Abstract:
A thin-film solar module consists of a number of solar cells tandem mounted and series-connected on a common substrate and a number of diodes disposed antiparallel and adjacent thereto. Overlap zones are formed by a projecting edge area of an electrode layer of a solar cell or diode engaging a recess of the corresponding electrode layer of the adjacent diode or solar cell. Each diode is connected in the reverse direction with the adjacent solar cell in at least two overlap zones, the front electrode layer of the diode with the back electrode layer of the solar cell in at least one of said overlap zones, and the back electrode layer of the diode with the front electrode layer of the solar cell in at least one other overlap zone. The photovoltaically active layer sequence is additionally separated by grooves in areas of the grooves of the back electrode layer.

Description:
FIELD OF THE INVENTION 
     This invention relates to a thin-film solar module. 
     BACKGROUND OF THE INVENTION 
     A solar module known from DE 198 03 326/U.S. Pat. No. 6,013,870 contains a number of solar cells tandem mounted and series-connected on a common substrate. The module also includes a number of adjacent diodes, also referred to as bypass diodes, likewise tandem mounted and connected in series but antiparallel to the solar cells on the same substrate. The structure consists for example of a glass wafer as the substrate , the front electrode layer deposited thereon, the photovoltaically active layer sequence located thereon, and the subsequently applied back electrodes (See FIG. 3 of DE 198 03 326/U.S. Pat. No. 6,013,870). The substrate and front electrode layer are transparently designed so that sunlight can penetrate into the photovoltaically active layers through said structure in order to produce the necessary mobile electric charge carriers. This is known as a superstrate structure. 
     The solar module can also be constructed as follows. On the substrate (e.g. a glass wafer) the back electrode layer is first deposited, then the photovoltaically active layer sequence , and subsequently the front electrode layer. In this case sunlight penetrates into the photovoltaically active layers through the last-named layer, which is now transparently designed. This module structure is called a substrate structure 
     In a module according to DE 198 03 326/U.S. Pat. No. 6,013,870, an electric connection is present between a bypass diode and adjacent solar cell by reason of an electric conductivity (transverse conductivity) of the photovoltaically active layer sequence. Then the front and back electrode layers of the diode and its adjacent solar cell are interconnected by a direct electric contact. Consequently, the electric power of the solar module is reduced. This effect can occur because the photovoltaically active layer is not separated in the area of the separation of the front or back electrode layer in the grooves and of this module. 
     In the above-described module, the bypass diodes are also not covered upon incidence of light on the side facing the light and thus reduce the power of the solar cell by reason of their opposite polarity to the cell. The produced photocurrent of the solar cell is reduced by the amount of the photocurrent of the bypass diode. 
     SUMMARY OF THE INVENTION 
     The invention provides a solar module which can be produced using integrated thin-film technology, has a diode connected in the reverse direction for each individual solar cell (see DE 198 03 326/U.S. Pat. No. 6,013,870). The solar module avoids power losses caused by the transverse conductivity between the diode and the adjacent cell due to the photoactive layer sequence. A further object of the invention is that it prevents power loss of the solar module arising from the illuminated bypass diodes by an opaque mask of the bypass diodes. This is accomplished by means of a lacquering or screen print on the front glass wafer. 
     It is accordingly first provided that the front and back electrode layers of adjacent diodes are not electrically contacted directly with each other. This eliminates the direct series connection of the diodes. Further, overlap zones are formed by a projecting edge area of an electrode layer of a solar cell or diode engaging a recess of the corresponding electrode layer of the adjacent diode or solar cell and thus overlapping the superjacent or subjacent zone of the other electrode layer of said adjacent diode or solar cell. Finally, each diode is connected in the reverse direction with the adjacent solar cell in at least two overlap zones. Specifically, the front electrode layer of the particular diode is electrically contacted with the back electrode layer of the particular solar cell in at least one of said overlap zones. Also, the back electrode layer of said diode is electrically contacted with the front electrode layer of said solar cell in at least one other of said overlap zones. 
     The abovementioned overlap zones can be produced in simple, time-saving and cost-effective fashion in the course of the integrated industrial process by corresponding structuring of the particular electrode layers, as will become clearer below with reference to the embodiments. The contacting in the overlap areas also ensures firstly that each individual solar cell has assigned thereto a diode connected in the reverse direction thereto. Secondly, it causes the diodes to be series-connected altogether but in the reverse direction to the solar cells. While the series connection of the solar cells is effected directly in the usual way, i.e. by contacting the front electrode layer of a solar cell with the back electrode layer of the adjacent cell, the series connection of the diodes is effected by indirect means via the overlap zones and the electrode layers of the assigned solar cells. 
     To prevent each diode from being electrically short-circuited with its adjacent solar cell by a shunt resistance, represented by the transverse conductivity of the photovoltaically active layer sequence, the photovoltaically active layer sequence is removed between diode and solar cell. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, two embodiments (substrate and superstrate technology) of the invention will be explained in more detail with reference to the schematic figures, in which: 
     For superstrate technology: 
     FIG. 1 shows an equivalent circuit diagram of part of the solar module, 
     FIG. 2 shows part of the solar module in a plan view, 
     FIG. 3 shows a first cross section through said part of the solar module along line  3 — 3  of FIG. 2, 
     FIG. 4 shows a second cross section along line  4  of FIG. 2, 
     FIG. 5 shows a third cross section along line  5 — 5  of FIG. 2, 
     FIGS. 6,  7  and  8  show three different versions of overlap zones. 
     For substrate technology: 
     FIG. 9 shows part of the solar module with the reverse layer sequence in a plan view, 
     FIG. 10 shows a first cross section through said part of the solar module with the reverse layer sequence along line  10 — 10  of FIG. 9, 
     FIG. 11 shows a second cross section along line  11 — 11  of FIG. 9, 
     FIG. 12 shows a third cross section along line  12 — 12  of FIG. 9, 
     FIGS. 13,  14  and  15  show three different versions of overlap zones 
    
    
     DETAILED DESCRIPTION 
     The plan views of FIG. 2 and 9 show a detail of a solar module according to the invention, with solar cells  11  [ 11 ],  12  [ 12 ],  13  [ 13 ] and  14  [ 14 ] and diodes  21  [ 21 ],  22  [ 22 ],  23  [ 23 ] and  24  [ 24 ]. (The number sequences and other terms in square brackets relate to the associations to the substrate technology depicted in FIGS. 9 to  15 ). One sees substantially the structuring of the particular front and back electrode layers. This is done by a first system of grooves  5  [ 5 ] and by a second system of grooves  7  [ 7 ]. For clarity&#39;s sake grooves  5  [ 7 ] are shown only as thick unbroken lines, unlike grooves  7  [ 5 ]. The back [front] electrode layers structured by grooves  7  [ 5 ] are obliquely hatched. The structuring of the photovoltaically active layer sequence necessary for this invention is shown by grooves  25  [ 25 ], which are congruent with or narrower than grooves  7  [ 5 ] of the back [front] electrode layer. For better representation, grooves  25  [ 25 ] are shown with the same size as grooves  7  [ 5 ]. 
     Due to corresponding guidance of grooves  5  [ 7 ], projecting edge areas and recesses are formed in the front [back] electrode layers of the solar cells and diodes, resulting in overlap zones  10  [ 10 ] or  20  [ 20 ] in which said projecting edge areas come to lie under the superjacent edge zones of back [front] electrode layers. One also sees grooves  8  [ 8 ] as well as  6  [ 6 ] and  9  [ 9 ] which are for the electric contacting of overlapping electrode layers, said contacting being done through the photovoltaically active layer sequence located between the electrode layers (and not explicitly shown in FIG. 2 or  9 ), as indicated in detail by the sectional views of FIGS. 3 to  5  or  10  to  12 . 
     First, FIGS. 4 and 11 show sections only through solar cells  11  [ 11 ],  12  [ 12 ],  13  [ 13 ] and  14  [ 14 ]. The cells are connected in series in integrated fashion as usual. On substrate  1  [ 1 ], which is transparent in these embodiments, for example a glass wafer, front [back] electrode layers  2  [ 4 ] structured by grooves  5  [ 7 ] are first applied. Located thereon is continuous photovoltaically active layer sequence  3  [ 3 ] in which individual grooves  8  [ 8 ] are cut for the series connection. 
     The photovoltaically active layer sequence is also separated in the area of grooves  7  [ 5 ] by grooves  25  [ 25 ]. Grooves  25  [ 25 ] must not be wider than grooves  7  [ 5 ] since the front and back electrode layers would otherwise be electrically short-circuited. In these embodiments, however, grooves  7  [ 5 ] are shown with the same width as grooves  25 . Back [front] electrode layers  4  [ 2 ] separated by grooves  7  [ 5 ] are located on photovoltaically active layer sequence  3  [ 3 ], the material of back [front] electrode layers  4  [ 21  extending in grooves  8  [ 8 ] down to the surface of front [back] electrode layers  2  [ 4 ] and thus effecting the electric contacting necessary for the series connection. As seen by FIGS. 3 and 5, a lacquer or screen print mask  28  is applied to the exposed surface of substrate l over the diodes  21 ,  22 ,  23  and  24 . 
     The photovoltaically active layer sequence can be executed for example as a p-i-n structure (in superstrate technology) or n-i-p structure (in substrate technology) based on amorphous silicon (the term “based on amorphous silicon” being intended to include all kinds of variants of single and multiple cell structures as well as amorphous alloys containing elements besides silicon (e.g. a-Si, a-SiGe, a-Si/a-Si, a-Si/a-SiGe, a-Si/a-Si/a-SiGe, a-Si/a-SiGe/a-SiGe, a-SiC/a-Si/a-SiGe). However, it can also contain nano- or microcrystalline silicon (nc- or μc-Si) or poly-c-silicon, cadmium sulfide (CdS) or cadmium telluride (CdTe) or be based on chalkopyrites, such as CuInSe 2  (CIS), Cu(In,Ga)Se 2  (CIGS) or Cu(In,Ga) (Se,S) 2 . One can also use any other materials or layer sequences usual in solar cell technology which are suitable for producing and separating electric charges upon incidence of light. As front electrode layer  2  ( 2 ] one expediently uses a transparent conductive oxide layer, consisting for example of stannic oxide; as back electrode layer  4  [ 4 ] a highly electroconductive, for example nontransparent (opaque) metal layer which can also consist of a plurality of superimposed sublayers each of a different material. 
     The section shown in FIGS. 5 and 12 extend through tandem mounted diodes  21  [ 21 ],  22  [ 22 ],  23  [ 23 ] and  24  [ 24 ]. Like the solar cells, the diodes consist of front electrode layers  2  [ 2 ], back electrode layers  4  [ 4 ] and the abovementioned intermediate photovoltaically active layer sequence  3  [ 3 ] separated into individual areas in grooves  25  [ 25 ]. The diodes separated by groove system  25  [ 25 ] in the areas of grooves  5  [ 7 ], which are no longer shown here only as lines as in FIG. 2 or  9  but with a certain width, and grooves  7  [ 5 ] located thereabove, which have the same width as grooves  5  [ 7 ] in FIG. 5 or  12 , although this need not necessarily be the case. However, the width of grooves  5  [ 5 ],  25  [ 25 ] and  7  [ 7 ] must be selected such that the two electrode layers do not directly touch each other since they would otherwise be electrically short-circuited. In the embodiments of FIGS. 5 and 12, grooves  5  [ 5 ],  25  [ 25 ] and  7  [ 7 ] are executed with the same width but other designs not shown here are also possible. For example groove  7  [ 5 ] can be narrower than groove  25  [ 25 ] and groove  25  [ 25 ] can be narrower than groove  5  [ 7 ]. Thus, diodes  21  [ 21 ],  22  [ 22 ],  23  [ 23 ] and  24  [ 24 ] are electrically insulated from each other, at least in the shown cutting plane. 
     FIGS. 3 and 10 illustrate bent cross section according to line  3 — 3  of FIG. 2 or Line  10 - 10  of FIG. 9, respectively. These cross section views are divided into six portions a to f [a to f] each of which is straight. Designations are selected as in FIGS. 4 or  11  and  5  or  12 . Portions b [b] and f [f] correspond to partial sections from FIG. 5 or  12 , portion d [d] to a partial section from FIG. 4 or  11 . Portions c [c] and e [e] go through overlap zones  10  [ 10 ] and  20  [ 20 ] respectively. 
     In the first overlap zones  10  [ 10 ], a projecting edge area of front [back] electrode layer  2  [ 4 ] of diode  22  [ 22 ] is located under an edge zone of back [front] electrode layer  4  [ 2 ] of assigned solar cell  12  [ 12 ]. Groove  6  [ 6 ] is present in which the material of back [front] electrode layer  4  [ 2 ] of solar cell  12  [ 12 ] extends through photovoltaically active layer sequence  3  [ 3 ] down to the surface of the subjacent edge area of front [back] electrode layer  2  [ 4 ] of diode  22  [ 22 ] so that said two electrode layers are electrically contacted with each other there. To avoid an electric short circuit between diode and adjacent cell, generated by the transverse conductivity of photovoltaically active layer sequence  3  [ 3 ], photovoltaically active layer sequence  3  [ 3 ] is separated by grooves  25  [ 25 ] which extend under grooves  7  [ 5 ] and have the same width as grooves  7  [ 5 ], although this need not necessarily be the case. However grooves  7  [ 5 ] must not be narrower than grooves  25  [ 25 ] since the front and back electrode layers would otherwise be electrically short-circuited. 
     A similar situation is found in sectional area e [e], where one sees overlap zone  20  [ 20 ] formed in this case by a projecting edge area of front [back] electrode layer  2  [ 4 ] of solar cell  13  [ 13 ] and the superjacent edge zone of back [front] electrode layer  4  [ 2 ] of diode  23  [ 23 ]. Groove  9  [ 9 ] in intermediate photovoltaically active layer sequence  3  [ 3 ] ensures contacting between said two layers, by means of the material of back [front] electrode layer  4  [ 2 ] of diode  23  [ 23 ] extending in said groove down to the surface of front [back] electrode layer  2  [ 4 ] of solar cell  13  [ 13 ], and grooves  25  [ 25 ] under grooves  7  [ 5 ] for separating photovoltaically active layer sequence  3  [ 3 ]. 
     The equivalent circuit diagram of FIG. 1 shows, along with solar cells  11  to  14  and diodes  21  to  24 , corresponding front and back electrode layers  2 ,  4  which are contacted with each other in grooves  6  and  9  of said transition zones  10 ,  20  not shown here. The series connection of solar cells  11  to  14  and indirectly also of diodes  21  to  24  is effected via grooves  8 , as mentioned above. 
     FIGS. 6 to  8  and  13  to  15  show variants in the design of transition zones  10  [ 10 ] and  20  [ 20 ]. While overlap zones  10  [ 10 ] and  20  [ 20 ] are formed by projecting edge areas and recesses in the front [back] electrode layers of the correlated solar cells and diodes in the variant depicted in FIG. 2 or  9 , this is done for example according to FIG. 6 or  13  by projecting edge areas in back [front] electrode layers  4  [ 2 ]. These four embodiments therefore have in common that both one and the other of transition zones  10  [ 10 ] and  20  [ 20 ] of a diode and the adjacent solar cell are formed by projecting edge areas and recesses of the matching electrode layers, i.e. either the front [back] or the back [front] ones. 
     In the embodiment of FIG. 7 or  14 , transition zone  10  [ 10 ] is formed by a projecting edge area of back [front] electrode layer  4  [ 2 ] of the solar cell, and transition zone  20  [ 20 ] by a projecting edge area of front [back] electrode layer  2  [ 4 ] likewise of the solar cell. According to FIG. 8 or  15  this is done by projecting edge areas of the front [back] and back [front] electrode layers of only the diode. These two variants thus have in common that one transition zone is formed by a projecting edge area and a recess in the front [back] electrode layers, and the other transition zone by a projecting edge area and a recess in the back [front] electrode layers of the involved diode and solar cell. 
     FIGS. 6 to  8  or  13  to  15  each show a pair consisting of a diode (on the left) and the assigned solar cell (on the right). As in FIG. 2 or  9 , one sees front and back electrode layers  2  or  4  [ 2  or  4 ], the systems of grooves  5  and  7  [ 5  and  7 ] separating said layers, and the at least necessary two overlap zones  10  [ 10 ] and  20  [ 20 ] with grooves  6  [ 6 ] or  9  [ 9 ] present therein for contacting in the photovoltaically active layer sequence located between front and back electrode layers  2  or  4  [ 2  or  4 ], and grooves  25  [ 25 ] for separating said photovoltaically active layer sequence, which is again not explicitly shown here. Grooves  8  [ 8 ] for the series connection of adjacent solar cells are not shown either.