Patent ID: 12199202

REFERENCE NUMERALS

00: N-type doped silicon substrate,01: back surface,02: light receiving surface,10: sacrificial layer,11: tunneling oxide layer,12: N-type doped silicon crystal layer,13: dielectric insulation film,14: hole,21: intrinsic silicon layer,22: P-type doped silicon layer,23: opening,30: transparent conductive film,31: insulation groove,41: passivation film layer,42: doped film layer,43: anti-reflective film layer,51: fine grid line,52: main grid line.

DETAILED DESCRIPTION OF EMBODIMENTS

Endpoints and any value of ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to encompass values close to these ranges or values. For numerical ranges, endpoint values of the ranges can be combined with each other, endpoint values of the ranges and individual point values can be combined with each other, and individual point values can be combined with each other, so as to obtain one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.

Traditionally, in a back contact cell, etching is performed on a back surface using a mask to form a P-type electrode and an N-type electrode, and finally, an interdigitated electrode structure is formed. Unlike IBC or TBC characterized by high temperature diffusion, HBC characterized by a heterojunction passivation layer is sensitive to surface contact and mechanical damage, and especially, a first semiconductor layer which is first fabricated undergoes multiple high temperature heat treatments including a laser process, and chemical cleaning and etching steps. In the present disclosure, a TOPCON passivation film layer with a high-temperature fabricating process replaces the conventional heterojunction passivation film layer to serve as the first semiconductor layer, thus expanding a process window, and improving yield and a final conversion efficiency.

Specifically, in a first aspect, the present disclosure provides a hybrid passivation back contact cell, including: an N-type doped silicon substrate having a light receiving surface and a back surface, and a first semiconductor layer and a second semiconductor layer which are arranged on the back surface, wherein the second semiconductor layer includes an intrinsic silicon layer and a P-type doped silicon layer sequentially arranged in an outward direction perpendicular to the back surface, and the first semiconductor layer includes a tunneling oxide layer and an N-type doped silicon crystal layer sequentially arranged in the outward direction perpendicular to the back surface.

It may be understood that a junction between the second semiconductor layer and the N-type doped silicon substrate is a heterojunction.

FIGS.1a,1b,1cand1dshow relevant theoretically predicted photoelectric conversion performances of a conventional heterojunction back contact cell and a hybrid passivation back contact cell according to the present disclosure. As can be seen from the drawings, both a filling factor FF and a photoelectric conversion efficiency of the hybrid passivation back contact cell are improved, and the filling factor is significantly improved.FIGS.1a,1b,1c, and1dshow theoretical simulation values, the improvement of the filling factor FF is an improvement of conductivity of the first semiconductor layer due to introduction of a TOPCON technology. In comparison of actual experimental electrical properties, the FF improvement is more significant due to a laser opening eliminating a possibility of power leakage by pinhole.

In some preferred embodiments, the intrinsic silicon layer and the tunneling oxide layer have a thickness ratio of 1.2-11:1, preferably 1.5-5:1. In the preferred solution of the present disclosure, compared with the intrinsic silicon layer, the tunneling oxide layer has the appropriate thickness, which is more beneficial to an improvement of the electrical conversion efficiency of the back contact cell; presumably, the reason for this is that the tunneling oxide layer with a relatively suitable thickness provides fewer interface defects, an impurity energy level is annihilated in high temperature anneal, and a conduction mechanism thereof is quantum tunneling or accidentally occurring pinhole defects. In a traditional heterojunction cell structure, a layer of hydrogenated amorphous silicon provides main passivation, and also has certain conductivity, and electrons or holes are transited through band gap impurity energy levels in the layer of amorphous silicon.

In some more preferred embodiments, the tunneling oxide layer, the N-type doped silicon crystal layer, the intrinsic silicon layer, and the P-type doped silicon layer have a thickness ratio of 1: 11-300:1.2-11:3-50, preferably 1: 20-100:1.5-5:4-20. The preferred solution of the present disclosure is more beneficial to an improvement of the FF of the back contact cell, and presumably, the reason for this may be that, due to introduction of the TOPCON first semiconductor layer of the present disclosure, carriers may be transversely conducted (due to a hundreds-of-time conductivity improvement) and then vertically collected, a design of an opening ratio has a greater degree of freedom, and a migration rate of an introduced high temperature polycrystal may reach 200-300; the high-temperature polycrystal in the present disclosure can arbitrarily increase a thickness of a film layer, and the conductivity and FF of the whole back contact cell are obviously improved. An amorphous carrier migration rate of the traditional heterojunction is low (taking electrons as an example, the migration rate is approximately 0.5-1), and the migration rate of microcrystalline silicon is slightly improved and is about 10; and the FF of the cell is likely to be reduced when a thickness of a traditional amorphous silicon thin film is increased.

In some preferred embodiments, a ratio of a surface doping index of the N-type doped silicon crystal layer to a surface doping index of the P-type doped silicon layer is 0.07-40:1, preferably 0.07-20:1, more preferably 0.07-5:1, still more preferably 0.07-1:1; the surface doping index is a ratio of an effective doping concentration of the corresponding doped layer to the thickness of the doped layer. The preferred solution of the present disclosure is more beneficial to an improvement of the overall electrical conversion efficiency of the back contact cell, and presumably, the reason for this may be that the N-type doped silicon crystal layer with a relatively appropriate surface doping index introduced in the first semiconductor layer in the present disclosure enables the high temperature polycrystal to ensure that limited doping and nominal doping are almost completely consistent; that is, all elemental phosphorus is activated. In the traditional amorphous silicon film layer, especially a B-doped P-type amorphous thin film, activated B in the film layer is little and is only 5-7% of activated B in nominal doping, and the rest is reflected as defects of the film layer.

On the basis of satisfying the thickness ratio and/or the surface doping index ratio in the first semiconductor layer and the second semiconductor layer in the present disclosure, those skilled in the art can select a thickness and an effective doping concentration of each layer according to actual requirements.

Exemplarily, in some embodiments, the tunneling oxide layer has a thickness of 10-22 angstroms, preferably 15-20 angstroms. The preferred solution can guarantee a balance between optimal passivation and conductivity, and meanwhile, the process is simple and controllable, and the reason is that a thickness saturation value of a natural intrinsic silicon oxide layer (native oxide) is 15-20 angstroms, and the thickness will not be uncontrollably increased.

Exemplarily, in some embodiments, the N-type doped silicon crystal layer has a thickness of 30-250 nm and an effective doping concentration greater than 5e18 cm−3. More preferably, the N-type doped silicon crystal layer has a thickness of 150-200 nm and an effective doping concentration of 1e19-8e19 cm−3. Under the preferred solution of the present disclosure, the transverse conductivity of a first semiconductor is greatly enhanced, natural or design fluctuation caused by an insufficient carrier mean free path and low conductivity of a transparent conductive film can be eliminated, and maximization of the FF is ensured. A sheet resistance of the N-type doped silicon crystal layer can be selected by those skilled in the art according to requirements, and for example, the sheet resistance can be 30-200Ω/□, preferably 40-70Ω/□.

Exemplarily, in some embodiments, the intrinsic silicon layer has a thickness of 3-10 nm; the P-type doped silicon layer has a thickness of 7-45 nm and an effective doping concentration of 2e18-1e20 cm−3. The preferred solution of the present disclosure can guarantee the vertical conductivity of a device, and meanwhile, a short circuit of the device will not be caused when a weaker P-type second semiconductor and the extremely strong conductivity are lapped.

The thickness of the N-type doped silicon substrate in the present disclosure can be selected by those skilled in the art according to requirements, and the thickness is preferably 110-150 microns. Under the preferred solution of the present disclosure, a highest power generation efficiency can be achieved, and meanwhile, a silicon material is used most economically and feasibly.

In the present disclosure, the intrinsic silicon layer in the second semiconductor layer is a hydrogenated intrinsic amorphous silicon thin film (traditional heterojunction film layer).

In some embodiments, the P-type doped silicon layer is made of P-type doped amorphous silicon. The solution belongs to the traditional heterojunction technology and has an advantage of a low cost.

In some embodiments, the P-type doped silicon layer is made of P-type doped microcrystalline silicon, which is costly, does not provide significant benefits in back contact, and is difficult to destroy by etching with HF acid.

In some embodiments, the P-type doped silicon layer includes an incubation layer, a P-type oxygen-containing microcrystalline layer and a P-type oxygen-free microcrystalline layer, and the P-type oxygen-containing microcrystalline layer and the P-type oxygen-free microcrystalline layer have a thickness ratio of 1:0.25-7. Under the preferred solution, the P-type oxygen-containing microcrystalline layer and the P-type oxygen-free microcrystalline layer with a proper thickness ratio are more beneficial to an improvement of the open circuit voltage Voc, the filling factor FF and the conversion efficiency Eta of the cell; presumably, the reason for this is that the oxygen-containing microcrystalline layer has low conductivity, and the suitable film thickness is equivalent to the Debye length, such that an improvement of the electrical property can be sufficiently realized, and gradual transition is required for the oxygen-free microcrystalline layer to perform a chemical protection function on the oxygen-containing microcrystalline layer.

Those skilled in the art can select the thickness of the incubation layer according to practical requirements, which does not require creative efforts; exemplarily, the thickness ratio of the P-type oxygen-containing microcrystalline layer and the incubation layer is 1:0.1-20.

In some embodiments, the N-type doped silicon crystal layer is made of N-type doped polycrystalline silicon. The N-type doped polycrystalline silicon can be directly formed polycrystalline silicon, or is formed by microcrystalline silicon and an amorphous silicon film layer through high temperature modification, and the high temperature modification process at least includes one or more process steps at a temperature more than 600° C.

The tunneling oxide layer in the present disclosure is preferably made of tunneling silicon oxide.

In some preferred embodiments, the N-type doped silicon substrate is made of Czochralski single crystals or ingot single crystals.

In some preferred embodiments, the light receiving surface of the N-type doped silicon substrate is a textured surface, and the back surface is a polished surface. This preferred solution can satisfy requirements of back laser processing consistency, such that a laser processing surface has a polished structure, instead of a traditional textured light trapping structure.

The hybrid passivation back contact cell according to the present disclosure may further include other conventional components in the art, such as an insulation layer partially provided between the first semiconductor layer and the second semiconductor layer, a conductive layer provided above the second semiconductor layer, a metalized pattern formed on the back surface, such as fine grid lines, main grid lines, and welding pads, a passivation layer provided on the light receiving surface, or the like.

In some preferred embodiments, the hybrid passivation back contact cell further includes:a dielectric insulation film, provided on a surface of the first semiconductor layer, wherein the first semiconductor layer and the dielectric insulation film provided thereon are arranged at intervals along a direction parallel to the back surface as a whole, the second semiconductor layer is provided on a surface of the dielectric insulation film and covers a surface of the intervals, and an opening for exposing the first semiconductor layer is formed in the second semiconductor layer between adjacent intervals; anda transparent conductive film, provided on a surface of the second semiconductor layer and a surface of the first semiconductor layer exposed at the opening, wherein an insulation groove for exposing the second semiconductor layer is formed on the transparent conductive film between the adjacent interval and opening. Under this preferred solution, the arrangement of the dielectric insulation film between the first semiconductor layer and the second semiconductor layer can prevent electric leakage of the device, and the opening and the insulation groove required by the back contact cell are arranged, which can avoid the electric short circuit between the first semiconductor layer and the second semiconductor layer, avoid damage caused by mechanical contact, and meanwhile can avoid the pinhole defect of a dielectric insulation film, and improve the power generation conversion efficiency of the cell. The integral arrangement of the openings and the insulation grooves may be set by those skilled in the art according to requirements, for example, by adjusting the overlapping degree of light spots or the size of the light spots.

It may be understood that, in the above preferred embodiment, the back surface is formed by a region including direct contact between the second semiconductor and the N-type doped silicon substrate, a region including direct contact between the first semiconductor and the N-type doped silicon substrate, and a transition region therebetween; and in an outward direction perpendicular to the N-type doped silicon substrate, the transition region includes the first semiconductor layer, the dielectric insulation film and the second semiconductor layer which are sequentially distributed. The transparent conductive film on the back surface is also included in each region, and the transparent conductive film is not included in the insulation groove.

In the present disclosure, it may be understood that the hybrid passivation back contact cell further includes two electrodes formed over the first semiconductor layer and the second semiconductor layer. In some more preferred embodiments, the hybrid passivation back contact cell further includes: a first grid line provided over the second semiconductor layer at a surface at the interval to form a first metal electrode; and a second grid line provided over the first semiconductor layer at the opening to form a second metal electrode.

In some more preferred embodiments, the hybrid passivation back contact cell further includes: a passivation film layer, a doped film layer and an anti-reflective film layer which are arranged on a surface of the light receiving surface and sequentially arranged along an outward direction perpendicular to the light receiving surface.

In the above preferred embodiment, it may be understood that the second semiconductor layer substantially entirely covers the dielectric insulation film with the intervals on the back surface (a covering region includes a bottom and a side surface of the interval), and the openings are provided only between the adjacent intervals.

Composition, thicknesses, or the like, of the dielectric insulation film and the transparent conductive film, and the thicknesses of the passivation film layer, the doped film layer and the anti-reflective film layer can be selected by those skilled in the art according to actual requirements, which does not require creative efforts, and is not repeated herein.

In some specific embodiments, the passivation film layer is made of intrinsic amorphous silicon; the doped film layer is an N-type amorphous film layer or an N-type oxygen-containing microcrystalline film layer, preferably an N-type oxygen-containing microcrystalline film layer; the anti-reflective film layer is made of at least one of silicon nitride, silicon dioxide, silicon oxide and silicon oxynitride. This embodiment is more beneficial to an improvement of transmittance of sunlight.

Area proportions of the formed insulation grooves, the formed openings and the formed holes on the corresponding film layers can be selected by those skilled in the art according to actual requirements. The proportions or ratios of the insulation groove, the opening and the hole are measured by area in the present disclosure.

In a second aspect, the present disclosure provides a fabrication method of the hybrid passivation back contact cell of the first aspect, including:S101: providing an N-type doped silicon substrate;S102: sequentially plating a first semiconductor layer and a dielectric insulation film on a back surface of the N-type doped silicon substrate, wherein the first semiconductor layer includes a tunneling oxide layer and an N-type doped silicon crystal layer;S103: etching holes at intervals on the back surface of the N-type doped silicon substrate obtained in S102, so as to remove the first semiconductor layer on the back surface and the dielectric insulation film on the first semiconductor layer at intervals, and then cleaning to obtain the first semiconductor layer and the dielectric insulation film which are arranged at intervals;S104: forming a second semiconductor layer in a full cover mode on the back surface of the N-type doped silicon substrate obtained in S103, wherein the second semiconductor layer includes an intrinsic silicon layer and a P-type doped silicon layer; a second conductive region is formed at the holes and the second semiconductor layer provided thereon; it may be understood that the second semiconductor layer at the opening is in direct contact with the N-type doped silicon substrate;S105: etching an opening on the back surface of the N-type doped silicon substrate obtained in S104, so as to expose the first semiconductor layer on a part of the second semiconductor layer between adjacent intervals, and then cleaning to form first conductive regions, wherein the first conductive regions and the second conductive regions are alternately arranged;S106: depositing a transparent conductive film on the back surface of the N-type doped silicon substrate obtained in S105; etching an insulation groove on the transparent conductive film between the opening and the hole; forming a first electrode on a surface of the hole and forming a second electrode on a surface of the opening; andS107: sequentially forming a passivation film layer, a doped film layer and an anti-reflective film layer on a light receiving surface of the N-type doped silicon substrate.

In the present disclosure, the second semiconductor layer can be formed by adopting a PECVD or Hot-wire method, the first semiconductor layer can be formed by adopting a PECVD or Hot-wire method, and the passivation film layer, the doped film layer and the anti-reflective film layer can be formed by adopting a PECVD or Hot-wire method.

S101further includes: chemically cleaning the N-type doped silicon substrate, wherein alkali liquor can be adopted for the chemical cleaning, for example.

In some specific embodiments, the process of S101includes: cutting the Czochralski single crystal or the ingot single crystal by a diamond wire or mortar to form a silicon wafer substrate with a thickness of 100-250 microns, optionally, pre-cleaning the silicon wafer by a tank solution to remove organic pollution and large particles on a surface, then performing damage removal and texturing by alkali liquor to form a roughened light trapping structure, performing RCA cleaning (or a solution formula equivalent to the RCA cleaning), and finally removing a surface oxidation layer by an HF solution, and performing deionized water cleaning and surface drying dehydration processes. Although a single crystal proportion of the ingot single crystal is higher, a polycrystalline grain boundary and a lattice defect with a larger proportion still exist in the cell; if the used substrate is an ingot monocrystalline silicon wafer, before the heterojunction production process is introduced, pretreatment at different temperature sections is required to achieve effects of impurity absorption and dangling bond saturation, which belong to mature existing technologies in the art and are not repeated herein.

In some specific embodiments, S101further includes: allowing the N-type doped silicon substrate to have a structure with one textured surface and one polished surface. More preferably, the process includes: using a silicon nitride or silicon oxide film layer as a protective sacrificial layer on the light receiving surface, and keeping the textured light trapping structure of the light receiving surface of the substrate to realize back polishing, such that the light receiving surface of the N-type doped silicon substrate is the textured surface, and the back surface is the polished surface.

In some specific embodiments, the process of plating the first semiconductor layer in S102may include: forming a tunneling oxide layer on the back surface of the N-type doped silicon substrate by adopting wet oxidation, dry oxidation or plasma oxidation; and fabricating a silicon film layer on a surface of the tunneling oxide layer by using a low-pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD) or physical vapor deposition (PVD) method, and doping phosphorus (phosphorus doping can be realized in an in-situ doping mode or a high temperature phosphorus diffusion mode) on the polycrystalline film layer to form an N-type doped silicon crystal layer, so as to obtain the first semiconductor layer.

The tunneling oxide layer may be specifically formed by wet oxidation, including an ozone oxidation method, a nitric acid oxidation method, a hydrogen peroxide oxidation method, or the like. For example, oxygen, ozone, or hydrogen peroxide is introduced into a heated solution; and for example, the silicon wafer is soaked in a heated nitric acid solution. The tunneling oxide layer may also be formed by dry oxidation, including a thermal oxidation method, a PECVD in-situ oxidation method, or the like. For example, the silicon wafer is placed in a furnace tube type apparatus and heated to 500-700° C., oxygen or water vapor is introduced into the apparatus or water vapor adsorbed on a tube wall or a surface of the silicon wafer is utilized for oxidation, the thermal oxidation method is preferably adopted, and condition is as follows: a thermal oxidation temperature is 550-650° C., a gas source is oxygen, and an oxidation time is 10-30 min. The tunneling oxide layer may also be formed by plasma assisted oxidation.

In the formation of the N-type doped silicon crystal layer, the in-situ doping process may include, for example, introducing a phosphorus source (such as a phosphine gas) in a gas atmosphere for growing polycrystalline silicon, amorphous silicon or microcrystalline silicon; the high temperature phosphorus diffusion process may specifically include, for example, first growing a polycrystalline silicon, amorphous silicon, or microcrystalline silicon film layer (for example, the film layer may be fabricated by PECVD or obtained by PVD sputtering), performing high temperature annealing, and then forming effective diffusion of phosphorus in a diffusion furnace containing a phosphorus source (for example, a layer of PSG glass is first deposited on the surface); preferably, after a polycrystalline silicon, amorphous silicon or microcrystalline silicon film layer is deposited by LPCVD, diffusion is performed, a diffusion temperature is 830-880° C., a diffusion source is phosphorus oxychloride or oxygen, and a diffusion time is 80-180 min. All the processes are mature existing technologies in the art and will not be repeated herein.

The dielectric insulation film may be plated in S102using a PECVD method.

In some specific embodiments, in S103, hole etching is performed by using a conventional photoetching mode, and the process may, for example, include: exposing and developing photoresist to form a protective pattern, then performing wet chemical etching on an unprotected region by the photoresist to form an opening region, and finally removing the photoresist.

In some other more preferred embodiments, the etching in the present disclosure is performed by laser ablation in conjunction with optional chemical etching (preferably wet chemical etching, such as chemical etching using a hydrofluoric acid-containing solution), the first semiconductor layer, the second semiconductor layer and the transparent conductive film are removed by laser ablation, and the dielectric insulation film is removed by laser ablation or chemical etching, without causing a perforation phenomenon to the dielectric insulation film.

In some specific preferred embodiments, in S103, the process of etching the hole includes: performing first laser ablation on the first semiconductor layer and the dielectric insulation film on the first semiconductor layer by using laser beams, and performing partial hole formation in conjunction with wet chemical etching to remove the first semiconductor layer on the back surface and the dielectric insulation film on the first semiconductor layer at intervals for exposing the N-type doped silicon substrate.

More preferably, in S103, the removal of the first semiconductor layer in the etching of the hole is performed in a first laser ablation mode in which continuously scanning light spots are partially overlapped, and a laser absorption amount D1of the to-be-removed first semiconductor layer is more than 70% of a total absorption amount of all film layers. In the preferred solution of the present disclosure, most laser energy can be absorbed by the to-be-removed first semiconductor layer, thus avoiding deep subfissure of the N-type doped silicon substrate; the reason is that a direct absorption depth of the film layer is related to a laser wavelength, a direct absorption depth of polycrystalline silicon caused by 532 nm laser is 100-200 nm, and a direct absorption depth of polycrystalline silicon irradiated by 355 nm laser is 10-20 nm, such that by concentrating most laser on the to-be-removed first semiconductor layer, the laser acting on the substrate is reduced, and the deep subfissure of the substrate is avoided.

The “total absorption amount of all the film layers” in the present disclosure refers to the total absorption amount of all the film layers of the substrate, the back surface thereof and the light receiving surface thereof at the present moment.

Those skilled in the art can satisfy the above laser absorption amount and the above ratio by controlling the laser wavelength, pulse width, irradiation time, or the like. More preferably, condition for the first laser ablation is as follows: pulse laser is adopted, and a pulse width is less than 20 nanoseconds. More preferably, the used laser forms circular, elliptical or rectangular light spots on the back surface, which may be arranged in various partially overlapped ways, as shown inFIGS.5a,5b, and5c. More preferably, the used laser is spatially shaped as flat-top laser, which is spatially distributed on a processed surface in a shape of a square, circle or oval flat top, preferably a rectangular shape. The laser wavelength can be about 355 nm or 532 nm. A used laser device may be, for example, a laser device with a wavelength of about 355 nm obtained by tripling frequency of a YAG laser device, or a laser device with a wavelength of about 532 nm obtained by doubling frequency of a YAG laser device.

Those skilled in the art can select laser with different wavelengths, such as ultraviolet light or green light, to perform the first laser ablation according to the thickness of the first semiconductor layer, remove a part of the first semiconductor layer, and meanwhile avoid excessive damage to the N-type doped silicon substrate. An absorption depth of polycrystalline silicon or crystalline silicon by laser with a wavelength of about 355 nm is 10-20 nm, and an absorption depth of polycrystalline silicon or crystalline silicon by laser with a wavelength of about 532 nm is 100-200 nm. Preferably, an ultraviolet pulsed light source with a wavelength of 355 nm is adopted for the first laser ablation. An absorption main body of the first laser ablation in the present disclosure is the first semiconductor layer, and an additional optical sacrificial layer of CN114068731A is not required for absorption, such that the fabrication method is simple, and mass production and industrialization can be realized.

In S104, the second semiconductor layer is formed by PECVD full-area coverage. A PECVD apparatus power source can have a frequency of 13.56 MHz, 26 MHz or 40 MHz.

It can be understood in the present disclosure that, in S104, the dielectric insulation film on the back surface subjected to partial hole formation is covered with the second semiconductor layer in a full-area coating manner; then, in S105, the second semiconductor layer on an upper layer is removed by laser hole formation, and then, the dielectric insulation film is removed by chemical etching to expose the first semiconductor layer on a bottom layer.

The intrinsic silicon layer and the P-type doped silicon layer in the second semiconductor layer can be formed by those skilled in the art by using an existing method; process gas for forming the intrinsic silicon layer may include, for example, all or a combination of several of silane (SiH4), H2, CO2, and CH4; process gas for forming the P-type doped silicon layer may include, for example, all or a combination of several of SiH4, H2, CO2, B2H6 (diborane), or TMB (trimethylboron).

In some specific embodiments, in S105, opening etching may be performed by using a conventional photoetching mode, and the process may, for example, include: exposing and developing photoresist to form a protective pattern, then performing wet chemical etching on an unprotected region by the photoresist to form an opening region, and finally removing the photoresist.

In some other more preferred embodiments, in S105, the process of etching the opening includes: removing the second semiconductor layer of a partial region of the back surface by using laser beams, carrying out second laser ablation, and etching the dielectric insulation film below the partial region in a chemical etching manner to obtain the opening exposing the first semiconductor layer below the opening, so as to form the first conductive regions, the first conductive regions and the second conductive regions being alternately arranged.

More preferably, in S105, the removal of the second semiconductor layer in the etching of the opening is performed in a discontinuous-hole-formation or continuous-hole-formation second laser ablation mode. The latter is preferred.

In one specific embodiment, when the discontinuous-hole-formation mode is adopted, the formed light spots are not overlapped, and a laser absorption amount D2of the to-be-removed second semiconductor layer is more than 70%, preferably more than 80%, of the total absorption amount of all the film layers. In this solution of the present disclosure, the to-be-removed second semiconductor layer can absorb most laser energy, an opening section has a clear boundary, and meanwhile, the bottom film layer and the substrate are slightly damaged or are completely free of damage. Under this solution, chemical etching may be applied to remove the exposed dielectric insulation film; or the second laser ablation is repeatedly applied to the original opening position to remove the exposed dielectric insulation film, and in this case, the laser absorption amount of the N-type doped polycrystalline layer during the second laser ablation is more than 50% of the total absorption amount of all the film layers.

The thickness and refractive index of the dielectric insulation film may be further optimized by those skilled in the art to provide an effect of interference superposition at a vertical spatial position where the second semiconductor layer is located.

In a more preferred embodiment, when the continuous-hole-formation mode is adopted, the formed light spots are partially overlapped, the second semiconductor layer on a top is removed by first laser exposure ablation of the adjacent light spots, and at this point, a laser absorption amount D201required for removing the corresponding layer is more than 70% of the total absorption amount of all the film layers; and second laser exposure ablation caused by the overlap of part of the light spots removes the underlying dielectric insulation film and part of the top N-type doped silicon crystal layer at the bottom, and at this point, a laser absorption amount D202required for removing the corresponding layer is more than 50% of the total absorption amount of all the film layers. Under the preferred solution, in the second laser ablation mode of continuous hole formation, two times of laser exposure ablation can be carried out; since the film layer structure in the present disclosure is resistant to a high temperature, the underlying dielectric insulation film and part of the top N-type doped silicon crystal layer at the bottom can be removed through second laser exposure ablation without chemical etching.

Those skilled in the art can satisfy the above laser absorption amount and the above ratio by controlling the laser wavelength, pulse width, irradiation time, or the like. More preferably, condition for the second laser ablation is as follows: pulse laser is adopted, and a pulse width is less than 20 nanoseconds, preferably less than 100 picoseconds. The laser wavelength can be about 355 nm or 532 nm. More preferably, green laser having a pulse width less than 100 picoseconds is used. More preferably, the used laser forms circular, oval or rectangular light spots on the back surface (as shown inFIGS.6aand6b), which may be in a single column or multiple columns, so as to avoid a reduction of a power generation efficiency caused by laser damage. More preferably, the used laser is spatially shaped into rectangular, circular or elliptical flat-top laser, preferably rectangular laser; that is, spatial distribution of the laser on the processed surface has a shape of a rectangle, circle or elliptical flat top, so as to ensure that energy in the processed region tends to be uniform. A used laser device is preferably a laser device with a wavelength of 355 nm obtained by tripling frequency of a YAG laser device, or a laser device with a wavelength of 532 nm obtained by doubling frequency of a YAG laser device.

In the preferred solution of the present disclosure, the first semiconductor layer is partially removed by adopting the first laser ablation, the second semiconductor layer is partially removed by adopting the second laser ablation, the function of the first semiconductor layer below the second semiconductor layer is not damaged, the insulation groove is constructed by adopting the third laser ablation, but the second semiconductor layer below the insulation groove is not damaged, such that stability is good, and yield is high.

In the present disclosure, the cleaning in S103and S105includes chemical cleaning and smoothing for a silicon surface of the exposed region, thus providing a low-defect interface for subsequent effective fabrication of a film layer. These processes are conventional technologies in the art and will not be repeated herein.

In S106, the transparent conductive film may be deposited by PVD full-area coverage. A target material and a doping material of PVD can be selected by those skilled in the art according to requirements. For example, the target material used in PVD may be pure indium oxide, and then, hydrogen or water vapor is introduced into the process gas to form a hydrogen doped indium oxide thin film.

In some specific embodiments, in S106, the etching of the insulation groove may be performed by using a conventional photoetching mode, and the process may, for example, include: exposing and developing photoresist to form a protective pattern, then performing wet chemical etching on an unprotected region by the photoresist to form an opening region, and finally removing the photoresist.

In some other more preferred embodiments, in S106, the process of etching the insulation groove includes: performing the third laser ablation by using laser beams, and removing part of the transparent conductive film between the first conductive region and the second conductive region, so as to form the insulation groove between two adjacent conductive regions. The insulation groove is provided to physically insulate the N electrode of the first conductive region from the P electrode of the second conductive region.

More preferably, in S106, the insulation groove is etched in a third laser ablation mode in which the continuously scanning light spots are partially overlapped, and a laser absorption amount D3of the to-be-etched transparent conductive film and the second semiconductor layer overlapped therewith is more than 70%, preferably more than 85%, of the total absorption amount of all the film layers. In a preferred solution of the present disclosure, a position with great optical interference is located in the second semiconductor or the transparent conductive film in contact with the second semiconductor, and the transparent conductive film to be etched can absorb most laser energy, so as to protect integrity of the underlying dielectric insulation film and the first semiconductor layer from being damaged. It may be understood that, under this solution, the total absorption amount of all the film layers includes the total absorption amount of the film layers of the substrate, the first semiconductor layer and the second semiconductor layer on the substrate, and the light receiving surface below the substrate.

Those skilled in the art can satisfy the above laser absorption amount and the above ratio by controlling the laser wavelength, pulse width, irradiation time, or the like. Further preferably, condition for the third laser ablation is as follows: pulse laser is adopted, and a pulse width is less than 100 nanoseconds. The laser wavelength may be about 355 nm. More preferably, the used laser forms circular, elliptical or rectangular light spots on the back surface.

The laser ablation in the present disclosure can be performed using ultraviolet laser, purple laser or green laser.

It may be understood that in S103and S106in the present disclosure, the continuously scanning light spots are partially overlapped, which means that adjacent light spots are overlapped in the formed light spots.

In some embodiments, the process of forming the first electrode or the second electrode in S106includes: applying conductive silver paste on the back surface of the obtained N-type doped silicon substrate to form metalized patterns including the fine grid line, the main grid line perpendicular to the fine grid line and the welding pad, which is favorable for realization of effective electric contact. A method for applying the conductive silver paste can be a screen printing method or an ink-jet printing method.

The passivation film layer, the doped film layer and the anti-reflective film layer in S107can be deposited using a PECVD method. The process gas for the passivation film layer may include, for example, all or a combination of several of SiH4, H2, CO2, and CH4.

The present disclosure will be described below in further detail in conjunction with specific examples.

Example 1

A hybrid passivation back contact cell as shown inFIGS.2and3was fabricated by the following steps as shown inFIGS.4aand4b.(a) Chemically texturing and cleaning an N-type doped Czochralski monocrystalline silicon wafer substrate to form an N-type doped silicon substrate00with a structure with two textured surfaces.(b) Plating a protective sacrificial layer10on a light receiving surface02, and chemically etching a back surface01for polishing, so as to form an N-type doped silicon substrate00with a structure with the textured light receiving surface02and the polished back surface01.(c) Then fabricating a first semiconductor layer on the back surface01, and plating a dielectric insulation film13above the first semiconductor layer by using a PECVD method, wherein a process of fabricating the first semiconductor layer included: firstly, placing the N-type doped silicon substrate00in a furnace tube type apparatus, heating the N-type doped silicon substrate00to 600° C., introducing oxygen into the apparatus for oxidation for 10-30 min, and forming a tunneling oxide layer11on the back surface01; and then depositing polycrystalline silicon by LPCVD, and then adding a diffusion source for diffusion to form an N-type doped silicon crystal layer12, with a diffusion temperature being 850° C., a diffusion source being phosphorus oxychloride, and a diffusion time being 100 min.(d) Performing first laser ablation on the back surface01obtained in step (c), and removing part of the first semiconductor layer and the dielectric insulation film13on the first semiconductor layer at intervals in combination with a wet chemical etching mode, so as to expose the N-type doped silicon substrate, and form a hole14, wherein a laser absorption amount D1of the to-be-removed first semiconductor layer was more than 70% of a total absorption amount of all the film layers, wherein condition of the first laser ablation was as follows: ultraviolet pulsed laser having a wavelength of about 355 nm with partially overlapped continuously scanning light spots was adopted, and a pulse width was 15 nanoseconds. The used laser formed circular light spots on the back surface01, as shown inFIG.5. The used laser was spatially shaped into flat-top laser.(e) Then, after cleaning, fabricating a second semiconductor layer on the back surface01by a PECVD full-area covering method, that is, sequentially forming an intrinsic silicon layer21and a P-type doped silicon layer22, and sequentially fabricating a passivation film layer41(intrinsic amorphous silicon), a doped film layer42(N-type amorphous film layer) and an anti-reflective film layer43(silicon nitride) on the light receiving surface02by a PECVD method.(f) Performing second laser ablation on the back surface01obtained in step (e), wherein laser exposure ablation was performed twice to remove the second semiconductor layer, part of the dielectric insulation film13below the second semiconductor layer and part of the top N-type doped silicon crystal layer12at the bottom, and an opening23was formed without chemical etching. In the first laser exposure ablation, the laser absorption amount D201of the to-be-removed second semiconductor layer was more than 70% of the total absorption amount of all the film layers; in the second laser exposure ablation, the laser absorption amount D202of the to-be-removed underlying dielectric insulation film13and part of the top N-type doped silicon crystal layer at the bottom was more than 50% of the total absorption amount of all the film layers. Condition of the second laser ablation was as follows: continuous-hole-formation green pulsed laser with a wavelength of about 532 nm was adopted, and a pulse width was 20 picoseconds, thus avoiding a reduction of a power generation efficiency caused by laser damage. The light spots formed on the back surface by the used laser were rectangular, and the adjacent light spots were partially overlapped. The used laser was spatially shaped into rectangular flat-top laser to ensure that energy in a processed region tended to be consistent.(g) Fabricating a transparent conductive film30on the obtained back surface01in a full covering mode.(h) Performing third laser ablation on the transparent conductive film30on the back surface01to form an insulation groove35, wherein parts of the transparent conductive film30on both sides of the insulation groove35were electrically insulated from each other, wherein a mode that continuous scanning light spots were partially overlapped was adopted in the third laser ablation, and the laser absorption amount D3of the transparent conductive film to be etched was more than 85% of the total absorption amount of all the film layers. Condition of the third laser ablation was as follows: pulsed laser having a laser wavelength of 355 nm was adopted, and a pulse width was 10 nanoseconds. The used laser formed circular light spots on the back surface01.(i) By screen printing, forming a metalized pattern of a main grid line52electrode on a surface of the hole14, forming a metalized pattern of a fine grid line51electrode perpendicular to a main grid line52on a surface of the opening23, and forming a metalized pattern of a pad for welding, which was beneficial to realization of effective electric contact.

A thickness ratio of the tunneling oxide layer11, the N-type doped silicon crystal layer12(N-type doped polycrystalline silicon), the intrinsic silicon layer21(intrinsic amorphous silicon), and the P-type doped silicon layer22(P-type doped amorphous silicon) was 1:88:2.9:4. A ratio of a surface doping index of the N-type doped silicon crystal layer12to a surface doping index of the P-type doped silicon layer22was 0.3:1, wherein the surface doping index was a ratio of an effective doping concentration of the corresponding doped layer to the thickness of the doped layer.

The resulting hybrid passivation back contact cell was tested for a short circuit current Isc, an open circuit voltage Voc, a filling factor FF, a conversion efficiency Eta, and yield and a material cost of this bath were measured, with results shown in Table 1.

The back surface of the hybrid passivation back contact cell obtained in Example 1 was irradiated with laser having a wavelength of about 532 nm, and formed E2(square value of electric field intensity) distribution of the laser in the first semiconductor layer and the second semiconductor layer is shown inFIG.7. As can be seen fromFIG.7, optical absorption sensed by the first semiconductor layer is 4-5 times or more that of an underlying layer due to an interference effect and can be adjusted correspondingly in order with the thickness of the dielectric insulation film13, thus ensuring that the opening is effectively formed in the second semiconductor layer without a need for additional chemical smoothing correction.

A comparative diagram of minority carrier lifetime of the hybrid passivation back contact cell, a TOPCON passivation method and a traditional heterojunction passivation method is shown inFIG.8. As can be seen fromFIG.8, a surface passivation ability of the N-type passivation TOPCON is equal to or stronger than the heterojunction thin film passivation ability in terms of passivation ability.

Example 2

Referring to the method of Example 1, the difference was that a conventional fabrication method was used instead of laser ablation, which specifically included following steps.

step (d): during the removal of the first semiconductor, smearing a paste etching material by screen printing, carrying out a sintering reaction at a medium temperature (80-120° C.) after crystal solidification, removing the first semiconductor layer fabricated by an amorphous silicon film plating mode, removing the dielectric insulation film13on the first semiconductor layer by a chemical etching mode, and then repeating multi-process cleaning to remove high-residue etching paste.

Step (f): selectively removing the second semiconductor layer by an etching paste printing mode, and removing the dielectric insulation film13thereunder by means of chemical etching, wherein a set temperature of the sintering reaction was higher and was 200° C. due to the P-type doping in the second semiconductor layer. Due to the high temperature, other surfaces of the cell were also corroded by migrating corrosive gas, and multiple protective ink layers were required to be applied to a front surface and a back surface.

Step (h): forming an insulation groove position to be provided with an insulation groove in a flowing mode by printing protective ink, and chemically etching the transparent conductive film in a full-cell soaking mode to ensure that the N-type electrode and the P-type electrode were not short-circuited.

Corresponding tests were carried out, results of which are shown in Table 1.

Example 3

Referring to the method of Example 1, the difference was that the thickness ratio of the intrinsic silicon layer and the tunneling oxide layer was 6:1. Corresponding tests were carried out, results of which are shown in Table 1.

Example 4

Referring to the method of Example 1, the difference was that the ratio of the surface doping index of the N-type doped silicon crystal layer to the surface doping index of the P-type doped silicon layer was 3:1. Corresponding tests were carried out, results of which are shown in Table 1.

Example 5

Referring to the method of Example 1, the difference was that the doped film layer42was an N-type oxygen-containing microcrystalline film layer. Corresponding tests were carried out, results of which are shown in Table 1.

Example 6

Referring to the method of Example 1, the difference was that the P-type doped silicon layer22included an incubation layer, a P-type oxygen-containing microcrystalline layer and a P-type oxygen-free microcrystalline layer, and the P-type oxygen-containing microcrystalline layer, the P-type oxygen-free microcrystalline layer and the incubation layer had a thickness ratio of 1:2.5:0.5. Corresponding tests were carried out, results of which are shown in Table 1.

Comparative Example 1

Referring to the method of Example 1, the difference was that the first semiconductor layer was made of intrinsic amorphous silicon and N-type doped amorphous silicon prepared at a low temperature, and the thickness ratio and the surface doping index of the layers were the same as those of Example 1; and for the fabrication or etching method thereof, reference was made to CN114068731A. Corresponding tests were carried out, results of which are shown in Table 1.

Comparative Example 2

In the comparative example, a N-type and P-type staggered structure with TOPCON passivation was adopted; specifically, the back contact cell included a crystalline silicon substrate (N-type doped silicon substrate), a light receiving surface thereof was sequentially provided with a tunneling oxide layer, a thin film silicon layer and a low-temperature-process anti-reflective film layer, a back light surface thereof was provided with a tunneling oxide layer, the tunneling oxide layer was provided with p-type and n-type heavily doped amorphous silicon layers arranged at intervals, and each of the p-type and n-type heavily doped amorphous silicon layers was sequentially provided with a transparent conductive thin film layer and a metal electrode layer, wherein thicknesses and effective doping concentrations of the crystalline silicon substrate, the tunneling oxide layer, and the p-type and n-type heavily doped amorphous silicon layers were the same as those of Example 1. For the fabrication method thereof, reference was made to CN110634961A. Corresponding tests were carried out, results of which are shown in Table 1.

TABLE 1ExampleMaterialnumberIsc/KAVoc/VFFEtaYieldcost/yuan/pieceExample 11111100%0.95Example 2110.990.9992%1.2Example 30.9910.980.9797%0.96Example 410.990.970.9697%0.94Example 51.01111.01100%0.95Example 611.0021.0051.00795%1.1Comparative110.990.9995%1.2Example 1Comparative1.0220.96210.983100%0.95Example 2

As can be seen from the above examples, comparative examples and Table 1, the short circuit current Isc, the open circuit voltage Voc, the filling factor FF, and the conversion efficiency Eta of the cell obtained in the examples of the present disclosure are all at high levels, and both high yield and a suitably low material cost can be considered. The comprehensive effect of the solution of the comparative examples cannot reach the effect level of the present disclosure.

As can be seen from Examples 1 and 2, the preferred solution of the fabrication method of laser ablation according to the present disclosure is more favorable for an improvement of the filling factor FF, the conversion efficiency Eta, and the yield. As can be seen from Example 1 and Examples 3 to 4, the preferred solution of the structures of the first semiconductor layer and the second semiconductor layer of the present disclosure is more favorable for the overall electrical conversion efficiency. As can be seen from Example 1 and Example 5, the preferred solution of the doped film layer of the present disclosure is more beneficial to an improvement of the short circuit current Isc and the conversion efficiency Eta. As can be seen from Examples 1 and 6, from the perspective of pursuing a better cell performance, compared with Example 1, the solution of Example 6 of the present disclosure is more favorable for an improvement of the open circuit voltage Voc, the filling factor FF, and the conversion efficiency Eta of the cell; and from the perspective of considering both the cost and the conversion efficiency, the preferred solution of Example 1 of the present disclosure is more favorable for a balance between the stability of a manufacturing cost and the conversion efficiency, and thus is most favorable for large-scale commercialization of the mass production of heterojunction back contact.

Test Example

Taking the hybrid passivation back contact cell of Example 1 as an example, on the premise that the dielectric insulation film thereof was made of 50-100 nm silicon nitride, laser with a wavelength of 532 nm was emitted into the back surface of the hybrid passivation back contact cell, and results of optical absorption amounts of the first semiconductor layer and the second semiconductor layer caused by formed pulsed laser and the relative selectivity therebetween are shown in table 2. The relative selectivity was characterized by a selection ratio, the higher the selection ratio is, the easier the removal of the upper second semiconductor layer without damaging the first semiconductor layer close to the substrate is. A calculation mode of the selection ratio was as follows: second semiconductor layer absorption amount/first semiconductor layer absorption amount.

TABLE 2Thickness of dielectric insulation filmSiNAbsorption amount50 nm70 nm100 nmN-type doped silicon crystal1.391.061.16layer/%Other absorption of first1.511.171.29semiconductor layer/%Total absorption of first2.902.232.45semiconductor layer/%Intrinsic silicon layer/%9.527.484.31P-type doped silicon layer/%9.466.282.81Total absorption of second18.9813.767.12semiconductor layer/%Selection ratio6.56.22.9

As can be seen from Table 2, as the thickness of the dielectric insulation film increases, the selection ratio gradually decreases, which indicates that the thickness of the dielectric insulation film has a significant influence on the light absorption of the first semiconductor layer and the second semiconductor layer, and an appropriate thickness of the dielectric insulation film can ensure that the upper second semiconductor layer can be more easily removed during laser ablation without damaging the first semiconductor layer close to the substrate.

The preferred embodiments of the present disclosure have been described in detail above, but the present disclosure is not limited thereto. Within the scope of the technical idea of the present disclosure, many simple modifications can be made to the technical solution of the present disclosure, including various technical features being combined in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the present disclosure, and all fall within the scope of the present disclosure.