CN117096223A - Laser activation heavy doping method, photovoltaic cell and preparation method thereof - Google Patents

Laser activation heavy doping method, photovoltaic cell and preparation method thereof Download PDF

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CN117096223A
CN117096223A CN202311354274.6A CN202311354274A CN117096223A CN 117096223 A CN117096223 A CN 117096223A CN 202311354274 A CN202311354274 A CN 202311354274A CN 117096223 A CN117096223 A CN 117096223A
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polysilicon
silicon
oxide layer
laser
doping
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董雪迪
张武
林佳继
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Laplace Wuxi Semiconductor Technology Co Ltd
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Laplace Wuxi Semiconductor Technology Co Ltd
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Abstract

The invention provides a laser activated heavy doping method, a photovoltaic cell and a preparation method thereof, wherein the laser activated heavy doping method comprises the following steps: locally heating and melting polycrystalline silicon on the tunneling oxide layer by adopting laser to obtain molten silicon; cooling and crystallizing the molten silicon to form supersaturated doping of electroactive impurity atoms, thereby obtaining heavily doped polysilicon; wherein the polysilicon includes p doped with impurity atoms + Polycrystalline silicon and/or n + Polysilicon, heavily doped polysilicon including p ++ Polycrystalline silicon and/or n ++ And (3) polycrystalline silicon. The method reduces the contact resistance between metal and semiconductor by heavily doping impurity atoms in the polysilicon, has shorter doped junction depth, does not damage a tunneling oxide layer, and has no influence on a silicon substrate by the impurity atoms, thereby avoiding Auger recombination and electric conductionThe cell damage does not affect passivation quality while realizing high doping concentration, and the obtained photovoltaic cell has high conversion efficiency and large open-circuit voltage, and is suitable for industrial mass production.

Description

Laser activation heavy doping method, photovoltaic cell and preparation method thereof
Technical Field
The invention belongs to the technical field of photovoltaic cells, relates to a heavy doping method, and particularly relates to a laser activated heavy doping method, a photovoltaic cell and a preparation method thereof.
Background
The mass production efficiency of the current mainstream P-type PERC battery gradually approaches the theoretical conversion efficiency limit of 24.5%, the future lifting space is limited, and the lifting difficulty is extremely high. The TOPCon technology is used as the next generation battery technology, has the theoretical conversion efficiency limit of up to 28.7%, is mature in process and clear in efficiency improving path, can be directly upgraded from a PERC production line, greatly reduces equipment investment cost, and is a technical route for key layout of each main stream battery manufacturer.
In TOPCon technology, the double-sided TOPCon battery corresponds to the highest conversion efficiency of 28.7%, and the TOPCon structure (tunnel oxide layer+polysilicon) is prepared on the front side, so that doped polysilicon or selective coating is deposited on the whole area of the front side, the carrier recombination rate on the surface of the battery is further reduced, and the contact resistance is reduced. However, the front-side global deposition of doped polysilicon will result in additional parasitic absorption, affecting light transmittance, while selective plating will involve masking and chemical etching, further increasing process complexity.
In the process of preparing the TOPCon structure (tunneling oxide layer+polysilicon) on the front surface of the photovoltaic cell, the doping mode of polysilicon is one of the key factors influencing the performance of the photovoltaic cell, and the traditional implementation of high doping concentration by adopting a diffusion mode can lead to doping atoms entering a silicon substrate through the tunneling oxide layer, so that auger recombination is increased, and further passivation quality is damaged.
Therefore, how to provide a heavy doping method, to reduce the contact resistance between metal and semiconductor, to avoid the influence of doping atoms on the silicon substrate, to avoid auger recombination and battery damage, and to improve passivation quality, is an urgent problem to be solved by those skilled in the art.
Disclosure of Invention
The invention aims to provide a laser activation heavy doping method and a photovoltaic cell, wherein the method reduces contact resistance between metal and semiconductor by heavy doping of impurity atoms in polysilicon, the doped junction depth is short, a tunneling oxide layer is not damaged, the impurity atoms have no influence on a silicon substrate, thus Auger recombination and cell damage are avoided, passivation quality is not influenced while high doping concentration is realized, the conversion efficiency of the obtained photovoltaic cell is high, and open-circuit voltage is high, so that the method is suitable for industrial scale mass production.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method of laser-activated heavy doping, the method comprising:
locally heating and melting polycrystalline silicon on the tunneling oxide layer by adopting laser to obtain molten silicon;
and cooling and crystallizing the molten silicon to form supersaturated doping of electroactive impurity atoms, thereby obtaining the heavily doped polysilicon.
Wherein the polysilicon includes p doped with impurity atoms + Polycrystalline silicon and/or n + Polysilicon, the heavily doped polysilicon including p ++ Polycrystalline silicon and/or n ++ And (3) polycrystalline silicon.
According to the invention, the polysilicon on the tunneling oxide layer is heated and melted locally by laser to obtain molten silicon, so that impurity atoms in the molten silicon break through the limit of solid solubility and are fixed in the polysilicon in the process of cooling and crystallization, supersaturation doping of electroactive impurity atoms is formed, namely, high active impurity atom concentration is formed locally in a metallization region, the contact resistance between metal and semiconductor is reduced, the doped junction is relatively short, the tunneling oxide layer is not damaged, the doped concentration is rapidly reduced at the interface of the polysilicon/tunneling oxide layer/silicon substrate, the doped curve is controllable, and the impurity atoms have no influence on the silicon substrate, thereby avoiding auger recombination and battery damage, and realizing high doped concentration without influencing passivation quality. The Poly-finger structure of the photovoltaic cell manufactured by the method is easy to pattern polysilicon, has less compounding, high passivation quality and large open-circuit voltage, remarkably improves the conversion efficiency, and is suitable for industrial mass production.
It should be noted that the tunnel oxide layer also serves as a barrier to molten silicon in addition to conventional passivation. The tunnel oxide layer ensures that, within certain laser energy limits, the molten silicon does not come into direct contact with the underlying monocrystalline silicon, thereby recrystallizing it into polycrystalline silicon rather than monocrystalline silicon. In addition, based on the barrier of the tunneling oxide layer and the difference of diffusion coefficients of impurity atoms in the molten silicon and the solid silicon, the underlying monocrystalline silicon is not affected by the impurity atoms, thereby realizing the special doping property that the doping concentration at the interface position is rapidly reduced.
In the present invention, the electrically active impurity atoms are impurity atoms in the polysilicon which are activated by laser light, not all impurity atoms diffused into the polysilicon have electrical activity, for example, impurity atoms located at grain boundaries, and such impurity atoms which do not have electrical activity cannot be detected by ECV (electrochemical capacitance-voltage method) and do not contribute to electrical properties.
In certain embodiments, the p + The impurity atoms in the polycrystalline silicon include any one of boron atoms, indium atoms, or gallium atoms.
Setting said p + The hole concentration in the polysilicon is the first hole concentration, the p ++ And if the hole concentration in the polysilicon is a second hole concentration, the second hole concentration is larger than the first hole concentration.
In certain embodiments, the n + The impurity atoms in the polysilicon include any one of phosphorus atoms, antimony atoms, or arsenic atoms.
Setting said n + The electron concentration in the polysilicon is a first electron concentration, n ++ And if the electron concentration in the polysilicon is a second electron concentration, the second electron concentration is larger than the first electron concentration.
In the present invention, the p + Polysilicon refers to polysilicon with higher concentration of 'holes' doped with impurity elements (such as boron element or indium element or gallium element). Said n + Polysilicon refers to polysilicon doped with impurity elements (such as phosphorus element or antimony element or arsenic element, etc.) and containing higher electron concentration. The p is ++ Polysilicon refers to p + Heavily doping impurity atoms in the polysilicon to obtain polysilicon, and p ++ The impurity element concentration of the polysilicon is greater than p + And (3) polycrystalline silicon. Said n ++ Polysilicon refers to n + Impurity in polycrystalline siliconHeavily doping atoms to obtain polysilicon, and n ++ The impurity element concentration of the polysilicon is greater than n + And (3) polycrystalline silicon.
In some embodiments, the laser includes a pulse laser, for example, a green nanosecond laser, so long as laser activation and heavy doping of impurity atoms in polysilicon can be achieved, and specific types of the pulse laser are not particularly limited herein.
In certain embodiments, the pulsed laser satisfies: 1J/cm 2 The energy density is less than or equal to 5J/cm 2 For example, it may be 1J/cm 2 、1.5J/cm 2 、2J/cm 2 、2.5J/cm 2 、3J/cm 2 、3.5J/cm 2 、4J/cm 2 Or 4.5J/cm 2 But are not limited to, the recited values, and other non-recited values within the range of values are equally applicable.
The invention is characterized in that the energy density of the pulse laser is limited to 5J/cm 2 The blocking effect of the tunneling oxide layer on the molten silicon is further improved, the rapid reduction of the doping concentration at the interface position is realized, the doping depth is smaller than or equal to the thickness of the polysilicon layer, the silicon substrate is not influenced by high-concentration doping, and auger recombination is avoided. In addition, the energy density of the pulse laser is not lower than 1J/cm 2 Otherwise, a pulsed laser below the activation threshold does not have the effect of activating the impurity atoms.
The invention can realize partial melting or complete melting of the polysilicon layer by regulating and controlling the energy density of the laser activation process, regulates and controls the doping curve, and does not influence the passivation quality.
In some embodiments, the pulsed laser has a wavelength of 300-1500nm, such as 355nm, 365nm, 405nm, 532nm, 540nm, 660nm, 1064nm, or 1080nm, although not limited to the recited values, and other non-recited values within the range are equally applicable.
It can be understood that the wavelength of the pulse laser is 300-1500nm, which is favorable for the absorption of the battery piece and improves the processing efficiency of the battery piece.
In some embodiments, the pulse width of the pulse laser is 10ps-500ns, for example, 10ps, 50ps, 100ps, 500ps, 1ns, 10ns, 50ns, 100ns or 500ns, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.
It can be understood that the pulse width of the pulse laser is 10ps-500ns, and the penetration depth of impurity elements can be ensured under the condition that the deposition thickness of polysilicon is 50-300nm, and the thermal damage of a tunneling oxide layer can be prevented, thereby being beneficial to the processing of the battery piece.
In some embodiments, the pulse overlap ratio of the pulse laser is 1% -99%, for example, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 99%, but not limited to the recited values, and other non-recited values within the range are equally applicable.
It can be understood that the pulse overlap ratio of the pulse laser is 1% -99%, which is beneficial to battery piece processing.
In some embodiments, the pulsed laser is beam shaped to produce a rectangular flat-top spot, and the rectangular flat-top spot has a size of (250-350) μm× (550-650) μm, which may be, for example, 250 μm×550 μm, 260 μm×560 μm, 280 μm×580 μm, 300 μm×600 μm, 320 μm×620 μm, 340 μm×640 μm, or 350 μm×650 μm, although not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The invention shapes the pulse laser to obtain rectangular flat-top light spots through beam shaping, so that the light power of a laser processing area is uniformly distributed, thereby ensuring that the tunnel oxide layer is not locally damaged while the polysilicon is melted, and the laser processing efficiency can be improved through shaping the rectangular light spots into large-area rectangular light spots.
In some embodiments, the deposition form of the tunnel oxide layer includes single-sided deposition or double-sided deposition, and the deposition thickness is 1-2nm, for example, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm, or 2nm, but not limited to the recited values, and other non-recited values within the range of values are equally applicable.
The invention limits the deposition thickness of the tunneling oxide layer within the range of 1-2nm, ensures passivation and carrier tunneling effects, and simultaneously can make the tunneling oxide layer play a role of blocking molten silicon so as to prevent the monocrystalline silicon below from being influenced by impurity atoms and ensure the special doping property of rapidly reducing the doping concentration at the interface position.
In certain embodiments, the deposited form of polysilicon includes single sided deposition or double sided deposition, and the deposition thickness is 50-300nm, such as 50nm, 60nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm, or 300nm, but is not limited to the recited values, and other non-recited values within this range are equally applicable.
In some embodiments, the doping of the impurity atoms in the polysilicon includes in-situ doping or ex-situ doping.
In a second aspect, the present invention provides a photovoltaic cell, which is subjected to laser-activated heavy doping of impurity atoms in polysilicon during the preparation process by using the method described in the first aspect, and is any one of a single-sided TOPCon cell, a double-sided TOPCon cell or a TBC cell.
In the invention, the TBC battery is a tunneling oxide passivation back contact battery.
In the invention, the maximum doping concentration of boron atoms in the polysilicon after heavy doping is more than or equal to 5 multiplied by 10 20 cm -3 For example, it may be 5X 10 20 cm -3 、5.2×10 20 cm -3 、5.4×10 20 cm -3 、5.6×10 20 cm -3 、5.8×10 20 cm -3 、6×10 20 cm -3 、6.2×10 20 cm -3 、6.4×10 20 cm -3 、6.6×10 20 cm -3 、6.8×10 20 cm -3 Or 7X 10 20 cm -3 But are not limited to, the recited values, and other non-recited values within the range of values are equally applicable.
The maximum doping concentration of impurity atoms in the polysilicon after heavy doping is more than or equal to 5 multiplied by 10 20 cm -3 The high-activity boron doping concentration mainly has the following two technical advantages: (1) Obtaining metal-semiconductorThe low contact resistance of the body interface, the traditional way of diffusion doping in polysilicon, the maximum solid solubility of boron in silicon limits the achievement of high doping concentration and corresponding low contact resistance; (2) The high active boron concentration provides etching barrier in alkali liquor, and p can be realized ++ Maskless patterning of the polysilicon layer.
In the invention, the doping depth of impurity atoms in the polysilicon after heavy doping is less than or equal to the thickness of the polysilicon, namely, short junction deep doping is realized, the silicon substrate is not influenced by high-concentration doping, and Auger recombination is avoided.
In certain embodiments, the photovoltaic cell is a bifacial TOPCon cell comprising:
a silicon substrate;
an emitter arranged on one surface of the silicon substrate;
the anti-reflection layer is positioned on one side of the emitter facing away from the silicon substrate and is arranged on the surface of the emitter;
p ++ the polycrystalline silicon sequentially penetrates through the anti-reflection layer and the emitter and is used for conducting electricity;
a first tunneling oxide layer arranged on the p ++ The polysilicon is arranged between the polysilicon and the silicon substrate;
the aluminum oxide layer is positioned on one side of the silicon substrate, which is away from the emitter, and is arranged on the other surface of the silicon substrate;
the silicon nitride layer is positioned on one side of the aluminum oxide layer, which is away from the silicon substrate, and is arranged on the surface of the aluminum oxide layer;
n + the polycrystalline silicon sequentially penetrates through the silicon nitride layer and the aluminum oxide layer and is used for conducting electricity;
a second tunneling oxide layer arranged on the n + And the polysilicon is arranged between the polysilicon and the silicon substrate.
In certain embodiments, the photovoltaic cell is a TBC cell comprising:
a silicon substrate;
a front surface field arranged on one surface of the silicon substrate;
the anti-reflection layer is positioned on one side of the front surface field away from the silicon substrate and is arranged on the surface of the front surface field;
the silicon nitride layer is positioned on one side of the silicon substrate, which is away from the front surface field, and is arranged on the other surface of the silicon substrate;
p ++ the polycrystalline silicon penetrates through the silicon nitride layer and is used for conducting electricity;
a first tunneling oxide layer arranged on the p ++ The polysilicon is arranged between the polysilicon and the silicon substrate;
n + polysilicon, and p ++ The polysilicon is arranged at intervals, penetrates through the silicon nitride layer and is used for conducting electricity;
and the second tunneling oxide layer is arranged between the n+ polycrystalline silicon and the silicon substrate.
Conventional polysilicon impurity element diffusion processes have low doping concentrations, and generally use an increase in impurity element diffusion temperature to increase the doping concentration, which can cause damage to the tunnel oxide layer, and impurity atoms will be doped into the silicon substrate, resulting in a decrease in passivation quality. The laser activation of the invention well solves the difficulty of considering the doping concentration and passivation quality, and does not damage the tunneling oxide layer while realizing the doping concentration of local high-activity impurity elements. The emitter and surface field structures of the photovoltaic cell are prepared in the method, and high sheet conductivity and low surface recombination can be obtained, so that the conversion efficiency of the cell is improved. In addition, the high doping concentration obtained by laser activation can realize maskless patterning of the polysilicon layer, and a simple battery process route is provided for industrial mass production.
It can be appreciated that such a double sided TOPCon cell structure can achieve higher sheet conductance and lower surface recombination, thereby improving cell conversion efficiency.
Similarly, the TBC battery structure can obtain higher sheet conductivity and lower surface recombination, thereby improving the battery conversion efficiency.
In a third aspect, the present invention provides a method for preparing a photovoltaic cell, the method comprising the method according to the first aspect, comprising: p to be doped with impurity atoms + Polysilicon is laser excitedThe p is obtained after the active heavy doping ++ Polysilicon, and then etching and cleaning to remove p + Polysilicon to retain p ++ Polysilicon, get patterned p ++ And (3) polycrystalline silicon.
And/or n to be doped with impurity atoms + The polysilicon is subjected to laser activation heavy doping to obtain n ++ Polysilicon, etching and cleaning to remove n + Polysilicon to retain n ++ Polysilicon, get patterned n ++ And (3) polycrystalline silicon.
The two modes utilize p + Polysilicon and p ++ Polysilicon and n + Polysilicon and n ++ The difference of etching resistance of polysilicon in etching liquid, p is removed by the etching liquid + Polycrystalline silicon and/or n + Polysilicon to retain p ++ Polycrystalline silicon and/or n ++ The polysilicon is patterned without an additional mask, so that the production process of the photovoltaic cell is greatly simplified.
In the invention, when the photovoltaic cell is a single-sided TOPCON cell, the preparation method comprises tunneling oxide layer deposition, doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
In the invention, when the photovoltaic cell is a double-sided TOPCON cell, the preparation method comprises tunneling oxide layer deposition, doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
In the invention, when the photovoltaic cell is a TBC cell, the preparation method comprises tunneling oxide layer deposition, back first doped polysilicon layer deposition, mask deposition, laser grooving, back second doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, the polycrystalline silicon on the tunneling oxide layer is heated and melted locally by laser to obtain molten silicon, so that impurity atoms in the molten silicon break through the limit of solid solubility and are fixed in the polycrystalline silicon in the process of cooling and crystallization, supersaturation doping of electroactive impurity atoms is formed, namely, high active impurity atom concentration is formed locally in a metallization region, the contact resistance between metal and semiconductor is reduced, the doped junction depth is shorter, the tunneling oxide layer is not damaged, the doped concentration is rapidly reduced at the interface of the polycrystalline silicon/tunneling oxide layer/silicon substrate, the doped curve is controllable, the impurity atoms have no influence on the silicon substrate, thereby avoiding auger recombination and battery damage, and passivation quality is not influenced while realizing high doped concentration;
(2) The Poly-finger structure of the photovoltaic cell manufactured by the method is easy to pattern polysilicon, has less compounding, high passivation quality and large open-circuit voltage, remarkably improves the conversion efficiency, and is suitable for industrial mass production.
Drawings
Fig. 1 is a schematic cross-sectional view of a double-sided TOPCon cell obtained in example 1;
FIG. 2 is a schematic cross-sectional view of the TBC battery obtained in example 3.
Wherein, 1-silicon substrate; a 2-tunneling oxide layer; 3-p ++ A polysilicon layer; 4-emitter; 5-n + A polysilicon layer; a 6-alumina layer; a 7-silicon nitride layer; 8-metal contact; 9-front surface field.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
The invention provides a method for activating heavy doping by laser, which specifically comprises the following steps: locally heating and melting polycrystalline silicon on the tunneling oxide layer by adopting laser to obtain molten silicon; and cooling and crystallizing the molten silicon to form supersaturated doping of electroactive impurity atoms, thereby obtaining the heavily doped polysilicon.
Wherein the polysilicon includes p doped with impurity atoms + Polycrystalline silicon and/or n + Polysilicon, heavily doped polysilicon including p ++ Polycrystalline silicon and/or n ++ And (3) polycrystalline silicon.
In the present invention, p + Impurity atoms in the polycrystalline silicon include any one of boron atoms, indium atoms, or gallium atoms; setting said p + The hole concentration in the polysilicon is the first hole concentration, the p ++ And if the hole concentration in the polysilicon is a second hole concentration, the second hole concentration is larger than the first hole concentration.
In the present invention, n + Impurity atoms in the polysilicon include any one of phosphorus atoms, antimony atoms, or arsenic atoms; setting said n + The electron concentration in the polysilicon is a first electron concentration, n ++ And if the electron concentration in the polysilicon is a second electron concentration, the second electron concentration is larger than the first electron concentration.
In the present invention, the laser light includes a pulse laser light, and satisfies: 1J/cm 2 The energy density is less than or equal to 5J/cm 2 。
In some embodiments, the laser has a wavelength of 300-1500nm, a pulse width of 10ps-500ns, and a pulse overlap ratio of 1% -99%.
In some embodiments, the laser is beam shaped to produce a rectangular flat top spot, and the rectangular flat top spot has a specification of (250-350) μm× (550-650) μm.
In certain embodiments, the deposition form of the tunnel oxide layer comprises single sided deposition or double sided deposition, and the deposition thickness is 1-2nm.
In certain embodiments, the deposition form of polysilicon includes single sided deposition or double sided deposition, and the deposition thickness is 50-300nm.
In some embodiments, the doping of impurity atoms in the polysilicon includes in situ doping or ex situ doping.
The invention also provides a photovoltaic cell, which adopts the method to perform laser activation and heavy doping of impurity atoms in polysilicon in the preparation process, and is any one of a single-sided TOPCO cell, a double-sided TOPCO cell or a TBC cell.
In the invention, the maximum doping concentration of boron atoms in the polysilicon after heavy doping is more than or equal to 5 multiplied by 10 20 cm -3 And the doping depth of impurity atoms in the polysilicon after heavy doping is less than or equal to the thickness of the polysilicon.
The invention also provides a manufacturing method of the photovoltaic cellThe preparation method comprises the following steps: p to be doped with impurity atoms + The polysilicon is subjected to laser activated heavy doping to obtain p ++ Polysilicon, and then etching and cleaning to remove p + Polysilicon to retain p ++ Polysilicon, get patterned p ++ Polycrystalline silicon; and/or n to be doped with impurity atoms + The polysilicon is subjected to laser activation heavy doping to obtain n ++ Polysilicon, etching and cleaning to remove n + Polysilicon to retain n ++ Polysilicon, get patterned n ++ And (3) polycrystalline silicon.
In the invention, when the photovoltaic cell is a single-sided TOPCON cell, the preparation method comprises tunneling oxide layer deposition, doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
In the invention, when the photovoltaic cell is a double-sided TOPCON cell, the preparation method comprises tunneling oxide layer deposition, doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
In the invention, when the photovoltaic cell is a TBC cell, the preparation method comprises the steps of tunneling oxide layer deposition, back first doped polysilicon layer deposition, mask deposition, laser grooving, back second doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
Example 1
The embodiment provides a double-sided TOPCON battery and a preparation method thereof, and the method specifically comprises the following steps:
(1) Cleaning an N-type silicon wafer, and removing impurities on the surface of the silicon wafer to obtain a silicon substrate 1;
(2) A tunneling oxide layer 2 is deposited, siO with thickness of 1.5nm is deposited on the two side surfaces of the silicon substrate 1 2 The tunneling oxide layer 2 is obtained by the layer;
(3) Front side p + Polysilicon layer deposition on the front side of SiO 2 Depositing a boron doped polysilicon layer with the thickness of 150nm on the surface of the layer to obtain a front p + A polysilicon layer;
(4) The laser activates heavy doping, the wavelength is 532nm, the pulse width is 100ns, and the energy density is 3J/cm 2 Green nanosecond excitation of (2)Light (rectangular flat-top light spot with specification of 300 mu m multiplied by 600 mu m is obtained by beam shaping, and pulse overlapping rate is 10%) is locally heated to melt the front surface p + A polysilicon layer, which makes boron atoms in the molten silicon break through the limit of solid solubility and is fixed in the polysilicon in the process of cooling and crystallization to form supersaturation doping of electroactive boron atoms, thus obtaining p ++ Polycrystalline silicon;
(5) Patterning the front surface by p + Polysilicon and p ++ Polysilicon etch resistance difference, p is removed by potassium hydroxide solution + Polysilicon, forming patterned p ++ A polysilicon layer 3;
(6) Cleaning and texturing, pickling to remove an oxide layer, and alkali cleaning and etching to form a surface pyramid shape, so that surface light reflection is reduced;
(7) Preparing a front emitter 4, performing boron diffusion on the front surface of the battery piece, realizing low-concentration boron doping of a front non-metal contact area, and removing borosilicate glass formed in the boron diffusion process by utilizing hydrofluoric acid solution;
(8) Back surface n + A polysilicon layer 5 deposited on the back side SiO 2 Depositing a phosphorus doped polysilicon layer with the thickness of 150nm on the surface of the layer to obtain the back surface n + A polysilicon layer 5;
(9) Back surface patterning, forming etching mask by laser oxidation treatment of the metallized region, removing the non-metallized region by potassium hydroxide solution, and forming patterned n + A polysilicon layer 5;
(10) Passivation: depositing a silicon nitride layer 7 on the front surface of the battery piece, and sequentially depositing an aluminum oxide layer 6 and a silicon nitride layer 7 on the back surface of the battery piece, wherein the aluminum oxide layer 6 is used as a passivation layer, and the silicon nitride layer 7 is used as an anti-reflection layer;
(11) Screen printing, producing metal contacts 8 and annealing.
Fig. 1 is a schematic cross-sectional view of a double-sided TOPCon cell obtained in this example.
The p of the double-sided TOPCON cell obtained in this example was detected ++ The maximum doping concentration of boron atoms in the polysilicon layer 3 is 5×10 20 cm -3 The doping depth is150nm, the cell had an implied open circuit voltage of 722mV and a saturation current density of 6.7fA/cm 2 。
Example 2
This example provides a double sided TOPCon battery and method of making same except that the energy density of the green nanosecond laser is changed to 5J/cm 2 The other steps and conditions are the same as those of example 1, and thus are not described here.
The p of the double-sided TOPCON cell obtained in this example was detected ++ The doping depth of boron atoms in the polysilicon layer 3 exceeds 300nm, i.e. the tunneling oxide layer 2 is damaged, the boron atoms are doped into the silicon substrate 1, the implicit open circuit voltage of the cell is 624mV, and the saturation current density is 501fA/cm 2 。
Compared with the embodiment 1, the embodiment changes the energy density of the green nanosecond laser from the original 3J/cm 2 Up to 5J/cm 2 As a result, the doping depth of boron atoms is too great, the tunneling oxide layer is damaged and doped into the silicon substrate, the hidden open circuit voltage of the battery is reduced, the saturation current density is greatly increased, and the battery performance is remarkably reduced.
Example 3
The embodiment provides a TBC battery and a preparation method thereof, and the TBC battery specifically comprises the following steps:
(1) Cleaning an N-type silicon wafer, forming a pyramid-shaped light trapping structure on the front surface of the silicon wafer by adopting an alkali texturing mode, and reducing surface light reflection;
(2) A tunneling oxide layer 2+ back polysilicon layer is deposited, and SiO with thickness of 1.5nm is deposited on the back of the silicon substrate 1 2 A layer and an intrinsic polysilicon layer having a thickness of 150 nm;
(3) Phosphorus diffusion to form the back surface n + A polysilicon layer 5 and a front surface field 9 doped with front surface phosphorus;
(4) Mask deposition on the back side n + Depositing a silicon nitride layer 7 on the surface of the polysilicon layer 5 as a mask;
(5) Removing the mask outside the N region graphical region by laser grooving, and further removing the phosphorus doped polysilicon layer below by wet etching;
(6) Boron doped polysilicon layer depositionDeposition of p on the laser grooved open area + A polysilicon layer forming a P region pattern;
(7) Laser activation, wavelength of 532nm, pulse width of 100ns, and energy density of 3J/cm 2 Is subjected to local heating and melting of p by green nanosecond laser (rectangular flat-top light spots with the specification of 300 mu m multiplied by 600 mu m are obtained by beam shaping, and the pulse overlapping rate is 10 percent) + A polysilicon layer, which makes boron atoms in the molten silicon break through the limit of solid solubility and is fixed in the polysilicon in the process of cooling and crystallization to form supersaturation doping of electroactive boron atoms, thus obtaining p ++ Polycrystalline silicon;
(8) Alkaline washing, removing p by potassium hydroxide solution ++ P of polysilicon edge + A polysilicon layer forming PN region isolation;
(9) Etching to remove the mask and the front structure of the battery;
(10) Passivation, sequentially depositing a silicon oxide layer and a silicon nitride layer 7 on the front surface of the battery piece, and depositing the silicon nitride layer 7 on the back surface of the battery piece;
(11) Screen printing, producing metal contacts 8 and annealing.
Fig. 2 is a schematic cross-sectional view of a TBC cell obtained in this example.
The TBC cell obtained in this example was examined for p ++ The maximum doping concentration of boron atoms in the polysilicon layer 3 is 5×10 20 cm -3 The doping depth was 150nm, the implicit open circuit voltage of the cell was 734mV, and the saturation current density was 6.4fA/cm 2 。
Therefore, the polycrystalline silicon on the tunneling oxide layer is heated and melted locally by laser to obtain molten silicon, so that impurity atoms in the molten silicon break through the limit of solid solubility and are fixed in the polycrystalline silicon in the process of cooling and crystallizing later, supersaturation doping of electroactive impurity atoms is formed, namely high active impurity atom concentration is formed locally in a metallization region, contact resistance between metal and semiconductor is reduced, the doped junction depth is short, the tunneling oxide layer is not damaged, the doped concentration is rapidly reduced at the interface of the polycrystalline silicon/tunneling oxide layer/silicon substrate, the doped curve is controllable, the impurity atoms have no influence on the silicon substrate, auger recombination and battery damage are avoided, and passivation quality is not influenced while high doped concentration is realized. The Poly-finger structure of the photovoltaic cell manufactured by the method is easy to pattern polysilicon, has less compounding, high passivation quality and large open-circuit voltage, remarkably improves the conversion efficiency, and is suitable for industrial mass production.
The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims (10)

1. A method of laser activated heavy doping, the method comprising:
locally heating and melting polycrystalline silicon on the tunneling oxide layer by adopting laser to obtain molten silicon;
cooling and crystallizing the molten silicon to form supersaturated doping of electroactive impurity atoms, thereby obtaining heavily doped polysilicon;
wherein the polysilicon includes p doped with impurity atoms + Polycrystalline silicon and/or n + Polysilicon, the heavily doped polysilicon including p ++ Polycrystalline silicon and/or n ++ And (3) polycrystalline silicon.
2. The method of claim 1, wherein p is + Impurity atoms in the polycrystalline silicon include any one of boron atoms, indium atoms, or gallium atoms;
setting said p + The hole concentration in the polysilicon is the first hole concentration, the p ++ The hole concentration in the polysilicon is a second hole concentration, and the second hole concentration is larger than the first hole concentration;
said n + Impurity atoms in the polysilicon include any one of phosphorus atoms, antimony atoms, or arsenic atoms;
setting said n + The electron concentration in the polysilicon is a first electron concentration, n ++ And if the electron concentration in the polysilicon is a second electron concentration, the second electron concentration is larger than the first electron concentration.
3. The method of claim 1, wherein the laser comprises a pulsed laser, and the pulsed laser satisfies: 1J/cm 2 The energy density is less than or equal to 5J/cm 2 。
4. A photovoltaic cell, characterized in that the photovoltaic cell adopts the method of any one of claims 1-3 to perform laser activation heavy doping of impurity atoms in polysilicon during the preparation process, and the photovoltaic cell is any one of a single-sided TOPCon cell, a double-sided TOPCon cell or a TBC cell.
5. The photovoltaic cell of claim 4, wherein the maximum doping concentration of impurity atoms in the polysilicon after heavy doping is 5 x 10 or more 20 cm -3 。
6. The photovoltaic cell of claim 5, wherein the maximum doping concentration of boron atoms in the polysilicon after heavy doping is 5 x 10 or more 20 cm -3 。
7. The photovoltaic cell of claim 4, wherein the impurity atoms in the polysilicon have a doping depth of less than or equal to the thickness of the polysilicon after heavy doping.
8. The photovoltaic cell of claim 7, wherein the photovoltaic cell is a bifacial TOPCon cell comprising:
a silicon substrate;
an emitter arranged on one surface of the silicon substrate;
the anti-reflection layer is positioned on one side of the emitter facing away from the silicon substrate and is arranged on the surface of the emitter;
p ++ the polycrystalline silicon sequentially penetrates through the anti-reflection layer and the emitter and is used for conducting electricity;
a first tunneling oxide layer arranged on the p ++ The polysilicon is arranged between the polysilicon and the silicon substrate;
the aluminum oxide layer is positioned on one side of the silicon substrate, which is away from the emitter, and is arranged on the other surface of the silicon substrate;
the silicon nitride layer is positioned on one side of the aluminum oxide layer, which is away from the silicon substrate, and is arranged on the surface of the aluminum oxide layer;
n + the polycrystalline silicon sequentially penetrates through the silicon nitride layer and the aluminum oxide layer and is used for conducting electricity;
a second tunneling oxide layer arranged on the n + The polysilicon is arranged between the polysilicon and the silicon substrate;
alternatively, the photovoltaic cell is a TBC cell comprising:
a silicon substrate;
a front surface field arranged on one surface of the silicon substrate;
the anti-reflection layer is positioned on one side of the front surface field away from the silicon substrate and is arranged on the surface of the front surface field;
the silicon nitride layer is positioned on one side of the silicon substrate, which is away from the front surface field, and is arranged on the other surface of the silicon substrate;
p ++ the polycrystalline silicon penetrates through the silicon nitride layer and is used for conducting electricity;
a first tunneling oxide layer arranged on the p ++ The polysilicon is arranged between the polysilicon and the silicon substrate;
n + polysilicon, and p ++ The polysilicon is arranged at intervals, penetrates through the silicon nitride layer and is used for conducting electricity;
a second tunneling oxide layer arranged on the n + And the polysilicon is arranged between the polysilicon and the silicon substrate.
9. A method for the production of a photovoltaic cell, characterized in that it comprises a method according to any one of claims 1 to 3, comprising in particular: will be doped with impurity atomsP of (2) + The polysilicon is subjected to laser activated heavy doping to obtain p ++ Polysilicon, and then etching and cleaning to remove p + Polysilicon to retain p ++ Polysilicon, get patterned p ++ Polycrystalline silicon;
and/or n to be doped with impurity atoms + The polysilicon is subjected to laser activation heavy doping to obtain n ++ Polysilicon, etching and cleaning to remove n + Polysilicon to retain n ++ Polysilicon, get patterned n ++ And (3) polycrystalline silicon.
10. The method of claim 9, wherein when the photovoltaic cell is a single sided TOPCon cell, the method comprises sequentially performing a tunnel oxide layer deposition, a doped polysilicon layer deposition, and a laser activated heavy doping;
or when the photovoltaic cell is a double-sided TOPCON cell, the preparation method comprises tunneling oxide layer deposition, doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out;
or when the photovoltaic cell is a TBC cell, the preparation method comprises tunneling oxide layer deposition, back first doped polysilicon layer deposition, mask deposition, laser grooving, back second doped polysilicon layer deposition and laser activated heavy doping which are sequentially carried out.
CN202311354274.6A 2023-10-19 2023-10-19 Laser activation heavy doping method, photovoltaic cell and preparation method thereof Pending CN117096223A (en)

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