Method for preparing TBC battery by using silicon ink and TBC battery

Abstract

The invention relates to the technical field of photovoltaic cell manufacturing, and discloses a method for preparing a TBC cell by using silicon ink and the TBC cell, S1, providing a silicon substrate, and preparing a tunneling oxide layer on the back surface of the silicon substrate; s2, printing a preset first interdigitated graph and a preset second interdigitated graph on the tunneling oxide layer by using hydrogen-rich silicon ink; the hydrogen-rich silicon ink comprises a silicon nanocrystal and a hydrogen-rich carrier; and S3, carrying out in-situ collaborative sintering on the printed hydrogen-rich silicon ink by adopting a pulse energy source. Through in-situ hydrogenation repair, high-temperature furnace annealing which causes hydrogen loss is abandoned, and by utilizing the synergistic effect of laser and hydrogen-rich ink, the conductive layer is formed, the interface state density is remarkably reduced, and the open-circuit voltage of the battery is improved; the ink-jet printing is adopted to replace expensive LPCVD and photoetching mask processes, so that the preparation cost of the TBC battery is remarkably reduced; the laser only heats the back ink area, the silicon substrate is kept at low temperature, and warping of the silicon wafer and attenuation of minority carrier lifetime are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic cell manufacturing, in particular to a method for preparing a TBC cell by using silicon ink and a TBC cell. BACKGROUND

[0002] The TBC (Tunnel Oxide Passivated Contact Back Contact) cell combines the advantages of the IBC cell without front shielding and the TOPCon cell passivated contact, and has extremely high theoretical conversion efficiency. However, the preparation of the complex P / N cross structure on the back surface is the biggest bottleneck for mass production.

[0003] In the prior art (such as CN117790588A), a full film deposition combined with mask lithography, laser slotting and acid washing process is usually used to realize patterning. This path is long in procedure, expensive in equipment, and the acid washing process is easy to cause cross contamination.

[0004] In order to simplify the process, the industry tries to introduce printing technology. For example, CN118299471A proposes a method of first depositing amorphous silicon and then inkjet printing a doping source; CN103280401A proposes a method of printing silicon nano slurry. However, these methods all have a common defect: they must rely on subsequent global high-temperature furnace annealing (usually at 850-980℃ for more than 30 minutes) to realize the crystallization of silicon or the activation of the dopant.

[0005] According to the principles of semiconductor physics, when the temperature exceeds 450℃, the hydrogen atoms (Si-H bonds) located at the tunneling oxide / silicon interface will undergo serious desorption. The existing printing + high-temperature sintering route, although it solves the problem of patterning, sacrifices the interface passivation quality (i.e. the open-circuit voltage Voc) as a trade-off. Therefore, how to realize the preparation of "vacuum-free, patterning" while solving the problem of "hydrogen loss" caused by high temperature is a key technical bottleneck that needs to be solved in the preparation of high-efficiency TBC cells. SUMMARY

[0006] The present application provides a method for preparing a TBC cell by using silicon ink, which solves the problem of hydrogen loss at the tunneling oxide interface during the high-temperature sintering process of the existing silicon ink / slurry technology, thereby reducing the passivation effect of the TBC cell.

[0007] The present application provides the following technical solution: a method for preparing a TBC cell by using silicon ink, comprising the following steps: S1: providing a silicon substrate, and preparing a tunneling oxide layer on the back surface of the silicon substrate; S2: printing a preset first-finger cross pattern and a second-finger cross pattern on the tunneling oxide layer by using a hydrogen-rich silicon ink; the hydrogen-rich silicon ink comprises silicon nanocrystals and a hydrogen-rich carrier; S3: in-situ co-sintering the printed hydrogen-rich silicon ink by using a pulsed energy source; wherein the pulse width of the pulsed energy source is controlled to be between 10 ns and 500 ns, so as to match the thermal diffusion time of the silicon ink, so that a liquid phase covering layer is formed at the moment when the hydrogen-rich silicon ink absorbs the pulsed energy, thereby blocking the escape of hydrogen species, and at the same time, the hydrogen species produced by the decomposition of the hydrogen-rich carrier is diffused to the interface of the tunneling oxide layer, thereby realizing in-situ hydrogenation repair of the interface.

[0008] Preferably, the pulsed energy source is a nanosecond pulsed laser, and the wavelength is selected from one of 532 nm, 355 nm or 1064 nm. The single-pulse energy density is controlled to be between 0.2 and 1.5 J / cm².

[0009] Preferably, the hydrogen-rich carrier comprises at least one of polysilane derivatives, cyclopentasilane (CPS) or silicon quantum dots with Si-Hx bonds (x = 1-3) on the surface. The mass percentage of the hydrogen-rich carrier in the hydrogen-rich silicon ink is between 5% and 30%.

[0010] Preferably, in step S3, the in-situ co-sintering process satisfies the following thermodynamic conditions: The heating rate of the silicon ink layer is greater than 10^6 ℃ / s, and the overall temperature of the silicon substrate is maintained below 200 ℃, so as to form a cold-wall effect.

[0011] Preferably, the hydrogen-rich silicon ink comprises a first polarity ink and a second polarity ink. The first polarity ink comprises a boron source precursor, and the second polarity ink comprises a phosphorus source precursor. Alternatively, the first polarity ink and the second polarity ink are both intrinsic silicon ink, and the doping source is introduced above the tunneling oxide layer by plasma injection.

[0012] Preferably, the boron source precursor in the first polarity ink is decaborane or boron-doped silicon nanocrystals. The phosphorus source precursor in the second polarity ink is red phosphorus nanoparticles or phosphorus-doped silicon nanocrystals.

[0013] Preferably, the viscosity of the silicon ink is between 5 and 50 cP, and the surface tension is between 25 and 40 mN / m. The contact angle of the silicon ink on the surface of the tunneling oxide layer is controlled between 10° and 45°.

[0014] Preferably, after step S2 and before step S3, the method further comprises: The printed ink is subjected to low-temperature drying treatment, the drying temperature is 150-300℃, and the time is 1-5 minutes, so as to remove the organic solvent in the ink while keeping the hydrogen-rich carrier from thermal decomposition.

[0015] Preferably, the thickness of the tunneling oxide layer is 1.0-2.0 nm, and the material is silicon dioxide, aluminum oxide or silicon oxynitride.

[0016] A TBC cell prepared by using the silicon ink, the polycrystalline silicon layer on the back surface of the TBC cell has a columnar crystal microstructure formed by laser rapid melting, and the interface state density (Dit) of the polycrystalline silicon / tunneling oxide layer interface is lower than 1×10^11 eV^-1 cm^-2, indicating that the TBC cell has not undergone a high-temperature furnace annealing process which can cause hydrogen desorption.

[0017] The present application has the following advantages: 1. The method for preparing a TBC cell by using a silicon ink, through in-situ hydrogenation repair, discards the high-temperature furnace annealing which can cause hydrogen loss, and by using the synergistic effect of laser and hydrogen-rich ink, the interface state density is significantly reduced while forming a conductive layer, and the open-circuit voltage of the cell is improved. The inkjet printing is adopted to replace the expensive LPCVD and photolithography mask process, so that the preparation cost of the TBC cell is significantly reduced. The laser only heats the ink area on the back surface, and the silicon substrate remains at low temperature, so that the silicon wafer warping and the bulk minority carrier lifetime decay are avoided. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a process flow chart of the present application.

[0019] Figure 2 is a schematic diagram of the micro-interface "liquid phase capping and hydrogen diffusion" mechanism in the laser sintering process in the present application.

[0020] Figure 3 is a comparison diagram of the electrical properties of the TBC cells prepared in the examples and the comparative examples of the present application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be described in detail below with reference to the drawings and specific embodiments.

[0023] A method for preparing a TBC battery by using silicon ink, comprising the following steps: S1: providing a silicon substrate, and preparing a tunneling oxide layer on the back surface of the silicon substrate; S2: printing a preset first finger cross pattern and a second finger cross pattern on the tunneling oxide layer by using hydrogen-rich silicon ink; the hydrogen-rich silicon ink comprises silicon nanocrystals and a hydrogen-rich carrier; S3: performing in-situ collaborative sintering on the printed hydrogen-rich silicon ink by using a pulse energy source; In the method, the pulse width of the pulse energy source is controlled to be between 10 ns and 500 ns, so as to match the heat diffusion time of the silicon ink, so that a liquid phase covering layer is formed by the hydrogen-rich silicon ink absorbing the pulse energy instantaneously, the hydrogen species is blocked from escaping outward, and the hydrogen species produced by the decomposition of the hydrogen-rich carrier is diffused to the interface of the tunneling oxide layer while the polycrystalline silicon conductive layer is formed by crystallization, so as to realize in-situ hydrogenation repair of the interface.

[0024] In a preferred embodiment, the pulse energy source is a nanosecond pulse laser, and the wavelength of the nanosecond pulse laser is selected from one of 532 nm, 355 nm and 1064 nm. The single pulse energy density is controlled to be between 0.2 J / cm² and 1.5 J / cm².

[0025] In a preferred embodiment, the hydrogen-rich carrier comprises at least one of polysilane derivatives, cyclopentasilane (CPS) or silicon quantum dots with Si-Hx bonds (x=1-3) on the surface. In the hydrogen-rich silicon ink, the mass percentage of the hydrogen-rich carrier is between 5% and 30%.

[0026] In a preferred embodiment, in the step S3, the in-situ collaborative sintering process satisfies the following thermodynamic conditions: The heating rate of the silicon ink layer is greater than 10^6 ℃ / s, and the overall temperature of the silicon substrate is maintained below 200 ℃, so as to form a cold wall effect.

[0027] In a preferred embodiment, the hydrogen-rich silicon ink comprises a first polarity ink and a second polarity ink. The first polarity ink comprises a boron source precursor, and the second polarity ink comprises a phosphorus source precursor. Alternatively, the first polarity ink and the second polarity ink are both intrinsic silicon ink, and a doping source is introduced above the tunneling oxide layer by a plasma injection method.

[0028] In a preferred embodiment: the boron source precursor in the first polarity ink is decaborane or boron-doped silicon nanocrystals; The phosphorus source precursor in the second polarity ink is red phosphorus nanoparticles or phosphorus-doped silicon nanocrystals.

[0029] In a preferred embodiment: the viscosity of the silicon ink is 5-50 cP, and the surface tension is 25-40 mN / m; The contact angle of the silicon ink on the surface of the tunneling oxide layer is controlled to be between 10° and 45°.

[0030] In a preferred embodiment: after step S2 and before step S3, further comprising: After printing, the ink is subjected to low-temperature drying treatment, the drying temperature is 150-300°C, and the time is 1-5 minutes, which is used to remove the organic solvent in the ink while retaining the hydrogen-rich carrier from thermal decomposition.

[0031] In a preferred embodiment: the thickness of the tunneling oxide layer is 1.0-2.0 nm, and the material is silicon dioxide, aluminum oxide, or silicon oxynitride.

[0032] A TBC battery prepared using a silicon ink, the polycrystalline silicon layer on the back of the TBC battery has a columnar crystal microstructure formed by laser rapid melting, and the interface state density (Dit) of the polycrystalline silicon / tunneling oxide layer interface is less than 1×10^11 eV^-1 cm^-2, indicating that it has not undergone a high-temperature furnace annealing process that would cause hydrogen desorption.

[0033] It should be noted that the parameter measurement method mentioned in the embodiments of the present application is as follows: Open-circuit voltage (i-Voc) and minority carrier lifetime: measured by Sinton WCT-120 minority carrier lifetime tester under the condition of an injection concentration of 1×10^15 cm^-3.

[0034] Interface state density (Dit): calculated by CV (capacitance-voltage) characteristic tester combined with high-frequency and low-frequency capacitance curves.

[0035] Contact resistivity: measured by TLM (transmission line model) method through four-probe tester.

[0036] Hydrogen-rich carrier content (5%-30%): when the mass ratio of hydrogen-rich carrier (such as CPS) is less than 5%, the hydrogen partial pressure generated by decomposition is insufficient to overcome the resistance to diffusion to the substrate, resulting in insignificant passivation repair effect; When the mass ratio is higher than 30%, too many bubbles are generated during sintering, which easily destroys the continuity of the ink layer, resulting in a sharp increase in contact resistivity. Therefore, 5%-30% is a balanced window that takes into account the electrical performance and passivation performance.

[0037] Pulse width (10ns–500ns): This range is determined based on the matching relationship between the "thermal diffusion length" and the "ink layer thickness". A pulse width that is too short (<10ns) is prone to surface ablation; a pulse width that is too long (>500ns) will cause heat to be conducted deep into the substrate, lose the cold wall effect, and give hydrogen enough time to escape laterally.

[0038] Laser wavelength selection (532nm / 355nm / 1064nm): 532nm / 355nm: Suitable for conventional nano-silicon inks (thickness <1μm), with high absorption coefficient and good surface heating effect.

[0039] 1064nm: Suitable for thicker ink layers (>1μm) or modified inks with added infrared absorbers. It utilizes its deeper penetration depth to achieve bulk heating, preventing surface overheating while the bottom remains unmelted.

[0040] Example 1: This example provides a method for preparing TBC batteries using hydrogen-rich silicon ink. The specific steps are as follows: S1: Substrate pretreatment and tunneling layer preparation N-type single-crystal silicon wafers (M10 specification) with resistivity of 1–3 Ω·cm were selected. The damaged layer was removed using a 2% NaOH solution, followed by RCA standard cleaning process to remove surface impurities. In a tube furnace, dry oxygen was introduced at 600°C to thermally oxidize and grow an ultrathin SiO2 tunnel oxide layer with a thickness of 1.5 nm.

[0041] S2: Preparation of P-type hydrogen-rich silicon ink Preparation of silicon nanocrystals: High-purity silicon nanocrystals with an average particle size of 20 nm were prepared by plasma chemical vapor deposition (PECVD) of silane (SiH4).

[0042] Synthesis of hydrogen-rich support: Liquid cyclopentasilane (CPS) was synthesized from diphenyldichlorosilane as a raw material under sodium condensation reaction, and used as a hydrogen-rich support and solvent.

[0043] Doping and dispersion: 75 parts by mass of silicon nanocrystals, 20 parts by mass of cyclopentasilane (CPS), and 5 parts by mass of decaborane (as a P-type dopant) were mixed. The mixture was then dispersed in an argon-filled glove box using an ultrasonic disperser for 2 hours to obtain a P-type hydrogen-rich silicon ink with a viscosity of 12 cP and a surface tension of 28 mN / m.

[0044] S3: Graphical Printing The prepared ink was filled into a piezoelectric inkjet print head (e.g. Dimatix DMP-2800), and a finger pattern was printed on the surface of the tunneling oxide layer prepared in step S1. The printing environment was controlled at 25°C and a relative humidity of less than 30%. The ink drop spacing was controlled so that the printed line width was 100 μm and the thickness was 500 nm.

[0045] S4: low-temperature drying The printed silicon wafer was placed on a hot plate and dried at 200°C for 3 minutes to remove the volatile components in the ink and preliminarily fix the pattern, but at this time the CPS had not yet decomposed and the hydrogen-rich property was retained.

[0046] S5: laser in-situ co-sintering A nanosecond pulsed green laser with a wavelength of 532 nm was used to scan the printed area.

[0047] Laser parameters: pulse width 20 ns, repetition frequency 100 kHz, single pulse energy density 0.8 J / cm2, and spot overlap rate 50%.

[0048] The laser beam scanned the ink layer, and the silicon nanocrystals and CPS absorbed the photon energy, rapidly heating to above 1414°C in 10-20 ns to form a molten silicon cover layer. The liquid silicon layer filled the pores by capillary action and simultaneously sealed the surface. In the molten state, the CPS rapidly decomposed to generate a large number of active hydrogen atoms and silicon atoms. Due to the "capping effect" of the liquid surface layer, the hydrogen atoms could not escape upwards and instead diffused downwards, penetrating the 1.5 nm tunneling oxide layer and saturating the dangling bonds at the Si / SiO2 interface. With the end of the laser pulse, the melt rapidly cooled and recrystallized in a microsecond time to form a heavily doped (B-doped) polysilicon layer, completing the preparation of the P+ region.

[0049] Example 2: The difference between this example and Example 1 is that an N-type doped ink and an ultraviolet laser were used, as follows: S2: preparation of N-type hydrogen-rich silicon ink An N-type silicon ink was prepared by mixing and grinding 80 parts of silicon quantum dots (as a hydrogen-rich component and silicon source) with Si-H3 bonds on the surface, 15 parts of n-dodecane (auxiliary solvent), and 5 parts of red phosphorus nanoparticles (N-type dopant).

[0050] S5: laser in-situ co-sintering A picosecond pulsed ultraviolet laser with a wavelength of 355 nm was used.

[0051] Laser parameters: pulse width 10 ps, energy density 0.6 J / cm2. Ultraviolet light has a higher absorption coefficient for amorphous / nano-silicon, enabling shallower layer heating and further reducing the thermal impact on the substrate.

[0052] Example 3: This example illustrates the application scenarios of a 1064nm wavelength laser.

[0053] When fabricating a thicker back electrode (e.g., thickness > 1.5 μm to further reduce resistance), the penetration depth of the 532 nm laser is limited, which may lead to surface vaporization while the bottom remains unmelted.

[0054] At this point, a 1064nm infrared nanosecond laser (pulse width 100ns) is selected. Its weak absorption coefficient is used to achieve volume heating. Combined with a small amount of carbon black or infrared absorbing dye added to the ink, uniform melting and hydrogenation of the thick film can be achieved.

[0055] Comparative Example 1: This comparative example uses the existing slurry + furnace annealing process.

[0056] Differentiated steps: Printing is performed using the same substrate and ink as in Example 1. In step S5, instead of using a laser, the dried silicon wafer is placed in a quartz tube furnace and annealed at 900°C for 30 minutes under nitrogen protection to achieve silicon ink crystallization and dopant activation.

[0057] Comparative Example 2: Ordinary silicon ink without hydrogen-rich carrier + laser Distinguishing steps: In step S2, instead of using cyclopentasilane (CPS) or other hydrogen-rich carriers, ordinary terpineol is used as the solvent, while the other components (silicon nanocrystals, boron source) remain unchanged.

[0058] Drying process: In step S4, terpineol almost completely evaporates at 200°C.

[0059] Sintering process: Laser sintering was performed with the exact same parameters as in Example 1. At this time, there was no additional hydrogen source release mechanism in the ink layer.

[0060] The performance of the above battery samples was tested, and the results are shown in the table below:

[0061] Compared with Comparative Example 1: The i-Voc of Example 1 is 36 mV higher than that of Comparative Example 1. Even with the same ink composition, prolonged high-temperature annealing at 900°C can lead to severe interfacial hydrogen loss, while laser in-situ sintering technology effectively avoids this thermal damage.

[0062] Compared with Comparative Example 2, the i-Voc of Example 1 was 23 mV higher than that of Comparative Example 2. This indicates that laser alone (cold wall effect) is insufficient; it must be combined with a hydrogen-rich carrier (such as CPS) to release hydrogen atoms at the moment of sintering in order to achieve active repair of the tunneling oxide layer. In Comparative Example 2, after the terpineol evaporated, the ink became "dry-burned" due to a lack of hydrogen source replenishment.

[0063] It has to be noted that, in the present document, the terms "first", "second", etc. merely serve to identify different entities or actions from each other in a relative way and do not necessarily require or imply any actual relationship or order between these entities or actions. Also, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0064] The foregoing is merely illustrative of the principles of the application, and various modifications can be made by those skilled in the art without departing from the scope and spirit of the application. The scope of the application is thus indicated by the appended claims, and all changes which come within the meaning and range of equivalents are intended to be embraced therein.

[0065] While embodiments of the application have been shown and described, it is to be understood that various modifications can be made by those skilled in the art without departing from the spirit and scope of the present application, which is defined by the following claims.

Claims

1. A method of fabricating a TBC cell using a silicon ink, characterized by, The method comprises the following steps: S1: providing a silicon substrate, and preparing a tunneling oxide layer on the back surface of the silicon substrate; S2: printing a preset first finger cross pattern and a second finger cross pattern on the tunneling oxide layer by using hydrogen-rich silicon ink; the hydrogen-rich silicon ink comprises silicon nanocrystals and a hydrogen-rich carrier; S3: performing in-situ collaborative sintering on the printed hydrogen-rich silicon ink by using a pulse energy source; wherein the pulse width of the pulse energy source is controlled to be between 10 ns and 500 ns, so as to match the heat diffusion time of the silicon ink, so that a liquid phase covering layer is formed by melting the hydrogen-rich silicon ink at the moment of absorbing the pulse energy, hydrogen species is blocked from escaping outward, and the hydrogen species generated by the decomposition of the hydrogen-rich carrier is diffused to the interface of the tunneling oxide layer while forming a polycrystalline silicon conductive layer, so as to realize in-situ hydrogenation repair of the interface.

2. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: The pulse energy source is a nanosecond pulse laser, and the wavelength is selected from one of 532 nm, 355 nm or 1064 nm; The single pulse energy density is controlled to be between 0.2 and 1.5 J / cm².

3. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: The hydrogen-rich carrier comprises at least one of polysilane derivatives, cyclopentasilane (CPS) or silicon quantum dots with Si-Hx bonds (x=1-3) on the surface; The mass percentage of the hydrogen-rich carrier in the hydrogen-rich silicon ink is between 5% and 30%.

4. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: In step S3, the in-situ collaborative sintering process satisfies the following thermodynamic conditions: The heating rate of the silicon ink layer is greater than 10^6 ℃ / s, and the overall temperature of the silicon substrate is maintained below 200 ℃ to form a cold wall effect.

5. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: The hydrogen-rich silicon ink comprises first polarity ink and second polarity ink; The first polarity ink comprises a boron source precursor, and the second polarity ink comprises a phosphorus source precursor; Alternatively, the first polarity ink and the second polarity ink are both intrinsic silicon ink, and a doping source is introduced above the tunneling oxide layer by means of plasma injection.

6. The method of claim 5, wherein the method further comprises: The boron source precursor in the first polarity ink is decaborane or boron-doped silicon nanocrystals; The phosphorus source precursor in the second polarity ink is red phosphorus nanoparticles or phosphorus-doped silicon nanocrystals.

7. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: The viscosity of the silicon ink is between 5 and 50 cP, and the surface tension is between 25 and 40 mN / m; The contact angle of the silicon ink on the surface of the tunneling oxide layer is controlled to be between 10° and 45°.

8. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: After step S2 and before step S3, the following steps are further included: The printed ink is subjected to low-temperature drying treatment, the drying temperature is between 150 ℃ and 300 ℃, and the time is between 1 and 5 minutes, so as to remove organic solvents in the ink while keeping the hydrogen-rich carrier from thermal decomposition.

9. The method of claim 1, wherein the method of fabricating a TBC battery using a silicon ink is characterized by: The thickness of the tunneling oxide layer is between 1.0 nm and 2.0 nm, and the material is silicon dioxide, aluminum oxide or silicon oxynitride.

10. A TBC battery prepared by the method according to any one of claims 1-9. The polysilicon layer of the TBC battery backside has a laser rapid melt formed columnar crystal microstructure, and the interface state density (Dit) of the polysilicon / tunneling oxide layer interface is less than 1*10^11 eV^-1 cm^-2, indicating that it has not undergone a high-temperature furnace annealing process that will cause hydrogen desorption.

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