Solar cell manufacturing

Abstract

Solar Cell Fabrication This description relates to a process for manufacturing a solar cell, the process comprising, in order: the formation of a tunnel oxide (52) on at least one surface of a semiconductor substrate (50); the formation of a doped layer with a dopant of a first type of conductivity on the tunnel oxide; the formation of a mask (56) on the doped layer; and the application, in a gaseous atmosphere (62) containing a dopant of a second type of conductivity, of doping at least a first region (66) of the doped layer using a laser. Figure for the abstract: Fig. 26

Description

Title of the invention: Manufacturing of solar cells Technical field

[0001] This description relates generally to solar cells and, more particularly, to back-contact solar cell structures and their manufacturing process. Prior art

[0002] Solar cells are devices designed to convert sunlight into electrical energy. Generally, a solar cell structure is based on the presence of a p-type region and an n-type region on the same semiconductor substrate. In a back-contact solar cell, each region is coupled to metallic contacts on the back face of the solar cells to allow an external electrical circuit or device to be coupled to and powered by the solar cell, as described in US2016 / 0351737 and US7468485. Summary of the invention

[0003] There is a need to improve solar cells and the manufacturing process of current solar cells, in particular to reduce the duration of the process.

[0004] An embodiment overcomes all or part of the drawbacks of known solar cells and their manufacturing process.

[0005] One embodiment provides a method for manufacturing a solar cell, the method comprising, in order:

[0006] the formation of a tunnel oxide on at least one surface of a semiconductor substrate;

[0007] the formation of a layer doped with a dopant of a first type of conductivity on the tunnel oxide;

[0008] the formation of a mask on the doped layer; and

[0009] the implementation, in a gaseous atmosphere containing a dopant of a second type of conductivity, of a doping of at least a first region of the doped layer using a laser.

[0010] According to one embodiment, the process comprises the formation of trenches extending into the mask, into the tunnel oxide and into the doped layer, after the formation of the mask.

[0011] According to one embodiment, trenches separate the first regions of the doped layer from the second regions of the doped layer.

[0012] According to one embodiment, the gas comprises phosphoryl chloride.

[0013] According to one embodiment, the process comprises texturizing the semi-substrate driver on another surface.

[0014] According to one embodiment, the process includes the formation of a passivation film on the doped layer, the passivation layer covering the inside of the trenches.

[0015] One embodiment provides for a solar cell with interdigitated back contacts or IBC obtained by the process described above.

[0016] One embodiment provides for a solar panel comprising solar cells with interdigitated back contacts. Brief description of the drawings

[0017] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0018] Fig. 1 illustrates a cross-sectional view showing an example of a solar cell;

[0019] Figure 2 illustrates a cross-sectional view showing a step in an example of a process of manufacturing of the solar cell illustrated in [Fig.1];

[0020] [Fig.3] illustrates another step in the manufacturing process of [Fig.2];

[0021] [Fig.4] illustrates another step in the manufacturing process of [Fig.2];

[0022] [Fig.5] illustrates another step in the manufacturing process of [Fig.2];

[0023] [Fig.6] illustrates another step in the manufacturing process of [Fig.2];

[0024] [Fig.7] illustrates another step in the manufacturing process of [Fig.2];

[0025] [Fig.8] illustrates another step in the manufacturing process of [Fig.2];

[0026] [Fig.9] illustrates another step in the manufacturing process of [Fig.2];

[0027] [Fig. 10] illustrates another step in the manufacturing process of [Fig. 2];

[0028] [Fig.1 1] illustrates another step in the manufacturing process of [Fig.2];

[0029] [Fig. 12] illustrates another step in the manufacturing process of [Fig. 2];

[0030] [Fig. 13] illustrates another step in the manufacturing process of [Fig. 2];

[0031] [Fig. 14] illustrates another step in the manufacturing process of [Fig. 2];

[0032] [Fig. 15] illustrates another step in the manufacturing process of [Fig. 2];

[0033] [Fig. 16] illustrates another step in the manufacturing process of [Fig. 2];

[0034] [Fig. 17] illustrates a cross-sectional view of a solar cell according to an embodiment of the present description;

[0035] [Fig. 18] illustrates a cross-sectional view showing a step in a process for manufacturing a solar cell according to the embodiment of the present description;

[0036] [Fig. 19] illustrates another step in the manufacturing process of [Fig. 18];

[0037] [Fig.20] illustrates another step in the manufacturing process of [Fig. 18];

[0038] [Fig.21] illustrates another step in the manufacturing process of [Fig.18];

[0039] [Fig.22] illustrates another step in the manufacturing process of [Fig. 18];

[0040] [Fig.23] illustrates another step in the manufacturing process of [Fig. 18];

[0041] [Fig.24] illustrates another step in the manufacturing process of [Fig. 18];

[0042] [Fig.25] illustrates another step in the manufacturing process of [Fig. 18];

[0043] [Fig.26] illustrates another step in the manufacturing process of [Fig. 18];

[0044] [Fig.27] illustrates another step in the manufacturing process of [Fig. 18];

[0045] [Fig.28] illustrates another step in the manufacturing process of [Fig. 18];

[0046] [Fig. 29] illustrates another step in the manufacturing process of [Fig. 18]; and

[0047] [Fig.30] illustrates another step in the manufacturing process of [Fig. 18]; Description of the embodiments

[0048] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0049] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been represented and are detailed.

[0050] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or linked through one or more other elements.

[0051] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0052] Unless otherwise specified, the expressions "approximately", "roughly", and "on the order of" mean within 10%, preferably within 5%.

[0053] Fig. 1 is a cross-sectional view illustrating an example of a solar cell.

[0054] The solar cell shown in [Fig. 1] consists of a semiconductor substrate 10 having a front face portion intended to receive solar radiation during normal operation and a rear face portion where the metallic contacts of the solar cell are formed. The solar cell has a textured front face covered with a doped layer 37.

[0055] The solar cell of [Fig. 1] comprises first regions 32 of a first type of conductivity, such as p-type regions, and second regions 36 of a second type of conductivity, such as n-type regions, formed in an undoped layer 30B on the rear face of the substrate 10. A tunnel oxide layer 20B can be formed on the back face of substrate 10, more precisely, between substrate 10 and the undoped layer 30B. Layer 37 is of the second type of conductivity.

[0056] Metallic contacts 41 are connected to regions 32 and 36 to allow external circuits and devices to receive power from the solar cell.

[0057] The solar cell of [Fig.1] may include passivation layers 38, 39 and 40 to protect the structure from external electrical damage.

[0058] Figures 2 to 16 are cross-sectional views illustrating steps in an example of a manufacturing process for the solar cell illustrated in [Fig. 1].

[0059] The manufacturing process for the contact of the solar cell shown in [Fig. 1] may include: - the preparation ([Fig.2]) of the semiconductor substrate 10; - the formation ([Fig.3]) of a 20F tunnel oxide layer on a front face 101 of substrate 10 and another tunnel oxide layer 20B on a back face 103 of substrate 10; - the formation of a 30F semiconductor layer on the front face of the 20F layer and another 30B semiconductor layer on the back face of the 20B layer; - the formation ([Fig.4]) of a layer 31 on the back face of layer 30B, consisting of a doped layer, which is formed over the entire 30B layer, and an undoped layer formed over the entire doped layer. The doped layer includes a dopant of a first type of conductivity (p or n); - the formation ([Fig.5]) of openings 310 in layer 31 using, by for example, a wet etching process; - the formation ([Fig.6]) of zones 32 in layer 30B by diffusion thermal transfer of dopants from layer 31 to layer 30B using a laser - the deposition ([Fig.7]) of a masking layer 33 all around the structure; - the removal ([Fig.8]) of the masking layer 33 from the front face of the structure and more specifically the front face of layer 30F and the lateral sides of layer 30F, layer 20F and part of substrate 10; - the removal ([Fig.9]) of layer 20F and layer 30F and a tex process front face transformation of layer 30F; - the formation ([Fig. 10]) of openings 34 in the masking layer 33; - the treatment ([Fig. 1 1]) under a gaseous atmosphere 35 containing a dopant of a second type of conductivity in order to form a zone 36 in layer 30B and a layer 37 on the front face of substrate 10; - the removal ([Fig. 12]) of the masking layer 33; - the heat treatment ([Fig. 13]) in order to diffuse the dopant from zone 36 throughout the depth of layer 30B; - the formation ([Fig. 14]) of a passivating and anti-reflective film 38 in the front face of layer 37; - the formation ([Fig. 15]) of a passivation film 39 on the rear face of the structure and a passivation film 40 on the lateral sides of the structure; and - the formation ([Fig. 16]) of electrodes 41 on the rear face of the structure by a wet etching step of layer 39 and a metal deposition step.

[0060] Fig. 17 is a cross-sectional view illustrating a solar cell according to an embodiment of the present description.

[0061] The solar cell illustrated in [Fig. 17] consists of a semiconductor substrate 50 having a front face portion intended to receive solar radiation during normal operation and a rear face portion where metallic contacts with the solar cell are formed. The solar cell has a textured front face covered with a doped layer 64.

[0062] The solar cell of [Fig. 17] comprises one or more regions 541 of a first type of conductivity, such as p-type regions, and one or more regions 66 of a second type of conductivity, such as n-type regions, formed on the rear face of the substrate 50. A tunnel oxide layer 52 can be formed on the rear face of the substrate 50, more precisely, between the substrate 50 and the regions 541, 66.

[0063] Metallic contacts 76 and 78 are connected, respectively, to regions 541 and 66 to allow external circuits and devices to receive power from the solar cell.

[0064] The solar cell of [Fig. 17] may include passivation layers 70, 72, 74 to protect the structure from external electrical damage.

[0065] Furthermore, the solar cell represented in [Fig. 17] may include regions 66 and regions 541, trenches 60, between regions 66 and regions 541, and, in the substrate 50, a shallow depth of the substrate 68 doped with dopants of the second type of conductivity.

[0066] Fig. 18 illustrates a manufacturing step of a contact solar cell according to the embodiment of the present description.

[0067] In the present embodiment, the substrate 50 is a semiconductor substrate, for example a silicon wafer, preferably doped with an n-type dopant such as phosphorus (P), or with a p-type dopant such as gallium (Ga) or boron (B).

[0068] The substrate 50 has a front face 501 and a rear face 503. The front face 501 is the face of the solar cell intended to receive solar radiation. The substrate 50 is thinned to a thickness of, for example, about 240 pm using a process that also eliminates surface damage from the edge by etching (saw defect etching - SDE).

[0069] Fig. 19 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0070] In [Fig. 19], a tunneling oxide layer 52 is formed on the rear face 503 and, for example, on the front face of the substrate. The tunneling oxide layer 52 is formed to be sufficiently thin to increase the probability of direct passage of electrons by tunneling through the tunneling oxide layer 52. The tunneling oxide layer 52 can have a thickness of approximately 7 Angstroms to approximately 20 Angstroms. According to one embodiment, the tunneling oxide layer 52 has a thickness of approximately 10 Angstroms. The tunneling oxide layer 52 can be formed, for example, by thermal growth or by chemical deposition (e.g., plasma-activated chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD)). The tunnel oxide layer 52 can be formed using an ozone oxidation process, which involves digging the substrate 50 into a bath comprising ozone suspended in deionized water.For example, substrate 50 can first undergo wet etching using potassium hydroxide to thin the substrate 50, then a rinsing-cleaning cycle, and then the ozone oxidation process to form a tunnel oxide layer 52 entirely in the same equipment. During the ozone oxidation process, a tunnel oxide layer grows on both sides of substrate 50.

[0071] According to an alternative embodiment, a tunnel oxide layer 52 can also be formed using other processes without diminishing the advantages of the present description.

[0072] Figure 20 illustrates another step in the manufacture of a contact solar cell according to the method of implementation described herein.

[0073] In [Fig.20], a doped layer 54, for example a p-doped polycrystalline silicon layer, is formed on the tunnel oxide layer 52.

[0074] The polycrystalline silicon layer 54 can have a thickness of approximately 2000 Angstroms. The polycrystalline silicon layer can be deposited on the tunnel oxide 52 by PECVD or LPCVD using boron trichloride (BC13) or diborane (B2H6) with silane (SiH4).

[0075] Fig. 21 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0076] In [Fig.21], a masking layer 56 is formed on the layer 54, on the front face and on the back face, in order to completely envelop the structure of the [Fig.20]. The masking layer 56 can be used in a subsequent laser etching process (Figures 23 and 24), exposing parts of the layer 54. The masking layer 56 can be formed, for example, by thermal growth or chemical deposition (PECVD or LPCVD). However, various other processes can be applied to form the masking layer 56.

[0077] The masking layer 56 may be made of a material chosen for being an undoped material having no conductive dopant and for its ability to prevent the diffusion of the dopant with conductivity n. In one example, the masking layer 56 may be a single layer comprising silicon oxide (SiOx), silicon nitride (SiHj), silicon oxynitride (SiOxNy), intrinsic amorphous silicon, or silicon carbide (SiC). In particular, when the masking layer 56 is a single layer made of silicon carbide, the masking layer 56 can effectively prevent the diffusion of the dopant.

[0078] Fig. 22 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0079] In [Fig.22], the masking layer 56 is removed from the front face (from the side of the front face 501 of the substrate 50) and, for example, from part of the lateral sides of the structure.

[0080] Fig. 23 illustrates another manufacturing step of a solar cell according to the embodiment of the present description.

[0081] In [Fig. 23], the masking layer 56 is removed from the back face (the back face of the substrate 50) in certain areas to create openings 58 through the masking layer 56 and the layer 54. In the present embodiment, two openings 58 are made in the masking layer 56; however, the number of openings may be different from two. Each opening has a width between 30 nm and 200 pm and a depth approximately equal to the thickness of the masking layer 56. The openings 58 are, for example, made using a laser.

[0082] Fig. 24 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0083] In [Fig. 24], the front face 501 of the substrate 50 is textured. The front face 501 can be textured using a wet etching process or another chemical etching process including, for example, potassium hydroxide and isopropyl alcohol or a solution of TM AH (tetramethylammonium hydroxide). The wet etching process textures the front face 501 with random pyramids, thus advantageously improving the solar radiation collection efficiency.

[0084] In [Fig. 24], the masking layer 56 is used during the etching of the p-type dopant layer 54 and the tunnel oxide layer 52. According to one embodiment, the layer 54, the layer 52, and the substrate 50 are configured using a process of Wet etching comprising buffered hydrofluoric acid, potassium hydroxide with isopropyl alcohol, or a solution of TM AH (tetramethylammonium hydroxide). The wet etching process etches portions of layer 54, tunnel oxide layer 52, and substrate 50 not covered by the masking layer 56. The wet etching process etches to create trenches 60 extending from openings 58 in layer 54, tunnel oxide layer 52, and substrate 50. The trenches 60 separate regions of layer 54 to form regions 541 and 542 within layer 54.

[0085] According to one embodiment, the front face 501 of the semiconductor substrate 50 is textured before the trenches 60 are formed

[0086] However, the embodiment is not limited to this. Thus, the front face 501 of the semiconductor substrate 50 can be textured after the trenches 60 are formed or in a separate process.

[0087] Fig. 25 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0088] The structure shown in Figure 24 is, in Figure 25, placed in a gaseous atmosphere 62 containing an n-type conductivity dopant. The gaseous atmosphere 62 can be created using various gases containing the n-type conductivity dopant. In one example, when the conductive dopant is phosphorus (P), the gaseous atmosphere 62 can include phosphoryl trichloride (POC13).

[0089] At this stage, the front face 501 of the semiconductor substrate 50 can be doped with the n-type conductivity dopant. Thus, a front surface field zone 64 can also be formed during the doping process. However, the embodiment described herein is not limited to this. Thus, during the doping process, an anti-diffusion film can be formed on the front surface 501 of the semiconductor substrate 50 so that no front surface field zone 64 is formed during the doping process. In such a case, the front surface field zone 64 can be formed by a separate process selected from various processes including, for example, ion implantation, thermal diffusion, or laser illumination doping.

[0090] Fig. 26 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0091] Fig. 26 illustrates the doping of regions 542 to create regions 66. The process of doping regions 66 is carried out using a laser.

[0092] Regions 68 are formed during this doping process. Field areas 64 can also be produced during the present doping step, both under POC13.

[0093] The laser can have a wavelength of 1064 nm or less. This is due to the fact It is difficult to produce a laser with a wavelength exceeding 1064 nm. In other words, any wavelength within the infrared, ultraviolet, and visible light spectrum can be used as a laser. Currently, for example, a laser with a wavelength in the range of 500 nm to 650 nm—that is, a green laser.

[0094] Fig. 27 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0095] In [Fig. 27], the substrate 50 is doped using the laser mentioned in [Fig. 26]. According to one embodiment, the substrate 50 is doped simultaneously with the doping of region 542. At this stage, the mask 56 is removed and the structure is ejected from the gaseous atmosphere 62.

[0096] Fig. 28 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0097] In [Fig. 28], an insulating film 70 is formed on the front surface of the semiconductor substrate 50. The insulating film 70 comprises a front surface passivation film and an anti-reflective film, which are formed on the front surface of the layer 64. For example, the front surface passivation film and the anti-reflective film are formed over the entire front surface of the layer 64. The front surface passivation film and the anti-reflective film can be formed using various processes such as, for example, vacuum deposition, chemical vapor deposition, spin coating, screen printing, or spray coating. The formation sequence of the front surface passivation film and the anti-reflective film is not defined.

[0098] Fig. 29 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0099] In [Fig.29], insulating films 72 and 74 are formed respectively on the rear surface and on the lateral surface of the structure.

[0100] For example, the rear surface passivation film 72 is formed over the entire rear surface of the structure. The rear surface passivation film 72 can be formed using various processes such as, for example, vacuum deposition, chemical vapor deposition, spin coating, screen printing, or spray coating.

[0101] Fig. 30 illustrates another manufacturing step of a contact solar cell according to the embodiment of the present description.

[0102] Fig. 30 illustrates the formation of first and second electrodes 76 and 78, which are connected respectively to the conducting regions 541 and 66.

[0103] The first and second electrodes 76 and 78 can be formed by applying a paste to the rear surface, for example, by screen printing, and then by carrying out, for example, contact is achieved through thermal diffusion or laser illumination. The back surface is etched, for example, the passivation film 72 is etched, before the deposition of a metal, in order to create metallizations.

[0104] An advantage of the second embodiment is that the deposition of the tunnel oxide, the doped layer and the mask is carried out in a single step, unlike the first embodiment.

[0105] One advantage of the second embodiment is that the manufacturing process for solar cells is shorter and cheaper than the first embodiment.

[0106] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0107] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Claims

1. A method of manufacturing a solar cell, the method comprising, in order: forming a tunnel oxide (52) on at least one surface (503) of a semiconductor substrate (50); forming a layer (54) doped with a dopant of a first conductivity type on the tunnel oxide; forming a mask (56) on the doped layer; and forming trenches (60) extending into the mask (56), the tunnel oxide (52) and the doped layer (54); and performing, in a gaseous atmosphere (62) containing a dopant of a second conductivity type, doping at least a first region (542, 66) of the doped layer, using a laser.

2. The method of claim 1, wherein trenches (60) separate the first regions (542, 66) of the doped layer from second regions (541) of the doped layer.

3. The method of claim 1 or 2, comprising forming a passivation film (72) on the doped layer (54), the passivation layer covering the interior of the trenches (20).

4. A method according to any one of claims 1 to 3, wherein the gas comprises phosphoryl chloride.

5. A method according to any one of claims 1 to 4, comprising texturing the semiconductor substrate (50) on another surface (501).

6. An IBC solar cell comprising: - a tunnel oxide (52) on at least one surface (503) of a semiconductor substrate (50); - a layer (54) doped with a dopant of a first conductivity type on the tunnel oxide; and - at least a first region (542, 66) of said layer, doped with a dopant of a second conductivity type, the cell comprising trenches (60) extending in the tunnel oxide (52) and in the doped layer (54), between said at least one first region (542, 66) and second regions (541) of the doped layer (54)

7. A solar panel comprising IBC solar cells according to claim 6.

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