KR101532721B1 - Spatially selective laser annealing applications in high-efficiency solar cells - Google Patents

Abstract

Discloses various laser processing methods for generating various types of heterojunction emitter and homojunction emitter solar cells. Methods include base and emitter contact openings, selective doping, metal ablation, annealing to improve passivation, and selective emitter doping through laser heating of aluminum. Also disclosed are laser processing methods suitable for selective amorphous silicon ablation and selective doping for heterojunction solar cells. Disclose laser ablation techniques that leave the underlying silicon in a substantially intact state. These laser processing techniques include crystalline silicon substrates, which are planar or textured / three dimensional, and can also be fabricated through wire subwaffer processes or through epitaxial deposition processes or through other < RTI ID = 0.0 > The present invention can be applied to a semiconductor substrate that further includes a crystalline silicon substrate. These techniques are well suited for crystalline semiconductors including crystalline silicon thin films.

Description

[0001] SPATIALLY SELECTIVE LASER ANNEALING APPLICATIONS IN HIGH-EFFICIENCY SOLAR CELLS [0002]

Cross-reference to related application

This application claims priority to U.S. Provisional Patent Application No. 61 / 488,684, filed May 20, 2011, the disclosure of which is incorporated herein by reference in its entirety. This application is also a continuation-in-part of U.S. Patent Application No. 13 / 303,488, filed November 23, 2011, the disclosure of which is incorporated herein by reference in its entirety.

This disclosure relates generally to solar cells and, more particularly, to a high-efficiency crystalline semiconductor including crystalline silicon, and to laser processing techniques for manufacturing other types of photovoltaic solar cells.

Laser processing offers several advantages in terms of efficiency improvement and manufacturing cost reduction for high-performance, high-efficiency solar cell processing. First, an improved crystalline silicon solar cell can benefit from making dimensions of major features, such as electrical contacts, much smaller than current industrial implementations. In order to provide a higher conversion efficiency in the front contact solar cell, it is necessary that the contact area of the rear metal to the base as well as the contact area of the front metal wiring to the emitter be small (or the contact area ratio should be considerably small, Should be much smaller than less than 10%). All back-contact back-junction solar cells with the emitter and base regions forming the p / n junction on the same side of the metal wiring and back-contact solar cell (the backside of the cell is opposite the solar side) The dimensions of the various features are typically small for high efficiency. Typically, in such a cell where the emitter and base regions alternately form a stripe (interdigitated back-contact, or IBC architecture), the width of these regions (particularly the width of the base contact) tends to be small . In addition, the dimension of the metal contact with respect to these regions also tends to be small proportionally. Then, it is necessary to pattern the metal wiring connected to the emitter and base regions to a corresponding finer scale. In general, lithography and laser processing are techniques that have relatively fine resolution capabilities to provide the required control and small dimensions. Of these technologies, only laser processing provides the low cost advantages needed for solar cell fabrication. Although lithography requires photoresists (which increase process cost and complexity) and consumables such as subsequent resist developers and strippers, laser processing is a non-contact dry direct write patterning method and requires no material consumables, Which makes it possible to simplify and simplify the process for the process. In addition, laser processing is an all-dry process that does not use any material consumables, such as chemicals, making it an excellent choice for environmentally benign manufacturing.

In addition, to reduce the cost of solar cells, the thickness of the crystalline silicon used must be reduced, and at the same time the cell area must be increased for greater power per cell and the manufacturing cost per watt must be reduced. Laser processing is a perfectly non-contact dry process and can be easily scaled to larger cell sizes, making it suitable for such thin wafer and thin film cell substrates.

Laser processing is also attractive because it is an environmentally benign "green" process that generally does not use or require toxic chemicals or gases. By properly selecting the laser and processing system, the laser processing offers very low cost of ownership and high productivity.

Despite these advantages, the use of laser processing in the manufacture of crystalline silicon solar cells has been limited, since no laser processes have been developed to provide high performance cells. Described herein are laser processes that utilize methods tailored to each key application to fabricate solar cells with high efficiency. Specific embodiments for the application of laser processing in the manufacture of thin film crystalline silicon solar cells, such as those made using sub-50 [mu] m silicon substrates formed by epitaxial silicon growth, are also disclosed.

Various laser processing methods for producing heterojunction emitter and homojunction emitter solar cells are disclosed herein. These methods include base and emitter contact openings, front and back field formation, selective doping, metal ablation, annealing, and passivation. Also disclosed are laser processing methods suitable for selective doping and selective amorphous silicon ablation for heterojunction epitaxial solar cells. These laser processing techniques further include a crystalline silicon substrate that is manufactured through a wire saw wafering process or an epitaxial deposition process that includes a crystalline silicon substrate and is planar or textured / It can be applied to a semiconductor substrate. These techniques are well suited for thin crystalline semiconductors including crystalline silicon thin films.

Base to emitter isolation (including but not limited to shallow trench isolation) for all back-contact homojunction emitter solar cells (such as high efficiency back-contact crystalline silicon solar cells), openings for base doping, (Controlling the contact area ratio to less than about 10%, for example, to reduce contact recombination losses and increase cell efficiency) and emitter contact openings (base and / or emitter Formation of patterned metallization layers such as selective doping (such as contact doping), metal ablation (subsequent attachment of the backplane to the cell and generation of a patterned metallization seed layer on a thin film monocrystalline silicon solar cell prior to separation from the reusable host template) ) Are referred to as front joining and all rear contact rear joining Lt; RTI ID = 0.0 > photovoltaic < / RTI > solar cells. In addition, it is also possible to use selective amorphous silicon ablation and oxide ablation (such as a transparent conductive oxide (TCO)), and heterojunction solar cells (such as a back contact solar cell comprising a heterojunction amorphous silicon emitter on a single crystal silicon base) Disclosed are laser processing methods suitable for metal ablation for patterning. These laser processing techniques may be applied to a semiconductor substrate that further includes a crystalline silicon substrate that is manufactured through a wire-sided wafering process or an epitaxial deposition process, which may include a crystalline silicon substrate and may be planar or textured / Where the three-dimensional substrate can be obtained using epitaxial silicon lift-off techniques using a porous silicon seed / release layer or other type of sacrificial release layer. These techniques are well suited for thin crystalline semiconductors comprising crystalline silicon thin films obtained using epitaxial silicon deposition on a template comprising a porous silicon release layer or using other techniques in the art.

All the rear contact allogeneic solar cells can be formed on a crystalline silicon substrate, where laser processing is used to perform one or a combination of the following. That is, the emitter and base regions, including the base-to-emitter isolation, as well as the openings for the base are provided in the micromachine or patterning, providing selective doping of the emitter and base, forming openings for the base and emitter for the metal contacts, Provision of metal patterning, provision of annealing, and provision of passivation. Front-contact homojunction (emitter) solar cells can be fabricated using laser processing for selective doping of the emitter and using openings for metal contacts for the front side and back side metallization. Heterojunction Emitters All back-contacting back-junction solar cells can be fabricated using laser processing to form conductive oxide isolation with the base region.

The features, nature, and advantages of the disclosure will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like features.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a scanning electron microscope (SEM) image of a shallow trench formed in silicon for the application of all rear contact back junction solar cells in accordance with the present disclosure;
Figure 2 shows the profile of silicon shallow trenches for the application of all rear contact back junction solar cells.
Figures 3a-3d illustrate a procedure for selecting laser fluences to obtain a silicon dioxide (or oxide) ablation with reduced damage, Figure 3a shows the size of an ablative spot depending on laser fluence, Figure 3b shows the irregular interlayer delamination of the oxide, Figure 3c shows the damage free spot, and Figure 3d shows the greatly damaged silicon of the spot opening.
4 is a diagram illustrating approximately parallel rows of contacts opened in an oxide using pulsed laser ablation in accordance with the present disclosure;
5 is a screen shot with an oxide ablation spot for a metal contact;
6A and 6B illustrate a laser ablated region by forming an ablative spot overlapping in the x and y directions, and FIG. 6A shows a 1000 A BSG (boron doped oxide) / 500 A USG (undoped oxide) And FIG. 6B is a view showing a 90 占 퐉 wide stripe opened to 1000A USG (undoped oxide) for the base region.
FIG. 7A is a diagram illustrating a threshold for oxide damage in which the metal can be removed without metal penetration of the oxide layer in the case of less than a threshold. FIG.
FIG. 7B shows metal runners completely separated after 20 scans. FIG.
Figure 7c shows an optical micrograph of a trench formed in this metal stack.
8A and 8B are top and cross-sectional views of a pyramid TFSC.
9A and 9B are top and cross-sectional views of a prism TFSC.
10A and 10B are process flow diagrams for producing and delaminating a planar epitaxial thin film silicon solar cell substrate (TFSS).
11A and 11B are process flow diagrams for a planar epitaxial thin film silicon solar cell substrate when the TFSS is so thin that it can not be supported or erected by itself.
12A and 12B are process flow diagrams for generating a microform template (or reusable template) for manufacturing a 3-D TFSS.
Figures 12c and 12d are process flow diagrams for 3-D TFSS generation using reusable micro mold templates.
13 is a process flow diagram for fabricating a planar front-contact solar cell in accordance with the present disclosure, wherein the TFSS is self supporting and thick enough to be erected (e.g., about 50 microns thick for a small 100 mm x 100 mm substrate, lt; / RTI > thick for a x 156 mm substrate).
14 is a process flow chart for manufacturing a planar contact solar cell according to the present disclosure, wherein the TFSS is very thin and can not be supported by itself.
15 is a process flow diagram for fabricating a 3-D front contact solar cell according to the present disclosure;
16A-16D are process flow diagrams for fabricating an intermeshing rear-facing rear junction solar cell in accordance with the present disclosure, wherein the TFSS is thick enough to be self-supporting.
17 is a flow chart for fabricating an intermeshing rear-facing rear junction solar cell using thick TFSS without an in situ emitter deposited according to the present disclosure, but instead a BSG (boron doped oxide) layer is deposited over the epitaxial silicon Deposited on the film and patterned to create a base isolation region.
18 is a process flow diagram for fabricating an intermeshing rear-facing back-junction solar cell in accordance with the present disclosure, wherein the TFSS is not thick enough to support itself and forms a base isolation opening using a laser ablation of the silicon and an in- box.
19A-19H are process flow diagrams for fabricating an intermeshing rear-facing back junction solar cell in accordance with the present disclosure, wherein the TFSS is not thick enough to support itself, and instead of an in situ emitter, an emitter BSG Oxide) deposition and selective laser etchback to form a base isolation opening.
20 is a process flow diagram for fabricating an intermeshing rear-facing rear junction solar cell using 3-D TFSS in accordance with the present disclosure;
21 is a process flow diagram for fabricating an intermeshing rear-facing back-junction heterojunction solar cell in accordance with the present disclosure;
Figures 22 to 30 show, in U.S. Patent Application No. 13 / 118,295, entitled " LASER PROCESSING FOR HIGH-EFFICIENCY THIN CRYSTALLINE SILICON SOLAR CELL FABRICATION, " filed by Virendra V. Rana on May 27, .
Figures 22A and 22B are schematic diagrams showing the profiles of a Gaussian beam and a flat top beam, respectively.
23 is a sectional view of the rear contact / rear surface junction cell.
24A-24F are rear / rear views of a rear contact solar cell during fabrication.
Fig. 25 is a rear / rear view of the rear contact solar cell of Fig. 24A, in which the metal wires are alternately in contact with the emitter region and the base region; Fig.
Figures 26a-26c illustrate three ways in which a flat top beam profile can be created.
27A and 27B are schematic views each showing profiles of a Gaussian beam and a flat top beam emphasizing an ablation threshold value;
Figures 28A and 28B show the Gaussian beam and flat top beam ablation area profile / footprint, respectively.
Figure 28c is a graph of overlap and scan speed.
29A and 29B show a beam alignment window of a Gaussian beam and a flat top beam, respectively;
Figures 29c and 29d are diagrams respectively showing a Gaussian beam area profile and a flat top beam area profile;
FIG. 29E is a chart showing the results of Table 1; FIG.
30 is a process flow diagram of an NBLAC cell.
31 is a schematic cross-sectional view of an NBLAC cell.
32 is a graph showing the minority carrier lifetime in the case of using laser annealing and in the case of not using laser annealing.
33A and 33B are process flow diagrams for all rear contact solar cells using oxide ablation.
34A and 34B are diagrams illustrating an oxide ablation process;
35A and 35B show an oxide ablation process using an amorphous silicon layer.
36 is a view showing a process for forming passivation with an FSF;
37 is a view showing a process for forming passivation and FSF using amorphous silicon;
Figures 38a and 38b are schematic diagrams of selective laser scanning of the metal on the emitter region and thus the formation of a selective emitter.
39 is a diagram showing a P ⁺⁺ selective emitter;
40 shows an aluminum silicon phase diagram.
41 is a view showing a selective emitter of the front contact battery;
42 is a view showing an aluminum BSF;
Figures 43 and 44 illustrate two schematic embodiments of a rear bonded rear-surface contact epitaxial silicon cell process flow using floodlights.
45 is a schematic cross-sectional view of a solar cell;
46 is a graph of the results obtained using pulsed laser annealing using flood light.

Although the present disclosure is described with reference to specific embodiments, those skilled in the art will be able to apply the principles set forth herein to other embodiments and / or examples without undue experimentation.

Here we describe pulsed laser processing methods that are designed to initiate laser processing, and more specifically, to address the various requirements of different processes.

The disclosed methods may be useful in the field of semiconductor device ablation, particularly in the field of crystalline silicon ablation. Typically, laser removal using a laser involves silicon melting and evaporation which leaves undesirable residual damage to the silicon substrate (due to so-called heat affected sites (HAZ)). Such damage degrades the minority carrier lifetime and increases the surface recombination speed (SRV) which reduces solar cell efficiency. Thus, wet scrubbing of the silicon substrate and weakly wet etching are commonly used to remove this damaged layer. This damage is reduced to an acceptable level for high efficiency solar cell fabrication that does not require post-laser treatment wet cleaning / etching, thereby providing a way to simplify the process flow and reduce the overall solar cell fabrication cost.

Damage remaining on the silicon substrate when ablating a predetermined thickness of the silicon substrate by using a laser is related to the amount of laser energy absorbed by the substrate without being used by the abrasive material. If we can manage to use the majority of the laser energy in the removal of the material, some of the incident energy penetrating into the silicon substrate is minimized, thereby minimizing damage to the laser induced substrate and SRV degradation. The laser energy penetrating into the silicon depends on the laser pulse length (also called the pulse width) and the wavelength. An infrared (IR) laser beam with a wavelength of 1.06 占 퐉 has a relatively long penetration depth up to about 1000 占 퐉 into silicon while a green laser beam with a wavelength of 532nm penetrates only about 3 to 4 占 퐉. The penetration of the UV laser beam at a wavelength of 355 nm is even shorter, only about 10 nm. It is clear that the use of microwave pulses of UV or EUV wavelength limits the laser energy penetrated into the silicon. Further, the shorter the laser pulse length is, the shorter the thermal diffusion into the silicon becomes. Nanosecond pulses can lead to thermal diffusions in the range of about 3 to 4 microns in the silicon while picosecond pulses reduce the thermal diffusion to about 80 to 100 nm and the femtosecond pulse is very short so that the No heat dissipation. Thus, the use of shorter pulses of shorter wavelengths reduces damage to the laser ablation substrate. For higher throughput, green or IR wavelengths may be used depending on the degree of acceptable laser damage. Even under ideal conditions, a certain portion of the energy still seeps into the substrate, which can further reduce this absorption and undesirable side effects by reducing the laser power. As a result, however, the thickness of the silicon to be ablated can be further reduced (or the silicon ablation rate or throughput can be reduced). It has been found that it reduces the pulse energy but increases the overlap of the laser pulses to cause silicon removal, thereby smoothing the silicon shallow isolation trenches. This indicates low silicon surface damage. At very small pulse energies, the thickness of the silicon to be removed may be small. A desired depth can then be obtained by using multiple overlapping scans of the pulsed laser beam.

Pulsed laser beams of picosecond length with pulses of approximately 355 nm or less are suitable for low-damage silicon ablation that enables a low surface recombination rate (SRV) for passivated ablation surfaces. Fig. 1 shows a laser beam spot having a depth of 2.25 mu m formed in a silicon substrate and a depth of nearly 100 mu m formed in a silicon substrate by using a picosecond UV laser beam having a Gauss profile (M < 1.3) Width trenches. This ablation depth was obtained using 20 superimposed scans of the laser to remove about 112 nm of silicon for each scan. Figure 2 shows a smooth profile of a 4 탆 depth and 110 탆 width trench in silicon obtained using the same picosecond laser beam with UV wavelengths. Note the flatness of the profile. These silicon abrasions are used in all rear contact back junction solar cells to form regions that separate base regions from emitter regions. By using a femtosecond laser, it is possible to further reduce laser damage during silicon ablation.

Embodiments of the present disclosure can also be applied to ablation of amorphous silicon. Using a similar method, a desired thickness of amorphous silicon can be ablated by a pulsed laser beam having a femtosecond pulse length and in some embodiments by a pulsed laser beam having a UV or green wavelength. Since the amorphous silicon is required to have much smaller energy than the crystalline silicon, this method can be effectively used to selectively ablate the amorphous silicon film from the crystalline silicon surface for application to the heterojunction solar cell.

The present disclosure can also be applied to selective oxide ablation for a substrate that may be crystalline or amorphous silicon. The oxide film is transparent to the laser beam up to the UV wavelength. If the underlying oxide is removed using a nanosecond pulse length laser, the oxide removal is done by heating and melting the underlying silicon. Due to the pressure from the underlying abrasive silicon, the underlying oxide is broken and removed. However, this causes serious damage to the silicon substrate, and typically removes this damaged layer for use in high-efficiency cells using a wet cleaning process.

Here we present a method for selectively removing the oxide layer from the silicon surface without appreciable damage to the silicon surface. During laser ablation, in addition to heating the material to melt or vaporize the material, other effects such as plasma formation occur. Sometimes, complex processes can be done at the interface. By using a laser with a picosecond pulse length, the oxide to silicon interface is affected. By using a picosecond laser having a UV wavelength, the interface effect is improved, and separation and peeling of the oxide film from the silicon surface occur. The remaining silicon surface is substantially free of damage. Also, picosecond laser radiation having a green or infrared (IR) wavelength may be used depending on how much penetration damage of the silicon substrate is acceptable. The present disclosure addresses an overview of a procedure for selectively ablating oxide from a silicon surface without damage.

Figures 3a-3d disclose a procedure to obtain ablation without damaging the oxide. 3A shows the variation of the laser spot opening of a 1000A PSG (doping oxide) / 500A USG (undoped oxide) stack on a 35 mu m thick epitaxial silicon film on a template using a picosecond UV laser beam. The oxide layers were deposited using APCVD (atmospheric pressure CVD) technology. For a given thickness of oxide, the spot size depends on the laser fluence (J / cm). Laser fluence is the laser pulse energy divided by the area of the laser beam. In this case, the diameter of the laser beam was about 100 μm with a Gauss profile (M2 <1.3). In very low fluences, spots are irregular as shown in FIG. 3B and the oxide is stripped irregularly from the silicon surface, while at very high fluences, silicon is heavily damaged as shown in FIG. 3D. The range of fluences shown by line a-a 'indicates the optimum range in which damage to the silicon substrate is minimal as shown in Fig. 3C.

Figure 4 shows rows of cell contact openings selectively opened in oxide for application to all rear contact (and back junction) solar cells. Figure 5 is an enlarged view of such contacts. The laser ablation spots may be superimposed in the x and y directions to open any desired length and width area on the wafer as shown in Figures 6a and 6b. 6A shows a 180 탆 wide opening formed by selectively removing BSG (boron doped oxide) for a base isolation region using a picosecond UV laser beam while superposing ablation spots in the x and y directions. Likewise, FIG. 6B shows a 90 [mu] m wide region open into USG (undoped oxide) for forming the base region.

As disclosed herein, selective etching of oxides from silicon surfaces can be used in many ways in the manufacture of solar cells. In one application, if an in situ emitter is used for a back contact cell, this process is used to open the tracks of the oxide film to expose the underlying emitter. This exposed emitter can be removed using a wet etch. This region is then used for base to emitter isolation and a base is formed therein.

In another application, this process is used to open areas to be used to form metal contacts. For front-facing cells, oxide passivation can be used on the backside of the cell. Then, using the method described herein, these contacts are opened for subsequent deposition of metal on the contacts. In this way, the metal has a conductive contact with high battery efficiency. For the backside contact cell, contacts for both the base and the emitter can be opened using this method.

In the solar cell process flow, it may be necessary to remove the doped oxide without causing any doping of the underlying silicon (i.e., without any noticeable heating of the doped oxide and the silicon structure). As described above, when the picosecond laser beam is used, the oxide is removed by separation at the oxide / silicon substrate interface, thereby removing the oxide while restricting the pickup of the dopant from the oxide film to be ablated.

Uses selective ablation of silicon nitride (SiN _x ) for the front-contact solar cell. By using laser ablation, the contact area to the emitter surface can be reduced, thereby minimizing the area where the SiN passivation is removed. This causes a higher V _OC . A nanosecond UV laser may be used, but a picosecond laser with UV or green wavelength is suitable for this application.

Selective metal ablation from the oxide surface using lasers has long been difficult. This is because at high pulse energies required to ablate the metal, the energy is so large that it damages the underlying oxide and allows the metal to penetrate into the oxide. In fact, this is fundamental to the process of "laser fire contact" (LFC) used in solar cells.

Disclose three methods of selectively removing metal from an oxide (or other dielectric) surface without the metal penetration of the oxide (or other dielectric such as silicon nitride) and the fracture or cracking of the oxide. In all of these methods, aluminum is the first metal in contact with the base and emitter (aluminum is used as the contact and light trapping back mirror layer). A laser with a picosecond pulse length is suitable for this application. For a high metal removal rate, the IR wavelength is quite suitable. According to a first method, the metal is ablated with a pulse energy less than a threshold value for the oxide emulsion. If the thickness of the metal removed in one scan is less than the desired thickness, multiple overlapping scans are used to remove the entire thickness of the metal. Since the pulse energy is less than the oxide ablation threshold, the metal is cleanly removed from the oxide surface. However, the exact recipe used depends largely on the type of metal in the stack, the thickness of the metal, and the surface roughness.

Figures 7A-7C show the ablation results when patterning a 2400A PDV-deposited bilayer stack of 1200A of Al on oxide. It is desirable to completely remove the metal between the runners without breaking through the underlying oxide layer (to prevent shunting in the cell). FIG. 7A shows the threshold of the pulse energy, and the metal stack can be removed without oxide transmission below this threshold. This threshold depends not only on the scan speed but also on laser parameters, such as spot overlap, obtained using a predetermined pulse repetition rate of the laser, in addition to being dependent on the metal stack characteristics described above. Increasing the pulse overlap reduces the critical pulse energy, which is due to the energy stored in the metal. FIG. 7B shows that the metal runners are completely separated as determined by the 100M-ohm resistance between the parallel lines, using pulse energy below the threshold for oxide damage and scanning beyond 20 times. Figure 7c shows a clean 75 占 퐉 trench formed in a 2400A NiV / 1200 Al metal stack.

According to the second high throughput method, high pulse energy is used because a significant portion of the incident energy is absorbed when ablated and thus the damage to the oxide is reduced. This approach makes laser ablation of the metal a very high throughput process. Using this method, a 1250A Al / 100-250A of NiV was successfully ablated with or without tin (Sn) coatings of up to 2500A thickness using a two-step process. In the first step, a more flexible metal is removed using a 15 microjoule pulse, and then a 30 microjoule pulse is used 15 times. For thick aluminum, such as 2000A, the second step is run at 50 microjoule with the same number of pulse overlays.

The third method of metal ablation is applicable to high reflective films, for example, to Al / Ag stacks (where Al contacts the cell and Ag on Al) and most of the incident energy of the picosecond laser is reflected Ablation is abruptly reduced. In this case, the surface of the reflective metal (Ag) is first recessed using a long pulse length nanosecond laser having a pulse length of 10 to 800 nanoseconds and then using picosecond cleanup of underlying aluminum.

The present disclosure is also applicable to selective doping of a substrate. For successful doping of silicon using an overlayer of dopant-containing material, the pulse energy should be large enough to melt the silicon, but not so large as to ablate silicon or ablate the dopant layer thereon. As the silicon melts, the dopant dissolves into the silicon. Upon recrystallization of such a silicon layer, a doped layer is obtained. In this application example, a nanosecond pulse length laser having a green wavelength is very suitable because penetration into the silicon is limited.

The above-described laser processing techniques are applicable to planar and 3D thin film crystalline silicon substrates. The laser processes described herein are suitable for any thickness of a silicon substrate. This includes current standards in which the wafer thickness exceeds 150 [mu] m, which is used in crystalline silicon solar cells. However, laser processes are more advantageous for thin and brittle wafers and substrates because the process is performed without any contact with the substrate. This can be achieved either by an improved wire sourcing technique or by hydrogen implantation followed by epitaxial deposition of silicon on a sacrificial separation / release layer, such as porous silicon, to a thin film monocrystalline substrate (in the range of several micrometers to 80 micrometers) And a wafer thinner than 150 [micro] m obtained from a monocrystalline CZ ingot or a polycrystalline brick by other techniques such as a subsequent lift-off, and the like.

Laser processing is particularly well suited for three-dimensional substrates obtained using silicon micromachining techniques and pre-structuring of reusable templates. One such method is disclosed in the '731 application (published as US 2010/10304522). Figures 8A-9B illustrate a 3-D thin film silicon substrate obtained using the techniques disclosed in that published document. Figure 8a shows a top view of the TFSS so obtained, while Figure 8b shows a cross-sectional view. For a pyramid substrate, the tips may be flat or have sharp points. 9A and 9B illustrate a TFSS with a prism structure obtained using a reusable pre-structured 3D template disclosed in the above-mentioned document.

The laser process and process flow described herein are applicable to any thickness (less than 1 [mu] m to more than 100 [mu] m) of the silicon substrate, but here the epitaxial silicon of the reusable template or the porous Discloses a solar cell fabricated using a thin silicon substrate having a thickness ranging from less than 1 [mu] m to about 80 [mu] m, including, but not limited to, substrates obtained using silicon (or other sacrificial layer) . To facilitate understanding of the application example, the process flow for obtaining a desired thickness (e.g., less than 10 [micro] m to about 120 [micro] m) of the planar single crystal TFSS according to the document is usually greater than about 50 [ 10A and 10B for a planar TFSS that can be treated as a possible substrate and is typically thinner than about 50 microns so that it is not self-supporting during the cell processing (and thus reinforced before being separated from the corresponding host template) Planar TFSS is shown in Figs. 11A and 11B. 12A to 12D show a process flow for obtaining a three-dimensional pyramidal silicon substrate. Although a similar process can be used to obtain a three-dimensional prism-like substrate, lithography or screen printing patterns may be used that provide for that structure.

A thin planar substrate obtained using the process flow of FIGS. 10A and 10B can be processed according to the process flow of FIG. 13 to obtain a high efficiency front contact solar cell. It should be noted that for the self-supporting TFSS, it is advantageous to first process the template side of the TFSS before proceeding to the other side. Since the template side of the TFSS is textured while the pseudo-single crystal silicon remaining on the TFSS after being separated from the template is removed, such template side is preferably the front side or the sun side of the solar cell. Laser processes for selectively ablating silicon nitride (SiN) and silicon oxide are advantageous for use in the manufacture of such front-contact solar cells.

Fig. 14 shows an application example of various laser processes for manufacturing a high efficiency front contact solar cell using a planar TFSS that can not be built up due to the TFSS being very thin during cell processing and not being self-supporting. In this case, it should be noted that the non-template side is first processed by the TFSS on the template. Once this process is completed, the TFSS is first attached to the exposed plate or sheet (also known as the backplane) of the process side and then separated from the template. After removal of the backplane attached (or backplane laminated) thin film crystalline silicon solar cell, the removal of residual porous silicon, texture etching, and SiN passivation / ARC deposition, and forming gas annealing (FGA) (Which is the front surface of the battery).

15 shows an application example of various laser processes for manufacturing a high efficiency front contact solar cell using 3-D front TFSS. In this application, it is advantageous to provide pyramid tips on the template side that are not sharp and have a flat ledge at the end.

The processes described herein are more uniquely suited to simplify all rear contact cell process flows.

16A-16D illustrate laser processes used in a planar epitaxial substrate to fabricate a back contact / rear junction solar cell in which the TFSS is self-supported (i.e., the backplane is not attached to the cell). In this application, the epitaxial emitter is deposited in situ during epitaxial silicon-based deposition followed by silicon epitaxy. The emitter is then removed from the base isolation regions using a silicon abrasion. At the same time, four fiducials are etched with oxide to align subsequent abrasions with this pattern. Next, the thermal oxide is grown to passivate the silicon surface to be the rear surface of the rear contact back junction solar cell. The epitaxial silicon film is then separated (or separated) from the template (by mechanical separation from the porous silicon interface). Next, the remaining porous silicon layer is wet etched and the surface textured (all of which can be done using an alkaline etch process). This results in the textured front or sun side of the solar cell. Now, a picosecond UV laser is used to ablate the thermal oxide to form the base opening in the base isolation region. The base openings are first aligned in a base isolation region (trench) formed first by a silicon abrasion using a starting point etched in silicon, as described above. Next, a phosphorus-containing oxide layer (PSG) is blanket deposited on the surface. By scanning with a nanosecond green or IR laser aligned to the base opening using the origin, the base is doped. In addition, regions with contact openings to the emitter are also doped in a similar manner using aligned scans of nanosecond green or IR lasers. Next, a contact opening is formed in the base and emitter regions thus doped using a picosecond UV laser. Again, alignment of these contact openings is made using the origin of silicon. Now, using a suitable method such as PVD (physical vapor deposition) technology, a metal stack layer (e.g., a stack of 1250A Al / 100-250A NiW 2250 Sn) containing aluminum as a first layer in contact with the cell Lt; / RTI &gt; Next, the layer is patterned using a picosecond IR laser so that metal runners are individually connected to the base and emitter regions. After the optional foaming gas annealing (FGA), the cells are reinforced by embedded (Al or Cu) high conductivity interconnects or by interconnecting the cells to the backplane without embedded interconnects (in the latter case, Which may be formed by a plating process). Now, the battery is ready for testing and use. 17 illustrates laser processes used in a planar epitaxial substrate to fabricate a back-contacting solar cell in which an epitaxial silicon base is not deposited with the emitter layer. Instead, a boron-containing oxide (BSG) layer is deposited and patterned to open the base isolation region. Except that the emitter and the base are simultaneously formed during the thermal oxidation step according to the process flow schematically illustrated in FIG. 17, the same process as described above is performed.

Figure 18 shows a process flow in which laser processes are used on an epitaxial substrate to produce a back contact / rear junction solar cell in which the TFSS is not self-supporting (thus the backplane is used). In this flow, a base isolation region is formed using a silicon abrasion of an in situ doping emitter.

19A-19H illustrate a process flow that utilizes a laser process on an epitaxial substrate to produce a planar back-contacting solar cell in which the TFSS is not self-supporting. In this flow, instead of the in situ emitter layer, an emitter is formed as well as a base isolation region using BSG deposition followed by thermal oxidation (or thermal annealing or thermal oxidation annealing) and selective laser ablation.

Figure 20 shows the process flow for fabricating a back-contacting 3-D solar cell, with the advantage that the template side of the pyramidal end has a relatively sharp point. Since the 3-D TFSS can be self-supporting with a relatively small thickness (e.g., silicon as thin as about 25 占 퐉), the process flow is similar to that shown in Fig. Once again, it is clear that there is a choice of performing post-thermal oxidation (or thermal annealing, or thermal oxidation annealing) with laser ablation of the post-in-situ emitter, or BSG diffusion, and selective laser ablation.

In an application of a heterojunction solar cell, the heterojunction emitter can be formed by a doped amorphous silicon layer in contact with the doped crystalline silicon base on the opposite side. For an intermeshing back-contact solar cell, an amorphous silicon layer and a transparent conductive oxide (TCO) are patterned using selective laser ablation of the crystalline layer. A femtosecond pulse width laser of UV or green wavelength is suitable for this application. The process flow is illustrated in FIG. Several variations of this process flow are possible.

The various embodiments and methods of the present disclosure include at least the following aspects. Processes for obtaining silicon abrasion of crystalline and amorphous silicon with reduced damage, processes for obtaining oxide abrasion for both doped and undoped oxides with no or reduced damage to silicon, dielectric for solar cell metallization Processes for obtaining fully separated metal patterns on the surface, processes for selectively doping emitter and base contact regions, pulsed laser processing on thin film wafers including planar and 3-D silicon substrates, The use of pulsed laser processing on substrates obtained using epitaxial deposition on reusable templates made using a variety of pulsed laser processes in the manufacture of front contact allogeneic solar cells, The use of various pulsed laser processes in manufacturing, The use of various pulsed laser processes in the fabrication of both cells.

Although the front contact solar cell is described as a p-type base and the rear contact back junction solar cell is described as an n-type base, the laser processes described herein conform to the substrate having opposite doping uniformly, that is, The p-type bases for the n-type P ⁺ emitter for the cell and the back-contact back-junction solar cell for the cell can be described as p-type bases and n ⁺ emitters.

The following description, tables and figures illustrate application of a flat-top laser beam to a laser processing method for an intermeshing back-contact battery (IBC). The following description relates to a method for forming a back-contacting solar cell using a flat top laser beam compared to a conventional Gaussian laser beam. In addition, the implementation of the flattened laser beam for the laser processing methods described throughout this specification considerably reduces damage to silicon, improves solar cell throughput and reduces patterns embedded in other patterns , Patterns of the emitter and base regions).

22A and 22B are schematic diagrams respectively showing profiles of a Gaussian beam (FIG. 22A) and a flat top beam (FIG. 22B). The beam intensity of the Gaussian beam is smoothly reduced from the maximum value at the beam center to the outside of the beam. In contrast, the intensity is "flat" or uniform for a flat top beam through most of the beam's profile (from center to out).

As disclosed herein, a high efficiency back contact rear junction cell with intermeshing backside contact (IBC) metallization benefits from using at least one or several steps of pulsed laser processing. The laser processing may include defining the emitter and base regions (or base to emitter isolation), defining the back field (BSF) region, doping to form the back field, contact openings in the dielectric to the base and emitter, Can be used in various processes over the formation of a rear contact cell including patterning. Some of these steps require large area laser processing typically generated by superposing Gaussian beam laser spots. Overlapping can greatly reduce the cell throughput rate and can cause silicon damage, which can degrade cell performance and yield. By replacing smaller diameter Gauss spots with a relatively wide flat top laser beam, the throughput is significantly improved. Since the overlap of spots is drastically reduced, semiconductor (e.g., crystalline silicon) substrate damage is significantly reduced. Figures 23 to 25 illustrate embodiments of a back-contacting solar cell that may be formed according to the disclosed flat-top laser beam processing methods.

23 is a cross-sectional view of a back contact / back side junction cell having intermeshing back contact (IBC) metallization formed from an n-type substrate as disclosed herein. As shown in FIG. 23, the alternating emitter regions and base regions are separated by relatively lightly n-doped substrate regions (n-type base). The backside / backside is covered by a surface passivation layer that provides a slow rear-surface recombination rate to good surface passivation, and can be deposited using techniques such as, for example, PECVD or APCVD, using thermal silicon dioxide, deposited silicon dioxide , Or silicon oxide / silicon nitride layers (and / or aluminum oxide deposited by molecular layer deposition (ALD)). Following this surface passivation process, an opening may be formed in the passivation layer that serves as a 'local contact' to the emitter and base regions. The emitter region and the base region can then be individually connected by performing conductor deposition and patterning (e.g., aluminum as shown in Figure 23).

24A is a rear / back view of an intermeshing rear contact base and emitter design back contact solar cell in which the emitter region and base region are laid out in an alternating parallel line. This back side can be formed, for example, by delineating the base region, starting with the surface completely covered by the emitter region, to form the patterned emitter region. The base contact regions are then doped with phosphorus and the contacts are opened relative to the base and emitter regions for metallization.

24B-24F are rear / back views of a rear-contact solar cell illustrating the rear contact cell after the main processing steps, wherein any one or more of the steps may be performed according to a laser process with or without a flat top beam A combination can be performed. Various laser patterning steps of this particular exemplary method are illustrated in Figures 24B-24E. Beginning with an n-type silicon substrate, a BSG layer is deposited over the entire surface. Next, as shown in Fig. 24B, an emitter-to-BSF separation region is defined using laser ablation of the BSG. This step, i.e., delineating the base and emitter regions, is referred to herein as the "BSG opening" step. Alternatively, a BSF region defined using laser ablation of silicon and a Si buffer layer can be deposited during silicon epitaxy.

After the emitter-to-BSF isolation region is defined in the BSG opening step, after the USG layer is deposited on the wafer, this layer is laser ablated with the patterns formed relative to the BSG opening region, as shown in Figure 24C. This patterning step is referred to herein as the BSF opening step or the base opening step. BSF openings must be separated from the edges of the BSG openings to prevent shunt formation as the shunt will adversely affect solar cell efficiency.

Next, a PSG layer is deposited on the wafer, and the silicon exposed to the PSG of the BSF opening is doped using selective laser scanning of this region. The doped BSF regions (base regions) are shown in Figure 24D.

Next, as shown in FIG. 24E, laser ablation is used to form contacts for the base and the emitter. Note that the contacts may be point contacts as shown in FIG. 24E or line contacts as shown in FIG. 24F. In addition, the number of contacts or the number of lines should be optimized for minimum series resistance of the current conduction path for the solar cell, and thus the design and method of the disclosed contents is not limited to the exemplary embodiments shown herein . It is also important to properly align the contact openings within a particular doping region so that current leakage is avoided.

As described above, a nanosecond pulse length laser may be used, but a picosecond pulse length laser may be used for the oxide ablation process of BSG openings, BSF openings, and contact openings. In addition, although IR wavelengths can be used, green or UV or even smaller wavelengths are more suitable because penetration into the silicon is reduced.

In particular, for BSF doping, nanosecond pulse length lasers may be more suitable due to penetration into the silicon. And although IR wavelengths may be used, the green wavelength may be more suitable for the typically desired doping depth, as penetration is reduced compared to IR.

Fig. 25 is a rear / rear view of the rear contact solar cell of Fig. 24A where metal lines alternately contact emitter regions and base regions. Note that the metal lines for the emitter and base regions are individually connected to bus bars not shown in FIG. 25 for the sake of simplicity of the drawings. This metal pattern can be formed by laser ablation of the subsequent metal to isolate the blanket deposition of the metal and the base contact from the emitter contact. Since thinner metal stacks, such as aluminum / nickel-vanadium / tin, are first deposited and patterned by a laser, since relatively thick metal lines (generally more than 20 microns thick) are required for good current conduction, It is possible to perform selective deposition of a thicker metal such as copper using plating or electroless plating. Alternatively, a backplane having a relatively thick conductor can be applied to attach to a cell having a thin conductor line. A picosecond pulse length laser with an IR wavelength may be best suited to ablate the metal stack because it has good selectivity for the underlying oxide layer.

The disclosed flat-top laser beam processing steps that may be used to enable this structure are those that are performed by laser ablation of deposited boron-doped dielectrics or emitters (such as borosilicate glass (BSG) deposited by APCVD) Outline of the BSF region by opening the dielectric covering the openings formed in the BSG, N ⁺ doping (e.g., using phosphorus) of the base, and outline description of the base regions (BSF and emitter to BSF isolation) Opening of the metallization contacts to the base and emitter regions, and metal patterning using metal laser ablation to separate the base and emitter contacts. Figures 26a-26c illustrate three ways in which a flat top beam profile can be created (see Laser Beam Shaping: Theory and Techniques, FM Dickey and SC Holswade, Mercel Dekker Inc., NY The entirety of which is hereby incorporated by reference). 26A shows one technique for generating a flat top beam profile, so-called "aperture " of a beam. By using this method, the Gaussian beam is flattened by expanding the Gaussian beam, using the aperture to select a significant flattened area and to cut off the progressively decreasing 'sidewall' area of the beam. However, with this method, the beam power can be significantly lost.

A second method for producing a flat top beam, as shown in Figure 26B, uses beam integration, where a plurality of aperture optical elements, such as a microlens array, divides the beam into a number of smaller beams, Lt; / RTI &gt; This beam integration method can be very suitable for a beam having a large M value.

As shown in FIG. 26C, a third beamforming system for generating a flat top beam uses diffraction grating or a diffractive lens to redistribute the energy and map it to the output plane. Any known method, including the three techniques disclosed in Figures 26A-C, may be used to obtain a flat top beam profile for the applications described herein. The suitability and choice of the flat top laser beam forming method depends on various factors, including available beam features and desired results.

FIGS. 27A and 27B are schematic views showing profiles of a Gaussian beam and a flat top beam emphasizing an ablation threshold value. FIG. As shown in Figs. 27A and 27B, the flat top laser beam can significantly reduce the laser damage during the ablation and doping process, especially compared to the Gaussian beam. For the Gaussian beam, there is a fairly excessive laser intensity that is greater than the value needed for ablation, especially at the center of the beam (as shown in Fig. The flat top beam is configured to be such that the peak intensity is slightly greater than the value required to ablate the material (the ablation threshold as shown in Figure 27B) and to avoid damage that may be caused by the high intensity of the Gaussian beam .

The flat top beam provides a particularly advantageous throughput advantage over the Gaussian beam, regardless of the square or rectangular cross section. 28A shows a Gaussian beam ablation area profile / footprint. The circular spots of the Gaussian beam should be substantially superimposed to minimize the zigzag outline of the pattern, typically by 50% overlap (Figure 28A). 28B is a diagram showing the flat top ablation zone profile / footprint. The square or rectangular flat top beam has a flat edge, thus creating a flat outline, and the overlap can be significantly reduced (Fig. 28B). FIG. 28C is a graph showing an improvement in scan speed as the beam overlap is reduced. Notice that even at 30% overlap, the scan speed can increase by 33%.

29A is a view illustrating a beam alignment window of a Gaussian beam, and FIG. 29B is a view illustrating a beam alignment window of a flat beam. 29A and 29B, another advantage of using a flat top beam to form the inlaid patterns is that the alignment window provided by the flat top beam is large. The circular spots obtained from the Gaussian beam create zigzag edges of the ablation areas (Figure 29A). As shown in Fig. 29A, the alignment margin of M is reduced and limited to M-a-b due to the bending of the zigzag edge profile.

However, the ablation area edge generated using the flat top beam is linear, so that the alignment margin can be maintained at M. For the back contact back junction solar cell described herein, a BSF opening is formed in the BSG opening region, and a contact opening is formed in the BSF region. Thus, a larger alignment margin is important, as it allows smaller BGS openings, BSFs, and contact areas. Thus reducing electrical shading and improving solar cell performance.

The overlay of the square or rectangular flat top beam can be reduced in the x and y directions during large area ablation or doping, thereby significantly improving throughput. Also, the size of the square or rectangular flat beam can be increased without causing excessive zigzag around, thereby further increasing throughput. Table 1 shows the reduction in the number of scans required to open a 150 um width line as used to delineate the base area by ablating the BSF film.

Table 1 below shows the throughput of the Gauss-to-flattop laser beam to create a base opening of 90 m wide. The results of Table 1 are shown graphically in Figure 29e.

fair Line width
(um) Spot size
(um) Overlap% Scan pitch
(um) Number of scans per line BSG ablation using Gaussian 150 30 50 15 9 BSG ablation using flat top 150 30 20 24 6 BSG ablation using flat top 150 60 20 48 3

Figure 29e illustrates the throughput advantages of a flat top beam compared to a Gaussian beam (a 30 占 퐉 flat top beam area profile is shown in Figure 29c) for a high productivity laser system capable of processing four wafers at a time A 60 占 퐉 flat top beam area profile is shown in Figure 29d). In order to further reduce the cost, for example, two lasers may be used, but each laser beam may again be divided into two. However, many variations of these flat top laser beam hardware and fabrication methods are possible.

In addition, since the overlap in the x and y directions is significantly reduced when a flat top beam is used, the laser induced damage of silicon is significantly reduced compared to the Gaussian beam.

Opening the oxide region for BSF, doping the BSF region with the added PSG, using the flat top beam to form the base and metal contact openings when the base and metal contacts are line contacts and metal abrasive separation lines are used , Similar throughput advantages may also occur, all of which have current advantages with reduced silicon damage. Also, the use of a flat top beam offers the advantage of increased alignment windows for BSF openings in the BSF and BSF openings in the BSF. In addition, the flat top laser processing methods can increase the throughput to form the backside field. For example, the backside field can be formed by doping the base region and can be opened with an n-type dopant such as phosphorus as described above. To this end, the base is covered with a layer of doped silicon oxide (PSG), and doping can be performed by irradiating this region with a laser beam. Overlap is required to uniformly doping this region using a Gaussian laser beam, but superposition can be minimized using a flat top beam, or can be completely reduced. For the base, emitter region contour and rear field contour depictions described herein, the use of a flat top laser beam provides the advantage of significant throughput and damage reduction as the required overlap is reduced. Note that in order to form the backside field, the beam needs to be a flat beam only in one direction, i.e., in the direction normal to the scan, while it may be a gaussian in the direction of the scan. This type of beam is referred to as a hybrid flat top beam.

Importantly, to form a separate base contact or emitter contact, superposition is not an issue, but unlike Gaussian, since there is no high intensity peak at the center of the beam (as shown in Figures 27A and 27B) The silicon damage is still reduced by using the top beam.

Other aspects of the present disclosure relate to the use of laser annealing and more specifically to the improvement of the passivation characteristics of the dielectric coating surface (or reducing the rate of surface recombination) And more particularly to pulsed laser annealing for improving the conversion efficiency performance of silicon nitride (SiN) coated surfaces (with and without a thin hydrogenated amorphous silicon intermediate layer). The silicon nitride layer may have a single stoichiometry or graded stoichiometry (e.g., a more stoichiometric and thicker top layer of silicon nitride with a lower refractive index over a thinner, higher refractive index silicon-rich silicon nitride intermediate layer). The improved front passivation characteristics become apparent as reduced front recombination speed (or reduced FSRV) and increased effective minority carrier lifetime, resulting in improved minority carrier aggregation and improved cell conversion efficiency. This technique is particularly advantageous for high efficiency rear-surface-junction back-contacting cells with intermeshing metal wiring (IBC), which also anneals the emitter on the back surface of the solar cell and the base metal contacts simultaneously using annealing of the SiN coated front, Reduces contact resistance and improves solar cell fill factor (FF). The laser annealing method of this disclosure is applicable to a thick wafer-based solar cell such as a crystalline semiconductor solar cell using a semiconductor absorption layer over a wide range of thickness, that is, a crystalline silicon wafer solar cell having a wafer thickness of several micrometers to several hundreds of micrometers Applicable. Further, more particularly, the non-contact laser annealing process and method of the present disclosure is based on the use of an extremely thin crystalline silicon solar cell (e.g., a crystalline silicon solar cell And the thickness is several 占 퐉 to 50 占 퐉. This is also an inline replacement of the annealing process in batches. The laser annealing process and method can be used as a final step in the cell manufacturing process flow or just after deposition of the front passivation and anti-reflection coating (ARC) layer. The processes and methods of the present disclosure enable the formation of high quality surface passivation and antireflective coatings, i.e. ARC layers, using passivation such as silicon nitride deposited by low temperature PECVD and a low temperature, low thermal cost deposition process for the ARC layer do.

The passivation of the surface of an inline N ⁺ emitter using silicon nitride for a standard front-facing solar cell with a p-type silicon bulk (or p-type base) is well known and widely used in the solar industry. The SiN film functions as an antireflective coating to reduce optical return loss and increase solar trapping, but also serves as a very important task for passivating the surface of an in-rich N ⁺ emitter by a well-known hydrogenation process. Hydrogen separating from the hydrogen-containing SiN layer satisfies the opening bond on the silicon surface (or a silicon dangling bond that causes surface states and traps), and thus the surface recombination rate or the ratio of minority carriers by such dangling bond sites . For a cell made of polycrystalline or polycrystalline silicon, this hydrogen provided by the SiN layer not only removes the grain boundary trap sites, but also reacts further with impurities and defects in the bulk of the silicon wafer, Reduces minority carrier recombination, and increases the effective fractional carrier lifetime of the bulk of the material.

The separation of hydrogen and consequently the surface and bulk passivation of silicon is typically obtained during a so-called "metal firing" process in the flow of standard frontal bonded, front-contact solar cell manufacturing processes currently used in the solar cell manufacturing industry. The screen printing metal firing process consists of multi-stage heating of the solar cell using carefully designed temperature and time sequences with final dwell at about 850 to 900 占 폚 before the desired cooling sequence. This firing cycle is optimized after careful experimentation. Since hydrogen is a small element, it can diffuse out of the wafer if the wafer temperature is too high or the annealing time is too long. On the other hand, if the temperature is too low or the annealing time is too short, the hydrogen passivation may be unsatisfactory. Thus, the hydrogen-passivation phenomenon has been the subject of in-depth research and research in the solar cell industry, and is regarded by many as a technology, not a mere science, (as it still requires a complete understanding of many areas). Thus, it is clear that a process that can provide a high degree of control is desirable.

For a standard mainstream front contact solar cell with a p-type silicon bulk (or p-type boron doping base) and an n ⁺ doping emitter, the front contact surface is in contact with silver while the backside is in contact with aluminum, Or may form an optional contact through an opening formed in the back side dielectric surface. To obtain a low resistance contact, during the metal firing process described above, silver is cross-mixed with frontal silicon and backside aluminum. Based on the description of the above metal firing process, the practice of obtaining a low-resistance contact of a solar cell and thus a high FF is complicated. Again, a process that can provide a high degree of control is desirable.

Further, all the rear-contact rear-bonding solar cells using the same metal, aluminum, which are in contact with both the n ⁺ contact and the p ⁺ contact on the back side are doped with n ⁺ contact by aluminum and the p- And therefore can not be heated to a very high temperature. In addition, due to the overheating of aluminum, which far exceeds 450 ° C, the optical reflectivity of aluminum may deteriorate (thereby increasing the optical loss of the infrared photons of the battery). Preferably, low temperature heating in which the contact of aluminum with silicon is controlled to be in the range of 200 캜 to 450 캜 by reducing and absorbing the oxide on the silicon surface is highly desirable.

Here, the front or sun side of the solar cell is in a selected region irradiated with a fairly uniform or laser beam, and a semiconductor (e.g., silicon) is selectively implanted to allow the hydrogen atoms to separate from the SiN and thereby effectively passivate the silicon surface Heating, decreasing the surface state density, reducing the front recombination speed (FSRV), and increasing the effective minority carrier lifetime of the solar cell. In addition, the processes and methods of the present disclosure can reduce the bulk trap density and improve the bulk minority carrier lifetime. One embodiment of the disclosed method is based on the use of a pulsed laser source having a wavelength less than the wavelength of a semiconductor (e.g., silicon) band gap. In this embodiment (e.g., using pulsed green or UV laser sources for crystalline silicon surface annealing), the front side is selectively heated using pulsed laser source irradiation, And is kept substantially cooler than the front side. Another embodiment of the disclosed method is based on the use of a pulsed laser source having a wavelength close to or greater than the wavelength of the semiconductor bandgap. In this embodiment (e.g., using a pulsed IR laser source for crystalline silicon surface annealing) while the front side is heated using pulsed laser source irradiation, the back side of the cell is also heated and annealed. In an alternative embodiment, simultaneously, the laser beam penetrates into the backside of the solar cell heating the Al / silicon contact to reduce the contact resistance and improve the overall battery fill factor and efficiency. The laser annealing process and method of the present disclosure can be performed immediately at the conclusion of the solar cell manufacturing process flow or after testing of the cells after formation of the passivation / ARC layer and sorting for module packaging. Alternatively, the laser annealing process and method of the present disclosure may be performed after assembling and packaging the cells of the PV module and through the front glass cover of the module assembly. In this case, it is necessary to use a wavelength capable of passing through glass such as infrared rays.

(Including laser source wavelength, pulse width, power, and the like) so that the passivation layer (e.g., PECVD SiN layer) does not deteriorate during this process so that sunlight can pass through this antireflective coating without significant optical absorption loss It is important to optimize the annealing process. Also, the surface texture should not be affected so that light trapping is not reduced. It is clear that the type of pulsed laser source and laser process parameters must be carefully selected to meet all of these requirements.

The laser pulse length should be long enough so that there is no nonlinear optical interaction with the passivation / ARC layer (e.g., SiN layer) so that the passivation / ARC layer is unaffected. For this application, lasers or continuous waves with pulse lengths ranging from 1 nanosecond to microseconds can be used, but the choice depends on the desired depth of penetration. With a shorter pulse length, the heat is limited to a shallow depth. In addition, the wavelength must be selected based on the depth of the semiconductor (e.g., crystalline silicon) that needs to be heated. In order to apply to a single crystal solar cell in which only front passivation needs to be improved, the green wavelength may be more suitable. For applications where improved bulk silicon passivation is required and / or back contact annealing is desired, the IR wavelength may be more suitable. It is clear that, based on the desired application, a range of laser pulse lengths and wavelengths can be used.

Processes involving rear contact cells having intermeshing metallization, referred to as NBLAC cells, are disclosed in related applications (see, for example, U.S. Patent Application Serial No. 13 / 057,104).

Figure 30 shows one embodiment of the NBLAC process flow, while Figure 31 is a schematic cross-sectional view of the battery (the backplane is not shown for convenience). The low temperature front passivation / ARC: PECVD (silicon nitride) + laser annealing process step of Figure 30 involves the deposition of SiN at a temperature lower than the temperature used in the art (< 350 [deg.] C). Subsequently, the surface is preferentially subjected to the frontal side of the silicon by pulsed laser irradiation to improve the passivation of the silicon surface with hydrogen from SiN. In particular, the laser annealing process and method of the present invention are particularly suitable for laser annealing processes and methods which are deposited at a low temperature as low as 90 占 폚, more specifically at a conventional deposition temperature range of 90 占 폚 to 250 占 폚 (such as a bilayer SiN with single- ) Enabling the formation of high quality passivation and ARC layers.

In some embodiments, the SiN to be annealed may contain a desired amount of phosphorus dopant. In this case, the annealing step may result in silicon doping using phosphorus. This process will be described below with reference to FIG.

In addition to SiN, on a silicon oxynitride (Si _x O _y N _z), or silicon carbide (Si _x C _y) single layer, or amorphous silicon-layer stack of silicon oxide having a SiN on the _{(a-Si) (SiO 2} ) A bilayer stack with SiN or a bilayer stack with SiN on silicon oxynitride may be used for silicon surface passivation. For example, it is known that an amorphous silicon layer can passivate the silicon surface fairly well. However, current industrial processes require significant surface cleaning of silicon and process optimization of the a-Si deposition process. Laser annealing of a-Si films with hydrogenated SiN can activate hydrogen of SiN, as measured by a significantly increased effective minority carrier lifetime and significantly reduced front recombination rate, which can dramatically improve passivation.

Figure 30 Pulsed picosecond laser ablation and PVD Al / NiV / Sn contact and backside enhancement BSR steps for Al-lined cell base & emitter Al-line steps are applied to the base and emitter on the back side of the solar cell. Thereby forming a metal contact. These contacts are shown in cross-section in Fig. It is clear that the laser beam penetrating the back surface of the silicon film simultaneously anneals the rear contacts to reduce the contact resistance and increase the fill factor of the solar cell.

The results obtained using the laser anneal are shown in Fig. It can be seen that up to 100 effective lifetime improvements were obtained on the low temperature deposited passivation layer of SiN without relying on high temperature metal firing. In the NBLAC process, thin epitaxial silicon is supported on the backplane. If this backplane can not withstand high temperatures, the SiN deposition temperature is reduced to facilitate thin epitaxial / backplane assembly processing and to handle the integration to accommodate a heat-sensitive backplane assembly. For such a thermal backplane, laser annealing is well suited because heat can be confined to the front side of the silicon while maintaining the backside of the silicon within an acceptable value for the backplane by properly selecting the laser pulse length and wavelength.

The non-contact laser annealing process is well suited for NBLAC cells that use epitaxial films with a thickness in the range of approximately several micrometers to 50 micrometers that can be easily broken during handling.

For improved throughput and improved process control, the laser sources used in these applications include a top-hat profile (where the beam power is relatively uniform over at least 100 mu m) to reduce the total surface scan time Lt; / RTI &gt; This also eliminates the possibility of damage to the beam overlap regions.

This laser annealing process is an inline cost effective process and therefore an attractive alternative to furnace annealing.

According to another aspect of the present disclosure, selective laser ablation and patterning of electrically insulating layers, such as thermally grown or chemically vapor deposited silicon oxide, on silicon is performed using a crystalline silicon solar cell process to obtain a relatively high cell efficiency value Used in flow. In this application, it is advantageous that negligible damage is introduced to the underlying silicon substrate, or damage is not introduced, as any significant abrasive induced damage may result in an increase in minority carrier recombination losses resulting in further loss of cell conversion efficiency. Here, we present a novel method of ensuring that the solar cell semiconductor (e.g., silicon) surface is not damaged during pattern selective ablation of the dielectric (e.g., silicon oxide) overlayer. The present disclosure includes introducing a thin intermediate layer of silicon that stops the laser beam from reaching the silicon substrate. This thin intermediate silicon layer can be placed close to the underlying silicon surface separated by only a thin buffer layer of silicon oxide. The oxide layer on this intermediate silicon layer is ablated by a laser beam that interacts and separates the silicon oxide-intermediate silicon layer interface. A very thin (e.g., 3 nm to 30 nm) silicon oxide layer beneath this intermediate silicon layer prevents a significant damage-induced effect of laser action at this interface from reaching the silicon substrate. Subsequently, the intermediate silicon layer is oxidized (using a thermal oxidation process or an oxidation annealing process), thereby eliminating any unwanted interactions in subsequent laser processing. This method is particularly suitable for applications of the design of all rear-contact back-junction solar cells, such as NBLAC solar cells, which use laser ablation of the dielectric layer, such as silicon oxide, several times.

In one embodiment of the process flow, the oxide ablation process is used three times to form an oxide pattern, i. E. Delineate the emitter and base regions using a BSG (or BSG / USG stack) / USG stack). The base region is defined using ablation, and the contact to the base is finally opened using PSG (phosphosilicate glass oxide) ablation, and the BSG / USG / The contact is opened. The techniques described herein can be advantageously used in the first stage of ablation of the BSG layer to define patterned emitter and base regions (for solar cells using an n-type base). If necessary, this technique can be further used during USG ablation to define openings for N ⁺ (this polarity reversed for solar cells using p-type bases) base region.

Figure 33A shows a process flow for all rear contact solar cells comprising oxide ablation at three different stages. Figure 33B shows that the BSG / USG (USG is undoped silicate glass or undoped silicon oxide) deposition step where a very thin a-Si layer is deposited on the thin USG layer before the remaining BSG / USG stack is deposited is slightly modified (In some embodiments, in situ within the same APCVD BSG deposition equipment). During the laser ablation process, the laser beam separates the BSG / a-Si interface and thus removes the BSG / USG stack. This thin silicon layer is oxidized during subsequent steps as described in Figure 33 (b).

34 schematically shows a standard oxidation ablation process using a laser beam having a pulse width in the range of a few picoseconds. It can be seen that the interface functioning by the laser is the surface of the silicon substrate which can be damaged if the correct pulse energy is not used. Figure 35 illustrates how a very thin amorphous silicon layer is deposited after a very thin USG layer is deposited. As can be seen in Figure 35b, the interface for laser action is the BSG / amorphous silicon interface. This interface serves as an ablation stop layer and shields the crystalline silicon surface from laser irradiation, thereby preventing or suppressing any possible crystalline silicon surface damage, and as a result, a high efficiency battery is possible.

Perfect stack USG / a-Si / BSG / USG can be deposited in situ using APCVD for solar cell fabrication. APCVD equipment can be a high productivity inline APCVD equipment with multiple sequential inline deposition zones to enable the deposition of the entire stack with a single APCVD equipment. By using the APCVD equipment, a thin undoped silicon layer can be deposited in one of the APCVD deposition zones (for example, after deposition of the initial USG layer, using a silane and argon (or silane and nitrogen) Zone). &Lt; / RTI &gt; Alternatively, it can be deposited using PECVD technology. Based on the specific process flow, a wide range of thicknesses of thin USG and thin a-Si can be utilized. Typically, the USG contacting the crystalline silicon surface may be in the range of 10 nm to 100 nm, while the amorphous silicon layer may be in the range of 3 nm to 30 nm. However, as outlined above, thicknesses outside this range will also function if the remainder of the process flow is modified to accommodate the thickness of such films.

Also, if necessary, the same process can be used to open the oxide layer for the base regions to be doped to form the N ⁺ layer. In that case, the process flow is modified to ensure oxidation of the a-Si layer.

According to another aspect of the present disclosure, a front field (FSF) is formed using laser doping. It is well known in the solar cell to reduce the minority carrier recombination loss and increase the current collection using surface fields away from the p / n junction. The substrate can be doped with the same polarity of the substrate and dopant, but at a higher concentration, while the substrate is doped with a polarity opposite to the substrate to produce an electrical p / n junction. This creates a built-in electric field due to a doping concentration gradient that allows fractional carriers to be collected beneficially to the emitter contacts by moving away the minority carriers from the base contact. This electric field is advantageously used at the front of the rear-joining rear-facing solar cell where the p / n junction is behind the wafer. This front field increases current collection at the emitter contact on the backside of the solar cell. This is achieved by suppressing the loss of minority carriers at the front recombination site (e.g., the surface state at the front passivation layer / silicon interface).

The front field (FSF) is a unique field that includes using a passivation layer, such as silicon nitride, containing dopants of a desired polarity (e.g., FSF for n-type base and boron FSF for p-type base) (In some embodiments, silicon) front facets of the rear-bonding rear-facing solar cell using pulsed laser doping techniques. In this case, the front side of the silicon needs to be heated to a temperature at which the dopant diffuses in the semiconductor layer and at a temperature high enough to activate the dopant. Again, by properly selecting laser parameters such as pulse length and wavelength, the front side of the semiconductor is selectively heated to a temperature without significant heating of the solar cell bulk or backside (or at least without diminishing heat). See FIG. This enables the use of a thermal backplane for supporting the silicon thin film.

Alternatively, the present disclosure is directed to a thin (e.g., 2 nm to 20 nm) amorphous silicon layer (or, alternatively, a sub-stoichiometric silicon-rich silicon layer) containing a major passivation such as PECVD silicon nitride and a thin An oxide layer or a sub-stoichiometric silicon-rich silicon nitride layer), followed by laser doping the solar cell front side to selectively dope the silicon surface. Again, it is necessary to raise the laser doping temperature so that the dopant diffuses in the silicon and the electrical activation of the dopant is sufficient. The amorphous silicon crystallizes epitaxially on single crystal silicon upon cooling. This also significantly improves the quality of front side passivation (not only through the formation of thin FSF layers, but also with a significant reduction in surface state density and a significant reduction in front side surface recombination speed, both effective heating and activation of the passivation layer through). See FIG. In addition, as described above, again, by appropriately selecting the laser parameters, the thermal backplane can be used to support the silicon thin film by preventing heat penetration into the back side.

In addition, the techniques of this disclosure can be used to form an emitter and a BSF in a front contact cell. The BSF directs the minority carriers collected by the emitter contacts to the front face of the cell (or alternatively, to the collector emitter contacts of the back side of the back contact solar cell) Lt; / RTI &gt;

In some embodiments, heating on the opposite side of the solar cell is limited to a temperature below 500 占 폚, and in some embodiments is limited to a temperature below 150 占 폚.

In these pulsed laser doping applications, the laser pulse length must be long enough that there is no nonlinear optical interaction with the SiN, so that the SiN ARC and passivation properties are not degraded. Lasers with pulse lengths> 1 nanosecond to microseconds or even CW (continuous wave) may be suitable for this application. Some embodiments of the present disclosure use a pulsed laser source having a pulse length in the range of a few microseconds in excess of 10 nanoseconds, and in some embodiments, a range of about 100 nanoseconds to 5 microseconds is used. The wavelength should be selected based on the depth of silicon that needs to be doped. In the case where the silicon film is supported on the thermal backplane, there is a further requirement that heat should be confined to the front side of the solar cell. The NIR (near-infrared) wavelength can also function in this application, but the green wavelength may be more suitable to keep the heating zone close to the surface being irradiated with the laser and sufficiently doped. Based on the desired application, it is clear that the range of laser pulse length and wavelength is suitable and can be used as various embodiments of the present disclosure.

In addition to phosphorus doped SiN, a stack of SiN on amorphous silicon (a-Si) for silicon surface passivation, or alternatively, a stack of SiN on Si-rich SiO _x or Si rich SiN _x may be used. In this case, the amorphous silicon layer (or a Si-rich SiO _x or Si-rich SiN _x layer) is in situ doped during layer deposition in a desired phosphorous amount (e.g., by PECVD). Laser annealing of phosphorus doped a-Si (or Si-rich SiO _x or SiN _x ) films covered with hydrogenated SiN results in doping of silicon with phosphorous and at the same time improves passivation of the silicon surface with hydrogen in PECVD SiN . The process sequence is schematically shown in Figure 37, which illustrates FSF formation using an indoped a-Si underlayer. Alternatively, a doped Si-rich SiO _x or SiN _x underlayer may be used.

Using a doping glass (with respect to the n-type base) for a crystalline semiconductor thin film supported on a thermally protected backplane that is heat-inhibited at the front by appropriately selecting the laser wavelength and pulse length using laser doping technology The boron doped glass can be used to form the FSF.

This process using pulsed laser doping has the disadvantage that the thin rear contact jig with the backplane can not withstand high temperatures after attaching the thin battery to the backplane and thus can not withstand the entire surface of the solar cell substrate and / Improvement and back side of the solar cell in the case of FSF formation) are not applicable to conventional high temperature doping processes.

The technique also provides a FSF for epitaxial films where in situ growth of the FSF is not useful during epitaxial deposition because the doping surface is lost during texturing. This is the case for NBLAC batteries.

a description will be given of a technique for application to an NBLAC cell having an n-type base substrate. The FSF can be formed using a p-type base substrate amorphous silicon film containing boron.

Further, using the technique, an emitter can be formed using a phosphorus-containing oxide film (PSG) for a p-type substrate or a boron-containing oxide (BSG) for an n-type substrate.

The contactless pulsed laser doping process is particularly suitable for a back contact solar cell using an epitaxial film with a thickness less than about 80 mu m which is liable to be brittle during handling. The laser doping process is also an inline cost effective process and is therefore an attractive alternative to doping.

According to another aspect of the present disclosure, laser annealing is used to dope the silicon substrate at selected regions with aluminum, thus providing the acceptor rich p ⁺ doped regions for the crystalline silicon solar cell. This technique is particularly advantageous for IBC cells in which the emitter contacts can be selectively doped with aluminum by selectively laser annealing the emitter contacts in contact with the deposited aluminum layer. By applying the same method, a selective emitter can be obtained in a back-junction front contact cell using n-type silicon as a base. Another application of this technique involves providing a backside field for a front-contact solar cell using a p-type substrate (or p-type base).

This disclosure includes a laser process capable of providing highly doped selective emitter contacts in such a rear contact cell with intermeshing metal interconnects and other back contact cells.

It is well known in the art of solar cell fabrication to obtain an acceptor rich (p ⁺ or p ⁺⁺ ) region by doping silicon with aluminum. For a standard front-facing cell using p-type silicon, the backside of the cell is screen printed with aluminum paste. By applying the firing annealing to a considerably high temperature, the aluminum dissolves the silicon layer in contact. At the time of cooling, aluminum functions as an acceptor or p-type dopant of silicon, so that the p-type (p ⁺ ) aluminum rich silicon layer is precipitated. This highly doped p-type p ⁺⁺ surface layer serves as a backside field so that the minority carriers deflect to the front where they are collected by the emitter contact from the backside. This increases the solar cell efficiency and current output (J _SC ). In addition, the Al / Si contact resistance is reduced, thereby improving the fill factor and further increasing the solar cell conversion efficiency.

Figures 38A and 38B schematically illustrate the disclosed laser scanning method. 38A shows a laser beam of the appropriate size and intensity used to scan only the emitter area, thereby heating the aluminum in contact with the emitter through the openings in the dielectric, and Fig. Emitter formation. When the metal and the silicon in contact with the metal are heated to a temperature exceeding 577 캜, which is the melting temperature for Al-Si, aluminum dissolves the silicon, and upon cooling below this temperature, the Al rich silicon layer is precipitated . This layer is epitaxially deposited on a silicon substrate and has no crystal defects. This is the same mechanism for providing Al-BSF in a standard Al paste printed cell.

Figure 39 shows a P ⁺⁺ selective emitter with aluminum saturated silicon formed by selectively performing laser scanning only in the emitter region.

The mechanism of formation of the Al rich silicon layer can be understood with the help of the Al rich phase diagram shown in FIG. The melt at 577 ° C is aluminum with 12.6% silicon fused. At higher temperatures, more silicon is melted. Upon cooling, the epitaxially deposited silicon saturates with Al and saturates up to 1.6%. This Al saturated silicon is high P ⁺⁺ doped and provides a low resistance contact to the emitter while suppressing minority carrier absorption in this region (providing selective BSF in the contact region).

It can be clearly seen that the same method can be used to obtain a selective emitter in a front contact cell using an n-type silicon substrate and a p ⁺ rear emitter. This method can be understood from Fig. 41 which follows.

As is widely known, a significant energy improvement is obtained for a standard front contact cell using a p-type silicon base when the entire surface aluminum contact of the backside base is replaced with a local contact. The efficiency is further increased if the BSF region is provided to the local contact. As shown in FIG. 42, Al BSF can be provided using the laser scanning method described above. This mechanism has been described above.

The following description is more relevant to the present application. The disclosure is directed to increasing the spatial selective absorption of the pulsed laser beam energy at the front and near the front of the cell while reducing pulsed laser beam penetration and absorption from the front and rear of the cell (where the platen may be located) Intensity blanket light incident on the side of the cell having the passivation layer (such as the solar side or the solar light receiving surface for the back side / back side contact solar cell / front side of the solar cell) during the laser annealing process on the same battery side . &Lt; / RTI &gt; This reduces the penetration depth of the laser beam, thereby reducing the depth of the laser heating and thus reducing the heating of the backplane supporting the crystalline silicon thin film. This technique enables spatial selective heating and annealing of the cell by concentrating the temperature rise near the front of the cell where the front side passivation layer, where the front side passivation layer is annealed, concentrates the absorbed pulsed laser energy.

The surface of the solar cell is exposed to the high intensity floodlight and at the same time the surface of the same cell as the pulsed laser irradiation is exposed to the high intensity floodlight, thereby improving the spatial selective annealing of the solar cell. Silicon, or other semiconductor material, and additional films are selectively heated on the illuminated side of the cell so that the embedded hydrogen atoms are stripped from the additional hydrogen or amorphous silicon-SiN stack containing silicon nitride (SiN) It effectively passivates the silicon surface by reducing the surface state density through passivation of the silicon dangling bonds by reaction with atoms. As a result, the front recombination speed (FSRV) is decreased, the effective fractional carrier lifetime is increased, the minority carrier diffusion length in the solar cell is increased, and thus the solar cell efficiency is increased.

Due to the pulsed laser beam absorption in the semiconductor layer (e.g. crystalline silicon), the interbands and intraband transitions of charge carriers occur depending on the wavelength of the laser beam. For photon energy higher than the bandgap of silicon (1.1 eV), due to photon absorption, the charge carriers transition from the valence band to the conduction band, thus creating an electron hole pair. This results in direct heating of the silicon (aside from the thermal shrinkage of excess photon energy when the electron hole pairs recombine and over the bandgap), since the cell is heated as the free charge carriers so generated absorb the photons Do not. Intra-band transitions and free carrier absorption are therefore important for laser heating of silicon, especially using pulsed laser sources operating in the near infrared (IR) region of the spectrum. Due to this absorption, non-linear interaction with the pulsed laser beam occurs and is absorbed to a much shorter depth near the illuminated surface of the cell. Alternatively, the photon energy may be near the band gap of silicon. As more free carriers are created, the spatially selective absorption of the laser beam near the cell surface is improved and is limited to a shorter distance near the surface of the cell, so that the backside of the cell is far less than the front side of the illuminated surface of the cell (I. E., It is possible to heat and anneal the front side of the cell at a much higher peak efficiency temperature than the backside of the battery, where the heat sensitive battery plate or backplane may optionally be present) Do).

High intensity floodlighting may be used to generate these excess carriers for spatially selective annealing and heating of the illumination front side of the cell using pulsed laser annealing (such as pulsed nanosecond IR laser annealing). By using such a flood light source during pulsed laser irradiation, it is possible to limit most of the effective heating and temperature rise to the front of the cell and to reduce heat transfer (and much lower temperature rise) (such as a battery reinforcement plate or backplane being connected to the back side of the cell The high temperature annealing is limited to the backside of the silicon film which is detrimental to the integrity of the backplane-cell structure.

From this explanation, photons with wavelengths below the IR wavelength of 1.1 m (or photon energies above 1.1 eV crystalline bandgap of the gap) exceed the silicon band gap of the photons, It is clear that the most effective use is in generating excess free carriers near the front of the cell. These excess free carriers enable spatially selective free carrier absorption of pulsed laser photons (including photons of near-infrared wavelengths) for selective heating / annealing on the battery front side. Preferably, the flood light source for excessive free carrier absorption must have photonic energy in excess of the crystalline silicon bandgap (1.1 eV), wherein a pulsed laser source (such as an IR laser source) Hole pairs can efficiently create a high density of excess electron-hole pairs near the front of a cell that functions as a free carrier absorption layer for spatial selective heating / annealing of the cell front. Thus, flood light sources with blue and / or green and / or visible wavelengths can be used for efficient absorption of silicon (as most photons are absorbed at very shallow skin depths of the illuminated silicon region), silicon Due to the efficient creation of excessive electron-hole pairs within the silicon, and the limited penetration depth into the silicon. Alternatively, the floodlight may have an infrared wavelength. The floodlight source need not be a single wavelength and may be a broadband or multiwavelength light source with an output power ranging from tens of watts to hundreds of watts to illuminate a typical square cell of 15.5 cm by 15.6 cm dimensions.

While the application of the disclosure during the battery fabrication process flow is described as a process for battery FSRV reduction and efficiency improvement, this application may be used after completion of the module assembly process to further increase the overall module efficiency and power.

Figures 43 and 44 illustrate two representative embodiments of a back junction / back contact epitaxial silicon cell (so-called NBLAC) process flow. 45 is a schematic cross-sectional view of a solar cell (an optional backplane is not shown for convenience).

The process step 16 in FIG. 43 is a process for the simultaneous exposure to high intensity green-to-visible floodlight, activating the hydrogen passivation process and pulsed laser annealing at the front (or solar side of the cell) Deposition of an amorphous silicon / SiN stack at a temperature lower than that used in the industry (typically in the range of 300 ° C to 450 ° C) (typically deposition at a temperature range of 90 ° C to 180 ° C). The floodlight illumination is used to generate large concentrations of excess electron-hole pairs near the front of the cell to facilitate spatially selective absorption of the pulsed laser energy near the cell front through free carrier absorption and at much lower temperatures And is used to perform spatial selective heating of the front surface side of the battery while maintaining the back surface of the battery. Using an amorphous silicon / a-Si stack deposition temperature as low as 90 占 폚, typically using a deposition temperature range of 90 占 폚 to 250 占 폚 and then using laser annealing according to the disclosure, an improved front side passivation .

46 is a graph of the results obtained using a 150 watt metal halide pulsed arc of the color temperature of a 4300 K floodlight bulb and pulsed laser annealing using the following laser parameters. That is, pulse energy = 1.7 mJ, pulse length = 700 nanosec, IR wavelength, repetition rate = 50 KHz, scan rate = 3600 mm / sec. It can be seen that under similar laser irradiation conditions, more wafers achieve higher cell efficiency when using high intensity green-visible light. According to laser annealing with or without light, V _OC and J _SC are generated. However, in the absence of floodlights, there is a possibility that the laser beam reaches the backplane and the backplane is heated to reduce the battery fill factor (FF), thereby reducing battery efficiency. In the presence of floodlight, the laser beam can not penetrate into the backplane, allowing for higher battery efficiency, avoiding FF degradation.

The non-contact laser annealing process is particularly suitable for typical backside junction / back contact thin film monocrystalline silicon cells using epitaxial films in the thickness range from several micrometers to over 100 micrometers. Such batteries are often brittle at the time of stand-alone handling and are thus supported by a reinforcing plate, preferably as a backplane attached to the rear surface of the battery.

This process is also applicable to other passivation layers, such as oxide / nitride, silicon oxynitride, silicon carbide, etc., either independently or together with the top layer of silicon nitride. The technique may also be used to passivate the surface of a monocrystalline or polycrystalline silicon wafer-based solar cell. For polycrystalline substrates, this technique can also be used to passivate bulk defects.

In operation, the following method and apparatus embodiments are disclosed. To improve the surface passivation characteristics of the passivation layer on the crystalline semiconductor solar cell including the crystalline silicon solar cell by reducing the surface recombination rate, increasing the effective fractional carrier lifetime, and increasing the effective minority carrier diffusion length. Intensity light (e.g., in one embodiment where most of the floodlight power using photonic energy exceeds the semiconductor bandgap, in one embodiment, greater than 1.1 eV for a crystalline silicon cell, single wavelength or broadband or multiwavelength floodlights Source) is present, a scanning pulsed laser beam is used. The presence of the floodlight source increases the absorption of the laser beam near the front, resulting in the spatial selective heating / annealing of the illuminated surface of the cell (such as the front), while maintaining the opposite side of the cell at low temperatures , Method and apparatus.

 Most of the floodlighting power using photon energy (such as silicon nitride, silicon nitride, silicon nitride, silicon nitride, silicon nitride, silicon nitride, silicon nitride, Using a scanning pulsed laser beam in the presence of a single wavelength or a broadband or multi-wavelength floodlight source exceeding a band gap, e.g., greater than 1.1 eV for a crystalline silicon cell, and Device.

A scanning speed laser beam is used in the presence of high intensity light so as to improve surface passivation by heating a SiN or amorphous Si / SiN-coated single crystal thin film (which may range from a few microns to a few hundred microns thick) Device.

A method and apparatus for use in all back-to-back inter-meshing metallization solar cells to improve front passivation of SiN coated n-type surfaces or amorphous Si / SiN coated p-type surfaces.

To improve the front passivation of SiN coated n-type surfaces or amorphous Si / SiN coated p-type surfaces using single crystal silicon thin films (which can range from a few microns to several hundreds of micrometers thick), all rear contact interlocking metal wiring solar cells Method and apparatus used.

In the presence of high intensity light to anneal a single-layer SiN film on silicon or a bilayer film on silicon, including SiN, silicon oxynitride, or silicon carbide on amorphous silicon to improve silicon surface passivation and improve effective bulk minority carrier lifetime Using a scanning pulsed laser beam.

(Most of the floodlight power using photon energy exceeds the semiconductor bandgap so that the surface and bulk passivation can be improved by selectively heating the SiN coated polysilicon film (with or without underlying layer) For example, in one embodiment, a scanning pulsed laser beam is used in the presence of a single wavelength or a broadband or multi-wavelength floodlight source in excess of 1.1 eV for a crystalline silicon cell.

A SiN coated monocrystalline or polycrystalline silicon film (with or without an underlayer such as amorphous silicon) is heated using a scanning pulsed laser beam in the presence of high intensity light to enhance surface passivation wherein SiN and the underlayer RTI ID = 0.0 &gt; 90 C &lt; / RTI &gt; to 250 C.

Those skilled in the art will recognize that the disclosed embodiments relate to various fields besides the specific examples described above.

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 departing from the spirit of the invention. Accordingly, the claimed subject matter is not intended to be limited to the embodiments illustrated herein but is to be accorded the widest scope consistent with the novel features and principles disclosed herein.

And all such additional systems, methods, features, and advantages included in this description are intended to be included in the scope of the claims.

Claims (21)

As a method for improving the efficiency of a photovoltaic solar cell,
Providing a crystalline semiconductor-based photovoltaic solar cell having a dielectric passivation layer on its front side;
Providing a pulsed laser irradiation of laser fluences less than an ablation threshold of the dielectric passivation layer on the front side of the crystalline semiconductor-based photovoltaic solar cell, wherein the laser irradiation is selective to the front side and the dielectric passivation layer To enable a reduction in surface recombination speed at the front face and an annealing process without physical deterioration of the dielectric passivation layer for the solar cell,
Providing a floodlight source having a floodlight power having photon energy above the semiconductor bandgap in combination therewith during the pulsed laser irradiation annealing process to generate a free carrier at the front face and to generate a free carrier at the front face of the pulsed laser irradiation Thereby increasing the absorption of the photovoltaic cell. The method of claim 1, wherein the semiconductor comprises silicon. 3. The method of claim 2, wherein the silicon comprises monocrystalline silicon. 3. The method of claim 2, wherein the silicon comprises polycrystalline silicon. 3. The method of claim 2, wherein the silicon comprises quasi-mono-crystalline silicon. The method of claim 1, wherein the passivation layer comprises silicon nitride. The method of claim 1, wherein the floodlight source has photon energy exceeding a bandgap energy of the crystalline semiconductor. delete The method of claim 1, wherein the floodlight source has photon energy in excess of 1.1 eV. The method of claim 1, wherein the floodlight source comprises a green wavelength or a blue wavelength, or a visible wavelength. 2. The method of claim 1, wherein the floodlight source comprises an infrared wavelength. The crystalline semiconductor-based photovoltaic cell according to claim 1, wherein an interdigitated back contact metallization for connecting to the base region and the emitter region is formed on all of the rear contact back junctions -back-junction back-junction solar cells. 3. The method of claim 1, wherein the passivation layer is formed of silicon nitride, silicon oxynitride, silicon carbide, silicon nitride on amorphous silicon, silicon nitride on silicon oxide, silicon oxide on amorphous silicon, silicon nitride on amorphous silicon oxide, A low refractive index silicon nitride over a nitride, and a silicon nitride over a silicon oxynitride. 13. The method of claim 12, wherein the passivation layer is deposited at a temperature in the range of 90 &lt; 0 &gt; C to 250 &lt; 0 &gt; C. The method of claim 1, wherein the crystalline semiconductor-based photovoltaic solar cell has a thickness in the range of 5 탆 to 100 탆. The method of claim 1, wherein the crystalline semiconductor based photovoltaic solar cell comprises an epitaxial silicon thin film solar cell. 17. The method of claim 16, wherein the epitaxial thin film solar cell has a thickness in the range of 10 mu m to 100 mu m. 18. The method of claim 17, wherein the crystalline semiconductor-based photovoltaic solar cell is supported on a stacked backplane. The method of claim 1, wherein the pulsed laser irradiation has photon energy greater than a bandgap of the semiconductor. The method of claim 1, wherein the pulsed laser irradiation has a wavelength larger than a bandgap of the semiconductor. The method according to claim 1,
Wherein the passivation layer is an amorphous silicon and silicon nitride stack.

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