KR101289787B1 - Laser processing for high-efficiency thin crystalline silicon solar cell fabrication - Google Patents

Abstract

According to one embodiment of the present invention, by forming an emboss on the top coat layer coated with a fluororesin paint or polyester resin paint, by coating a clear layer to prevent the elastic fluororesin paint is restored, It is possible to obtain a coating embossed color steel sheet capable of realizing a beautiful appearance such as a hologram pattern while minimizing the pressing force applied when forming the boss.

Description

LASER PROCESSING FOR HIGH-EFFICIENCY THIN CRYSTALLINE SILICON SOLAR CELL FABRICATION}

TECHNICAL FIELD The present invention relates to solar photovoltaic devices, and more particularly, to laser processing technology for the production of crystalline semiconductors, including crystalline silicon, and other types of photovoltaic solar cells.

Laser processing offers several advantages in terms of improved efficiency and reduced manufacturing costs for high performance, high efficiency solar cell processing. First, next-generation crystalline silicon solar cells can be advantageous in that the size of important features such as electrical contacts can be made very small compared to the current industry. In front contacted solar cells, the contact area between the front metal structure and the emitter needs to be low (or the contact area ratio should be very small, preferably 10%, as well as the contact area between the back metal and the base). Should be very small). In an all back-contact back-junction solar cell, the emitter and base regions that form the p / n junction and the metal sheath are on the same side (cell opposite the solar direction). Back), the size of the various features is generally small for high efficiency. In such cells, the emitter and base regions generally form alternating stripes, and the width of these regions (particularly the width of the base contact) is small. Also, the size of these regions and the metal contacts are relatively small. The metal sheath connected to the emitter and base regions must be patterned in a precise structure correspondingly. In general, lithography and laser processing methods are relatively precise resolution techniques, providing the small size and control required. In this technique, the laser processing method provides the low cost advantage required for solar cell manufacturing. While lithography requires consumables such as photoresist, photoresist, and stripper, laser processing methods are non-contact, dry, and direct write methods and do not require consumables. Therefore, a simpler and more economical process can be achieved in solar cell manufacturing. In addition, the laser processing method is excellent as an environmentally friendly manufacturing method because it is an all-dry process that does not use consumables such as chemicals.

On the other hand, while reducing the thickness of the crystalline silicon used to reduce the cost of solar cells, it is necessary to increase the cell area to produce more power per cell and to reduce manufacturing cost per watt (W). . The laser processing method is suitable for such thin wafers and thin film battery substrates because it is a completely non-contact, dry process and can be easily applied to large-scale batteries.

In addition, laser processing is generally superior as an environmentally friendly method that does not use toxic chemicals or gases. By properly selecting the laser and the processing system, the laser processing method shows very high productivity at very low cost.

Despite these advantages, the use of laser processing methods in the production of crystalline silicon solar cells has been limited because no laser processing methods have been developed to provide high performance batteries. The present invention relates to a laser processing method for manufacturing a high efficiency solar cell using processes optimized for each main step. In addition, certain embodiments of applying laser processing methods in the manufacture of thin film crystalline silicon solar cells, such as those made using silicon substrates of 50 μm or less formed by epitaxial silicon growth, are described. Is disclosed.

Base emitter-to-base emitter separation in all back-contact homo-junction emitter solar cells (e.g., high efficiency back contact crystalline silicon solar cells), including but not limited to Openings for base doping and base emitter contact openings (e.g., having a small contact area ratio controlled substantially less than 10%, for example, to reduce contact recombination losses and improve cell efficiency), selective doping (e.g., , Base and / or emitter contact doping, and metal ablation in front contact and full back contact / back junction homojunction emitter solar cells (e.g., host plate reusable and reusable host templates patterning, such as creating a patterned metal clad seed layer on a thin film monocrystalline silicon solar cell prior to detachment from the template The laser processing method conforming to the requirements such as the formation of the metal coating layer) is disclosed. Optional amorphous silicon ablation, oxide (eg transparent conductive oxide) ablation, and metals in heterojunction solar cells (eg, back contact solar cells comprising heterojunction amorphous silicon emitters on a monocrystalline silicon base). A laser machining method suitable for metal ablation for patterning is disclosed. Such laser processing techniques further include crystalline silicon substrates and crystalline silicon substrates produced by planar or textured / 3-dimensional wire saw wafering or epitaxial deposition processes. Applicable to semiconductor substrates, three-dimensional substrates can be obtained using epitaxial silicon lift-off techniques using porous silicon seed / release layers or other types of sacrificial release layers. This technique is well suited for thin crystalline semiconductors including thin crystalline silicon films obtained by epitaxial silicon deposition on templates containing porous silicon release layers or obtained using other techniques known in the industry, The thickness may be in the range of 1 µm or less to 100 µm or more (in a thin film monocrystalline silicon solar cell, the silicon thickness is preferably 50 µm or less).

All back-contact homojunction solar cells are formed on crystalline silicon substrates and microfabrication or patterning of emitter and base regions including base emitter separation and base openings, selective doping of emitters and bases , Forming openings in the base and emitter for metal contact, and performing one or a combination of metal patterning. Front contact homojunction (emitter) solar cells can be fabricated using laser processing methods to form openings in the front and back of the metal sheath for selective doping and metal contacts of the emitter. Heterojunction all back-contact solar cells can be fabricated using laser processing methods for separating the base region and conductive oxide.

The features, properties, and advantages of the present invention will become more apparent from the detailed description when taken in conjunction with the following drawings, in which like reference characters indicate features.
1 is a scanning electron microscope (SEM) image of a shallow trench formed in silicon applied to an all back-contact solar cell according to the present invention.
2 is a cross-sectional view of a shallow trench of silicon applied to an all back-contact solar cell.
3A-3D illustrate the process of selecting laser fluence to perform intact silicon dioxide (or oxide) ablation. 3A shows the size dependence of the ablation point in laser fluence; 3b shows non-uniform exfoliation of oxides; 3C shows the point without damage; 3D shows heavily damaged silicon at the point openings.
4 shows an arrangement of substantially parallel contacts formed in an oxide using pulsed laser ablation according to the present invention.
5 is an image of an oxide ablation point at a metal contact.
6A and 6B show laser ablation areas formed by creating overlapping ablation points along the x and y directions. FIG. 6A shows streaks having a width of 18 μm formed in 1000 A boron-doped oxide (BSG) / 500 A undoped oxide (USG) in the base isolation region; FIG. 6B shows streaks of 90 μm in width formed in 1000 A USG (undoped oxide) in the base region.
7A shows a threshold of oxide damage, in which metal can be removed without metal penetration of the oxide layer.
7B shows that the metal runners are completely disconnected after 20 scans.
FIG. 7C is an optical microscope image of a trench to be formed in a metal stack. FIG.
8A and 8B are a plan view and a cross-sectional view of a pyramidal thin film silicon solar cell (TFSC).
9A and 9B are a plan view and a cross-sectional view of a prismatic thin film silicon solar cell.
10A and 10B show process flows for the generation and release of planar epitaxial thin film silicon solar cell substrates (TFSS).
11A and 11B illustrate a processing sequence of a planar epitaxial thin film silicon solar cell substrate when the thin-film silicon solar cell substrate (TFSS) is excessively thin and hard to be fixed or supported by itself.
12A and 12B show a process flow for processing a micromold template (or reusable template) for the manufacture of a three-dimensional thin film silicon solar cell substrate.
12C and 12D show a process flow for manufacturing a three-dimensional thin film silicon solar cell substrate using a reusable micromolded template.
FIG. 13 shows that the thickness of a thin film silicon solar cell substrate according to the present invention is thick enough to be fixed and self-supporting (eg, thicker than about 50 μm for a 100 mm × 100 mm substrate, and thicker than about 80 μm for a 156 mm × 156 mm substrate). ) Shows a process flow for manufacturing a planar front contact solar cell.
14 illustrates a process flow of manufacturing a planar front contact solar cell when the thickness of the thin film silicon solar cell substrate according to the present invention is excessively thin and difficult to support by itself.
15 shows a process flow of manufacturing a three-dimensional front contact solar cell according to the present invention.
16A-16D illustrate a process flow for fabricating an interdigitated back contact back junction solar cell thick enough for the thin film silicon solar cell substrate to support itself in accordance with the present invention.
FIG. 17 is a thick thin film silicon solar cell substrate in which no in-situ emitters are deposited, and a BSG layer is deposited and formed on the epitaxial silicon film to form a base isolation region in accordance with the present invention. It shows the process flow of manufacturing a cross-back contact back junction solar cell using.
18 is a cross-back contact back junction embodiment in which in-situ emitter and laser ablation of silicon are used to form a base separation, and not thick enough for the thin film silicon solar cell substrate to support itself. The process flow for producing a battery is shown.
19A-19H illustrate that BSG deposition and selective laser etching instead of in-situ emitters are used to form the base separation, according to the present invention, and the thin film silicon solar cell substrate is not thick enough to support itself. Back contact Shows the process flow for manufacturing back junction solar cells.
20 shows a process flow for fabricating a cross back contact back junction solar cell using a three dimensional thin film silicon solar cell substrate, in accordance with the present invention.
21 shows a process flow for fabricating a cross back contact back junction heterojunction solar cell, in accordance with the present invention.

While this disclosure describes certain embodiments, those skilled in the art may apply the subject matter disclosed herein to other applications and / or embodiments without undue experimentation.

The present invention relates to a laser processing method, and more particularly, to a pulse laser processing method and a form thereof which have been improved to satisfy various requirements of other types of processes.

The invention may be useful in the field of semiconductor device ablation, in particular crystalline silicon ablation. In general, the removal of silicon using a laser involves melting and evaporating silicon leaving unnecessary residue damage on the silicon substrate. This damage causes a reduction in minority carrier lifetime and an increase in surface recombination velocity (SRV), which degrades the solar cell's efficiency. Thus, wet cleaning of silicon substrates is generally used to remove such damaged layers. The present invention discloses a process for reducing such damage to a level suitable for manufacturing high efficiency solar cells, thus simplifying the process and reducing the process cost since it does not require post-laser-processing wet cleaning. Can reduce the cost.

When roughing a certain thickness of a silicon substrate, the damage remaining on the silicon substrate is related to the amount of laser energy that is absorbed by the substrate and not utilized by the melted material. If most of the laser energy used to remove the material can be controlled, the ratio of incident energy absorbed by the silicon substrate can be minimized, thereby minimizing laser induced substrate damage and reduced surface recombination rate. Penetration of laser energy into silicon depends on the laser pulse length (also called 'pulse width') and wavelength. An infrared (IR) laser beam with a wavelength of 1.06 μm has a long penetration depth up to about 1000 μm in silicon, while a green laser beam with a wavelength of 532 nm penetrates a depth of about 3 μm to 4 μm. Beats. An ultraviolet (UV) laser beam with a wavelength of 355 nm penetrates about 10 nm, which is shorter. It is clear that the use of ultra-short pulses of ultraviolet or extreme ultra violet (EUV) determines the penetration of laser energy into silicon. Shorter laser pulse lengths also result in shorter thermal diffusion into the silicon. While nanosecond pulses cause heat diffusion in silicon in the range of about 3 μm to 4 μm, picosecond pulses reduce heat diffusion to about 80 nm to 100 nm, and femtosecond pulses are generally lasers. The heat spreading distance is so short that there is no heat spreading inside the silicon during the melting process. Thus, shorter pulses with shorter wavelengths reduce damage to the laser ablation substrate. To improve productivity, green or IR wavelengths can be used depending on the extent of laser damage acceptable. Since a certain percentage of energy can be absorbed into the substrate even under ideal conditions, this absorption and its unexpected side effects can be further reduced by reducing the laser intensity. However, this reduces the thickness of the silicon to be melted (or decreases the silicon melting speed or decreases the yield). Reducing the pulse energy without causing silicon removal by increasing the overlap of laser pulses is known to smooth silicon shallow trench isolation (STI). This means that the silicon surface damage is low. The thickness of silicon removed at extremely low pulse energy can be very small. The required depth can be obtained by using multiple overlapped scans of the pulsed laser beam.

Pulsed laser beams in the picosecond range and wavelengths up to about 355 nm are suitable for low damage silicon ablation that reduces the surface recombination velocity (SRV) with respect to passivated ablation surfaces. 1 shows a silicon substrate using a picosecond UV laser beam having a Gaussian profile (M ² <1.3), 4 μJ pulse energy and a diameter of about 110 μm, with laser spots overlapping about 15 times. Trenches with a depth of 2.25 μm and a width of about 100 μm formed. This depth of ablation can be obtained using 20 overlapping scans of a laser that removes 112 nm of silicon per scan. 2 shows a smooth profile of 4 μm deep and 110 μm wide trenches formed in silicon, obtained using the same picosecond laser beam of UV wavelength. Note the smoothness of the profile. This silicon ablation is used in all back-contact back-junction solar cells to form regions that separate base regions from emitter regions. Femtosecond lasers can be used to further reduce laser interstitial laser damage.

One embodiment of the present invention is also applicable to the ablation of amorphous silicon. A similar method may be used to ablate amorphous silicon to a desired thickness using a pulsed rain beam having a femtosecond pulse length and in some embodiments a UV or green wavelength. Since ablation of amorphous silicon requires much less energy than crystalline silicon, this method can be effectively used to selectively ablate amorphous silicon films from crystalline silicon surfaces in heterojunction solar cells.

In addition, the present invention is applicable to selectively grinding oxides against underlying substrates, crystalline or amorphous silicon. The oxide film passes through a laser beam of wavelengths leading to UV. If a nanosecond pulse length laser is used to remove the interposed oxide, the oxide is removed by heating and melting the underlying silicon. Due to the pressure from the fused bottom silicon, the interposed oxide is cracked and removed. However, since this causes great damage to the silicon substrate, a wet cleaning process is generally used to remove such damaged layers for use as a high efficiency battery.

A process is disclosed in which an oxide layer is selectively removed from a silicon surface without any appreciable damage to the silicon surface. In addition to heating and melting or evaporating the laser ablation material, other effects occur, such as plasma formation. In some cases, complex processes occur at the interface. By using a picosecond pulse length laser, the oxide-silicon interface is affected. By using a picosecond laser of UV wavelength, the interfacial effect is enhanced to cause separation and exfoliation of the oxide film from the silicon surface. The remaining silicon surface is substantially intact. Also picosecond laser radiation of green or infrared (IR) wavelength may be used depending on the degree of penetration damage of the acceptable silicon substrate. The present disclosure discloses an overview of a process for providing selective intact oxide ablation from silicon surfaces.

3A-3D illustrate a process for providing intact ablation of oxides. FIG. 3A shows the change of 1000 A Phosphorus-doped oxide (PSG) / 500 A undoped-oxide (USG) laser spot opening deposited on a 35 μm thick epitaxial silicon film on a template using a picosecond UV laser beam. The oxide layer is deposited by atmospheric-pressure CVD (APCVD). For certain thicknesses of the oxide the spot size depends on the laser fluence (J / cm ² ). Laser fluence is the laser pulse energy per laser beam area. In this case, the laser beam has a Gaussian profile (M ² <1.3) and a diameter of about 100 μm. As shown in FIG. 3B, the points at the extremely low fluence are non-uniform and irregular delamination of the oxide from the silicon surface occurs, while extensive silicon damage occurs at the extremely high fluence, as shown in FIG. 3D. As shown in FIG. 3C, the range of fluence, represented by straight line a-a ', indicates the optimal range where the silicon substrate damage is minimal.

4 shows an array of cell contact openings that are selectively open in oxide applied to a full back contact (and back junction) solar cell. 5 is a close-up image of these contacts. As shown in FIGS. 6A and 6B, laser ablation points may overlap along the x and y directions to open areas of arbitrary length and width on the wafer. 6A shows an opening of 180 μm width formed by selectively removing boron-doped oxide (BSG) with respect to the base separation region using a picosecond UV laser beam with overlapping melting points along the x and y directions. Similarly, Figure 6B shows an opening of 90 mu m width of the undoped oxide (USG) to form the base region.

As disclosed herein, selective ablation of oxides from silicon surfaces can be used in solar cell fabrication in several ways. According to one embodiment, when using an in-situ emitter for the back contact cell, this process is used to open the path to the oxide film to expose the underlying emitter. Exposed emitters can be removed using wet etching. This area is then used for base emitter separation and with the base formed therein.

According to another embodiment, this process is used to open the areas used to form the metal contacts. In front contact cells, oxide passivation may be used on the back of the cell. The process disclosed herein is then used to open the contacts with respect to the metal deposited on these contacts. As such, the metal has localized contacts that are conductive at high charge efficiency. In back contact cells, the contacts at the base and emitter can be opened using this process.

In solar cell processing processes, the doped oxide may need to be removed without causing any doping of the underlying silicon (ie, without any appreciable heating of the doped oxide and silicon). As described above, since oxides are removed by separation at the oxide / silicon substrate interface when using a picosecond laser beam, removal of the oxides occurs with limited pickup of dopants from the oxide film being melted. do.

Selective ablation of silicon nitride (SiN _x ) is used for front contact solar cells. Laser ablation can be used to minimize areas where SiN passivation is eliminated as the contact area of the emitter surface is reduced. This causes a high open circuit voltage (V _oc ). Picosecond lasers of UV or green wavelengths are suitable in this case, but nanosecond UV lasers can also be used.

Selective metal ablation from oxide surfaces has previously been difficult to use lasers. This is because at the high pulse energy needed to abrade the metal, the energy is excessively high, damaging the underlying oxide and causing metal penetration into the oxide. Indeed, this is the basis of the "laser fired contacts" (LFC) process proposed for use in solar cells.

The present invention discloses three processes for metal penetration to oxides (or other dielectric materials such as silicon nitride) and for selective metal removal from oxide (or other dielectric materials) surfaces without the destruction or cracking of oxides. . In all processes, aluminum is the first metal in contact with the base and emitter (aluminum is used as the contact and light trapping back mirror layer). Picosecond pulse length lasers are suitable in this case. For high metal removal rates, infrared (IR) wavelengths are very suitable. According to the first process, the metal is melted at a pulse energy lower than the limit of oxide melting. If the thickness of the metal to be removed in one scan is less than the required thickness, the multiply scan is used to remove the entire metal thickness. Since the pulse energy is below the oxide ablation threshold, complete removal of the metal from the oxide surface is obtained. However, the exact method used depends largely on the type, thickness and surface roughness of the metal in the laminate.

7A-7C show the results of ablation when patterning bilayers deposited on the oxide by physical vapor deposition (PVD) and stacked in the order of 1200 A Al and 2400 A NiV. The metal must be completely removed between runners without breaking the underlying oxide layer (to prevent shunt in the cell). 7A shows a threshold of pulse energy, below which the metal stack can be removed without oxide penetration. The limit value depends not only on the properties of the metal laminate structure described above, but also on laser parameters such as point overlap obtained using the constant pulse repetition rate of the laser as well as the scan rate. As the pulse overlap increases, the pulse energy limit may increase due to energy accumulation in the metal. FIG. 7B shows that when using sub-limit pulse energy for oxide damage, more than 20 scans provide complete separation of metal runners determined by 100 M-ohm resistance between parallel lines. . FIG. 7C shows a 75 μm smooth trench formed in a 2400 A NiV / 1200 A Al metal laminate. FIG.

According to the second high productivity process, higher pulse energy is used and a significant portion of the incident energy is absorbed during the ablation process, thus preventing oxide damage. This approach allows for high productivity laser ablation of metals. The process, which successfully used a two-step process, was lubricated with 1250 A Al / 100-250 A NiV with or without a tin (Sn) overlayer up to 2500 A thick. In the first step, softer metals are removed using 15 quantum overlaps of 30 μJ pulses after 15 μJ pulses. For thicker aluminum, such as 2000 A, the second step may be performed at 50 μJ with the same number of pulse overlaps.

In the third step of metal ablation, an aluminum (Al) / silver (Ag) laminated structure (aluminum (Al) is in contact with the battery and the aluminum (Al) phase) in which most of the picosecond laser incident energy is reflected and ablation is abruptly reduced. Applicable to highly reflective films such as silver (Ag). In this case, the surface of the reflective metal (Ag) is first recessed using a picosecond wash of the underlying aluminum after a long pulse of nanosecond laser with a pulse length of 10 to 800 nanoseconds.

The invention is also applicable to selective doping of substrates. In successfully doping silicon using a top layer of dopant containing material, the pulse energy should be high enough to melt the silicon but not high enough to melt the silicon or top dopant layer. As the silicon melts, the dopant dissolves into the silicon. The doped layer is obtained by recrystallizing the silicon layer. In this case, nanosecond pulse length lasers with green wavelengths are very suitable due to limited penetration into the silicon.

The above laser processing method is applicable to planar and three-dimensional thin film crystalline silicon substrates. The laser processing method described above is applicable to a silicon substrate having any thickness. This includes the current standard wafer thickness of at least 150 μm used in crystalline silicon solar cells. However, since the process is performed without contacting the substrate, it is more advantageous for a wafer or a substrate which is brittle.

Sacrificial separation / such as monocrystalline CZ ingots or polycrystalline brick structures, or porous silicon obtained by using wire sawing techniques or by annealing after hydrogen injection to separate wafers of desired thickness Wafers of 150 μm or less provided from a thin film monocrystalline substrate obtained using epitaxial deposition of silicon on the release layer and subsequent lift-off.

Laser processing methods are particularly suitable for three-dimensional substrates obtained using pre-structuring of reusable templates and silicon micromachining techniques. One method is described in the '713 application. 8A to 9B show thin film silicon substrates obtained using the techniques described in the three-dimensional publication. 8A is a plan view of the obtained thin film silicon substrate, and FIG. 8B is a sectional view. For pyramidal substrates, the tips may be flat or sharp points. 9A and 9B show a thin film silicon substrate having a prism structure, obtained using the reusable prefabricated three-dimensional template disclosed in the document.

Although the laser processing method and process flow is applicable to a silicon substrate having an arbitrary thickness (1 μm or less to 100 μm or more), epitaxial silicon on a porous silicon surface of a reusable template as disclosed in the '713 application may be used. Disclosed are applications for solar cells manufactured using thin silicon substrates in the range of 1 μm or less to about 80 μm in thickness, including but not limited to those obtained using. To facilitate understanding of the application, the process flow for obtaining the desired thickness (eg, about 10 μm or less to 120 μm) of a planar monocrystalline thin film silicon substrate is generally 50 μm or more in FIGS. 10A and 10B. It is shown for a planar thin film silicon substrate that can be manipulated to support the liver substrate on its own, and is generally 50 μm or less in FIGS. 11A and 11B, which is difficult to support itself between battery processing (hence, strengthened prior to separation from the host template). ) With respect to a planar thin film silicon substrate. 12A-12D show the process flow for obtaining a three-dimensional pyramidal silicon substrate. Three-dimensional prismatic substrates can be obtained by similar processes, except using lithography or screen printed patterns that provide such structures.

The thin planar substrate obtained using the processes of FIGS. 10A and 10B may be processed according to the process of FIG. 13 to obtain a high efficiency front contact solar cell. It should be noted that for self supporting thin film silicon substrates, it is advantageous to process the template side of the thin film silicon substrate before the other side. Since the template side of the thin film silicon substrate is woven while the quasi-monocrystalline silicon remaining on the thin film silicon substrate after separation from the template is removed, the template side is preferably front or sunnyside. to be. Selective ablation laser processing of silicon oxide and silicon nitride is advantageously used to fabricate the front contact solar cell.

FIG. 14 illustrates the application of various laser processing methods to fabricate a high efficiency front contact solar cell using a planar thin film silicon substrate that is excessively freely fixed or difficult to support itself during battery manufacturing. It should be noted that in this case a non-template side surface is first processed with the thin silicon substrate on the template. Once this process is complete, the thin silicon substrate is processed and attached to a reinforcement plate or sheet on the exposed side and then separated from the template. After the thin film crystalline silicon solar cell attached to the thick plate is separated, the remaining porous silicon, texture etch, and SiN passivation layer on the released face of the thin film silicon substrate (which is then the front face of the solar cell). passivation / ARC deposits, and forming-gas anneal (FGA) processes are performed.

FIG. 15 illustrates the application of various laser processing methods for manufacturing a high efficiency front contact solar cell using a three-dimensional front thin film silicon substrate. In this case, it is advantageous to have a pyramidal tip that is not sharp and flat on the template side.

The processing method according to the invention is particularly suitable for the manufacture of a full back contact battery.

16A to 16D show a process flow for manufacturing a back contact / back junction solar cell in which a thin film silicon substrate is self-supporting (ie, no back plate is attached to the cell) using a laser processing method on a planar epitaxial substrate. In this case, after the deposition of the epitaxial silicon base, the epitaxial emitter is deposited at the original position between the silicon epitaxy. Abrasion of silicon is then used to remove the emitter from the base isolation regions. At the same time, four fiducials are etched into the silicon to control subsequent ablation for this pattern. Next, a thermal oxide is grown to passivate the silicon surface, which is the backside of the back contact back junction solar cell. The epitaxial silicon film is then separated from the template (mechanically separated from the porous silicon interface). Next, the remaining porous silicon layer is wet etched and the surface is woven (both can be performed using both alkaline etching processes). This is the woven front or sunnyside of the solar cell. On the other hand, the thermal oxide is melted by a picosecond UV laser to form a base opening inside the base separation region. The base opening is arranged along the inside of the base isolation region (trench) formed by silicon etching using fiducials previously etched in silicon as described above. Subsequently, a blanket-containing oxide layer (PSG) is blanket deposited on the surface. Scanning with a nanosecond green or infrared (IR) laser along the base opening using reference points of silicon causes the base to be doped. Also, regions having emitter contact openings are doped in a similar manner using a straight scan of a nanosecond green or infrared (IR) laser. Next, contact openings are formed in these doped base and emitter regions using picosecond UV lasers. Again, an array of such contact openings is formed using the reference points of silicon. On the other hand, a metal laminate structure comprising aluminum as the first layer in contact with the cell is deposited using a suitable method such as physical vapor deposition (PVD). The layer is then patterned using a picosecond infrared (IR) laser and connected to the base and emitter regions with the metal runners separated. After selective forming-gas anneal (FGA), the cells are thick plates with connected and embedded highly conductive connectors (aluminum (Al) or copper (Cu)) or no embedded connectors. Together with the latter (in the latter case, the final cell metal sheath is formed by a copper plating process). As a result, the cell is tested and ready for use. FIG. 17 shows a process flow for fabricating a back contact solar cell in which epitaxial silicon base is not deposited with an emitter layer using a laser processing method on a planar epitaxial substrate. Instead, a boron containing oxide (BSG) layer is deposited and patterned to open the base isolation region. A process similar to that described above follows, except that the emitter and base are simultaneously formed between thermal oxidation processes according to the process flow shown in FIG. 17.

FIG. 18 shows a process flow for manufacturing a planar back contact / back junction solar cell in which a thin silicon substrate is not supported by itself using a laser processing method on an epitaxial substrate (thus, a thick plate is used). This process utilizes silicon ablation of the in-situ doped emitter to form a base isolation region.

19A to 19H show a process flow for manufacturing a planar back contact solar cell in which a thin film silicon substrate is not supported by itself using a laser processing method on an epitaxial substrate. In the present process, instead of the in-situ emitter layer, thermal oxidation (or thermal annealing or thermal oxidation annealing) after BSG deposition and selective laser ablation is used to form the base isolation region and emitter.

20 shows a process flow for manufacturing a back contact three dimensional solar cell, advantageously having a template side of a pyramidal end that is relatively sharp. Since the three-dimensional thin film silicon substrate can be supported by itself at a relatively low thickness (i.e., about 25 mu m of silicon thickness), the process flow is similar to that shown in FIG. It is apparent that laser ablation of silicon after in-situ emitter, or thermal oxidation (or thermal annealing or thermal oxidation annealing) alternatively after BSG deposition and selective laser ablation, may alternatively be used.

For application in heterojunction solar cells, the heterojunction emitter may be formed by a doped amorphous silicon layer in reverse contact with the doped crystalline silicon base. In cross back contact solar cells, the amorphous silicon layer and the transparent conducting oxide (TCO) are patterned using laser ablation selective to the crystalline layer. In this case femtosecond pulse width lasers with UV or green wavelengths are suitable. The process flow is disclosed in FIG. Modifications of this process flow are also possible.

Various embodiments and methods of the present invention include at least the following aspects: a process for obtaining intact silicon ablation of crystalline and amorphous silicon; To obtain oxide ablation for doped and undoped oxides that do not damage silicon; A process for obtaining a fully separated metal pattern on the dielectric surface of the solar cell metal coating; Selectively doping the emitter and base contact regions; The use of a pulsed laser processing method on thin wafers comprising planar and three-dimensional silicon substrates; The use of pulsed laser processing on substrates obtained using epitaxial deposition on reusable templates made using template preassembly techniques; The use of various pulsed laser processing methods for fabricating front contact homojunction solar cells; The use of various pulsed laser processing methods to fabricate all back contact homojunction solar cells; And the use of various pulsed laser processing methods in the production of heterojunction solar cells.

Although the front contact solar cell is described with a p-type base and the back contact back junction solar cell is described with an n-type base, the laser processing method according to the present invention is a reversely doped substrate (ie, p Equally suitable for n-type of front contact solar cells with ⁺ emitters, and p-type bases for p-type bases and back contact back junction solar cells with n ⁺ emitters).

Those skilled in the art will recognize that the embodiments according to the present invention are suitable for a wide variety of areas as well as the specific embodiments described above.

The above description of the preferred embodiments is provided to enable any person skilled in the art to make or use the technical details of the invention described in the claims. Various modifications to the above embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without creative abilities. Accordingly, the technical details of the invention described in the claims should not be limited to the embodiments shown herein, but should be construed broadly in the scope consistent with the described principles and novel features.

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

Claims (18)

Providing a thin crystalline silicon substrate having a substrate thickness in the range of 1 μm to 100 μm, suitable for all back-contact back-junction solar cells;
Forming base isolation regions in the thin crystalline silicon substrate;
Forming a base opening by pulse laser ablation (PLA) of a material selected from the group consisting of silicon oxide, silicon nitride, aluminum oxide, silicon oxynitride, and silicon carbide on the thin crystalline silicon substrate ;
Selectively doping base regions;
Selectively doping emitter regions;
Forming a contact of the base regions and the emitter regions;
Forming a metallization on the base regions and the emitter regions; And
Thin crystalline silicon comprising pulsed laser ablation (PLA) of a portion of the metal sheath to form first metal interconnects connected to the base regions and second metal interconnects coupled to the emitter region. Substrate processing method. The method of claim 1,
Pulse laser ablation of a portion of the metal cladding is performed below an oxide ablation threshold of the thin crystalline silicon substrate. The method of claim 1,
Pulse laser ablation of a portion of the metallization is performed above an oxide ablation threshold of the thin crystalline silicon substrate to fuse the metallization in a single-pass. The method of claim 3, wherein
The metallization includes a reflective metallization, and pulse laser ablation of a portion of the metallization may be performed with a first laser having a pulse width of 10 nanoseconds to 800 nanoseconds, followed by a pulse width of 700 nanoseconds or less. Grinding with a second laser having a. The method of claim 1,
Forming the base isolation region in the thin crystalline silicon substrate is performed by laser silicon ablation, using a pulse laser having a wavelength of 800 nm or less and a pulse width of 100 picoseconds or less. The method of claim 5, wherein
The wavelength is 355 nm or less. The method of claim 5, wherein
And the pulse width is less than 20 picoseconds. The method of claim 1,
Forming a base isolation region in the thin crystalline silicon substrate is performed by pulse laser ablation of the deposited borosilicate glass layer. The method of claim 1,
The metal coating comprises a laminated structure of a first metal, a second metal, and a third metal, the third metal comprising a low melting solder element comprising at least tin. The method of claim 9,
And the first metal comprises aluminum. 11. The method of claim 10,
And the thickness of the aluminum is 1,000 kPa to 10,000 kPa. The method of claim 9,
And said second metal is selected from the group consisting of nickel, nickel-vanadium, and cobalt. The method of claim 9,
And the thickness of the second metal is between 100 kPa and 1,500 kPa. The method of claim 11,
The solder is selected from the group consisting of tin solder, tin-lead solder, tin-bismuth solder, and tin-silver solder. 13. The method of claim 12,
And the thickness of the solder is 5,000 kPa or less. Providing a thin crystalline silicon substrate having a substrate thickness in the range of 1 μm to 100 μm, suitable for front contact solar cells;
Forming base isolation regions in the thin crystalline silicon substrate;
Forming a base opening by pulse laser ablation (PLA) of a material selected from the group consisting of silicon oxide, silicon nitride, aluminum oxide, silicon oxynitride, and silicon carbide on the thin crystalline silicon substrate ;
Selectively doping the emitter region by a laser doping process;
Forming a contact of the base regions and the emitter regions; And
Selectively grinding silicon oxide to form separate backside metal contacts. In providing a thin crystalline silicon substrate having a substrate thickness in the range of 1 μm to 100 μm, suitable for hetero-junction solar cells, the thin crystalline silicon substrate is at least oppositely doped. A doped amorphous silicon layer in contact with the crystalline silicon base and a transparent conductive oxide layer on the doped amorphous silicon layer;
Selectively grinding the transparent conductive oxide layer and a portion of the doped amorphous silicon layer by a pulse laser having a pulse width of 700 femtoseconds or less and a wavelength of 1.06 μm or less;
Forming an undoped amorphous silicon layer on the thin crystalline silicon substrate to separate the base and the emitter;
Selectively grinding a portion of the undoped amorphous silicon layer by the laser having a pulse width of 700 femtoseconds or less and a wavelength of 1.06 μm or less; And
Pulse laser ablation of an oxide to contact an emitter region and a base region on said thin crystalline silicon substrate. The method of claim 17,
Wherein the wavelength of the laser is 532 nm or less.

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