Abstract
The invention relates to a method for producing a thin film solar cell module and thin film solar cell module thus produces. The method comprises the steps of forming a multi-layer structure (100) of multiple electrically interconnected thin film solar cells (1) on a substrate (2), the multi-layer structure comprising a back contact layer (10), a photovoltaic active layer (11), and a front contact layer (13); and forming a conductive grid (3) underneath or onto the front contact layer by depositing a conductive material through a mask (4) before or after forming the front contact layer (13), by moving the substrate (2) and the mask (4) with respect to a deposition source (5) of the conductive material.
Claims
1. Thin film solar cell module comprising a multi-layer structure of multiple electrically interconnected thin film solar cells (1) on a substrate (2), the multi-layer structure comprising a back contact layer (10), a photovoltaic active layer (11), a front contact layer (13), and a conductive grid (3) underneath or on the front contact layer (13) made of a conductive material, characterized by that an elongated conductive line (31) of said conductive grid (3) in a cross-section plane perpendicular to its longitudinal direction has a surface contour (32) having a top section (321) and two side sections (322, 323) flanking the top section (321), whereby any tangent (5) on one or both of the side sections (322, 323) together with a layer surface (14) of said multi-layer structure underneath the conductive grid (3) create a maximum angle (a), which is smaller than 80, smaller than 70, or smaller than 60.
2. Thin film solar cell module according to claim 1, characterized by that said top section (321) and/or said one or both side sections (322, 323) are curved.
3. Thin film solar cell module according to claim 1, characterized by that said conductive line (31) has a cross section substantially in the shape of a bell curve.
4. Thin film solar cell module according to claim 1, characterized by that said conductive line (31) has a substantially v-shaped cross section.
5. Thin film solar cell module according to one of the claim 1, characterized by that said conductive line has a width along said cross section of between 60 m and 130 m, or between 80 m and 100 m.
6. Thin film solar cell module according to one of the claim 1, characterized by that said conductive grid (3) is a metal grid.
7. Thin film solar cell module according to one of the claim 1, characterized by that the conductive grid (3) consists of parallel elongated conductive lines (31) oriented along said longitudinal direction.
8. Thin film solar cell module according to claim 7, characterized by that the interconnected thin film solar cells on said substrate (2) are divided by dividing lines, whereby the conductive lines (31) are substantially parallel to the dividing lines.
Description
[0027] Some examples of embodiments of the invention will be explained in more detail in the following description with reference to the accompanying schematic drawings, wherein:
[0028] FIG. 1 shows the cross-section of a multi-layer structure of a thin film solar cell module;
[0029] FIG. 2 shows the cross-section of a multi-layer structure of a thin film solar cell module having a conductive grid;
[0030] FIG. 3 shows a surface contour of a conductive line according to one embodiment;
[0031] FIG. 4 shows a schematic cross-sectional view on a setup for depositing a conductive line through a mask;
[0032] FIG. 5 shows a surface contour of a conductive line according to a further embodiment;
[0033] FIG. 6 shows the cross-section of a mask for depositing a conductive line;
[0034] FIG. 7 shows a view onto a mask while the mask and substrate pass a deposition source according to one embodiment of a method for producing a thin film solar cell module;
[0035] FIG. 8 shows a view onto a mask while the mask and substrate pass a deposition source according to a different embodiment of a method for producing a thin film solar cell module;
[0036] FIG. 1 is a schematic cross-section of a multi-layer structure of a thin film solar cell 1. A substrate 2 is shown, on which the multi-layer structure is provided. The multi-layer structure comprises a back contact layer 10 placed on the substrate 2, a front contact layer 13 facing away from the substrate 2 and a photovoltaic active layer 11 sandwiched between the two contact layers 10, 13. There is a further buffer layer 12 on the photovoltaic active layer 11, which is optional.
[0037] FIG. 2 shows a similar structure as in FIG. 1 with the difference that this solar cell 1 comprises a conductive grid 3 having conductive grid lines 31, the cross-section of four of which can be seen in FIG. 2. Here, the conductive grid 3 is placed on a layer surface 14, which is a light incident surface of the front contact layer 13. In other embodiments not shown here, the conductive grid 3 may be placed underneath the front contact layer 13, such that the layer surface 14 may be an interface between the front contact layer 13 and the buffer layer 12 or between the front contact layer 13 and the photovoltaic active layer 11 in the case where there is no buffer layer 12.
[0038] The conductive lines 31 in FIG. 2 are shown with a curved surface contour 32, which is shown in more detail in FIG. 3. The contour 32 comprises a top section 321 flanked by two side sections 322, 323, namely a left slope 322 and a right slope 323. The contour 32 is symmetrical, so that the left slope 322 or left side section 322 is a mirror image of the right slope 323 or right side section 323. Tangents 6 of the side sections at a certain height therefore have the same but inverse angle with respect to the layer surface 14 on which the conductive line 3 is placed. One tangent 6 of the left side section 322 is shown in FIG. 3. The tangent 6 along the entire contour 32 has a maximum angle smaller or equal a, whereby a is 80 or less, depending on the embodiment.
[0039] Light incident perpendicular to the layer surface 14 and therefore perpendicular to the substrate (not shown in FIG. 3) onto the conductive line 3 will be reflected also perpendicular or nearly perpendicular back up, if it is incident on the top section of the contour 321. However, if the incident light hits either of the side sections 322, 323, it is reflected at an angle. When reaching an interface of the module from below, the reflected light will be reflected again, for example due to internal reflection, and impinge on the layer surface 14 at a position where there are no conductive lines 3.
[0040] FIG. 4 shows a setup for depositing the conductive line 3. The multi-layer structure 100 comprising the substrate 2 is covered by a mask 4, which has an opening 41 elongated in a direction perpendicular to the plane of the drawing. Only a section of the multi-layer structure 100 and the mask 4 are shown here, so that only one opening 41 is visible. A deposition source 5 such as an evaporator is placed below the multi-layer structure 100, on the side covered by the mask 4. The deposition source 5 is also elongated in the direction perpendicular to the plane of drawing and therefore parallel to the longitudinal direction of the opening 41. While the deposition source 5 is stationary, the multi-layer structure 100 together with the mask 4 are moved above the deposition layer 5, in the arrangement of FIG. 4 from left to right parallel to the drawing plane.
[0041] The deposition source 5 produces material beams 51 of the material to be deposited onto the layer surface 14 to form the conductive line 31. Different material beams 51 arrive at different angles through the opening 41 at the layer surface 14. During the movement of the multi-layer structure 100 over the deposition source 5, the conductive line 31 is being built up. Its form depends on the parameters of the deposition source 5 as well as on the aspect ratio of the opening 41 and the distance between the mask and the deposition source.
[0042] A contour 32 of a conductive line 3 having straight side sections 322, 323 is shown in FIG. 5. Here, the height of the conductive line 3 is defined as h, which is in the region of a few m, preferably between 1 and 10 m, while the width is defined as w. The ratio of height h to width w is preferably between 1:10 and 5:10, more preferably around 3:10. For a height of around 3 m, this corresponds to a width of around 10 m. In this special case, the width w is not defined as FWHM, but rather as the width of the base of the triangle making up the cross-section of the conductive line 3.
[0043] A cross-section of the mask 4 is shown in FIG. 6. As in FIG. 4, the mask 4 has an opening 41 elongated along a longitudinal direction running perpendicular to the plane of drawing. The mask 4 itself needs to have a minimum thickness in order to be robust and for easier handling. Therefore, in order to allow for a certain very small depth of the opening 41. There is a wider recess 42 provided behind the opening 41. Only the opening 41 will have an effect on the form and size of the resulting conductive line 3, while the recess 42 has a width and depth such that it does not affect the deposition process.
[0044] Two different deposition situations are shown schematically in FIGS. 7 and 8. They both show a bottom view onto a the mask 4 covering the multi-layer structure (not visible in FIGS. 7 and 8) such that the elongated openings 41 are visible. The arrow 7 shows the direction of movement of the substrate 2 and mask 4. On the right side, there is a schematic representation of a deposition source 5. In both cases, the length of the deposition source 5 perpendicular to the movement direction 7 is large enough to cover the entire dimension of the substrate 2 and mask 4 perpendicular to the movement direction, while the width of the deposition source 5, namely its extension along the movement direction 7 is narrow with respect to its length.
[0045] In FIG. 7, the substrate 2 and mask 4 are moved in a direction 7 perpendicular to the longitudinal direction of the elongated openings 41 in the mask 4. Therefore, due to the size and design of the deposition source 5, one conductive line 31 after the other is completed onto the multi-layer structure 100, while the substrate 2 and mask 4 move over the deposition source 5. The situation is different in FIG. 8, where the substrate 2 and mask 4 are moved in a direction 7 parallel to the longitudinal direction of the elongated openings 41 in the mask 4. Here, all conductive lines 31 are deposited at the same time, being built up along their length, while the substrate 2 and mask 4 move over the deposition source 5. In the case of FIG. 8 one can say that the material beams 51 having different angles with respect to each mask opening 41 are present for all openings 41 at all times during the deposition process, while in FIG. 7 the angles at which the material beams 51 arrive at each opening 41 changes with time as the mask 4 and the deposition source 5 are moved relative to each other.
REFERENCE NUMBERS
[0046] 1 thin film solar cell [0047] 10 back contact layer [0048] 11 photovoltaic active layer [0049] 12 buffer layer (optional) [0050] 13 front contact layer [0051] 14 layer surface [0052] 100 multi-layer structure [0053] 2 substrate [0054] 3 conductive grid [0055] 31 conductive (grid) line [0056] 32 surface contour [0057] 321 top section [0058] 322 left side sections (left slope) [0059] 323 right side sections (right slope) [0060] 4 mask [0061] 41 elongated opening [0062] 42 opening recess [0063] 5 deposition source [0064] 51 material beam [0065] 6 tangent [0066] 7 moving direction
