Solar cell

Abstract

An interdigitated back contact solar cell is provided The solar cell comprises: a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell; a plurality of first charge-carrier collection elements spaced apart along, and arranged on, the back surface of the substrate; a plurality of second charge-carrier collection elements spaced apart along, and arranged on, the back surface of the substrate, the first charge-carrier collection elements being interdigitated with the second charge-carrier collection elements; a first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate; and a second passivation layer comprising a plurality of B-portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate. The thickness of each B-portion of the second passivation layer in the depth direction is greater than or equal to 1 nm and less than or equal to 3 nm. Methods of manufacturing the interdigitated back contact solar cell are also provided.

Description

[0001] 008884900

[0002] SOLAR CELL

[0003] FIELD OF THE DISCLOSURE

[0004] The present disclosure relates to a solar cell, a solar cell module including said solar cell, a method of manufacturing said solar cell, and a method of manufacturing a solar cell module.

[0005] BACKGROUND

[0006] A typical solar module for providing electrical energy from sunlight comprises an array of solar cells, each comprising a photovoltaic element, or substrate.

[0007] A general aim for solar cell development is to attain high conversion efficiency balanced by a need for reduced production costs. Efforts to achieve this have focussed on interdigitated back contact (IBC) solar cells, as they allow front contact electrodes to be omitted from the solar cell. However, known IBC solar cells often require complex manufacturing methods with several patterning and alignment steps, which result in increased production time and cost. Moreover, there is a general desire to continue increasing the efficiency of solar cells.

[0008] US2009293948A1 describes a method of manufacturing an IBC solar cell where the same mask is used for both an etching step to provide a plurality of first charge-carrier collection elements and a deposition step of depositing a buffer layer and a plurality of second charge-carrier collection elements.

[0009] In spite of the effort already invested in the development of IBC solar cells, further improvements are desirable.

[0010] SUMMARY

[0011] In a first aspect, there is provided a method of manufacturing an IBC solar cell, the method comprising:

[0012] providing a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell;

[0013] arranging a first passivation layer on the back surface of the substrate;

[0014] subsequently, arranging a plurality of first charge-carrier collection elements on the back surface of the substrate, the first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate;

[0015] subsequently, arranging a second passivation layer on the back surface of the substrate; and subsequently, arranging a plurality of second charge-carrier collection elements on the back surface of the substrate, the second charge-carrier collection elements being interdigitated with the first charge-carrier collection elements, and the second passivation layer comprising a plurality of B-008884900

[0016] portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate; and

[0017] wherein the step of arranging the plurality of first charge-carrier collection elements comprises:

[0018] arranging a first doped layer on the back surface of the substrate; and hydrogen plasma etching portions of the first doped layer to leave the plurality of first charge-carrier collection elements.

[0019] By using a hydrogen plasma etching step to provide the plurality of first charge-carrier collection elements, it is possible to provide greater control over the etching depth compared to other etching methods (e.g. using NF3 etching) due to the slower etching rate provided by hydrogen plasma etching. This increased control over the etching depth can be very useful when trying to accurately control the thickness of layers in the solar cell, for example, where trying to partially etch the first passivation layer such that portions of the first passivation layer interposed between the back surface of the substrate and the second passivation layer have a thickness that is less than the thickness of the A-portions of the first passivation layer (e.g. less than 8 - 12 nm, typically around 5 - 7 nm), but is not completely removed when etching portions of the first doped layer. Moreover, by using hydrogen plasma etching, the possibility of causing fluorine radical contamination at the silicon substrate is eliminated, because no fluorine radicals are present in the etching plasma. The first doped layer may be a continuous layer (i.e. a blanket, or global, layer) over the back surface of the substrate (e.g. with the first passivation layer interposed between the first doped layer and the back surface of the substrate, and, optionally, with the first doped layer arranged directly on a back surface of the first passivation layer). In this manner, one or more layers that form the first charge-carrier collection element can be arranged on the back surface of the substrate without requiring deposition through a mask to provide the first chargecarrier collection elements. Each first charge-carrier collection element may comprise a portion of the first doped layer.

[0020] The method may further comprise conducting a hydrogen plasma treatment on the first passivation layer (e.g. the A-portions and / or C-portions of the first passivation layer). Such a hydrogen plasma treatment can help to provide the first passivation layer with a reduced microstructure factor compared to prior to the hydrogen plasma treatment, and thus improve the passivation of the back surface of the substrate, and thus reduced charge-carrier recombination and trapping occurs between the back surface of the substrate and the charge-carrier collection elements, and higher open circuit voltage (Voc) values are obtained from the solar cell. Moreover, the A-portions and C-portions with such a microstructure factor will have a higher conductivity than with a higher microstructure factor, thereby further improving solar cell performance by improved charge-carrier transport. This is because the hydrogen plasma treatment provides the A-portions and C-portions with a greater amount of atomic hydrogen, which can migrate towards the back surface of the substrate. The migration of the atomic hydrogen through the A-portions, and the C-portions where present, can affect the structure of these portions. In particular, the hydrogen plasma treatment may break Si-H2 bonds within these portions and re-form stronger Si-H bonds, thereby resulting in a lower microstructure factor, r*.008884900

[0021] The method may further comprise conducting a hydrogen plasma treatment on the second passivation layer (e.g. the B-portions of the second passivation layer). Such a hydrogen plasma treatment can help to provide the B-portions of the second passivation layer with a reduced microstructure factor compared to prior to the hydrogen plasma treatment, and thus improve the passivation of the back surface of the substrate, and thus reduced charge-carrier recombination and trapping occurs between the back surface of the substrate and the charge-carrier collection elements, and higher the open circuit voltage (Voc) values are obtained from the solar cell. In particular, where the spacing of the first charge-carrier collection elements is provided by a process that removes material and generates dangling bonds on the subsequently exposed surface (e.g. etching), the second passivation layer can help to passivate said dangling bonds and thus improve interface passivation in the solar cell. Moreover, the B-portions with such a microstructure factor will have a higher conductivity than with a higher microstructure factor, thereby further improving solar cell performance by improved charge-carrier transport. This is because the hydrogen plasma treatment provides the B-portions with a greater amount of atomic hydrogen, which can migrate towards the back surface of the substrate. The migration of the atomic hydrogen through the B-portions, and the C-portions where present, can affect the structure of these portions. In particular, the hydrogen plasma treatment may break Si-H2 bonds within these portions and re-form stronger Si-H bonds, thereby resulting in a lower microstructure factor, r*.

[0022] Each B-portion of the second passivation layer may have a thickness in the depth direction greater than or equal to 1 nm and less than or equal to 3 nm. By each B-portion of the second passivation layer having such a thickness, where a hydrogen plasma treatment is conducted on the second passivation layer, better passivation of the interfaces between layers of the solar cell is provided by migration of the atomic hydrogen through the thin B-portions of the second passivation layer and towards the back surface of the substrate.

[0023] The microstructure factor may be measured using FTIR spectroscopy, as described, for example, in B. Fischer, A. Lambertz, M. Nuys, W. Beyer, W. Duan, K. Bittkau, K. Ding, U. Rau, Insights into the Si-H Bonding Configuration at the Amorphous / Crystalline Silicon Interface of Silicon Heterojunction Solar Cells by Raman and FTIR Spectroscopy. Adv. Mater. 2023, 35, 2306351.

[0024]

[0025] The microstructure factor, r* may be calculated according to the equation:

[0026]

[0027] >

[0028] Where I2070is the intensity value of the band centred at around 2070 - 2100 cm-1obtained by deconvolution of the FTIR spectrum, and where I2000is the intensity value of the band centred at around 1990 - 2020 cm'1obtained by deconvolution of the FTIR spectrum. The deconvolution may comprise fitting two Gaussian functions to the FTIR spectrum in the wavenumber range of about 1900 cm-1to008884900

[0029] about 2200 cm1The intensity value of a band may be calculated as the integrated absorption of the band (i.e. the area underneath the gaussian function fitted to the spectrum, calculated according to the equation I, = ~1gi((i)')dM, where <u is the wavenumber, gtis the gaussian function centred at wavenumber i, and a and M are the starting and ending wavenumbers of the spectrum, respectively). The Gaussian functions may be fitted to the FTIR spectrum through a least-squares fit, for example, to minimise the objective function:

[0030]

[0031] Where T is the objective function to be minimised, eois the wavenumber, cr (to) is the FTIR absorption coefficient at wavenumber eo, ^(eo) is a Gaussian function centred at wavenumber i, S, n represents the Gaussian functions being fitted to the Raman spectrum at centred at different wavenumbers (e.g. g2000and g2070for the microstructure factor), and a and M are the starting and ending wavenumbers of the spectrum, respectively. The FTIR spectrum may be obtained using a Nicolet 5700 system from Thermo Electron Corporation in the range from 400 to 4000 cm-1.

[0032] The hydrogen plasma treatment on the first passivation layer may be conducted prior to arranging the first charge-carrier collection elements on the back surface of the substrate (i.e. between arranging the first passivation layer and arranging the first charge-carrier collection elements).

[0033] The hydrogen plasma treatment on the second passivation layer may be conducted prior to arranging the second charge-carrier collection elements on the back surface of the substrate (i.e. between arranging the second passivation layer and arranging the second charge-carrier collection elements).

[0034] The hydrogen plasma treatment on the first passivation layer may be conducted in a plasma chamber and may be applied to a carrier plate supporting the (part-fabricated) solar cell. The hydrogen plasma treatment on the first passivation layer may be conducted with one or more conditions selected from the group consisting of: a temperature greater than or equal to 180°C and less than or equal to 220°C; a pressure greater than or equal to 0.54 Torr and less than or equal to 0.66 Torr; a power density greater than or equal to 400 mW / cm2and less than or equal to 480 mW / cm2; a hydrogen gas flowrate of greater than or equal to 2500 SCCM and less than or equal to 3100 SCCM; a frequency of greater than or equal to 12 MHz and less than or equal to 15 MHz; a duration of greater than or equal to 13.5 second and less than or equal to 35 seconds; an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm; a hydrogen gas flowrate per unit volume of a plasma chamber greater than or equal to 0.88 SCCM / cm3and less than or equal to 1 .07 SCCM / cm3; and a hydrogen gas flowrate per unit surface area of the carrier plate greater than or equal to 0.18 SCCM / cm2and less than or equal to 0.22 SCCM / cm2. The temperature is preferably about 200°C. The pressure is preferably about 0.61 Torr. The power density is preferably about 444 mW / cm2. The hydrogen gas flowrate is preferably about 2800 SCCM. The plasma frequency is preferably about 13.56 MHz. The duration is preferably about 15008884900

[0035] s. By limiting the duration of the hydrogen plasma treatment to less than or equal to 35 seconds, preferably around 15 seconds, diffusion of atomic hydrogen into and through the layer can dominate over any etching effect on the first passivation that would act to reduce the layer thickness, in this way, hydrogenated sub-surface layers can form whilst the thickness of the first passivation layer remains constant. The electrode gap is preferably about 20 mm. The hydrogen plasma treatment on the first passivation layer may be conducted in a plasma chamber having a volume of about 2870 cm3. The hydrogen gas flowrate per unit volume of the chamber is preferably about 0.976 SCCM / cm3. The hydrogen plasma treatment on the first passivation layer may be applied to a carrier plate (supporting the (part-fabricated) solar cell) having a surface area of about 13665 cm2. The hydrogen gas flowrate per unit surface area is preferably about 0.205 SCCM / cm2. Such conditions can also contribute to the hydrogen plasma treatment causing no, or minimal, etching of the first passivation layer.

[0036] The hydrogen plasma treatment on the second passivation layer may be conducted in a plasma chamber and may be applied to a carrier plate supporting the (part-fabricated) solar cell. The hydrogen plasma treatment on the second passivation layer may be conducted with one or more conditions selected from the group consisting of: a temperature greater than or equal to 180°C and less than or equal to 220°C; a pressure greater than or equal to 0.54 Torr and less than or equal to 0.66 Torr; a power density greater than or equal to 45 mW / cm2and less than or equal to 55 mW / cm2; a hydrogen gas flowrate of greater than or equal to 900 SCCM and less than or equal to 1100 SCCM; a frequency of greater than or equal to 12 MHz and less than or equal to 15 MHz; a duration of greater than or equal to 13.5 second and less than or equal to 35 seconds; an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm; a hydrogen gas flowrate per unit volume of a plasma chamber greater than or equal to 0.32 SCCM / cm3and less than or equal to 0.38 SCCM / cm3; and a hydrogen gas flowrate per unit surface area of the carrier plate greater than or equal to 0.066 SCCM / cm2and less than or equal to 0.080 SCCM / cm2. The temperature is preferably about 200°C. The pressure is preferably about 0.61 Torr. The power density is preferably about 50 mW / cm2. The hydrogen gas flowrate is preferably about 1000 SCCM. The plasma frequency is preferably about 13.56 MHz. The duration is preferably about 15 s. By limiting the duration of the hydrogen plasma treatment to less than 35 seconds, preferably around 15 seconds, diffusion of atomic hydrogen into and through the layer can dominate over any etching effect on the second passivation that would act to reduce the layer thickness, in this way, hydrogenated sub-surface layers can form whilst the thickness of the second passivation layer remains constant. The electrode gap is preferably about 20 mm. The hydrogen plasma treatment on the second passivation layer may be conducted in a plasma chamber having a volume of about 2870 cm3. The hydrogen gas flowrate per unit volume of the chamber is preferably about 0.35 SCCM / cm3. The hydrogen plasma treatment on the second passivation layer may be applied to a carrier plate (supporting the (part-fabricated) solar cell) having a surface area of about 13665 cm2. The hydrogen gas flowrate per unit surface area is preferably about 0.073 SCCM / cm2. Such conditions can also contribute to the hydrogen plasma treatment causing no, or minimal, etching of the second passivation layer.008884900

[0037] The substrate may be crystalline, e.g. crystalline silicon. The crystalline (silicon) substrate may be mono- or poly-crystalline. The substrate may have a positive conductivity type (e.g. be p-type doped) or may have a negative conductivity type (e.g. be n-type doped). The substrate may define a photovoltaic element on which other layers of the solar cell are arranged (e.g., deposited). According to an exemplary arrangement, the photovoltaic element defines a crystalline silicon wafer which has been cut from an ingot, as will be understood by the skilled person.

[0038] The back surface of the substrate may be a surface of the substrate designed or intended to face away from a radiative source (e.g. the sun) in use. The front surface of the substrate may be a surface of the substrate designed or intended to face towards the radiative source in use. The back surface of the substrate may be a surface of the substrate which is opposite the front surface of the substrate. The solar cell may comprise a front surface, upon which light from a radiative source (e.g., the sun) is incident during normal use, and a back surface that is opposite the front surface. That is, the front surface of the solar cell may be configured in use to face the sun, whereas the back surface of the solar cell may be configured in use to face away from the sun. The front surface of the solar cell may be on the same side of the substrate (i.e. in the depth direction of the solar cell) as the front surface of the substrate and the back surface of the solar cell may be on the same side of the substrate (i.e. in the depth direction of the solar cell) as the back surface of the substrate.

[0039] The first charge-carrier collection elements may be spaced apart from each other in a widthwise or lengthwise direction of the solar cell. The second charge-carrier collection elements may be spaced apart from each other in a widthwise or lengthwise direction of the solar cell and interdigitated with the plurality of first charge-carrier collection elements. That is, it can be understood that the first chargecarrier collector and second charge-carrier collector are comprised by respective charge-carrier collection elements arranged in an alternating pattern on the back surface of the substrate. Each of the first charge-carrier collection elements may be elongate and spaced apart from the other first chargecarrier collection elements in a direction substantially perpendicular to their elongate dimension. Similarly, each of the second charge-carrier collection elements may be elongate and spaced apart from the other second charge-carrier collection elements in a direction substantially perpendicular to their elongate dimension. For example, the elongate dimension of the first and second charge-carrier collection elements may be substantially parallel to the widthwise direction of the solar cell, and thus the respective charge-carrier collection elements may be spaced apart from each other in a direction substantially parallel to the lengthwise direction of the solar cell.

[0040] The plurality of first charge-carrier collector elements may, together, define a first charge-carrier collector. The plurality of second charge-carrier collector elements may, together, define a second charge-carrier collector.

[0041] The first passivation layer may be (directly) arranged on the back surface of the substrate. In this way, passivation of the back surface of the substrate can be provided, thereby reducing charge-carrier008884900

[0042] trapping and recombination rates at the back surface of the substrate. The first passivation layer may be formed from intrinsic amorphous hydrogenated silicon (a-Si:H(i)). The second passivation layer may be formed from intrinsic amorphous hydrogenated silicon (a-Si:H(i)). At least part of the second passivation layer (e.g. the B-portions of the second passivation layer) may be arranged (directly) on a back surface of the first passivation layer. In some examples, all of the second passivation layer may be arranged (directly) on the back surface of the first passivation layer.

[0043] The first charge-carrier collection elements may have a back surface on the opposite side of the first charge-carrier collection elements to the substrate. The second charge-carrier collection elements may have a back surface on the opposite side of the second charge-carrier collection elements to the substrate.

[0044] The hydrogen plasma etching may be conducted in a plasma chamber and may be applied to a carrier plate supporting the (part-fabricated) solar cell. The hydrogen plasma etching may be conducted with one or more etching conditions selected from the group consisting of: a temperature greater than or equal to 180°C and less than or equal to 220°C; a pressure greater than or equal to 0.54 Torr and less than or equal to 0.66 Torr; a power density greater than or equal to 27 mW / cm2and less than or equal to 33 mW / cm2; a hydrogen gas flowrate of greater than or equal to 2700 SCCM and less than or equal to 3300 SCCM; a plasma frequency of greater than or equal to 25 MHz and less than or equal to 30 MHz; an etching time of greater than or equal to 100 s and less than or equal to 120 s; an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm; a hydrogen gas flowrate per unit volume of a plasma chamber greater than or equal to 0.96 SCCM / cm3and less than or equal to 1.15 SCCM / cm3; and a hydrogen gas flowrate per unit surface area of the carrier plate greater than or equal to 0.198 SCCM / cm2and less than or equal to 0.241 SCCM / cm2. The temperature is preferably about 200°C. The pressure is preferably about 80 Pa. The power density is preferably about 30 mW / cm2. The hydrogen gas flowrate is preferably about 3000 SCCM. The plasma frequency is preferably about 27.12 MHz. The etching time is preferably about 110 s. The electrode gap is preferably about 20 mm. The hydrogen plasma etching may be conducted in a plasma chamber having a volume of about 2870 cm3. The hydrogen gas flowrate per unit volume of the chamber is preferably about 1.05 SCCM / cm3. The hydrogen plasma etching may be applied to a carrier plate (supporting the (part-fabricated) solar cell) having a surface area of about 13665 cm2. The hydrogen gas flowrate per unit surface area is preferably about 0.219 SCCM / cm2.

[0045] The etching may comprise: arranging an etch mask on a back surface of the first doped layer such that the portions of the first doped layer to be etched are exposed through the etch mask; and etching the portions of the first doped layer exposed through the etch mask. The etch mask may be a hard mask. Arranging the etch mask on the back surface of the first doped layer may comprise depositing a continuous layer (i.e. blanket, or global, layer) of etch mask material, and subsequently etching the continuous layer of etch mask material into a pattern using a photoresist process.008884900

[0046] The etch mask may comprise a plurality of prongs spaced apart from each other in the widthwise or lengthwise direction of the solar cell and a first spine connecting together the plurality of prongs at a first end thereof. In this way, the etch mask can have a comb-like structure. The plurality of prongs may be connected together at a second end thereof by a second spine, such that the etch mask comprises a plurality of apertures, each aperture surrounded by a respective pair of prongs, the first spine and the second spine. In this way, the etch mask can have a structure of a sheet with a plurality of apertures provided therethrough.

[0047] Arranging the second passivation layer on the back surface of the substrate may comprise depositing the second passivation layer through the etch mask. Similarly, arranging the second charge-carrier collection elements on the back surface of the substrate may comprise depositing the second chargecarrier collection elements through the etch mask. In this way, a patterned second passivation layer and / or spaced second charge-carrier collection elements can be provided without needing to perform an alignment step as part of arranging these layers, since the etch mask is already in position. The method may further comprise, subsequent to arranging the second charge-carrier collection elements on the back surface of the substrate, removing the etch mask, for example, by a chemical dissolution process, as would be understood by the skilled person.

[0048] The first passivation layer may comprise a plurality of C-portions, each C-portion interposed between a respective B-portion of the second passivation layer and the substrate. The C-portions of the first passivation layer can protect the back surface of the substrate from damage during subsequent deposition of the second passivation layer and the second charge-carrier collection elements, and thus prevent a reduction in the open circuit voltage of the solar cell. The step of etching portions of the first doped layer may further comprise etching the C-portions of the first passivation layer. The etching of the C-portions may remove part of each C-portion such that the thickness of each C-portion in the depth direction is less than the thickness of each A-portion in the depth direction. As discussed above, compared to other etching methods (e.g. using NF3 etching), hydrogen plasma etching can provide greater control over the amount of material removed in the etching process, which can make manufacture easier where seeking to reduce the thickness of a C-portion without completely removing said C-portion. The B-portions of the second passivation layer may then be deposited directly on the back surface of respective C-portions of the first passivation layer. In other examples, the first passivation layer may not comprise such C-portions, and instead the second passivation layer (e.g. the B-portions of the second passivation layer) may be arranged directly on the back surface of the substrate. By way of example, the etching of the C-portions may remove all of each C-portion such that the back surface of the substrate is exposed in spaces between the first charge-carrier collection elements following etching. The second passivation layer (e.g. the B-portions of the second passivation layer) may then be deposited directly on the back surface of the substrate.

[0049] The thickness of each C-portion of the first passivation layer in the depth direction of the solar cell may be less than the thickness of each A-portion of the first passivation in the depth direction of the solar008884900

[0050] cell. This can provide the back surface of the substrate with protection from damage during subsequent deposition steps (e.g. of the second passivation layer), but also means that the combined thickness of the B-portions of the second passivation layer and the C-portions of the first passivation layer is not so great as to negatively impact the performance of the solar cell. The thickness of each C-portion of the first passivation layer in the depth direction may be greater than or equal to 5 nm. The thickness of each C-portion of the first passivation layer in the depth direction may be less than or equal to 7 nm.

[0051] The second passivation layer may comprise a plurality of D-portions, each D-portion interposed between a respective first charge-carrier collection element and an adjacent second charge-carrier collection element. The B-portions and D-portions of the second passivation layer may be arranged (e.g. deposited) simultaneously. In some examples, each adjacent pair of a first charge-carrier collection element and a second charge-carrier collection element may have a respective D-portion of the second passivation layer interposed therebetween. In some examples, each D-portion may be provided between a side surface of a respective first charge-carrier collection element (i.e. a surface of the first charge-carrier collection element substantially perpendicular to the depth direction of the solar cell) and a side surface of a respective second charge-carrier collection element (i.e. a surface of the second charge-carrier collection element substantially perpendicular to the depth direction of the solar cell). Each D-portion can electrically isolate said first charge-carrier collection element from said second charge-carrier collection element, thereby reducing charge-carrier recombination between the chargecarrier collection elements. The second passivation layer being intrinsic (i.e. non-doped) may assist in the D-portions providing electrical insulation between the first charge-carrier collection elements and second charge-carrier collection elements. To provide the D-portions interposed between adjacent first and second charge-carrier collection elements, the second passivation layer may be deposited after arranging the first charge-carrier collection element on the back surface of the substrate and prior to arranging the second charge-carrier collection element on the back surface of the substrate. In this way, the first charge-carrier collection element can be electrically isolated from the second charge-carrier collection element by the second passivation layer. In this way, the D-portions that provide electrical isolation between adjacent first and second charge-carrier collection elements can be arranged simultaneously with forming another element of the solar cell (the B-portions), and accordingly the total number of steps in fabricating the solar cell can be reduced.

[0052] The plurality of first charge-carrier collection elements may be spaced apart on the back surface of the substrate in a spacing direction. The spacing direction may be parallel to a widthwise direction of the solar cell, or parallel to a lengthwise direction of the solar cell. The plurality of second charge-carrier collection elements may be spaced apart on the back surface of the substrate in the spacing direction. The thickness of each D-portion of the second passivation layer in the spacing direction may be greater than or equal to 1 nm. The thickness of each D-portion of the second passivation layer in the spacing direction may be less than or equal to 3 nm.008884900

[0053] Each first charge-carrier collection element may comprise a layer of doped semiconductor material having a first conductivity type; each second charge-carrier collector may comprise a layer of doped semiconductor material having a second conductivity type. The first conductivity type may be different to the second conductivity type. Each of the first charge-carrier collection elements may comprise a layer of doped silicon (e.g. nano-crystalline silicon (nc-Si) or amorphous hydrogenated silicon (a-Si:H)). Each of the second charge-carrier collection elements may comprise a layer of doped silicon (e.g. nanocrystalline silicon (nc-Si) or amorphous hydrogenated silicon (a-Si:H)). The first charge-carrier collection elements may be n-type doped and the second charge-carrier collection elements may be p-type doped. Alternatively, the first charge-carrier collection elements may be p-type doped and the second chargecarrier collection elements may be n-type doped.

[0054] One or more of the layers or elements of the solar cell (e.g. one or more layers or elements selected from the group consisting of: the first charge-carrier collection elements, the second charge-carrier collection elements, the first passivation layer, the second passivation layer, the third passivation layer, and the anti-reflective coating) may be deposited using a chemical vapour deposition (CVD) process, e.g. a plasma-enhanced CVD process (PECVD), as would be understood by the skilled person.

[0055] The first passivation layer may be deposited using a PECVD process and from a precursor gas comprising silane, and optionally hydrogen. The first passivation layer deposition may be conducted in a plasma chamber and may be applied to a carrier plate supporting the (part-fabricated) solar cell. The first passivation layer may be deposited using a multi-stage (PECVD) process. A first stage of the (PECVD) process may comprise deposition from a precursor gas comprising silane and not comprising hydrogen (H2) (e.g. consisting of silane). In this way, the possibility of epitaxial growth of the first passivation layer on the substrate can be reduced. A subsequent (e.g. second) stage of the (PECVD) process may comprise deposition from a precursor gas comprising, or consisting of, silane and hydrogen.

[0056] The second passivation layer may be deposited using a PECVD process and from a precursor gas comprising silane, and optionally hydrogen, The second passivation layer deposition may be conducted in a plasma chamber and may be applied to a carrier plate supporting the (part-fabricated) solar cell. The PECVD process may be conducted with one or more conditions selected from the group consisting of: a temperature greater than or equal to 180°C and less than or equal to 220°C; a pressure greater than or equal to 0.50 Torr and less than or equal to 0.71 Torr; a power density greater than or equal to 30 mW / cm2and less than or equal to 60 mW / cm2; a hydrogen gas flowrate (where present) of greater than 0 SCCM and less than or equal to 3000 SCCM; a silane gas flowrate of greater than or equal to 500 SCCM and less than or equal to 1000 SCCM; a frequency of greater than or equal to 12 MHz and less than or equal to 15 MHz; a duration of greater than or equal to 30 second and less than or equal to 60 seconds; an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm; a hydrogen gas flowrate (where present) per unit volume of a plasma chamber greater than 0 SCCM / cm3and less than or equal to 1.05 SCCM / cm3; a silane gas flowrate per unit volume of a plasma chamber008884900

[0057] greater than or equal to 0.174 SCCM / cm3and less than or equal to 0.348 SCCM / cm3; a hydrogen gas flowrate (where present) per unit surface area of the carrier plate greater than 0 SCCM / cm2and less than or equal to 0.220 SCCM / cm2; and a silane gas flowrate per unit surface area of the carrier plate greater than or equal to 0.037 SCCM / cm2and less than or equal to 0.073 SCCM / cm2. The first passivation layer may be deposited using a multi-stage PECVD process. The first stage of the PECVD process may be conducted with a precursor gas consisting of silane (SiP ) (i.e. without any hydrogen dilution). In this way, the possibility of epitaxial growth of the second passivation layer on the substrate or first passivation layer (e.g. C-portions of the first passivation layer) can be reduced.

[0058] The solar cell may be a heterojunction IBC solar cell.

[0059] The substrate may be configured with the first conductivity type (e.g. a negative conductivity type). The first charge-carrier collection elements, having the same conductivity type as the substrate, provide a majority charge-carrier collector (e.g. an electron collector). The majority charge-carrier collector may be configured to selectively screen, or extract, charge-carriers from the substrate. Accordingly, when the solar cell is in use, electrons produced by light incident on the substrate may be collected in the electron collector, wherein they operate as majority charge-carriers. The second charge-carrier collection elements, having a different conductivity type to the substrate, provides a minority chargecarrier collector (e.g. a hole collector). The minority charge-carrier collector may be configured to selectively screen, or extract, minority charge-carriers in the substrate, which are then majority chargecarriers in the second charge-carrier collector. In an alternative arrangement, the substrate may be configured with the second conductivity type, i.e. the same conductivity type as the second chargecarrier collector (e.g. a positive conductivity type).

[0060] Where a layer or element has a negative conductivity type (e.g. is n-type doped), it may contain impurities of a group V element such as phosphor (P), arsenic (As), and antimony (Sb).

[0061] Where a layer or element has a positive conductivity type (e.g. is p-type doped), it may contain impurities of a group III element such as boron (B), gallium (Ga), and indium (In).

[0062] The IBC solar cell may further comprise a plurality of first electrodes, each first electrode arranged on a respective first charge-carrier collection element. The IBC solar cell may further comprise a plurality of second electrodes, each second electrode arranged on a respective second charge-carrier collection element. The electrodes may be metal electrodes (e.g. silver electrodes). In this way, the electrodes are arranged to extract photo-generated charge-carriers from the charge-carrier collection elements. The electrodes may be finger electrodes. Each finger electrode may be configured with an axial length which is substantially greater than its width. Both the width and axial length of the finger electrode may be measured in a plane parallel to the plane of the solar cell, but in perpendicular directions to each other. The electrodes may extend in a transverse direction which is parallel with the widthwise direction of the solar cell. The first electrodes arranged on the first charge-carrier collection elements may be008884900

[0063] spaced apart across a back surface of the first charge-carrier collection elements to define transversely-extending spaces between the electrodes. The first electrodes arranged on the first charge-carrier collection elements may be spaced apart in a lengthwise direction which is substantially parallel with the lengthwise direction of the solar cell. Accordingly, the plurality of first finger electrodes may form an array of parallel, longitudinally spaced (e.g. equally spaced) finger electrodes. The second finger electrodes may be equivalently configured with respect to, and are hereby restated in respect of, the second charge-carrier collection elements. Where the first and / or second charge-carrier collection elements are elongate, an elongate dimension of each first and / or second finger electrode may be substantially parallel to the elongate dimension of the respective first and / or second charge-carrier collection element it is arranged on.

[0064] The IBC solar cell may further comprise a plurality of first transparent conductive oxide (TCO) elements, each first TCO element arranged on a respective first charge-carrier collection element. The IBC solar cell may further comprise a plurality of second TCO elements, each second TCO element arranged on a respective second charge-carrier collection element. The first TCO elements and / or second TCO elements may be formed from indium tin oxide (ITO), tin (IV) oxide (SnO2), fluorine-doped tin (IV) oxide (FTO), zinc oxide (ZnO) or tin (II) oxide (SnO). Where a TCO element comprises ITO, the mass ratio of Indium oxide ( 2O3) to tin (SnO2) may be 97:3. Each first TCO element may be interposed between a respective first charge-carrier collection element and a respective first electrode. Each second TCO element may be interposed between a respective second charge-carrier collection element and a respective second electrode. The first and / or second TCO elements may be deposited using PECVD.

[0065] The IBC solar cell may further comprise a third passivation layer arranged on a front surface of the substrate. The IBC solar cell may comprise an anti-reflective coating arranged on a front surface of the substrate. The anti-reflective coating may be arranged on the third passivation layer.

[0066] The solar cell may have a substantially rectangular front and / or back surface. The solar cell may comprise four straight sides arranged at right angles to each other. At least one, or each, of the corners between the sides may be square, or pointed. Alternatively, the corners may be chamfered (or rounded), so as to define a pseudo-rectangular shape.

[0067] In exemplary arrangements in which the at least one solar cell is formed from a semiconductor wafer (e.g., a crystalline silicon wafer), the dimensions of the solar cell may substantially correspond to that of the wafer (e.g., a whole wafer silicon cell). The at least one solar cell may be formed from a wafer which is cut into a plurality of sections. For example, the substantially planar wafer may be cut along an in-plane direction (e.g., a widthwise or lengthwise direction of the wafer) to define a cut solar cell (e.g., a half-cut solar cell, where one of the length and width is roughly half as long as the other of the length and width).008884900

[0068] The substrate may divide the solar cell into a front portion which is forward (i.e. , in front of) of the substrate (i.e. arranged on the front surface of the substrate), and a rear portion which is rearward of the substrate (i.e. arranged on a back surface of the substrate). During operation of the solar cell, incident light (e.g., directly from the sun) may pass through the front portion, the substrate and then the rear portion.

[0069] A constituent structure (or layer) of the solar cell may be configured with a determined conductivity type (e.g., p-type or n-type) due to the presence of dopant atoms, or may be intrinsic (e.g. undoped) semiconductor.

[0070] The solar cell may comprise a substantially planar structure. For example, the solar cell may comprise a length and / or a width which is substantially greater than its thickness in the depth direction. The lengthwise and widthwise directions of the solar cell may define the plane of the solar cell. The depth direction may be substantially perpendicular to the widthwise and lengthwise directions.

[0071] At least one, or each, of the solar cell’s constituent elements / layers may be configured with a width, a length, and a thickness. The width and length of each element may be measured in perpendicular directions that are parallel to the plane of the solar cell. The thickness may be measured in a direction that is substantially perpendicular to the plane of the solar cell (i.e. in the depth direction) and / or the back surface of the substrate. At least one, or each of the elements may be configured such that its width and / or length may be substantially greater than its thickness.

[0072] The front and / or the back surface(s) of the solar cell or constituent elements / layers may be textured to form a textured surface corresponding to an uneven surface (i.e. a non-planar surface). In this way, the fraction of the light incident on the solar cell that passes into the substrate (rather than reflecting off a surface of the solar cell) increases because of the textured surface of the solar cell, and thus the efficiency of the solar cell is improved.

[0073] In a second aspect, there is provided a method of manufacturing an IBC solar cell, the method comprising: providing a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell; arranging a first passivation layer on the back surface of the substrate; subsequently, arranging a plurality of first charge-carrier collection elements on the back surface of the substrate, the first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate; subsequently, arranging a second passivation layer on the back surface of the substrate; and subsequently, arranging a plurality of second charge-carrier collection elements on the back surface of the substrate, the second charge-carrier collection elements being interdigitated with the first charge-carrier collection elements, and the second passivation layer comprising a plurality of B-portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate; and wherein: the method further comprises, between arranging008884900

[0074] the first passivation layer and arranging the first charge-carrier collection elements, conducting a hydrogen plasma treatment on the first passivation layer; and / or the method further comprises, between arranging the second passivation layer and arranging the second charge-carrier collection elements, conducting a hydrogen plasma treatment on the second passivation layer.

[0075] Any one or more of the optional features set out with respect to the first aspect are applicable to, and are hereby restated in respect of, the second aspect, except where such a combination is expressly avoided or clearly impermissible.

[0076] The step of arranging the plurality of first charge-carrier collection elements may comprise: arranging a first doped layer on the back surface of the substrate, the first doped layer having a back surface; and etching portions of the first doped layer to leave the plurality of first charge-carrier collection elements. The etching may comprise hydrogen plasma etching.

[0077] In a third aspect, there is provided an interdigitated back contact solar cell comprising:

[0078] a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell;

[0079] a plurality of first charge-carrier collection elements spaced apart along, and arranged on, the back surface of the substrate;

[0080] a plurality of second charge-carrier collection elements spaced apart along, and arranged on, the back surface of the substrate, the first charge-carrier collection elements being interdigitated with the second charge-carrier collection elements;

[0081] a first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate; and

[0082] a second passivation layer comprising a plurality of B-portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate; wherein the thickness of each B-portion of the second passivation layer in the depth direction is greater than or equal to 1 nm and less than or equal to 3 nm.

[0083] Any one or more of the optional features set out with respect to the first aspect and / or second aspect are applicable to, and are hereby restated in respect of, the third aspect, except where such a combination is expressly avoided or clearly impermissible.

[0084] The interdigitated back contact solar cell may be manufactured according to the method of the first aspect or second aspect.

[0085] In a fourth aspect, there is provided a solar module comprising one or more solar cells according to the third aspect and / or one or more solar cells manufactured according to the second and / or third aspects.008884900

[0086] Any one or more of the optional features set out with respect to the first, second, and third aspects are applicable to, and are hereby restated in respect of, the fourth aspect, except where such a combination is expressly avoided or clearly impermissible.

[0087] The solar module (e.g. a solar panel) may define an apparatus for generating electrical power from sunlight. The solar module may comprise at least one solar cell which is arranged (e.g. housed, or supported) by a structural frame, or housing. The at least one solar cell may be configured to absorb sunlight and generate electrical current.

[0088] The at least one solar cell may be configured with an electrical connector which enables electrical current to be extracted from the solar cell (e.g., to an electrical circuit of the solar module). The at least one solar cell and the electrical connector, when connected together, may define a solar cell assembly.

[0089] Two or more solar cells may be electrically connected in series (e.g., by one or more electrical connectors) to form a solar cell string. The solar module may comprise two or more solar cell strings, which may be electrically connected together in series and / or in parallel.

[0090] The solar module may comprise electrical circuitry which may be configured to extract electrical current from the solar panel to an external circuit (e.g., a second solar module).

[0091] The solar module may comprise a housing (e.g., a structural frame, or support) which houses a plurality of solar cells. The solar module housing may comprise a front plate and a back plate which are arranged, respectively, on the front and back sides of the plurality of solar cells. At least one or each of the front and back plates may be formed of glass (e.g., a glass sheet).

[0092] The solar module may comprise an encapsulant which may be configured to provide adhesion between the front and back plates and the plurality of solar cells. In this way, the encapsulant may be arranged between the glass sheet of the solar module housing, and the at least one solar cell. The encapsulant may be configured to prevent the ingress of moisture into the solar module housing. For example, the encapsulant may be formed of ethylene vinyl acetate (EVA), or any other suitably moisture resistant material.

[0093] In a fifth aspect, there is provided a method of manufacturing a solar module, the method comprising arranging one or more solar cells manufactured according to the first aspect and / or second aspect and / or one or more solar cells according to the third aspect in a housing.

[0094] Any one or more of the optional features set out with respect to the first, second, third, or fourth aspects are applicable to the fifth aspect, except where such a combination is expressly avoided or clearly impermissible.008884900

[0095] It will be understood that the terms ‘conductive’ and ‘insulating’ as used herein, are expressly intended to mean electrically conductive and electrically insulating, respectively. The meaning of these terms will be particularly apparent in view of the technical context of the disclosure, being that of photovoltaic solar cell devices. It will also be understood that the term ‘ohmic contact’ is intended to mean a non-rectifying electrical junction (i.e., a junction between two conductors which exhibits a substantially linear currentvoltage (l-V) characteristic).

[0096] It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0097] The above optional features of each of the aspects are equally applicable to, and are hereby restated in respect of, the other aspects and are applicable in any combination, except where such a combination is clearly impermissible or expressly avoided.

[0098] The preceding summary is provided for purposes of summarising some examples to provide a basic understanding of aspects of the subject matter described herein. Accordingly, the above-described features should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following text and the accompanying drawings.

[0099] BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Aspects, features, and advantages of the present disclosure will now be described by way of example only, with reference to the appended drawings in which like numerals denote like elements.

[0101] Figs. 1A and 1 B are schematic plan views of a solar cell module including a plurality of solar cells, wherein Fig. 1 a is a front view and Fig. 1 b is a back view;

[0102] Fig. 2A is a schematic cross-sectional side view of a solar cell according to the first aspect;

[0103] Fig. 2B is a schematic plan view of the back side of the solar cell in Fig. 2A;

[0104] Figs. 3A - 3F are schematic sectional side views of different stages of manufacturing the solar cell of Fig. 2;

[0105] Fig. 4 is a flow chart showing a method of manufacturing a solar cell according to the second aspect; and008884900

[0106] Fig. 5 is a flow chart showing constituent steps of arranging first charge-carrier collection elements on a back surface of a solar cell substrate.

[0107] DETAILED DESCRIPTION

[0108] Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0109] Figs. 1a and 1b show a solar cell module 100 (e.g., solar panel) according to the present disclosure. The solar cell module 100 includes a plurality of solar cells (including a first solar cell 10 and a second solar cell 10) which are arranged within a housing 102 (e.g., a structural frame, or support) of the solar module 100, as will be described in more detail below. The solar cells 10 are sandwiched between a front plate 104 and a back plate 108 of the housing 102.

[0110] The solar module 100 includes electrical circuitry (e.g., an electrical assembly) to enable electrical power to be extracted from the solar cells 10 arranged inside the module housing 102. The electrical circuitry includes a pair of electrical connectors 112 (as shown in Fig. 1b) which couple the module 100 to an external circuit (e.g., two adjacent solar modules 100). The external connector 112 is connected, at one end, to a junction box 110 which is arranged on the back side of the solar module 100 (e.g., mounted to the back plate 108). At least one further connector provides an electrical connection between the junction box 110 and the solar cells 10 which are arranged within the module 100 (e.g., an internal connector). The electrical circuity may include at least one diode (e.g., bypass diodes) which regulates the flow of charge between the solar cells 10 and / or between the solar module 100 and the external electrical circuit. The electrical circuitry components can be arranged within the junction box 110 and / or within the module housing 102 itself. It will be appreciated that the solar module 100 may comprise a plurality of connectors and / or junction boxes 110 as appropriate.

[0111] The solar module 100 has a length which is the horizontal dimension of Figs. 1 a and 1 b, a width which is the vertical direction of Figs. 1 a, and 1 b, and a thickness which is substantially into the page of Figs.

[0112] 1a, and 1 b.

[0113] According to the exemplary arrangement shown in Fig. 1a, the solar module 100 includes ninety-six solar cells 10 arranged in a rectangular array comprising six rows and sixteen columns (arranged horizontally and vertically, in Fig. 1a, respectively). It will be appreciated that the solar module 100 may be configured with any number of solar cells 10 (e.g., arranged in different array shapes, and comprising different numbers of columns and rows), without departing from the scope of the present disclosure. At least some of the solar cells 10 are electrically coupled together (e.g., in series) to form a solar cell string. The solar module 100 includes a plurality of solar cell strings. At least some of the strings are electrically coupled together in series. Two or more of the strings may be coupled together in parallel.008884900

[0114] Different strings may be connected together using one or more cross-connectors which are mounted within the solar module housing 102.

[0115] The front plate 104 of the housing 102 comprises a transparent (e.g., glass) sheet which is configured to allow light to pass through into a central chamber in which the solar cells 10 are mounted. The arrows at the top of Fig. 2A show the direction of the solar radiation which is incident upon the solar module 100 during use. The back plate 108 is arranged to enclose the solar cells 10 within the central chamber. The back plate 108 comprises a reflective sheet which reflects any light incident upon its front surface (i.e., front facing surface) back towards the solar cells 10. The central chamber is filled with an encapsulating material which prevents ingress of fluid (e.g. gas and / or liquid) which could degrade the solar module’s performance.

[0116] Fig. 2A is a schematic sectional side view of a solar cell 10 according to the first aspect. The solar cell 10 comprises a substrate 1 comprising a front surface 1a upon which light from a radiative source (e.g. the sun) is incident during normal use, and a back surface 1 b that is opposite the front surface 1 a. That is, the front surface 1a may be configured in use to face the sun, whereas the back surface 1b may be configured in use to face away from the sun.

[0117] The substrate 1 comprises crystalline n-type doped silicon (c-Si(n)). The substrate 1 divides the solar cell 10 into a front portion that is forward (i.e. in front of) of the substrate 1 , and a rear portion that is rearward of the substrate 1. Light incident on the solar cell 10 passes through the front portion, the substrate 1 and then the rear portion.

[0118] Each of the front and rear portions comprises a plurality of layers. The front portion is arranged on the front surface 1a of the substrate 1 and the rear portion is arranged on the back surface 1b of the substrate 1. The constituent layers of the front and rear portions are sequentially arranged (e.g. deposited) onto the respective front and back surfaces 1a, 1 b of the substrate 1.

[0119] Each of the layers of the front and rear portions are configured with a width, a length and a thickness. The solar cell 10 comprises a substantially planar structure, with the width dimension and length dimension of the solar cell 10 being substantially greater than its thickness dimension, such that the width and length dimensions define the plane of the solar cell 10. The width and length of each layer are measured in perpendicular directions that lie parallel to the plane of the solar cell 10. For each layer, its width and length are substantially greater than its thickness, which is measured in a depth direction that is substantially perpendicular to the plane of the solar cell 10 (i.e. vertically in the orientation of the solar cell 10 in Fig. 2A). Fig. 2A includes axes indicating the depth direction (D) and the length direction (L) of the solar cell 10. Fig. 2B includes axes indicating the width direction (W) and length direction (L) of the solar cell 10.008884900

[0120] In the rear portion, the solar cell 10 comprises a multi-layer structure, having a first passivation layer 2 arranged directly on the back surface 1b of the substrate 1 , and then a plurality of first charge-carrier collection elements 3a spaced apart along, and arranged on, the back surface 1b of the substrate 1 with the first passivation layer 2 interposed between the first charge-carrier collection elements 3a and the back surface 1 b of the substrate 1. The plurality of first charge-carrier collection elements 3a together provide a first charge-carrier collector of the solar cell 10. There is also a plurality of second charge-carrier collection elements 3b spaced apart along, and arranged on, the back surface 1b of the substrate 1 , with the first passivation layer 2 also interposed between the second charge-carrier collection elements 3b and the back surface 1 b of the substrate 1. The plurality of second charge-carrier collection elements 3b together provide a second charge-carrier collector of the solar cell 10. The first charge-carrier collection elements 3a are interdigitated with the second charge-carrier collection elements 3b on the back surface 1b of the substrate 1 , as illustrated in Figs. 2A and 2B.

[0121] The first passivation layer 2 comprises a plurality of A-portions 2a, each A-portion 2a interposed between a respective first charge-carrier collection element 3a and the back surface 1 b of the substrate 1. The first passivation layer 2 further comprises a plurality of C-portions 2b, each C-portion 2b interposed between a respective second charge-carrier collection element 3a and the back surface 1b of the substrate 1. The first passivation layer is formed of intrinsic amorphous hydrogenated silicon (a-Si:H(i)). As illustrated in Fig. 2A, the A-portions of the first passivation layer are thicker than the C-portions of the first passivation layer; is the thickness of the A-portions and C-portions is discussed further in relation to Fig. 3C below.

[0122] The solar cell 10 further comprises a second passivation layer 4 arranged on the back surface 1b of the substrate 1. The second passivation layer comprises a plurality of B-portions 4a, each B-portion 4a interposed between a respective second charge-carrier collection element 3b and a respective C-portion 2b of the first passivation layer 2. The second passivation layer 4 further comprises a plurality of D-portions 4b, each D-portion 4b interposed between a respective first charge-carrier collection element 3a and an adjacent second charge-carrier collection element 3b. Each D-portion is formed of intrinsic amorphous hydrogenated silicon (a-Si:H(i)) and electrically isolates said first charge-carrier collection element 3a from said second charge-carrier collection element 3b, thereby reducing chargecarrier recombination between the charge-carrier collection elements 3a, 3b.

[0123] The B-portions 4a of the second passivation layer 4 have a thickness of greater than or equal to 1nm and less than or equal to 3 nm in the depth direction of the solar cell, and have a reduced microstructure factor as a result of a hydrogen plasma treatment conducted on the B-portions 4a. Consequently, improved passivation of the surface that the second passivation layer is arranged on is provided, and thus reduced charge-carrier recombination and trapping occurs between the back surface of the substrate and the charge-carrier collection elements, and higher open circuit voltage (Voc) values are obtained from the solar cell.008884900

[0124] The surface of the crystalline silicon substrate contains surface defects and unsaturated bonds and the passivation layer(s) act to reduce the density of surface defects and saturate bonds. A certain thickness of a-Si(i) layer has the capability of reducing the defects and saturate the bonds. Since the thickness of the i-layer used for the device fabrication is less, Where the passivation layer(s) thickness is reduced to try to reduce resistance within the solar cell, then quality and structure of the layer becomes important. Where a passivation layer is deposited from pure silane gas (e.g. using PECVD), the free hydrogen content of that layer is typically high, but also negatively impacts the fill factor of the solar cell. Increasing the hydrogen (H2) content in the precursor gas can lead to epitaxial growth at the crystalline substrate surface. Accordingly, the first passivation layer is deposited in stages, with a first stage that deposits amorphous silicon from a precursor gas consisting of silane, and a subsequent stage where amorphous silicon is deposited from a precursor gas comprising silane and hydrogen. Additionally, hydrogen plasma treatment is conducted on the first passivation layer (e.g. the A-portions 2a and C-portions 2b) and a hydrogen plasma treatment is conducted on the second passivation layer (e.g. the B-portions 4a); these treatments increase the amount of atomic hydrogen in these portions, which can then migrate towards the back surface of the substrate to passivate the back surface of the substrate. The migration of the atomic hydrogen through the B-portions and the C-portions breaks Si-H2 bonds within these portions and re-forms stronger Si-H bonds, thereby resulting in a lower microstructure factor, r*. The hydrogen plasma treatment on the first passivation layer is discussed in more detail in relation to Fig.

[0125] 3A. The hydrogen plasma treatment on the second passivation layer is discussed in more detail in relation to Fig. 3D.

[0126] The first charge-carrier collection elements 3a are formed from amorphous or nanocrystalline silicon that has a negative conductivity type (i.e. the same conductivity type as the substrate 1), such that the first charge-carrier collection elements 3a provide the majority charge-carrier collector (electron collector) for the solar cell. During use of the cell 10, the electrons of electron-hole pairs generated in the substrate 1 when it absorbs photons from the light incident on the substrate 1 are collected in the first charge-carrier collection elements 3a.

[0127] The second charge-carrier collection elements 3b are formed from nanocrystalline silicon that has a positive conductivity type (i.e. a different conductivity type to the substrate 1), such that the second charge-carrier collection elements 3b provide the minority charge-carrier collector (hole collector) for the solar cell.

[0128] As no charge-carrier collector is positioned on the front surface 1a of the substrate 1 in the solar cell 10, the front portion of the solar cell 10 instead comprises a third passivation layer 5 and an anti-reflective coating 6.

[0129] The third passivation layer 5 comprises intrinsic amorphous silicon a-Si:H(i) and acts to passivate the front surface 1a of the substrate 10 in order to reduce charge-carrier trapping and recombination at the008884900

[0130] front surface 1 a. The anti-reflective coating 6 acts to reduce the reflectance of light from the front surface of the solar cell 10.

[0131] Although not illustrated in Fig. 2A, one or more of the layers of the solar cell 10 may have textured front and / or back surfaces in order to provide the surfaces of that layer with anti-reflective properties.

[0132] Fig. 2B further illustrates the structure of the IBC solar cell 10. Fig. 2B is a schematic of the back side of the solar cell 10 of Fig. 2A. Fig. 2B includes the line A - A that is the section along which the crosssection in Fig. 2A is taken. The first charge-carrier collector comprises the plurality of first charge-carrier collection elements 3a spaced apart from each other in the longitudinal direction of the solar cell 10, and these spaced-apart elements 3a are connected together by a spine portion of the first chargecarrier collector that extends between the ends of the spaced-apart elements 3a along a longitudinal edge (e.g. a first longitudinal edge) of the solar cell 10. The second charge-carrier collector comprises the plurality of second charge-carrier collection elements 3b spaced apart from each other in the longitudinal direction of the solar cell 10, with a first charge-carrier collection element 3a interposed between each adjacent pair of spaced apart second charge-carrier collection elements 3b in the longitudinal direction of the solar cell 10. The spaced-apart elements 3b of the second charge-carrier collector are also connected together by a spine portion of the second charge-carrier collector that extends between the ends of the spaced-apart elements 3b along the other longitudinal edge (e.g. a second longitudinal edge which is opposite and parallel to the first longitudinal edge) of the solar cell 10 to the spine portion of the first charge-carrier collector.

[0133] Figs. 2A and 2B also illustrate how each of the D-portions 4b of the second passivation layer 4 is interposed between a respective first charge-carrier collection element 3a and an adjacent second charge-carrier collection element 3b in order to prevent short-circuiting of the solar cell 10.

[0134] The structure of the solar cell 10 in Figs. 2A and 2B is discussed further with reference to Figs. 3A -3F, which illustrate steps within a method of manufacturing the solar cell 10, and Fig. 4, which provides a flow chart for the manufacturing method. Fig. 5 provides optional steps by which to conduct step S300 in Fig. 4.

[0135] Fig. 3A illustrates the first steps of manufacturing the IBC solar cell illustrated in Figs. 2A and 2B, corresponding to steps S100 and S200 in Fig. 4. At step S100, the substrate 1 is provided, for example, by cutting a crystalline silicon wafer from an ingot of n-type doped silicon and subsequently at step S200, the first passivation layer 2 is deposited on the back surface 1 b of the substrate 1 . The first passivation layer 2 is deposited as a continuous (i.e. blanket or global) layer on the back surface 1b of the substrate such that no patterning of the first passivation layer 2 is provided by step S200. Step S200 can be conducted by a PECVD process. Table 1 provides an example of PECVD conditions for conducting step S200. The deposition of the first passivation layer 2 is conducted in a plasma chamber008884900

[0136] having a volume of 2870 cm3and applied to the solar cell supported on a carrier plate, the carrier plate having a surface area of about 13665 cm2. The deposition comprises three sequential steps.

[0137] Table 1

[0138]

[0139] Subsequently, at step S250 in Fig. 4, the method comprises conducting a hydrogen plasma treatment on the first passivation layer 2. The hydrogen plasma treatment on the first passivation layer results in a reduction of the microstructure factor of the A-portions 2a and C-portions 2b of the first passivation layer 2 and improves the passivation quality of the first passivation layer 2, thereby providing the solar cell 10 with a higher Voc, as discussed above with reference to Fig. 2A. Table 2 provides an example of conditions for conducting the hydrogen plasma treatment on the first passivation layer. The hydrogen plasma treatment on the first passivation layer is conducted in a plasma chamber having a volume of 2870 cm3and applied to the solar cell supported on a carrier plate, the carrier plate having a surface area of about 13665 cm2.

[0140] Table 2

[0141]

[0142] Subsequently, at step S300 in Fig. 4, the first charge-carrier collector is arranged on the back surface 1b of the substrate 1. One way of conducting step S300 is illustrated by Figs. 3B and 3C and steps S310 - S330 in Fig. 5.

[0143] At step S310 in Fig. 5, a continuous first doped layer 3a’ of the first charge-carrier collector is deposited on the back surface 1b of the substrate 1 such that the first passivation layer 2 is interposed between the first doped layer 3a’ and the back surface 1b of the substrate 1. As illustrated in Fig. 3B, the first008884900

[0144] doped layer 3a’ is deposited as a continuous layer in the same manner as the first passivation layer 2. Step S310 can be conducted by a PECVD process.

[0145] Subsequently, at step S320 in Fig. 5, an etch mask 7 is arranged on the back surface 1 b of the substrate 1 such that it is positioned directly on a back surface of the continuous first doped layer 3a’. The etch mask 7 is provided by depositing a continuous layer (i.e. blanket, or global, layer) of etch mask material, and subsequently etching the continuous layer of etch mask material into a pattern using a photoresist process. As partially illustrated by Fig. 3B, and as can also be appreciated from the geometry of the first charge-carrier collector in Fig. 3B, the etch mask 7 has a comb-like structure, with a plurality of prongs covering the portions of the first doped layer 3a’ that will form the plurality of spaced-apart first charge-carrier collection elements 3a, and a spine connecting the prongs together at a first end of each of the prongs, the spine of the etch mask 7 covering the portions of the first doped layer 3a’ that will form the spine portion of the first charge-carrier collector.

[0146] Having deposited the etch mask 7, the method in Fig. 5 subsequently comprises step S330 of an etching step to remove portions of the continuous first doped layer 3a’ to provide the plurality of first chargecarrier collection elements 3a spaced apart from each other in the lengthwise direction of the solar cell 10. The result of the etching step S330 is illustrated in Fig. 3C.

[0147] As Fig. 3C illustrates, step S330 removes all of the portions of the first doped layer 3a’ that are not covered by the etch mask 7, and thus leaves behind the plurality of spaced apart first charge-carrier collection elements 3a. Although not illustrated by Fig. 3C, step S330 also leaves behind the spine portion of the first charge-carrier collector that connects the plurality of collection first charge-carrier collection elements 3a.

[0148] Fig. 3C also illustrates how the etching at step S330, in addition to removing portions of the first doped layer 3a’, also removes part of each of the C-portions 2b of the first passivation layer 2, such that the thickness of each C-portion in the depth direction is less than the thickness of each A-portion in the depth direction. The C-portions 2b, after etching at step S330, typically have a thickness between 5 nm and 7 nm, compared to between 8 nm and 12 nm for the A-portions 2a. The C-portions 2b having a reduced thickness compared to the A-portions 2a can provide the back surface 1b of the substrate 1 with protection from damage during subsequent deposition steps (e.g. of the second passivation layer 4), but also means that the combined thickness of the B-portions 4a of the second passivation layer 4 and the C-portions 2b of the first passivation layer 2 is not so great as to negatively impact the performance of the solar cell 10.

[0149] Step S330 is conducted by hydrogen plasma etching in order to provide greater control over the depth of the etching compared to other types of plasma etching (e.g. NF3 etching) and reduce contamination of the layers of the solar cell with species such as fluorine radicals. Table 3 provides suitable plasma etching conditions for conducting step S330.008884900

[0150] Table 3

[0151]

[0152] Returning to the flow chart of Fig. 4, subsequent to step S300, the method comprises step S400 of arranging the second passivation layer 2b on the back surface 1b of the substrate 1 prior to arranging the second charge-carrier collector on the back surface 1b of the substrate 1. As illustrated in Fig. 3D, the second passivation layer 4 is deposited through the etch mask 7. In this way, a patterned second passivation layer 4 is provided without needing to perform an alignment step as part of depositing this layer, since the etch mask 7 is already in position following step S320.

[0153] Because of the spaced apart geometry of the first charge-carrier collection elements 3a and the prongs of the etch mask 7, deposition of the second passivation layer 4, for example using PECVD, results in the a-Si:H(i) material that the second passivation layer 4 is made of being deposited both onto the remaining C-portions 2b of the first passivation layer 2, and also onto sides surfaces of the first chargecarrier collection elements 3a, such that when the second charge-carrier collection elements 3b are subsequently deposited, there are B-portions 4a of the second passivation layer 4 interposed between: I) the second charge-carrier collection elements 3b and II) the back surface 1 b of the substrate and the C-portions 2b of the first passivation layer, and a D-portion 4b of the second passivation layer 4 interposed between each adjacent first charge-carrier collection element 4a and second charge-carrier collection element 4b.

[0154] The B-portions 4a of the second passivation layer 4 passivate dangling bonds generated on the back surface of the C-portions 2b of the first passivation layer 2 by the etching at step S330, whilst the D-portions 4b of the second passivation layer 4 will act to act to electrically isolate the first charge-carrier collection elements from adjacent second charge-carrier collection elements 3b.

[0155] The second passivation layer 4 is deposited such that the B-portions 4a of the second passivation layer 4 have a thickness in the depth direction of greater than or equal to 1 nm and less than or equal to 3 nm. Table 4 provides an example of PECVD conditions for conducting step S400. The deposition of the first passivation layer 2 is conducted in a plasma chamber having a volume of 2870 cm3and applied to the solar cell supported on a carrier plate, the carrier plate having a surface area of about 13665 cm2.008884900

[0156] Table 4

[0157]

[0158] Subsequently, at step S500 in Fig. 4, the method comprises conducting a hydrogen plasma treatment on the second passivation layer. The hydrogen plasma treatment on the second passivation layer results in a reduction of the microstructure factor of the B-portions 4a of the second passivation layer and improves the passivation quality of the second passivation layer 4, thereby providing the solar cell 10 with a higher Voc, as discussed above with reference to Fig. 2A. Table 5 provides an example of conditions for conducting the hydrogen plasma treatment on the second passivation layer. The hydrogen plasma treatment on the second passivation layer is conducted in a plasma chamber having a volume of 2870 cm3and applied to the solar cell supported on a carrier plate, the carrier plate having a surface area of about 13665 cm2.

[0159] Table 5

[0160]

[0161] Having provided a second passivation layer 4 having a thickness of between 1 nm and 3 nm and a subjected it to a hydrogen plasma treatment to reduce the microstructure factor of the B-portions 4a and improve cell passivation, the method subsequently comprises step S600 in Fig. 4 of arranging the second charge-carrier collector on the back surface 1 b of the substrate 1. This comprises depositing the material of the second charge-carrier collection elements 3b through the etch mask 7, such that the008884900

[0162] second charge-carrier collection elements 3b are provided interdigitated with the first charge-carrier collection elements 3a and with the B-portions 4a of the second passivation layer 4 and the C-portions 2b of the first passivation layer interposed between the second charge-carrier collection elements 3b and the back surface 1 b of the substrate 1 , as shown in Fig. 3E. Deposition of the second charge-carrier collector through the etch mask 7 can be conducted by PECVD.

[0163] At step S700 in Fig. 4, the method comprises arranging the third passivation layer 5 on the front surface 1a of the substrate 1 and arranging the anti-reflective coating 6 on the front surface 1a of the substrate 1. Step S700 may be conducted by first depositing the third passivation layer 5 on the front surface 1a of the substrate 1 , e.g. by PECVD, and subsequently depositing the anti-reflective coating 6, e.g. by PECVD, such that the third passivation layer 5 is interposed between the substrate 1 and the anti-reflective coating 6, as shown in Fig. 3F.

[0164] After step S600, and either prior to or subsequent step S700, the etch mask 7 is removed from the back side of the solar cell 10, for example, by a chemical dissolution process, as would be understood by the skilled person.

[0165] It is to be understood that the present disclosure is not limited by specific construction details or process steps set forth in the following description and accompanying drawings. Rather, it will be apparent to those skilled in the art having the benefit of the present disclosure that the systems, apparatuses and / or methods described herein could be embodied differently and / or be practiced or carried out in various alternative ways.

[0166] Unless otherwise defined herein, scientific and technical terms used in connection with the presently disclosed inventive concept(s) shall have the meanings that are commonly understood by those of ordinary skill in the art, and known techniques and procedures may be performed according to conventional methods well known in the art and as described in various general and more specific references that may be cited and discussed in the present specification.

[0167] All examples implementing the present disclosure can be made and executed without undue experimentation in light of the present disclosure. While particular examples have been described, it will be apparent to those of skill in the art that variations may be applied to the systems, apparatus, and / or methods and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit, and scope of the inventive concepts). All such similar substitutions and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the inventive concept(s) as defined by the appended claims.

[0168] In the drawings, the thickness of layers, films, elements etc., are exaggerated for clarity. Furthermore, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be008884900

[0169] present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0170] The use of the term “a” or “an” in the claims and / or the specification may mean “one,” as well as “one or more,” “at least one,” and “one or more than one.” As such, the terms “a,” “an,” and “the,” as well as all singular terms, include plural referents unless the context clearly indicates otherwise. Likewise, plural terms shall include the singular unless otherwise required by context.

[0171] The use of the term “or” in the present disclosure (including the claims) is used to mean an inclusive “and / or” unless explicitly indicated to refer to alternatives only or unless the alternatives are mutually exclusive. For example, a condition “A or B” is satisfied by any of the following: A is true (or present), and B is false (or not present), A is false (or not present), and B is true (or present), and both A and B are true (or present).

[0172] As used in this specification and claim(s), the words “comprising, “having,” “including,” or “containing” (and any forms thereof, such as “comprise” and “comprises,” “have” and “has,” “includes” and “include,” or “contains” and “contain,” respectively) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0173] Unless otherwise explicitly stated as incompatible, or the physics or otherwise of the embodiments, examples, or claims prevent such a combination, the features of examples disclosed herein, and of the claims, may be integrated together in any suitable arrangement, especially ones where there is a beneficial effect in doing so. This is not limited to only any specified benefit, and instead may arise from an “ex post facto” benefit. This is to say that the combination of features is not limited by the described forms, particularly the form (e.g., numbering) of example(s), embodiment(s), or dependency of claim(s). Moreover, this also applies to the phrase “in one embodiment,” “according to an embodiment,” and the like, which are merely a stylistic form of wording and are not to be construed as limiting the following features to a separate embodiment to all other instances of the same or similar wording. This is to say, a reference to ‘an,’ ‘one,’ or ‘some’ embodiment(s) may be a reference to any one or more, and / or all embodiments, or combination(s) thereof, disclosed. Also, similarly, the reference to “the” embodiment may not be limited to the immediately preceding embodiment. Further, all references to one or more embodiments or examples are to be construed as non-limiting to the claims.

Claims

1. 008884900CLAIMS1. A method of manufacturing an interdigitated back contact solar cell, the method comprising:providing a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell;arranging a first passivation layer on the back surface of the substrate;subsequently, arranging a plurality of first charge-carrier collection elements on the back surface of the substrate, the first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate;subsequently, arranging a second passivation layer on the back surface of the substrate; and subsequently, arranging a plurality of second charge-carrier collection elements on the back surface of the substrate, the second charge-carrier collection elements being interdigitated with the first charge-carrier collection elements, and the second passivation layer comprising a plurality of B-portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate; andwherein the step of arranging the plurality of first charge-carrier collection elements comprises: arranging a first doped layer on the back surface of the substrate; andhydrogen plasma etching portions of the first doped layer to leave the plurality of first chargecarrier collection elements.

2. The method according to claim 1 , wherein:the method further comprises, between arranging the first passivation layer and arranging the first charge-carrier collection elements, conducting a hydrogen plasma treatment on the first passivation layer; and / orthe method further comprises, between arranging the second passivation layer and arranging the second charge-carrier collection elements, conducting a hydrogen plasma treatment on the second passivation layer.

3. A method of manufacturing an interdigitated back contact solar cell, the method comprising:providing a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell;arranging a first passivation layer on the back surface of the substrate;subsequently, arranging a plurality of first charge-carrier collection elements on the back surface of the substrate, the first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate;subsequently, arranging a second passivation layer on the back surface of the substrate; subsequently, arranging a plurality of second charge-carrier collection elements on the back surface of the substrate, the second charge-carrier collection elements being interdigitated with the first28008884900charge-carrier collection elements, and the second passivation layer comprising a plurality of B-portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate; andwherein:the method further comprises, between arranging the first passivation layer and arranging the first charge-carrier collection elements, conducting a hydrogen plasma treatment on the first passivation layer; and / orthe method further comprises, between arranging the second passivation layer and arranging the second charge-carrier collection elements, conducting a hydrogen plasma treatment on the second passivation layer.

4. The method according to any one of claims 1 to 3, wherein each B-portion of the second passivation layer has a thickness in the depth direction greater than or equal to 1 nm and less than or equal to 3 nm.

5. The method according to claim 3, or claim 4 as dependent on claim 3, wherein the step of arranging the plurality of first charge-carrier collection elements comprises:arranging a first doped layer on the back surface of the substrate, the first doped layer having a back surface; andetching portions of the first doped layer to leave the plurality of first charge-carrier collection elements.

6. The method according to claim 5, wherein the etching comprises hydrogen plasma etching.

7. The method according to any one of claims 1 , 2 or 6, wherein the hydrogen plasma etching is conducted with one or more etching conditions selected from the group consisting of:a temperature greater than or equal to 180 °C and less than or equal to 220°C;a pressure greater than or equal to 72 Pa and less than or equal to 88 Pa;a power density greater than or equal to 27 mW / cm2and less than or equal to 33 mW / cm2; a hydrogen gas flowrate of greater than or equal to 2700 SCCM and less than or equal to 3300 SCCM;a plasma frequency of greater than or equal to 25 MHz and less than or equal to 30 MHz; an etching time of greater than or equal to 100 s and less than or equal to 120 s; and an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm.

8. The method according to any one of claims 1 , 2, or 5 to 7, wherein the etching comprises: arranging an etch mask on a back surface of the first doped layer such that the portions of the first doped layer to be etched are exposed through the etch mask; andetching the portions of the first doped layer exposed through the etch mask.0088849009. The method according to claim 8, wherein arranging the second passivation layer on the back surface of the substrate comprises depositing the second passivation layer through the etch mask.

10. The method according to claim 8 or 9, wherein arranging the second charge-carrier collection elements on the back surface of the substrate comprises depositing the second charge-carrier collection elements through the etch mask.

11. The method according to any one of claims 1 , 2, or 5 to 10, wherein:the first passivation layer comprises a plurality of C-portions, each C-portion interposed between a respective B-portion of the second passivation layer and the substrate; andthe etching step further comprises removing part of each C-portion such that the thickness of each C-portion in the depth direction is less than the thickness of each A-portion in the depth direction.

12. The method according to claim 2 or 3, or any one of claims 4 to 11 as dependent on claims 2 or 3, wherein:the hydrogen plasma treatment on the second passivation layer is conducted with one or more conditions selected from the group consisting of:a temperature greater than or equal to 180°C and less than or equal to 220°C;a pressure greater than or equal to 0.54 Torr and less than or equal to 0.66 Torr; a power density greater than or equal to 45 mW / cm2and less than or equal to 55 mW / cm2;a hydrogen gas flowrate of greater than or equal to 900 SCCM and less than or equal to 1100 SCCM;a frequency of greater than or equal to 12 MHz and less than or equal to 15 MHz; a duration of greater than or equal to 13.5 second and less than or equal to 16.5 seconds;an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm; a hydrogen gas flowrate per unit volume of a plasma chamber greater than or equal to 0.32 SCCM / cm3and less than or equal to 0.38 SCCM / cm3; anda hydrogen gas flowrate per unit surface area of the carrier plate greater than or equal to 0.066 SCCM / cm2and less than or equal to 0.080 SCCM / cm2; and / orthe hydrogen plasma treatment on the first passivation layer is conducted with one or more conditions selected from the group consisting of:a temperature greater than or equal to 180°C and less than or equal to 220°C;a pressure greater than or equal to 0.54 Torr and less than or equal to 0.66 Torr; a power density greater than or equal to 400 mW / cm2and less than or equal to 480 mW / cm2;a hydrogen gas flowrate of greater than or equal to 2500 SCCM and less than or equal to 3100 SCCM;a frequency of greater than or equal to 12 MHz and less than or equal to 15 MHz;008884900a duration of greater than or equal to 13.5 second and less than or equal to 16.5 seconds;an electrode gap of greater than or equal to 18 mm and less than or equal to 22 mm; a hydrogen gas flowrate per unit volume of a plasma chamber greater than or equal to 0.88 SCCM / cm3and less than or equal to 1.07 SCCM / cm3; anda hydrogen gas flowrate per unit surface area of the carrier plate greater than or equal to 0.18 SCCM / cm2and less than or equal to 0.22 SCCM / cm2.

13. The method according to any one of claims 1 to 12, wherein:the second passivation layer comprises a plurality of D-portions, each D-portion interposed between a respective first charge-carrier collection element and an adjacent second charge-carrier collection element; andthe B-portions and D-portions of the second passivation layer are deposited simultaneously.

14. The method according to any one of claims 1 to 13, wherein:the first passivation layer comprises amorphous silicon;the first passivation layer is deposited in a first stage and a subsequent stage, the first stage comprising deposition of amorphous silicon from a precursor gas comprising silane and not comprising hydrogen, and the subsequent stage comprising deposition of amorphous silicon from a precursor gas comprising silane and hydrogen.

15. An interdigitated back contact solar cell comprising:a substrate having a front surface and a back surface, the front surface spaced from the back surface in a depth direction of the solar cell;a plurality of first charge-carrier collection elements spaced apart along, and arranged on, the back surface of the substrate;a plurality of second charge-carrier collection elements spaced apart along, and arranged on, the back surface of the substrate, the first charge-carrier collection elements being interdigitated with the second charge-carrier collection elements;a first passivation layer comprising a plurality of A-portions, each A-portion interposed between a respective first charge-carrier collection element and the back surface of the substrate; anda second passivation layer comprising a plurality of B-portions, each B-portion interposed between a respective second charge-carrier collection element and the back surface of the substrate;wherein the thickness of each B-portion of the second passivation layer in the depth direction is greater than or equal to 1 nm and less than or equal to 3 nm.

16. The interdigitated back contact solar cell according to claim 15, wherein the first passivation layer comprises a plurality of C-portions, each C-portion interposed between a respective B-portion of the second passivation layer and the substrate.00888490017. The interdigitated back contact solar cell according to claim 16, wherein the thickness of each C-portion of the first passivation layer in the depth direction is less than the thickness of each A-portion of the first passivation layer in the depth direction.

18. The interdigitated back contact solar cell according to claim 17, wherein the thickness of each C-portion of the first passivation layer in the depth direction is greater than or equal to 5 nm and less than or equal to 7 nm.

19. The interdigitated back contact solar cell according to any one of claims 15 to 18, wherein the second passivation layer comprises a plurality of D-portions, each D-portion interposed between a respective first charge-carrier collection element and an adjacent second charge-carrier collection element.

20. The interdigitated back contact solar cell according to claim 19, wherein:the plurality of first charge-carrier collection elements are spaced apart on the back surface of the substrate in a spacing direction; andthe thickness of each D-portion of the second passivation layer in the spacing direction is greater than or equal to 1 nm and less than or equal to 3 nm.

21. The interdigitated back contact solar cell according to any one of claims 15 to 20, wherein: each first charge-carrier collection element comprises a layer of doped semiconductor material having a first conductivity type;each second charge-carrier collection element comprises a layer of doped semiconductor material having a second conductivity type; andthe first conductivity type is different to the second conductivity type.

22. The interdigitated back contact solar cell according to any one of claims 15 to 21 , wherein each second charge-carrier collection element comprises nanocrystalline silicon.

23. The interdigitated back contact solar cell according to any one of claims 15 to 22, wherein the interdigitated back contact solar cell is manufactured according to the method of any one of claims 1 to 14.

24. A solar module comprising one or more solar cells according to any one of claims 15 to 23.

25. A method of manufacturing a solar module, the method comprising arranging one or more solar cells manufactured according to the method of any of claims 1 to 14 in a housing.32

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