Patent Description:
Nowadays P-type monocrystalline passivated emitter and rear cells (PERCs) are the mainstream cells in the market, and the efficiency of P-type PERC cells has reached the upper limit. However, with the demand of the market and the continuous development of technology in the industry, N-type crystalline silicon solar cell technology has received more and more attention in recent years, which mainly includes passivated emitter and rear totally-diffused (n-PERT) cells, tunnel oxide passivation contact (TOPCon) cells and heterojunction (HJT) cells. N-type crystalline silicon solar cells make further breakthroughs in the conversion efficiency of crystalline silicon solar cells.

HJT cells use low-cost amorphous silicon as an emission layer, and an emission layer is made of doped amorphous silicon material. When performing deposition process on the monocrystalline silicon, only about <NUM> will meet the temperature requirements, and the low temperature process ensures less interface damage to the monocrystalline silicon substrate. Meanwhile, the existence of an intrinsic layer gives rise to a better interface passivation performance. Heterojunction solar cells maintain the core advantage of high efficiency due to a large forbidden band width of the heterostructure. However, there are still some technical difficulties to be overcome, such as the passivation characteristics of the amorphous silicon layer and the transport characteristics of carriers in the structural layers, which all affect the photoelectric conversion efficiency of the HJT cells. Therefore, how to figure out a method of preparing a heterojunction cell that improves conversion rate of light is an urgent problem confronted by those skilled in the art.

Patent document <CIT> discloses a HJT solar cell with a p-type crystalline silicon substrate, an intrinsic amorphous silicon layer, a silicon oxide layer, and a n-type doped amorphous silicon layer.

In order to achieve the above purposes, the technical solution provided by this application is as follows.

A HJT cell having high photoelectric conversion efficiency according to the present application includes an N-type crystalline silicon wafer. An intrinsic amorphous silicon layer, a SiO<NUM> layer, a C-doped SiO<NUM> layer, a doped N-type amorphous silicon layer, a TCO conductive layer and electrodes are sequentially disposed on a front surface of the N-type crystalline silicon wafer, and an intrinsic amorphous silicon layer, a SiO<NUM> layer, a C-doped SiO<NUM> layer, a doped P-type amorphous silicon layer, a TCO conductive layer and electrodes are sequentially disposed on a back surface of the N-type crystalline silicon wafer.

Further, the intrinsic amorphous silicon layer includes a hydrogenated intrinsic amorphous silicon film layer.

Further, a thickness of the intrinsic amorphous silicon layer or the hydrogenated intrinsic amorphous silicon film layer ranges from <NUM> to <NUM>.

Further, a thickness of the SiO<NUM> layer and a thickness of the C-doped SiO<NUM> layer each range from <NUM> to <NUM>.

Further, a thickness of the doped P-type amorphous silicon layer from <NUM> to <NUM>, the doped P-type amorphous silicon layer includes a lightly B-doped amorphous silicon layer and a heavily B-doped amorphous silicon layer, the lightly B-doped amorphous silicon layer is located closer to the C-doped SiO<NUM> layer, and the heavily B-doped amorphous silicon layer is located closer to the TCO conductive layer.

Further, the lightly B-doped amorphous silicon layer is formed by doping with TMB gas, a thickness of the lightly B-doped amorphous silicon layer ranges from <NUM> to <NUM>, and a forbidden band width of the lightly B-doped amorphous silicon layer ranges from <NUM> eV to <NUM> eV.

Further, the heavily B-doped amorphous silicon layer is formed by doping with B<NUM>H<NUM> gas, a thickness of the heavily B-doped amorphous silicon layer ranges from <NUM> to <NUM>, and a forbidden band width of the heavily B-doped amorphous silicon layer ranges from <NUM> eV to <NUM> eV.

Further, a thickness of the doped N-type amorphous silicon layer ranges from <NUM> to <NUM>, the doped N-type amorphous silicon layer includes a lightly P-doped amorphous silicon layer and a heavily P-doped amorphous silicon layer, the lightly P-doped amorphous silicon layer is located closer to the C-doped SiO2 layer, the heavily P-doped amorphous silicon layer is located closer to the TCO conductive layer, a thickness of the lightly P-doped amorphous silicon layer ranges from <NUM> to <NUM>, and a thickness of the heavily P-doped amorphous silicon layer ranges from <NUM> to <NUM>. The heavily P-doped amorphous silicon layer can be formed by plasma chemical vapor deposition or formed by coating the lightly P-doped amorphous silicon layer with a liquid phosphorus source and then curing by laser heating.

A method for preparing a HJT cell having high photoelectric conversion efficiency according to the present application includes:.

Further, the forming the doped N-type amorphous silicon layer and the doped P-type amorphous silicon layer by plasma enhanced chemical vapor deposition including growing, at a temperature of a silicon wafer substrate of <NUM>-<NUM> and under a deposition pressure of <NUM> Pa -<NUM> Pa, the doped N-type amorphous silicon layer and the doped P-type amorphous silicon layer respectively by using H<NUM>, SiH<NUM>, and doping gases TMB, B<NUM>H<NUM> and PH<NUM> as reaction gases when a base vacuum of a vacuum chamber reaches <NUM>×<NUM>-<NUM> Pa.

Further, the forming the doped N-type amorphous silicon layer and the doped P-type amorphous silicon layer by plasma enhanced chemical vapor deposition includes growing, at a temperature of a silicon wafer substrate of <NUM>-<NUM> and under a deposition pressure of <NUM> Pa -<NUM> Pa, the doped N-type amorphous silicon layer and the doped P-type amorphous silicon layer on back surfaces of hydrogenated amorphous silicon oxycarbide films respectively by using H<NUM>, SiH<NUM>, and doping gases TMB, B<NUM>H<NUM> and PH<NUM> as reaction gases when a base vacuum of a vacuum chamber reaches <NUM>×<NUM>-<NUM>Pa.

Further, the depositing the TCO conductive layer by deposition or sputtering by reactive ions includes depositing a transparent conductive ITO film on a front surface and a back surface respectively by magnetron sputtering. The ITO film has a thickness of <NUM> to <NUM>, a transmittance of <NUM>% or more, and a sheet resistance of 50Ω/□ to <NUM>Ω/□.

Further, the forming the front and back electrodes by screen printing includes further printing a layer of low-temperature conductive silver paste on the front and back TCO conductive layers by screen printing, respectively, and then sintering the layers of low-temperature conductive silver paste at a low temperature of <NUM> to <NUM> to form good ohmic contact. An Ag grid line has a thickness of <NUM> to <NUM>, a width of <NUM> to <NUM>, and a pitch of <NUM> to <NUM>.

Compared to the existing known technologies, the technical solutions provided in the present application has the following significant effects.

<FIG> is a schematic structural diagram of a HJT cell having high photoelectric conversion efficiency according to the present application.

N-type crystalline silicon wafer; <NUM> (<NUM>), intrinsic amorphous silicon layer; <NUM> (<NUM>), SiO<NUM> layer; <NUM> (<NUM>), C-doped SiO<NUM> layer; <NUM>, lightly B-doped amorphous silicon layer; <NUM><NUM>, lightly P-doped amorphous silicon layer; <NUM>, heavily P-doped amorphous silicon layer; <NUM> (<NUM>), TCO conductive layer; <NUM> (<NUM>), electrode.

For understanding the content of the present application, the present application will be described in detail with reference to the accompanying drawings and embodiments.

In the structure of an existing HJT cell, an amorphous silicon intrinsic layer and a doped layer are formed on both sides of an N-type monocrystalline silicon. The amorphous silicon intrinsic layer is mainly to passivate the surface defects of the crystalline silicon, reduce surface-defect states, and thus reduce carrier recombination. The doped amorphous silicon layer mainly forms a PIN junction with crystalline silicon and a field effect passivation layer. However, in the existing art, a doped P-type amorphous silicon layer is formed by doping with B<NUM>H<NUM> gas, which has poor thermal stability. B atoms are easily diffused into the amorphous silicon intrinsic layer, affecting the passivation effect of the intrinsic layer and leading to a low open-circuit voltage of the solar cells, which in turn leads to a low conversion efficiency of the solar cells. In addition, the doped P-type amorphous silicon layer formed by doping with B<NUM>H<NUM> gas has a low forbidden band width, which absorbs more sunlight, resulting in more light loss in the long wavelength band, leading to a low short-circuit current of solar cells and a low overall conversion efficiency of solar cells.

<CIT>, entitled "Emitter structure of crystalline silicon heterojunction solar cell and method of making the same" has been found by search. The application discloses an N-type crystalline silicon wafer with an amorphous silicon intrinsic layer on both the front and back surfaces of the N-type crystalline silicon wafer. A transparent conductive oxide (TCO) conductive film is disposed on an outer surface of each amorphous silicon intrinsic layer. A number of Ag electrodes are provided on an outer surface of the TCO conductive film. A doped N-type amorphous silicon layer is provided between the amorphous silicon intrinsic layer and the TCO conductive film on one side of the N-type crystalline silicon wafer, and a trimethyl boron (TMB) doped layer and a B<NUM>H<NUM> doped layer are provided between the amorphous silicon intrinsic layer and the TCO conductive film on the other side of the N-type crystalline silicon wafer. The application uses TMB gas for doping to prevent the doping atoms B from diffusing to the amorphous silicon intrinsic layer and improve the open-circuit voltage. The TMB gas has a large forbidden band width, so that light can pass through the doped layer more effectively, increasing the short-circuit current. The B<NUM>H<NUM> gas is used for doping at the TCO side, so that the conductivity of the doped layer is better, which improves the photoelectric conversion efficiency of HJT solar cells. Although a lightly B-doped layer is provided near the amorphous silicon intrinsic layer in the application, some B atoms may diffuse to the amorphous silicon intrinsic layer, affecting the film quality of the amorphous silicon intrinsic layer, and reducing the open circuit voltage to some extent.

To overcome the shortcomings of the above existing art, the present application provides a HJT cell having high photoelectric conversion efficiency and a preparation method for making the same. In some embodiments, the present application takes a hydrogenated amorphous silicon oxide film as an intrinsic passivation layer and double-diffusion B-doped P-type layer to make a heterojunction solar cell, which has an increased photoelectric conversion efficiency of <NUM>% or more. The short-circuit current and the open circuit voltage are significantly improved, and the photoelectric conversion efficiency of the silicon heterojunction solar cell can be effectively improved.

Referring to <FIG>, a HJT cell having high photoelectric conversion efficiency according to this embodiment includes an N-type crystalline silicon wafer <NUM>. An intrinsic amorphous silicon layer <NUM>, a SiO<NUM> layer <NUM>, a C-doped SiO<NUM> layer <NUM>, a doped N-type amorphous silicon layer, a TCO conductive layer <NUM> and electrodes <NUM> are sequentially disposed on a front surface of the N-type crystalline silicon wafer <NUM>. An intrinsic amorphous silicon layer <NUM>, a SiO<NUM> layer <NUM>, a C-doped SiO<NUM> layer <NUM>, a doped P-type amorphous silicon layer, a TCO conductive layer <NUM> and electrodes <NUM> are sequentially disposed on a back surface of the N-type crystalline silicon wafer <NUM>.

The intrinsic amorphous silicon layer has a thickness of <NUM>.

The SiO<NUM> layer and C-doped SiO<NUM> layer each has a thickness of <NUM>.

The doped P-type amorphous silicon layer has a thickness of <NUM>, and the doped N-type amorphous silicon layer has a thickness of <NUM>. The TCO conductive layer has a thickness of <NUM>.

In this embodiment, broken bonds on a surface of the amorphous silicon layer that is disposed on a surface of a silicon substrate is passivated by the SiO<NUM> layer, and the C-doped SiO<NUM> layer accommodates and blocks the doping atoms from the p-typed and n-typed lightly doped amorphous silicon layers to avoid diffusion of the doping atoms into the amorphous silicon layer.

The HJT cell having high photoelectric conversion efficiency according to this embodiment is basically the same as that in Embodiment I, and the differences lie as below. The thickness of the intrinsic amorphous silicon layer is <NUM>.

The thicknesses of the SiO<NUM> layer and the C-doped SiO<NUM> layer are both <NUM>.

The thickness of the doped P-type amorphous silicon layer is <NUM>, and the thickness of the doped N-type amorphous silicon layer is <NUM>. The thickness of the TCO conductive layer is <NUM>.

The HJT cell having high photoelectric conversion efficiency in this embodiment is basically the same as that in Embodiment I, and the differences lie as below.

The thickness of the intrinsic amorphous silicon layer is <NUM>.

The thickness of the SiO<NUM> layer is <NUM>, and the thickness of the C-doped SiO<NUM> layer is <NUM>.

Referring to <FIG>, the HJT cell having high photoelectric conversion efficiency in this embodiment includes an N-type crystalline silicon wafer <NUM>. A hydrogenated intrinsic amorphous silicon film layer <NUM>, a SiO<NUM> layer. <NUM>, a C-doped SiO<NUM> layer <NUM>, a doped N-type amorphous silicon layer, a TCO conductive layer <NUM> and electrodes <NUM> are sequentially disposed on a front surface of the N-type crystalline silicon wafer <NUM>. A hydrogenated intrinsic amorphous silicon film layer <NUM>, a SiO<NUM> layer <NUM>, a C-doped SiO<NUM> layer <NUM>, a doped P-type amorphous silicon layer, a TCO conductive layer <NUM> and electrodes <NUM> are sequentially disposed on a back surface of the N-type crystalline silicon wafer <NUM>.

A thickness of the hydrogenated intrinsic amorphous silicon film layer (i-a-Si:H) is <NUM>.

Thicknesses of the SiO<NUM> layer and the C-doped SiO<NUM> layer are both <NUM>. The C-doped SiO<NUM> layer that is formed by using a homotope to dope the SiO<NUM> layer accommodates a small amount of lightly doping B or P atoms, so as to avoid unnecessary doping of the hydrogenated intrinsic amorphous silicon film layer (i-a-Si:H) which otherwise affects passivation quality.

A thickness of the doped P-type amorphous silicon layer is <NUM>. The doped P-type amorphous silicon layer includes a lightly B-doped amorphous silicon layer <NUM> and a heavily B-doped amorphous silicon layer <NUM>. The lightly B-doped amorphous silicon layer <NUM> is closer to the C-doped SiO<NUM> layer <NUM>, and the heavily B-doped amorphous silicon layer <NUM> is closer to the TCO conductive layer <NUM>. By changing the doping source and doping concentration, the forbidden band width of the doped layer can be adjusted, a doped layer with high thermal stability and a large forbidden band width can be formed on the light-receiving surface, allowing more incident light to passes through the doped layer on the light-receiving surface, and consequently, more light waves can be effectively absorbed to generate photon-generated carriers. Specifically, in this embodiment, the lightly B-doped amorphous silicon layer <NUM> is formed by doping with TMB gas, and has a thickness of <NUM> and a forbidden band width of <NUM> eV. The heavily B-doped amorphous silicon layer <NUM> is formed by doping with B<NUM>H<NUM> gas, and has a thickness of <NUM> and a forbidden band width of <NUM> eV.

The thickness of the doped N-type amorphous silicon layer is <NUM>. The doped N-type amorphous silicon layer includes a lightly P-doped amorphous silicon layer <NUM> and a heavily P-doped amorphous silicon layer <NUM>. The lightly P-doped amorphous silicon layer <NUM> is closer to the C-doped SiO<NUM> layer <NUM>, and the heavily P-doped amorphous silicon layer <NUM> is closer to the TCO conductive layer <NUM>. The lightly P-doped amorphous silicon layer <NUM> has a thickness of <NUM>, and the heavily P-doped amorphous silicon layer <NUM> has a thickness of <NUM>.

A thickness of the TCO conductive layer is <NUM>.

In this embodiment, the heavily doped P-type and N-type amorphous silicon layers form good electrical contact with the TCO layers respectively. The doped P-type amorphous silicon layer on the back surface has a double-layer structure. The doped P-type layer closer to the C-doped SiO<NUM> is doped with TMB gas, which prevents doping atoms B (boron) from diffusing to the intrinsic amorphous silicon layer, thereby ensuring passivation effect of the silicon substrate by the intrinsic amorphous silicon or the hydrogenated intrinsic amorphous silicon, and increasing the open circuit voltage Voc. The doped P-type layer closer to the intrinsic amorphous silicon layer is doped with TMB gas, which has a larger forbidden band width than that of a doped amorphous silicon layer doped with B<NUM>H<NUM> gas, and the doping atoms are thermally stable, so that the incident light can pass through the doped layer more effectively, thus enhancing the absorption of light by crystalline silicon and increasing the short-circuit current Isc. The doped P-type layer closer to the TCO layer side is heavily doped with B<NUM>H<NUM> gas, so that the doped layer has better conductivity and a series resistance Rs of solar cells is lower, which results in a higher filling factor FF and consequently an enhanced photoelectric conversion efficiency of the HJT solar cell.

The method for preparing the HJT cell having high photoelectric conversion efficiency of this embodiment includes following steps.

At step <NUM>, an N-type crystalline silicon wafer <NUM> is textured and cleaned.

At step <NUM>, hydrogenated intrinsic amorphous silicon film layers are formed on both sides of the N-type crystalline silicon wafer <NUM> by plasma enhanced chemical vapor deposition (PECVD).

At step <NUM>, SiO<NUM> layers and C-doped SiO<NUM> layers are formed by plasma enhanced chemical vapor deposition.

At step <NUM>, a doped N-type amorphous silicon layer and a doped P-type amorphous silicon layer are formed by plasma enhanced chemical vapor deposition. The doped N-type amorphous silicon layer includes a lightly P-doped amorphous silicon layer (i.e., an N-type amorphous silicon layer lightly doped with P atoms) and a heavily P-doped amorphous silicon layer (i.e., an N-type amorphous silicon layer heavily doped with P atoms). The doped P-type amorphous silicon layer includes a lightly B-doped P-type amorphous silicon layer formed by doping with TMB gas and a heavily B-doped P-type amorphous silicon layer formed by doping with B<NUM>H<NUM> gas.

The deposition of the doped layers includes growing, at a temperature of a silicon wafer substrate of <NUM> and under a deposition pressure of <NUM> Pa, the doped N-type amorphous silicon layer and the doped P-type amorphous silicon layer on back surfaces of hydrogenated amorphous silicon oxycarbide films respectively, by using H<NUM>, SiH<NUM>, and doping gases TMB, B<NUM>H<NUM> and PH<NUM> as reaction gases when a base vacuum of a vacuum chamber reaches <NUM>×<NUM>-<NUM>Pa.

At step <NUM>, a transparent conductive ITO film is deposited on the front and back surfaces respectively by magnetron sputtering. The ITO film has a transmittance of <NUM>% or more and a sheet resistance of <NUM>Ω/□.

At step <NUM>, a layer of low-temperature conductive silver paste is printed on the TCO conductive layers of the front and back surfaces respectively by screen printing, and then the layers of low-temperature conductive silver paste are sintered at a low temperature of <NUM> to form good ohmic contact. An Ag grid line has a thickness of <NUM>, a width of <NUM>, and a pitch of <NUM>.

The heterojunction solar cell according to this embodiment is made by including hydrogenated amorphous silicon oxide films as the intrinsic passivation layers and including a double-diffusion B-doped P-type layer, the photoelectric conversion efficiency can be increased to <NUM>% or more, the short-circuit current and the open-circuit voltage can be increased significantly, and thus the photoelectric conversion efficiency can be improved effectively.

The HJT cell having high photoelectric conversion efficiency of this embodiment is basically the same as that of embodiment <NUM>, and the differences lie as below.

The thickness of the hydrogenated intrinsic amorphous silicon film layer (i-a-Si:H) is <NUM>.

The doped P-type amorphous silicon layer has a thickness of <NUM>. The lightly B-doped amorphous silicon layer <NUM> has a thickness of <NUM> and a forbidden band width of <NUM> eV, and the heavily B-doped amorphous silicon layer <NUM> has a thickness of <NUM> and a forbidden band width of <NUM> eV.

The doped N-type amorphous silicon layer has a thickness of <NUM>. The lightly P-doped amorphous silicon layer <NUM> has a thickness of <NUM>, and the heavily P-doped amorphous silicon layer <NUM> has a thickness of <NUM>.

At step <NUM>, a doped N-type amorphous silicon layer and a doped P-type amorphous silicon layer are formed by plasma enhanced chemical vapor deposition. The deposition of the doped layers includes growing, at a temperature of a silicon wafer substrate of <NUM> and under a deposition pressure of <NUM> Pa, the doped N-type amorphous silicon layer and the doped P-type amorphous silicon layer on back surfaces of hydrogenated amorphous silicon oxycarbide films respectively, by using H<NUM>, SiH<NUM>, and doping gases TMB, B<NUM>H<NUM> and PH<NUM> as reaction gases when a base vacuum of a vacuum chamber reaches <NUM>×<NUM>-<NUM>Pa.

At step <NUM>, a transparent conductive ITO film is deposited on the front and back surfaces respectively by magnetron sputtering. The film has a thickness of <NUM>, a transmittance of <NUM>% or more, and a sheet resistance of <NUM>Ω/□.

The hydrogenated intrinsic amorphous silicon film layer (i-a-Si:H) has a thickness of <NUM>.

The doped P-type amorphous silicon layer has a thickness of <NUM>. The lightly B-doped amorphous silicon layer <NUM> has a thickness of <NUM> and a forbidden band width of <NUM> eV. The heavily B-doped amorphous silicon layer <NUM> has a thickness of <NUM> and a forbidden band width of <NUM> eV.

At step <NUM>, hydrogenated intrinsic amorphous silicon film layers are formed on both sides of the N-type crystalline silicon wafer <NUM> by plasma enhanced chemical vapor deposition.

At step <NUM>, SiO<NUM> layers and C-doped SiO<NUM> layers are formed by plasma enhanced chemical vapor deposition (PECVD).

Claim 1:
A HJT cell having high photoelectric conversion efficiency, comprising an N-type crystalline silicon wafer (<NUM>), wherein an intrinsic amorphous silicon layer (<NUM>), a SiO<NUM> layer (<NUM>), a C-doped SiO<NUM> layer (<NUM>), a doped N-type amorphous silicon layer, a TCO conductive layer (<NUM>) and electrodes (<NUM>) are sequentially disposed on a front surface of the N-type crystalline silicon wafer (<NUM>), and
an intrinsic amorphous silicon layer (<NUM>), a SiO<NUM> layer (<NUM>), a C-doped SiO<NUM> layer (<NUM>), a doped P-type amorphous silicon layer, a TCO conductive layer (<NUM>) and electrodes (<NUM>) are sequentially disposed on a back surface of the N-type crystalline silicon wafer (<NUM>).