JP2017508292A - Self-aligned contact for back contact solar cells - Google Patents

Abstract

According to one aspect of the disclosed subject matter, self-aligned contacts for back contact back junction solar cells are provided. A solar cell has a front surface that receives light and a back surface opposite the front surface, and includes a semiconductor layer attached to a back plate that is electrically insulated. A first metal layer having base and emitter electrodes self-aligned to the base and emitter regions is positioned on the back surface of the semiconductor layer. A patterned second metal layer that provides cell interconnection and is connected to the first metal layer by via plugs is positioned on the backplate. [Selection] Figure 5

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority to US Provisional Application No. 61 / 954,116, filed February 26, 2014, which is hereby incorporated by reference in its entirety.

  The present disclosure relates generally to photovoltaic (PV) solar cells, and more particularly to self-aligned contacts for solar cells.

  As solar cell technology is increasingly being adopted as an energy generation solution, there is a need for manufacturing and effectiveness improvements related to solar cell effectiveness, metallization, physical consumption, and manufacturing. A factor in manufacturing cost and conversion efficiency is to operate solar cell absorbers that are thinner and larger in size than ever, and thus the mechanical vulnerability, efficiency of solar cells based on these thin absorbers, In addition, complex processing and handling increased, and in particular, the brittle effect on crystalline silicon absorbers increased.

  In general, solar cell contact structures include conductive metallization on the base and emitter diffusion regions, for example, aluminum metal linking silicon in the base and emitter contact regions through relatively high concentrations of phosphorus and boron regions, respectively. Including

  The features, nature and advantages of the disclosed subject matter will become more apparent from the following detailed description when read with the drawings in which like reference numbers represent like features.

It is sectional drawing of a solar cell provided with a self-alignment contact structure. It is sectional drawing of a solar cell provided with a self-alignment contact structure. It is sectional drawing of a solar cell provided with a self-alignment contact structure. It is sectional drawing of a solar cell provided with a self-alignment contact structure. 1 is a cross-sectional view of a solar cell at various steps during the manufacture of an adjacent junction cross-finger back contact solar cell with self-aligned contacts. FIG. 1 is a cross-sectional view of a solar cell at various steps during the manufacture of an adjacent junction cross-finger back contact solar cell with self-aligned contacts. FIG. FIG. 3 is a cross-sectional view of a solar cell at various steps during the manufacture of non-adjacent junction cross-finger back contact solar cells with self-aligned contacts. FIG. 3 is a cross-sectional view of a solar cell at various steps during the manufacture of non-adjacent junction cross-finger back contact solar cells with self-aligned contacts. FIG. 3 is a cross-sectional view of a solar cell at various steps during the manufacture of non-adjacent junction cross-finger back contact solar cells with self-aligned contacts. FIG. 3 is a cross-sectional view of a solar cell at various steps during the manufacture of non-adjacent junction cross-finger back contact solar cells with self-aligned contacts. FIG. 3 is a cross-sectional view of a solar cell at various steps during the manufacture of non-adjacent junction cross-finger back contact solar cells with self-aligned contacts. 1B is a cross-sectional view of a solar cell with a self-aligned contact structure consistent with FIG. 1A and having multiple layers of metallization. FIG.

  Therefore, there is a need for a manufacturing method for back contact solar cells. In accordance with the disclosed subject matter, a method of manufacturing a back contact solar cell is provided. These innovations substantially reduce or eliminate the disadvantages and problems associated with previously developed back contact solar cell manufacturing methods.

  This patent relates to solar cells. In addition to those described herein, related patent applications that at least partially have joint inventions and provide solar cell structure and manufacturing details include: US filed on Feb. 2, 2014 Patent Application No. 14 / 179,526, US Patent Application No. 14 / 072,759 filed on November 5, 2013 (published as US Patent Application Publication No. 20140326295 on November 6, 2014) No. 13 / 869,928 filed Apr. 24, 2013 (published as U.S. Patent Application Publication No. 20130228221 on Sep. 5, 2013), filed Sep. 22, 2014 U.S. Patent Application No. 14 / 493,341, and U.S. Patent Application No. 14 / 493,335 filed September 22, 2014, all of which are Entire al which is incorporated herein by reference.

  According to one aspect of the disclosed subject matter, self-aligned contacts for back contact back junction solar cells are provided. A solar cell has a front surface that receives light and a back surface opposite the front surface, and includes a semiconductor layer attached to a back plate that is electrically insulated. A first metal layer having base and emitter electrodes self-aligned to the base and emitter regions is positioned on the back surface of the semiconductor layer. A patterned second metal layer that provides cell interconnection and is connected to the first metal layer by via plugs is positioned on the backplate.

  These and other advantages of the disclosed subject matter, as well as additional novel features, will be apparent from the description provided herein. The intent of this summary is not to be a comprehensive description of the subject matter, but rather to provide a short summary of some of the subject's functions. Other systems, methods, features, and advantages provided herein will become apparent to those skilled in the art upon review of the following drawings and detailed description. All such additional systems, methods, features, and advantages included in this description are intended to be within the scope of the claims.

  The disclosed subject matter provides structures and methods for making self-aligned contacts for back contact back junction solar cells. In particular, the disclosed subject matter and corresponding figures provide a low-profile for forming thin silicon solar cells using self-aligned contacts for back contact back junction (eg, interdigitated back contact IBC) solar cells. Provide damage, high efficiency, low cost process flow. The described novel self-aligned contact structure can achieve higher solar cell conversion efficiency. In addition, a method of manufacturing a solar cell with minimal or reduced process steps for the formation of a solar cell structure with self-aligned contacts is described.

  The term self-alignment describes a cell structure in which the heavily doped n + and p + regions under the base and emitter metal contacts are self-aligned to the contact openings as shown in FIGS. 1A-1D. FIG. 1A is a cross-sectional view of a selective emitter solar cell with a self-aligned contact structure having a dopant diffusion region with a heavier doping level (eg, greater than 1E18 cm −3) just below the metal toward the silicon absorber contact. . Self-aligned contact structures have heavily doped regions (n-type and p-type) in silicon for improved metal / silicon (Si) contact resistance and lower surface recombination rates at metal / Si contacts This can also provide higher solar cell efficiency by minimizing heavily doped regions in the solar cell (eg, doping higher than 1E18 cm −2) and thus reducing the total saturation current density. Alternatively, the self-aligned contact structure disclosed herein is formed by using a hetero / tunneling contact through a barrier layer between metal and Si, as shown in FIG. 1B. Also good. FIG. 1B is a cross-sectional view of a solar cell with a self-aligned contact structure formed using a hetero / tunneling contact through a barrier layer between metal and Si.

  The advantage of the self-aligned structure is that the heavily doped region is limited only under the contact that is required. If the contact opening needs to be matched with heavy doping with a non-self-aligned contact structure, the heavy diffusion needs to be much wider than the contact opening to meet the matching tolerances. Compared to non-self-aligned contact structures, the provided self-aligned contact structures can have higher efficiency for two obvious reasons. First, heavy doping can be detrimental when used under passivation, in other words heavy doping is more beneficial when used under poor passivation, such as metals, and in some cases is not Only useful when used under poor dynamics. Thus, the self-aligned structure removes heavily doped regions under high quality passivation. Second, two openings need to be created for the non-self-aligned structure, the first for doping and the second for contact openings. If these openings are created using a method that tends to cause damage in the silicon (eg in the case of laser processing), the self-aligned structure removes the outer nested openings and minimizes laser damage from this step If necessary, remove it. In addition to more effective advantages, the self-aligned structure requires fewer process steps and can therefore reduce battery costs.

Table 1 below shows a pre-process flow for the formation of selective emitter solar cells having self-aligned contacts and field emitters as shown in FIG. 1A using a dopant paste step.

  Table 1 shows the process flow for manufacturing high efficiency back contact back junction solar cells using self-aligned contacts. As shown, step 1 is the removal of saw damage to remove damage from a wafer (eg, a CZ wafer), but the provided process flow is epitaxially formed silicon that has been processed while on the mold. It is equally applicable to the substrate, where the removal of saw damage in step 1 replaces the steps of porous silicon and epitaxial silicon deposition as described in detail herein. Thus, in an epitaxial embodiment, the epitaxial substrate may be released from the mold in post-processing (e.g., mechanical or wet etching) before the described pre-process occurs on the exposed surface of the epitaxial substrate attached to the mold. release). The provided exemplary process flow is conveniently described in the context of manufacturing a high efficiency back contact back junction solar cell, and those skilled in the art will combine the various processing steps described in the overall process flow, It is important that it may be added or removed, changed or moved. In other words, the elements from each process flow described in the tables provided herein may be combined together or combined with other known solar cell manufacturing methods. For example, with respect to Table 1, the laser contact aperture shown in step 3 is split into two steps (eg, as shown in step 2) to form a self-aligned contact for only the base and emitter contacts separately. The dopant paste printing step shown in step 4 can have an additional third printing of the undoped paste on top of the already printed dopant paste (eg as shown in FIG. 8) Also good. Further, the wet etching step shown in step 6 of Table 1 and the step of removing the anneal dopant paste may be replaced with a dry HF vapor phase etching process, or the removing step 6 may be performed in all dry pre-process processes. May be omitted entirely (i.e. may be eliminated). Further, the laser contact opening step shown in step 6 of Table 1 may be replaced with an etching paste process that includes deposition, drying, and rinsing of an etching paste for a laser-less pre-process process.

Table 2 below shows a pre-process flow for the formation of a selective emitter solar cell using a dopant paste and having a self-aligned contact using a separate contact opening step.

Table 3 below shows a pre-process flow for the formation of selective emitter solar cells having self-aligned contacts with application of dopant paste and diffusion barrier.

  Alternatively, the diffusion barrier deposition shown in step 5 of Table 3 as APCVD.USG deposition may be undoped paste printing.

  The process flow embodiments of Tables 2 and 3 may be used to reduce self-doping from the dopant paste during diffusion annealing.

Table 4 below shows a pre-process flow for the formation of non-adjacent junction solar cells, as shown in FIG. 1C, having self-aligned contacts with diffusion barrier dopant paste printing. FIG. 1C is a cross-sectional view of a non-adjacent junction solar cell with a self-aligned contact structure having a dopant diffusion region with a higher doping level (eg, greater than 1E18 cm −3) directly below the contact metal toward the silicon absorber. .

  Alternatively, with respect to the non-adjacent junction solar cell flow of Table 4, steps 2, 3, and 4 of Table 4 follow the deposition of APCVD boron doped silicon oxide (BSG1) followed by two picosecond (ps) CO2 lasers. Steps may be substituted, and an alternative embodiment is called self-aligned contact with dopant paste printing and non-adjacent bonding with boron doped silicon oxide by APCVD.

Table 5 below shows the manufacturing process flow for a non-selective emitter solar cell with self-aligned contacts and using a phosphorus dopant paste.

Alternatively, Table 6 below shows a manufacturing process flow for a non-selective emitter solar cell having self-aligned contacts and using phosphate chloride POC13 (POC1).

Table 7 below shows a manufacturing process flow for a non-selective emitter solar cell having a self-aligned passive base contact using a dopant paste.

Table 8 below shows the manufacturing process flow for a solar cell with self-aligned base tunneling / heterojunction contact, as shown in FIG. 1B.

Table 9 below shows the manufacturing process flow for a solar cell having a self-aligned contact without heavy diffusion under the base contact.

  Alternatively, the self-aligned contact structures and methods described herein may be applied.

Table 10 below shows a pre-process flow for the formation of a solar cell having a self-aligned contact with an electric field base, as shown in FIG. 1D. FIG. 1D is a cross-sectional view of a solar cell with an electric field-based and self-aligned contact structure having a dopant diffusion region with a higher doping level (eg, greater than 1E18 cm −3) directly below the contact metal toward the silicon absorber. . Alternatively, for example, the HF vapor step 6 in Table 10 and the step of removing the anneal dopant paste may be replaced with a wet etch step.

Alternatively, Table 11 below shows a pre-process flow for the formation of solar cells with electric field-based self-aligned contacts with etch paste and dopant paste printing, as shown in FIG. 1D.

  2A-2E represent a process flow showing cross-sectional views of a solar cell at various steps during the manufacture of an adjacent junction cross-finger back contact solar cell having self-aligned contacts with a dopant paste. FIG. 2A shows an aluminum oxide (Al 2 O 3) layer deposited on a silicon substrate / wafer (eg, by APCVD). The aluminum oxide layer may also have an undoped silicate glass layer. Next, as shown in FIG. 2B, the nanosecond (ns or ps) laser opens the base and emitter contacts. This step may also include wet etching to remove any oxidation residue (eg, aluminum silicon oxidation residue). Next, as shown in FIG. 2C, the dopant paste is a diffusion anneal following paste printing in the emitter and base regions to implant / diffuse the dopant and form the base and emitter regions. The dopant paste is then removed (eg, by wet etching) as shown in FIG. 2D. Next, as shown in FIG. 2E, metal is printed on the base and emitter regions and annealing minimizes the risk of shunting.

  3A-3G represent a process flow showing a cross-sectional view of a solar cell at various steps during the manufacture of a non-adjacent junction cross-finger back contact solar cell with self-aligned contact with a dopant paste. FIG. 3A shows an aluminum oxide (Al 2 O 3) layer deposited on a silicon substrate / wafer (eg, by APCVD). The aluminum oxide layer may also have an undoped silicate glass layer. The nanosecond (ns) laser then opens the base contact, as shown in FIG. 3B. This step may also include wet etching to remove any oxidation residue (eg, aluminum silicon oxidation residue). Next, as shown in FIG. 3C, an undoped silicate glass layer is deposited (eg, by APCVD). Next, as shown in FIG. 3D, the picosecond (ps) laser ablates the base and emitter contact openings. Next, as shown in FIG. 3E, the dopant paste is a diffusion anneal following paste printing in the emitter and base regions to implant / diffuse the dopants and form the base and emitter regions. Next, as shown in FIG. 3F, the dopant paste is removed (eg, by wet etching). Next, as shown in FIG. 3G, metal is printed on the base and emitter regions, and annealing minimizes the risk of shunting.

  4A-4E are cross-sectional views of solar cells at various steps during the manufacture of non-adjacent junction cross-finger back contact solar cells having self-aligned contacts with a dopant paste using an undoped paste first. Represents the process flow. FIG. 4A shows an undoped silicic acid (SiO 2) paste printed only on the desired base region on the silicon substrate / wafer. Next, as shown in FIG. 4B, a doped layer (eg, doped aluminum oxide layer Al 2 O 3 or doped borosilicate glass layer BSG1) and an undoped silicate glass layer (USG) layer (eg, Deposited by APCVD). The undoped silicate glass layer may have a thickness of 3 to 4 times that of the undoped layer. Next, as shown in FIG. 4C, the picosecond (ps) laser ablates the base and emitter contact openings. Next, as shown in FIG. 4D, the dopant paste is a diffusion anneal following paste printing in the emitter and base regions to implant / diffuse the dopant and form the base and emitter regions. The dopant paste is then removed (eg by wet etching). Next, as shown in FIG. 4E, metal is printed on the base and emitter regions and annealing minimizes the risk of shunting.

  Although methods of manufacturing self-aligned back contact back junction solar cells have been generally described in connection with CZ wafers, these methods are equally applicable in connection with epitaxially grown back contact back junction solar cells. In addition, thick crystalline silicon (e.g. having an absorber with a thickness in the range of about 100 um to 200 um) as well as a thin crystalline silicon back contact back junction solar cell (e.g. having an absorber with a thickness in the range of about 5 um to 100 um) ) Is applicable to both.

  In general and specifically applicable to the process flows shown in the table below, the emitter or base contact is continuously performed using various field dielectric removal techniques such as laser or wet etching or etching paste. (In either order) or simultaneously opened. Also subsequently, a dopant source is deposited in the open contact, carrying the dopant into the silicon at high temperature, selectively removing / etching the dopant source while keeping the field dielectric intact from the etchant. . This leaves the dopant carried into the silicon only in the region where the contact is left open leaving a self-aligned structure.

  The described manufacturing method may be further classified by the source of the dopant in contact. These can be derived from dopant pastes (eg, n-type phosphorus and p-type boron), or from deposited films that incorporate dopants into boron or phosphorus doped SiO 2 films, eg, deposited by APCVD. Finally, N + and p + dopant sources are hybrid sources where one type of dopant is derived from APCVD and the other type of dopant is derived from a dopant paste. Further subcategories are defined by techniques to etch / remove dopant sources applicable to both wafer and epitaxial based absorbers, as well as dopant source categories (dopant pastes, APCVC films, and hybrid dopant sources). The As an example, a wet process with HF can be used for an oxide-based dopant source such as doped SiO2, or a dry process using HF vapor etching may be developed. Also, if the electric field region is also SiO2, wet HF is selectively obtained because a heavily doped SiOx film can be etched much faster than an undoped film. Alternatively, field region deposition may include Al 2 O 3 (eg, further deposited using APCVD). Once this film has been processed, for example, at a high temperature above 900 ° C., it may have high selectivity in aqueous HF solutions. Alternatively, the HF gas phase also etches the dopant source with high selectivity.

  In general, if the contacts are opened simultaneously, both dopant sources may be screen printed dopant pastes. If the contact is continuously opened, a film deposited on either the contact or the hybrid source may be utilized.

Table 12 shows the manufacturing flow of the pre-process self-aligned contact that results in separate bonds and is achieved using a dopant paste (eg, a screen printed dopant paste). In the isolated junction, the emitter doping is not adjacent to the base contact doping and is separated by the base background bulk doping. Step 2 shows the deposition of the cap following the emitter. The emitter source is also shown to be boron doped Al2O3 deposited by APCVD, although this may be a boron doped SiO2 layer or another dopant source layer deposited using a different means. Good. The first laser cutting (step 3) is to cut the separation between the emitter and the base doping so that there is a separation between the junctions during annealing. The stream proposes the use of laser nsUV and psUV. The base window may also be generated using a picosecond green laser, a femtosecond laser, or an etching paste or lithography technique. If a picosecond laser is used, a small wet etch of silicon may be followed to remove laser damage in the silicon. Step 5 of Table 12 may also be performed using a picosecond green laser or a femtosecond laser. Step 5 is a contact opening in the base window for base contact, as well as a contact opening for the emitter. Both contacts are incised in the same step, so the dopant source printing method should be selective printing on top of these contacts, such as screen printing of the dopant paste (as compared to the comprehensive deposition of a thin dopant source film) It is. After the anneal carrying the dopant in both contacts in step 7, the dopant source is wet etched or selectively etched using HF gas phase. In an isolated embodiment, if the dopant source is as conductive as the silicon-based dopant source, the etching step may be omitted (step 8).

  In another embodiment, the contact can be continuously opened if there is a risk of co-diffusion during drying or delivery of the dopant. In this scenario, either the base or emitter contact is first opened and the corresponding paste is printed and dried. The other contact is then opened and the corresponding paste is printed and dried. Finally, both pastes are carried simultaneously. This alternative can avoid cross-contamination within the contact during drying and combustion.

  If the problem of cross-contamination is more extreme when the dopant is in transit, contact opening, dopant paste printing, drying / burning, and annealing may be performed on one type of dopant. This procedure is followed by the same steps in the second type of contact. This results in two different anneals when the thermal budget is to be deleted.

  In the adjacent junction embodiment of the process flow of Table 12, step 3 and step 4 may be omitted, and contact can be opened directly to both the base and emitter.

  Finally, in another variation, the electric field region may be covered by a thin film that is resistant to the chemistry of the dopant source etchant. When the dopant source is SiOx-based and the etching chemistry is HF-based, the cap layer is made of APCVD-based Al2O3 (undoped or doped) or titanium oxide (TiO2) or amorphous silicon (a-Si). There may be.

Table 13 shows the process flow for a separate, isolated, self-aligned solar cell in the previous step that uses only an APCVD deposited film that serves as a dopant source. This flow is followed by the same steps as in Table 12 (having all the variations described above) until step 4. In step 5, only one type of contact is initially opened. In this case, the type is an emitter contact (for an n-type back contact cell). This is followed by an APCVD BSG film, which is a dopant source for emitter contact doping (step 6). The base contact is then opened and PSG is deposited using APCVD. In a variant, the order of the emitter and base contact openings can be reversed. The adjacent example of a separate bond flow described in Table 13 omits / removes step 3 and step 4 to create an adjacent bond.

Table 14 below shows the process flow of the separate junction self-alignment of the previous step using the hybrid approach. In this approach, one of the dopant sources is a deposited APCVD film, while the other type of dopant source is a printed dopant source.

  The flow in Table 14 shares the first four steps (with variants) with Table 13. In step 5 of Table 14, the emitter contact is opened. BSG is deposited in step 6 and step 7 opens the base contact with a laser (flow suggests the use of a ps laser, but different wavelength nano or femtosecond lasers meet the requirements for contact opening Note that this is not excluded as far as possible). Subsequently, in step 8, a phosphorus-based dopant paste is printed and dried. Step 9 is an annealing step to carry the dopant from the BSG and from the phosphor paste to produce the contacted doped region, while Step 10 is a dopant based on either wet or HF gas phase techniques. Remove source. The adjacent example of a separate bond flow described in Table 14 omits / removes step 3 and step 4 to create an adjacent bond.

  In the flow variant in Table 14, the order of BSG2 (step 6) and phosphorus dopant paste (step 8) is reversed. Base contact is opened first, followed by phosphorus paste. This is followed by emitter contact and BSG2 deposition, and the rest of the flow is similar.

  In another variation, the hybrid dopant source is APCVD PSG and APCVD PSG so that the base contact is made with a SiO2 film deposited and doped with APCVD, while the emitter contact is made using a boron-based dopant paste. Based on the dopant paste boron. This variant further has a variant in which the order of the contact opening and the associated dopant source has two possibilities.

Table 15 below is a pre-process flow showing a variation of the hybrid approach of Table 14 where both dopant paste and doped dielectric film are used as dopant sources for the contacted doped base and emitter. is there.

  In the variation of Table 15 compared to Table 14, both the emitter and base contacts are separated by APCVD-PSG and diffusion annealing. This is done to reduce the risk of dopant co-diffusion during diffusion annealing. Co-diffusion is the process by which a dopant source from the base or emitter contact diffusion region (phosphorus or boron) moves from the dopant paste (phosphorus or boron) through the gas phase to another polarity (base or emitter). . As shown in Table 15, this process can be avoided, for example, by placing a solid phase dopant source (APCVD-PSG) on top of the PSG and applying an anneal prior to the next contact emitter contact opening step. In some cases, the paste is phosphorous, the base is opened first (relative to the n-type back contact cell), and in a variant, the paste is boron paste, and the emitter is opened first.

The process flow variations in Table 15 form adjacent joints by omitting Step 3 and Step 4, as shown in Table 16 below. Throughout this disclosure, the variations described in connection with Table 15 are equally applicable to adjacent joint flows.

  In the variations of Tables 15 and 16, the risk of co-diffusion can be avoided by removing APCVD-PSG or removing diffusion annealing.

Note that all self-aligned process flows with the variations described so far are equally effective with epitaxially grown thin film solar cells. A representative process flow (separate junction with dopant paste) corresponding to the approach outlined in Table 12 is shown in Table 17 for an epitaxial thin film solar cell. The epitaxial flow may use the HF vapor phase technique to keep the flow almost dry, while the epitaxial absorber is still on the mold. All other embodiments with adjacent and separate junctions with a hybrid dopant source or all APCVD dopant sources (shown for a CZ wafer) have a modified flow based on Table 16. Equally effective as an epitaxial solar cell having. The present application provides a more detailed flow for other aspects of epitaxial formation. The self-aligned property, along with its manufacturing method, can be combined with any previously studied variants of process flows based on epitaxial and CZ wafers.

  After completing the base and emitter regions on the back side of the solar cell, the solar cell structure described herein is comprised of an on-cell base and emitter metallization first level metal (M1), and a first level metal. Multi-layer metallization structures such as a two level metallization structure with a second level metal (M2) that collects power (voltage and current) (and thus completes the metallization of the solar cell) may be utilized. This may also form interconnections between the batteries. The second level metal (M2) is a cross pattern of base and emitter current collection fingers, and optionally a solar cell base and emitter bus (eg, M2 base and emitter fingers are respectively base and emitter buses). May be provided). The first level metal (M1) is crossed at a relatively fine pitch (much more than the second level metal pitch) placed perpendicular / perpendicularly or possibly parallel to the crossed fingers of M2. An interdigitated back contact metallization structure with a fine pitch) may be provided. A relatively thin electrically insulating backplate formed between M1 and M2 and attached to the solar cell provides structural support for the solar cell, electrical insulation for M1, and solar cell manufacturing (especially M2 manufacturing and The processing of the front face of the solar cell) can be improved. The backplate sheet may be laminated to or otherwise attached to a back contact / back junction solar cell, eg, a solar cell semiconductor substrate material (eg, silicon solar cell) before completing the remaining solar cell manufacturing process steps. For example, it may be a continuous flexible material close to the CTE that matches the crystalline silicon.

  Multi-level metallization designs, such as first level on-cell metal M1 (eg, fine pitched interdigitated metallization structure comprising aluminum or another suitable metal), and second level metal M2 (eg, In a two-level metal design with a coarse pitched interdigitated metallization structure with aluminum, copper, or a suitable conductive metal, M1 is the interdigitated base and emitter line (eg, base-emitter finger). M2 (possibly with crossed fingers substantially perpendicular / perpendicular to M1's fingers, and a much coarser base-emitter pitch compared to M1) Has an electrical connection between the base and emitter lines of M1 (ie a busbarless M1 pattern, but arbitrarily It may be placed on the pattern of M2 a bus bar). The metal layer in the disclosed multi-level metal design is a resin / fiber prepreg material that forms a continuous backplate for each of a plurality of solar cells in a solar cell array placed on the continuous backplate; Alternatively, it is separated by a dielectric such as a suitable plastic or polymer material or an electrically insulating layer. Importantly, the back plate is preferably compared to a CTE that matches the CTE of the semiconductor absorber (eg, crystalline silicon) so as to minimize CTE (thermal expansion coefficient) mismatch stress or warping effects during heat treatment. Need to be close. For example, a specially devised aramid fiber prepreg material may provide a near CTE consistent with silicon, while other desirable such as flexible electrical insulation, thermal and chemical stability, and effective crack-free lamination Processing and reliable features can be provided. The M1 / M2 interconnect structure is positioned between M1 and M2, ie, an insulating layer (eg, prepreg back) that is laminated or attached to the back of the solar cell after formation of the patterned M2 layer. A conductive material filled in vias through an insulating dielectric layer such as a faceplate.

  Specifically, the provided solar cell is a relatively thin patterned metal (eg, aluminum paste screen printing, aluminum ink inkjet printing, formed directly on the back of the solar cell prior to back plate lamination. Alternatively, a preferred busbar-less (but optionally busbar may be used) first using an aluminum target followed by thin aluminum formed by laser sputtering or plasma sputtering by wet etching patterning) Level of contact metallization (M1), as well as a second level of thin patterned metal M2 (eg, about 3 to 5 microns thick Al or alternatively about 1 to 1) formed after lamination of the backplate It has several microns of copper, and in both cases it is arbitrarily soldered, such as tin Comprises may) be covered by injury can coating, metallization schemes of the two levels may be used. The patterned M2 layer may also be formed using plating or lamination and patterning a highly conductive metal foil (including copper or aluminum). The layers of M1 and M2 are separated by a back plate and interconnected at designated areas through conductive via plugs (which may be formed during the formation of M2). M1 has a fine pitch pattern, and M2 is preferably orthogonal (or substantially perpendicular) to M1 and has a coarse pitch pattern (and therefore has fewer base and emitter fingers than M1). Patterned M2 completes battery level electrometallization and may also provide electrical interconnections between cells for multiple solar cells stacked on a continuous backplate, and in some cases There is no need to separate tab connections / bus connections / soldering between batteries. Further, M2 may form an array / module level bus coupling or interconnection when an array / module electrical interconnection design is desired.

  In some cases, voltage and current scaling (eg, higher voltage and lower current solar cells) may relax and reduce the conductivity requirements and limitations of M2. For example, considering other factors, thin M2 metal (eg about 2-5 microns deposited by PVD) compared to thick M2 metallization (eg about 50-80 microns thick electroplated copper) Thick aluminum, or about 1 to several microns of copper formed by plasma sputtering or vapor deposition) is utilized. Significantly, the thickness of the M1 and M2 metallization layers may be adjusted based on the number, size, and shape of the intersecting fingers on the M1 and M2 layers. M1 may be conveniently patterned with finer crossed fingers compared to M2's crossed fingers. However, the provided battery construction and fabrication embodiments are adaptable to various dual level metallization schemes that utilize the backplate and M2 metallization layer.

  Prior to the backplate lamination, the metallization pattern of the solar cell base and emitter contacts can be, for example, screen printed, ink jet printed, plasma sputtered (PVD), or deposited aluminum (or aluminum). (Silicon alloy or Al / Niv / Sn stack) is formed directly on the back of the battery using a thin layer of material layer. This first layer of metallization (referred to herein as M1) defines the metallization pattern of solar cell contacts, eg, fine pitched interdigitated back contact (IBC) conductor fingers are IBC The base and emitter regions of the battery are defined. The M1 layer extracts the current and voltage of the solar cell (and hence the power of the solar cell), and the power of the solar cell through the conductive via plug formed in the back plate is converted to that of the highly conductive solar cell formed after M1. Transmit to the second level / layer of metallization (referred to herein as M2). The conductive via plug can be formed simultaneously with the formation of the patterned M2 layer, for example, after laser drilling a via hole in the back plate layer.

  The backplate material attached to the back surface of the solar cell (s) and placed between the patterned M1 and M2 layers is a thin polymeric material with a sufficiently low coefficient of thermal expansion (CTE) ( For example, the sheet may be about 25 microns to 1 mm, and in some cases about 25 microns to 250 microns. This CTE closely matches the CTE of the semiconductor absorber layer so as not to cause excessive heat-induced stress and warpage on the solar cell array. In addition, the backplate material provides chemical resistance during post-process battery manufacturing processes, particularly wet texturing of the front of the battery, and thermal stability during PECVD deposition of the front passivation and anti-reflective coating (ARC) layers. Should meet the required process integration. Furthermore, the backplate material that is further electrically insulated should meet the requirements of the module level lamination process and long-term reliability. Various suitable polymers (plastics, fluoropolymers, prepregs, etc.) and suitable non-polymeric materials (glass, ceramics, etc.) may be used as the backplate, but the choice of backplate material is limited to this Although not, it depends on many considerations including material costs, ease of process integration, reliability, flexibility, mass density, and the like.

  A convenient material choice for the backplate material is prepreg, more specifically aramid fiber resin prepreg. In some cases, non-woven aramid fibers are particularly advantageous. Generally, prepregs are reinforcements pre-impregnated with resin and can be used immediately to produce composite parts (prepregs can be used to produce composite parts more quickly and easily than wet layup systems). The prepreg may be manufactured by combining a specially devised pre-catalyzed resin with a reinforcing fiber or fabric using an instrument designed to ensure consistency. In general, an inexpensive prepreg material is used for the printed circuit board.

  The back plate (eg, prepreg sheet) may be attached to the back surface of the solar cell using a vacuum laminator. When a combination of heat and pressure is applied, a thin backplate (eg, a prepreg sheet) is permanently laminated or attached to the backside of a partially processed (or more fully processed) solar cell. In the case of partially processed solar cells, the next post-stacking manufacturing process steps are (i) completing the texturing and passivation steps on the solar side (front) of the solar cell, and (ii) ) Completing the highly conductive metallization (M2) on the back surface of the solar cell (which may include a portion on the back plate of the solar cell). Highly conductive metallized M2 layers (e.g. comprising aluminum, copper, or silver, where aluminum and / or copper are preferred over silver due to much lower material costs), including both emitter and base polarity Formed on a laminated back plate attached to the back of the substrate.

  After formation of the back plate (on, in, or around the M1 layer), a highly conductive metallized M2 layer is formed on the back plate. Via holes (possibly hundreds or thousands of via holes for one solar cell) are drilled into the backplate (eg laser drilling, etching, or etching following partial laser drilling) Combination), may have a diameter in the range of about 50-500 microns (specifically, a diameter in the range of about 100-300 microns) (optionally tapered). These via holes are placed in the predesignated landing pad area of M1 for electrical connection between the patterned M2 and M1 layers through conductive plugs formed in these via holes. It is burned. In some cases, the vias may be coated or at least partially filled with conductive metallization, M2 may be deposited in a separate step, and in other cases the deposition of M2 is the same M2 The via is at least partially covered or partially filled with a deposition or formation step. Subsequently or in conjunction with via hole filling and conductive plug formation, a patterned highly conductive metallized layer M2 (eg, by plasma sputtering, plating, vapor deposition, or combinations thereof, eg, aluminum, Al / NIV, Al / NiV / Sn, or M2 material comprising copper or soldered copper). For IBC solar cells with fine pitched interdigitated back contact (IBC) fingers (eg, hundreds of fingers) on M1, the patterned M2 layer is designed orthogonal to M1 fingers. In other words, the rectangular or tapered M2 finger is substantially perpendicular to the M1 finger. Because of this orthogonal deformation, the patterned interdigitated M2 layer is much less than the M1 layer and has a wider IBC finger (eg, about 10-50 fewer M2 fingers than M1 fingers). You may have. Therefore, the M2 layer may be formed in a much coarser pattern with IBC fingers wider than the M1 layer. Arbitrarily, the solar cell bus bar may be positioned on M2 rather than on the M1 layer (in other words, M1 is busbarless) to remove the electrical shade loss associated with the on-cell busbar. Both the base and emitter interconnections and the bus bar may be positioned on the M2 layer on the back plate on the back of the solar cell, so that from the back of the solar cell to both the base and emitter terminals of the solar cell on the back plate. Electrical access is provided.

  FIG. 5 is a cross-sectional view of a solar cell with a self-aligned contact structure consistent with FIG. 1A and having multiple levels of metallization. In particular, FIG. 5 shows a first level of emitter-coupled second level metal M2 through backplate vias that are patterned orthogonally to M1 crossed fingers to second level metal M2. The level of metal M1 is shown.

  The previous description of the exemplary embodiments is provided to enable any person skilled in the art to make or use the claimed subject matter. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without use of new functionality. Good. Accordingly, the claimed subject matter is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. Intended.

All additional systems, methods, features, and advantages as included herein are intended to be included within the scope of the claims.

Claims (1)

A deposited semiconductor layer comprising:
A front side for capturing light with a passive layer;
A doped base region;
A doped back emitter region having a polarity opposite to that of the doped base region;
A deposited semiconductor layer; and
A back passivated dielectric layer and a patterned reflective layer on the back emitter region;
A self-aligned back emitter contact and back base contact coupled to a metal interconnect forming a first level interdigitated metallization pattern on a back surface of the back contact back junction thin solar cell;
At least one permanent support enhancement positioned on the back side of the thin solar cell of the back contact back junction;
A second metal layer separated from a first layer by the permanent back support reinforcement structure, wherein the second layer localizes the interdigitated pattern of holes in the permanent back support reinforcement structure. A back contact back junction thin solar cell comprising: a second metal layer in contact with said first level metallization pattern passing through.

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