous process. 
     In practice it has been found that the method for making a photovoltaic slat according to the present invention achieves the intended aim and objects, since it is simpler, quicker and more cost-effective with respect to the prior art. 
     Another advantage of the method, according to the invention, resides in that it is more flexible and versatile in the design with respect to the prior art. 
     A further advantage of the method, according to the invention, resides in that it provides photovoltaic slats having an assembly that is easier with respect to the prior art. 
     Another advantage of the method according to the invention resides in that it provides slats which require less maintenance with respect to the prior art. In the preferred embodiments, substantially no maintenance is required. 
     A further advantage of the method, according to the invention, resides in that mass production is easier and less costly with respect to the prior art. 
     Another advantage of the method according to the invention resides in that it avoids defects in the photovoltaic slats. 
     The method thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept. 
     In practice the materials used, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to the requirements.