WO2018214023A1 - Back-contact heterojunction solar cell and emitter thereof, and preparation method for solar cell - Google Patents

Abstract

The present invention relates to the technical field of solar cells, and provides an emitter (4) of a back-contact heterojunction solar cell, and the back-contact heterojunction solar cell using the emitter (4) and a preparation method therefor. The emitter (4) comprises at least one layer of CrOx thin film (41) from top to bottom. The structure can greatly improve the efficiency of the solar cell.

Description

Back contact heterojunction solar cell and emitter thereof, solar cell preparation method Technical field

The invention relates to the technical field of solar cells, in particular to a back contact heterojunction solar cell and an emitter thereof, and a solar cell preparation method.

Background technique

Heterojunction back contact (HBC) solar cell is a kind of high-efficiency solar cell, which combines interdigitated back contat (IBC) solar cell and heterojunction (Heterojunction with Intrinsic Thin). Layer, referred to as HIT) The advantages of solar cells can greatly improve solar cell efficiency.

The structure of a general HBC solar cell includes, in order from top to bottom, a passivation layer, a crystalline silicon layer, an amorphous silicon passivation layer, an emitter, and an emitter electrode and a base electrode. Among them, based on the advantages of the IBC solar cell, the front surface of the HBC solar cell also has no metal electrode, but forms the emitter and back field regions of the interdigitated structure on the back surface of the silicon wafer through a mask or photolithography process, and The emitter and back field regions are provided with corresponding emitter electrodes and base electrodes, thereby avoiding shading loss caused by the provision of metal electrodes on the front surface of the silicon wafer, thereby improving battery efficiency. Based on the advantages of HIT solar cells, HBC solar cells are high-efficiency cell structures formed of crystalline silicon (c-Si) and heavily doped amorphous silicon (a-Si:H), and are heavily doped amorphous. The interface between silicon and crystalline silicon introduces a layer of intrinsic amorphous silicon as a passivation layer. This can reduce the composite of the crystalline silicon wafer and reduce the interfacial recombination, so that the HBC solar cell has a higher open circuit voltage and short circuit. Current. In summary, HBC solar cells formed from crystalline silicon (c-Si) and heavily doped amorphous silicon (a-Si:H) are not only highly efficient, but also one that achieves the efficiency limit (30%) of crystalline silicon solar cells. Important way.

Although the battery efficiency of the HBC solar cell is high, the emitter of the current HBC solar cell is formed by heavily doping amorphous silicon, and the doping source of amorphous silicon is borane or phosphine, which are both flammable and explosive. And highly toxic, these will increase the cost of HBC batteries, hinder the large-scale use of HBC batteries; at the same time, as the doping concentration increases, it will increase the composite of the emitter (ie surface recombination and Auger recombination), thus Reducing the open circuit voltage of the battery, and reducing the open circuit voltage of the battery further limits the improvement of the efficiency of the battery, so that the efficiency of the HBC solar cell cannot be improved.

Summary of the invention

In order to solve the above problems, the present invention provides a back contact heterojunction solar cell emitter, so that the efficiency of the back contact heterojunction solar cell can be further improved.

A back contact heterojunction solar cell emitter comprising at least one layer of CrO _x film from top to bottom.

Preferably, when the CrO _x film is two or more layers, a metal film is further disposed between the adjacent two layers of the CrO _x film.

Preferably, when the back contact heterojunction solar cell emits a layer of CrO _x film, the thickness of the CrO _x film is 5-20 nm; or when the emitter of the back contact heterojunction solar cell includes when two film CrO _x, CrO _x film thickness of the two layers is provided with the sum of the thickness of the metal thin film between two layers of said CrO _x film of 5-20 nm; or when the heterojunction solar cell back contact When the emitter includes two layers of CrO _x film, the thickness of the two layers of the CrO _x film is 5 nm, and the thickness of the metal film between the two layers of the CrO _x film is 4 nm.

Preferably, the metal thin film is one of an Au thin film, an Ag thin film, a Pd thin film, a Cu thin film, a Ni thin film, a Mo thin film, a W thin film, and an Al thin film.

In order to solve the same technical problem, the present invention also provides a back contact heterojunction solar cell, comprising: a silicon substrate, a first passivation layer disposed on a front surface of the silicon substrate, and a back disposed on the silicon substrate a second passivation layer of the surface, an emitter as described above disposed on a back surface of the second passivation layer, an emitter electrode disposed on the emitter, and a second passivation layer Base electrode.

Preferably, the back contact heterojunction solar cell further includes a back field layer disposed between the base electrode and the second passivation layer, or the back contact heterojunction solar cell further includes An anti-reflection film on the front surface of the first passivation layer.

Preferably, the back field layer is one of a LiF _x film, a TiO ₂ film, a MgF _x film, and a Cs ₂ CO ₃ film.

Preferably, an interdigital structure is formed between the base electrode and the emitter electrode, and no contact between two adjacent base electrodes and the emitter electrode.

In order to solve the same technical problem, the present invention also provides a preparation method for preparing the above-mentioned back contact heterojunction solar cell, comprising the following steps:

Selecting a crystalline silicon wafer to form the silicon substrate after cleaning;

Depositing the first passivation layer and the second passivation layer on a front surface and a back surface of the silicon substrate, respectively;

Fixing a positioning template on a back surface of the second passivation layer, embedding a first metal mask in the positioning template, and sequentially depositing the CrO _x film and/or metal on a back surface of the second passivation layer a thin film, the emitter electrode;

Removing the first metal mask, inserting a second metal mask matched with the first metal mask into the positioning template, and depositing on the back surface of the second passivation layer by evaporation The base electrode.

Preferably, the step of depositing the base electrode on the back surface of the second passivation layer comprises sequentially depositing a back field layer and the base electrode on a back surface of the second passivation layer; or Depositing the first blunt surface of the front surface of the silicon substrate The step of forming a layer further includes depositing the anti-reflection film on a front surface of the first passivation layer.

Compared with the prior art, the beneficial effects of the present invention are:

(1) by depositing a CrO _x film on the back surface of the silicon substrate as an emitter of a solar cell, the arrangement being such that the emitter electrode provided on the emitter does not face the front of the silicon substrate Forming a light occlusion on the surface to increase the light absorption rate of the silicon substrate; on the other hand, using a CrO _x film as an emitter, the CrO _x film not only causes a Fermi level at a contact area of the back surface of the silicon substrate; Move to bring it close to the conduction band of silicon, that is, CrO _x film can induce the surface band of silicon to bend to generate space charge region, so that it can obtain selective contact of carriers and ensure the role of emitter; and use CrO _x film as emission The pole also enables the emitter to be realized without doping during the preparation process, so that the composite of the emitter (ie, surface recombination and Auger recombination) does not occur, and thus the CrO _x film is used as the back of the emitter. The open circuit voltage of the contact heterojunction solar cell is improved, thereby improving the efficiency of the solar cell as a whole;

(2) Using a CrO _x film or adding a metal film between adjacent two layers of CrO _x film as the emitter of the solar cell, the solar cell of this structure has not been reported in the literature and patents, and is a new material of silicon-based sun. battery;

(3) Since the emitter of the present invention adopts a CrO _x film, neither doping nor low temperature can be performed in the preparation process thereof, so that not only the doping source in the preparation process of the conventional solar cell emitter can be avoided. The use of flammable and explosive gases improves safety and stability of solar cells, and can reduce production costs and facilitate large-scale production of HBC solar cells;

(4) In the preparation process, the solar cell using the emitter can reduce the defect state of the emitter region by introducing an oxygen bias, and improve the recombination of the emitter region;

(5) The solar cell of the present invention can passivate at a contact interface with a silicon substrate by providing a first passivation layer and a second passivation layer on the front surface and the back surface of the silicon substrate to reduce interface defect state. Improve the open circuit voltage of the back contact heterojunction solar cell, thereby further improving battery efficiency.

DRAWINGS

1 is a schematic view showing the structure of a back contact heterojunction solar cell emitter applied to a back contact heterojunction solar cell in the embodiment of the present invention, wherein the back contact heterojunction solar cell emits a layer of CrO _x film;

2 is a schematic structural view of a back contact heterojunction solar cell emitter applied to a back contact heterojunction solar cell in the embodiment of the present invention, wherein the back contact heterojunction solar cell emits a three-layer film structure by From top to bottom, a CrO _x film, an Au film, and a CrO _x film are sequentially included;

3 is a schematic diagram of a method for preparing a back contact heterojunction solar cell according to an embodiment of the present invention, which includes five graphs a, b, c, d, and e, each of which corresponds to a back contact heterogeneity under different steps. The structure of the solar cell;

4 is a schematic structural diagram of a positioning screen in the embodiment of the present invention;

5 is a schematic structural view of a first metal mask in the embodiment of the present invention;

6 is a schematic structural view of a second metal mask in the embodiment of the present invention;

7 is a flow chart of a method for preparing a back contact heterojunction solar cell in an embodiment of the present invention;

8 is a graph showing changes in external quantum efficiency (EQE) versus wavelength (Wavelength) of different back contact heterojunction solar cells in an embodiment of the present invention;

9 is a graph showing Suns-Voc test results of different back contact heterojunction solar cells in the embodiment of the present invention, which reflects the effective solar number (Voc) of different back contact heterojunction solar cells (Effective Suns). Change curve

FIG. 10 is a graph showing the efficiency of the back contact heterojunction solar cell with the emitters of the CrO _x film and the Wo _x film as a function of time (Days, ie, days) in the embodiment of the present invention; FIG.

Wherein, 1, a silicon substrate; 2, a first passivation layer; 3, a second passivation layer; 4, an emitter; 41, a CrOx film; 42, a metal film; 5, an emitter electrode; 6, a back field layer; 7. Base electrode; 8. Anti-reflection film; 9. Positioning template; 91, first metal mask; 92, second metal mask.

detailed description

The specific embodiments of the present invention are further described in detail below with reference to the drawings and embodiments. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Example 1:

As shown in FIG. 1, the back contact heterojunction solar cell of the present invention comprises a silicon substrate 1, a first passivation layer 2 disposed on a front surface of the silicon substrate 1, and a back surface of the silicon substrate 1. a second passivation layer 3 on the surface, the emitter 4 disposed on the back surface of the second passivation layer 3, the emitter electrode 5 disposed on the emitter 4, and the second blunt The base electrode 7 on the layer 3.

The emitter 4 is the back contact heterojunction solar cell emitter 4 of the present invention. In the embodiment, the emitter 4 is composed of a CrO _x film 41 having a thickness of 5-20 nm. The structure of the emitter 4 is not limited to the structure of one layer of the CrO _x film 41. The back contact heterojunction solar cell of the present invention converts absorbed light energy into electrical energy, wherein the light absorbing layer of the battery is mainly the silicon substrate 1, and the electron holes generated by the silicon substrate 1 after absorbing photons will It is delivered to the base electrode 7 and the emitter electrode 5, respectively.

In general, the base electrode 7 is disposed on the back surface of the silicon substrate 1, and the emitter electrode 5 is disposed on the emitter 4, since the emitter 4 in this embodiment is Provided on the back surface of the silicon substrate 1, and thus also the emitter electrode 5 is also located on the back surface of the silicon substrate 1, avoiding the formation of light shielding on the front surface of the silicon substrate 1 to improve the silicon The light absorption rate of the substrate 1 increases the battery efficiency. At the same time, since the emitter 4 in the embodiment is a CrO _x film 41 which is used, and the material of the CrO _x film 41 is a high work function material, the material may be on the back surface of the silicon substrate 1. The contact area causes the Fermi level to move closer to the conduction band of silicon, that is, the CrO _x film 41 can induce the silicon surface band to bend to generate a space charge region, so that it can obtain selective contact of the carrier and emit The role of the pole 4 (ie, the transport and collection of carriers); moreover, the use of the CrO _x film 41 as the emitter 4 also enables the emitter 4 to be implemented without doping during the preparation process, so that no emission occurs. The recombination of the pole 4 (ie, surface recombination and Auger recombination), as such, also increases the open circuit voltage of the back contact heterojunction solar cell using the emitter 4, thereby improving the overall efficiency of the battery.

In addition, since the emitter 4 does not need to be doped during the preparation process, the use of the flammable and explosive gas caused by the doping source in the preparation process of the conventional solar cell emitter 4 can be avoided, the safety can be improved, and the production cost can be reduced. It facilitates mass production of HBC solar cells.

In order to reduce the recombination of the front surface and the rear surface of the silicon substrate 1, the first passivation layer 2 is also disposed on the front surface of the silicon substrate 1 in the embodiment, on the back surface of the silicon substrate 1. The second passivation layer 3 is disposed between the emitter 4 and the second passivation layer 3, and the second passivation layer 3 is a SiO _x film. Of course, TiO ₂ and Al may also be used. _A film such as ₂ O _{3 is} used as a passivation layer. Specifically, the SiO _x film can be passivated at a contact interface with the silicon substrate 1 to reduce the interface defect state to improve the open circuit voltage of the back contact heterojunction solar cell, thereby further improving the cell efficiency.

In addition, in the embodiment, a back field layer 6 is further disposed between the second passivation layer 3 and the base electrode 7. Specifically, the back field layer 6 is a LiF _x film, and may of course be a film made of a low work function material such as a TiO ₂ film, a MgF _x film, or a Cs ₂ CO ₃ film. Since the material used for the LiF _x film is a low work function material, together with the above-described emitter 4 having a high work function material, the Fermi level of the surface contact region of the silicon substrate 1 can be well promoted, and the current carrying current is promoted. The separation of the sub-pairs for better carrier-selective transport further enhances cell efficiency.

It can be understood that in order to absorb light as much as possible and further improve the efficiency of the battery, a trap structure can be added. Specifically, in the embodiment, an anti-reflection film 8 is disposed on the front surface of the first passivation layer 2 of the back contact heterojunction solar cell, and the anti-reflection film 8 is passed through the silicon substrate 1 The surface is formed by the trapping structure formed by the pyramidal suede, which can further improve the light absorption rate of the battery, thereby improving the battery efficiency.

In order to obtain the above-mentioned back contact heterojunction solar cell, in this embodiment, the steps shown in FIG. 7 are used for preparation:

Step S100: selecting a crystalline silicon wafer, and forming the silicon substrate after cleaning.

Specifically, the n-type single crystal silicon wafer is selected, and the silicon wafer is cleaned by the RCA cleaning process to remove the cutting marks and impurities on the silicon wafer to make the silicon substrate 1 in the subsequent process (as shown in FIG. 3). a) can have higher purity and avoid affecting the efficiency of the overall battery.

Wherein, RCA cleaning process is primarily by the ratio of H ₂ SO ₄ :H ₂ O SPM = 3 ₂ solution to remove organic matter on a silicon wafer, by the ratio of DHF HF:H ₂ O = 1:30 to The solution is used to remove the oxide layer on the silicon wafer and pass through an APM solution having a ratio of NH ₄ OH:H ₂ O ₂ :H ₂ O= ₁ : ₁ : ₅ to remove particulate impurities on the silicon wafer, and the ratio is HCl: H ₂ O ₂ :H ₂ O = ₁ : ₁ : ₆ HPM solution to remove metal impurities on the silicon wafer.

Step S200: depositing the first blunt on the front surface and the back surface of the silicon substrate 1 by using Plasma Enhanced Chemical Vapor Deposition (PECVD) as shown in FIG. 3, FIG. The layer 2 and the second passivation layer 3, that is, a SiN _x film. Among them, the deposition power is 2400 W, the deposition gas pressure is 20 Pa, the gas flow ratio of ammonia gas and silane is 2:1, the deposition temperature is 450 ° C, and the thickness of the deposited SiN _x film is 75 nm. Further, an anti-reflection film 8 (shown as c in FIG. 3) may be deposited on the second passivation layer 3 as needed.

Step S300: As shown in FIG. 3, a positioning template 9 (shown in FIG. 4) is fixed on the back surface of the second passivation layer 3, and the first metal mask 91 is disposed as shown in FIG. Inserting the emitter template 4 (CrO _x film 41) and the substrate on the back surface of the second passivation layer 3 by evaporation using a resistive thermal evaporation coating machine in a frame formed by the positioning template 9. The emitter electrode 5 (Al film) is described.

The first metal mask 91 is matched with the positioning template 9 , wherein the positioning template 9 is a frame structure, and the shape generally corresponds to the shape of the silicon substrate 1 , and the first metal mask can be 91 forms a good limit to prevent the first mask from moving during the preparation process. The first mask is in the shape of a comb. When the first mask is covered on the back surface of the second passivation layer 3, the first mask can block part of the area. The CrO _x film 41 is deposited on a region where the back surface of the second passivation layer 3 is not covered by the first mask, thereby also forming the emitter 4 formed by the CrO _x film 41 and deposited thereon. The emitter electrode 5 on the CrO _x film 41 is also in the shape of a comb.

In the above deposition process, the degree of vacuum is controlled to be about 5 × 10 ^-4 Pa, and oxygen is introduced, and the oxygen bias is 3 × 10 ^-2 Pa, and the coating rate is

Thus, the thickness of the deposited CrO _x film 41 can be controlled at 5-20 nm, and the thickness of the emitter electrode 5 is 1 μm, so that the emitter 4 can be sufficiently contacted with the emitter electrode 5, and the thickness can be ensured. The resistance loss on the emitter electrode 5 is low. Since the deposition process is performed at a normal temperature, not only the equipment is simple, the cost is low, but also mutual diffusion between materials due to high temperature can be avoided, and the battery efficiency can be ensured. In addition, since the oxygen bias is also introduced during the deposition process, the defect state of the emitter 4 body region can also be reduced, and the emitter 4 body region recombination can be improved. Of course, the CrO _x film 41 can also be deposited by other methods.

Step S400: As shown in FIG. 3, after the emitter 4 and the emitter electrode 5 are prepared, the first metal mask 91 is removed, and the first metal mask is removed. A 91 matching second metal mask 92 (shown in FIG. 6) is embedded in the positioning template 9, and is still deposited on the back surface of the second passivation layer 3 by a resistive thermal evaporation coating machine by evaporation. The base electrode 7 is described.

Of course, in order to improve the efficiency of the battery, the back field layer 6 (LiF _x film) may be deposited on the back surface of the second passivation layer 3 by an evaporation type thermal evaporation coating machine, followed by the evaporation. The base electrode 7 (Al film) is deposited on the field layer 6, and in the present embodiment, the back field layer 6 has a thickness of 1.5 nm, and the base electrode 7 is 1 μm.

In this process, since the second metal mask 92 is matched to the shape of the first metal mask 91, it is also a comb shape, and thus, by depositing the second metal mask 92 at the time of deposition, After the positioning template 9 is inside, the second metal mask 92 can cover the emitter 4 and the emitter electrode 5 well, thereby avoiding the back field layer 6 and the base region formed subsequently. The electrodes 7 are connected to the emitter 4 and the emitter electrode 5, respectively. Preferably, the mask used in the embodiment can form an interdigitated structure between the base electrode 7 and the emitter electrode 5, and two adjacent base electrodes 7 and The emitter electrodes 5 are not in contact with each other. Specifically, in the present embodiment, the distance between two adjacent base electrode 7 and the emitter electrode 5 is 75 μm, of course, the smaller the pitch, the better.

Example 2:

As shown in FIG. 2, the difference between this embodiment and Embodiment 1 is that the emitter 4 of the back contact heterojunction solar cell in this embodiment is a three-layer film structure, which is a layer of CrO _x film from top to bottom. 41. A metal film 42 and a CrO _x film 41, wherein the CrO _x film 41 has a thickness of 5 nm, and the metal film 42 has a thickness of 4 nm. The metal thin film 42 in this embodiment is an Au thin film, and may of course be a metal thin film 42 of other high work function materials, such as an Ag thin film, a Pd thin film, a Cu thin film, a Ni thin film, a Mo thin film, a W thin film, and an Al thin film. It can be understood that the back contact heterojunction solar cell emitter 4 may also be composed of a plurality of CrO _x films 41, and a metal film 42 is disposed between two adjacent CrO _x films 41, and is not limited to the implementation. The structure in the example.

Correspondingly, the back contact heterojunction solar cell in this embodiment is different from the first embodiment in the preparation process. In the embodiment, when the emitter 4 is deposited, the process in the embodiment 1 is used. 5nm film of Au are sequentially deposited film 41,4nm CrO _x and CrO _x film 41 of 5nm. Of course, the CrO _x film 41 and the metal film 42 may be deposited by other methods in this embodiment.

Since the emitter 4 of the back contact heterojunction solar cell in this embodiment adopts a structure of a metal oxide film/metal film 42/metal oxide film (OMO), not only the emitter 4 can be blended. Miscellaneous and low temperature preparation, and can also increase the carrier concentration of the metal oxide to form a low emitter 4 body region, interfacial recombination and low contact resistance inductive pn junction, thereby improving cell efficiency.

Example 3:

In this embodiment, the CrO _x film 41 having different thicknesses and the back field layer (LiF _x film) of different thicknesses prepared by the preparation method of the embodiment 1 are used, and the back contact heterojunction solar cell (the battery area is 4 cm ² ) is used. The front surface of the solar cell adopts a SiNx/SiOx laminated anti-passivation film, and the device performance parameters of the solar cell are obtained under the STC condition. The device performance parameters of the solar cell are as shown in Table 1:

Table I

It can be found from Table 1 that the back contact heterojunction solar cell emitting extremely 5 nm CrO _{x has} a maximum photoelectric conversion efficiency of 13.55% compared to a back contact heterojunction emitting 10 nm, 15 nm and 20 nm CrO _x . The solar cell has a fill factor of up to 59.80%.

Table 1 shows that as the thickness of the CrO _x film increases, the series resistance of the solar cell increases, resulting in a decrease in the fill factor, thereby indicating that the CrO _x film has a large bulk resistivity. The open-circuit voltage of the back contact heterojunction solar cell emitting extremely 5 nm CrO _x is lowered because the film is still in a discontinuous state, and the surface of the silicon wafer cannot be completely covered, and has a high composite current density. The emission of a very large 10 nm CrO _x film can achieve a continuous read state during the deposition process, so that a good passivation performance can be formed for the emitter region, so that the open circuit voltage of the corresponding solar cell reaches 600 mV.

By comparison the back surface field layer 2nm LiF _x film and the back contact 1nmLiF _x film heterojunction solar cells, respectively, can be found with the decrease of the film thickness of LiF _x, corresponding to the open circuit voltage of the solar cell and the fill factor decreased, and therefore The back field layer is set to reduce surface recombination. Specifically, as shown in FIG. 8, the curve shown in FIG. 8 corresponds to the external quantum efficiency (EQE) of the different back contact heterojunction solar cells in which the oxygen bias of 2×10 ⁻² Pa is introduced in Table 1. As can be seen from the figure, a back contact heterojunction solar cell using 2 nm LiF _x as the back field layer, and EQE in the wavelength range (wavelength) ranging from 400 nm to 850 nm, up to 90% or more, indicating the emitter and back field There is a small composite in the layer. The EQE of a back contact heterojunction solar cell using 1 nm LiF _x as the back field layer is reduced. Mainly because there is electrical occlusion in the back contact battery, the back field layer of 1nm LiF _x has a large recombination, and the minority carriers are recombined in the process of lateral transmission to the emitter in the silicon body region, resulting in a decrease in short circuit current density of 2 mA/cm. ² .

By comparing emission film and the manufacturing process without introducing oxygen 5nm CrO _x extremely biased back contact solar cell with a heterojunction emitter is 5nm film preparation process and the introduction of oxygen in contact with a back bias CrO _x heterojunction solar cells can be found in The open-circuit voltage of a back contact heterojunction solar cell emitting an extremely 5 nm CrO _x film without introducing an oxygen bias during the fabrication was reduced by 65 mV, and its fill factor was reduced by 2.8%. This is mainly because CrO ₃ generates a large amount of oxygen vacancies during thermal evaporation, causing a decrease in the CrO _x /n-Si band bending amount, which lowers the fill factor and the open circuit voltage. Therefore, the introduction of an oxygen bias can reduce the formation of oxygen vacancies in the CrO _x film and improve the performance of the battery.

Further, as shown in FIG. 9, FIG. 9 is a graph of Suns-V _OC test results of different back contact heterojunction solar cells corresponding to Table 1. As can be seen from FIG. 9, CrO _x films of different thicknesses are shown. The open-circuit voltage of the corresponding back contact heterojunction solar cell under high light injection does not show reverse deflection. Therefore, there is no Schottky junction in each of the back contact heterojunction solar cells, which forms an effective inducing type. Pn junction. At the same time, this result also shows that the back contact heterojunction solar cell prepared by using the CrO _x film as the emitter has high potential.

Example 4:

In this embodiment, the performance parameters of a back contact heterojunction solar cell emitting a layer of 5 nm CrO _x film, a layer of 10 nm CrO _x film and two layers of 5 nm CrO _x film (with a 4 nm Au film in between) are compared. See Table 2. Wherein, a back contact heterojunction solar cell emitting a very 5 nm CrO _x film or a 10 nm CrO _x film is used in the first embodiment, and the back contact heterojunction emitting two layers of 5 nm CrO _x film is used. The solar cell adopts the preparation method of Example 2, and the corresponding steps of the three batteries are identical in the preparation process.

Table II

From Table 2, it can be found that the battery efficiency of the back contact heterojunction solar cell emitting two layers of 5 nm CrO _x film is 1.88% and 3.47% higher than that of the other two back contact heterojunction solar cells. And the 4nmAu film inserted 10nm CrO _x film significantly improved solar cell open circuit voltage and fill factor, which is mainly due to 4nm Au increases the concentration of CrO _x film carriers, reducing body 10nm CrO _x film resistance.

Figure 10 compares the stability of a back contact heterojunction solar cell with an emitter of 5 nm CrO _x film and a 10 nm WO _x film, respectively. From the graph, it can be seen that the back contact heterojunction emitting a 10 nm WO _x film. The solar cell has experienced continuous decay, that is, the battery efficiency continues to decrease with time, which is mainly due to the influence of moisture and carbon impurities in the air. The back contact heterojunction solar cell emitting a very 5 nm CrO _x film showed attenuation in the first 10 days, and then the efficiency increased to 15%. Therefore, the use of CrO _x film in the emitter can make the corresponding back contact heterojunction solar cell have higher stability performance.

The above is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make several improvements and substitutions without departing from the technical principles of the present invention. It should also be considered as the scope of protection of the present invention.

Claims (10)

1. An emitter of a back contact heterojunction solar cell, characterized in that it comprises at least one layer of CrO _x film from top to bottom.
2. The emitter of a back contact heterojunction solar cell according to claim 1, wherein when the CrO _x film is two or more layers, a metal film is further disposed between the adjacent two layers of the CrO _x film. .
3. The emitter of a back contact heterojunction solar cell according to claim 2, wherein when said back contact heterojunction solar cell emits a layer of CrO _x film, said CrO _x film has a thickness of 5 -20 nm; emission or when the back contact solar cell electrode heterojunction CrO _x film comprising two layers, the thickness of the two layers CrO _x film and the metal thin film disposed between two layers of the CrO _x film The total thickness is 5-20 nm; or when the emitter of the back contact heterojunction solar cell comprises two layers of CrO _x film, the thickness of the two layers of the CrO _x film is 5 nm, and the CrO _x is provided in two layers. The thickness of the metal thin film between the films was 4 nm.
4. The emitter of the back contact heterojunction solar cell according to claim 2 or 3, wherein the metal thin film is an Au thin film, an Ag thin film, a Pd thin film, a Cu thin film, a Ni thin film, a Mo thin film, a W thin film, and One of the Al films.
5. A back contact heterojunction solar cell, comprising: a silicon substrate, a first passivation layer disposed on a front surface of the silicon substrate, and a second passivation layer disposed on a back surface of the silicon substrate An emitter according to any one of claims 1 to 4, an emitter electrode disposed on the emitter, and a second passivation layer disposed on the back surface of the second passivation layer Base electrode.
6. The back contact heterojunction solar cell of claim 5, wherein the back contact heterojunction solar cell further comprises a back field disposed between the base electrode and the second passivation layer The layer, or the back contact heterojunction solar cell, further includes an anti-reflection film disposed on a front surface of the first passivation layer.
7. The back contact heterojunction solar cell according to claim 6, wherein the back field layer is one of a LiF _x film, a TiO ₂ film, a MgF _x film, and a Cs ₂ CO ₃ film.
8. A back contact heterojunction solar cell according to claim 5, wherein an interdigitated structure is formed between said base electrode and said emitter electrode, and two adjacent said base electrode are The emitter electrodes are not in contact with each other.
9. The invention relates to a method for preparing a back contact heterojunction solar cell, which is used for preparing the back contact heterojunction solar cell according to any one of claims 5-8, characterized in that it comprises the following steps:

   Selecting a crystalline silicon wafer to form the silicon substrate after cleaning;

   Depositing the first passivation layer and the second passivation layer on a front surface and a back surface of the silicon substrate, respectively;

   Fixing a positioning template on a back surface of the second passivation layer, embedding a first metal mask in the positioning template, and sequentially depositing the CrOx film and/or a metal film on a back surface of the second passivation layer The emitter electrode;

   Removing the first metal mask, inserting a second metal mask matched with the first metal mask into the positioning template, and depositing on the back surface of the second passivation layer by evaporation The base electrode.
10. A method of fabricating a back contact heterojunction solar cell according to claim 9, wherein

    The step of depositing the base electrode on a back surface of the second passivation layer comprises sequentially depositing a back field layer and the base electrode on a back surface of the second passivation layer;

    Or after depositing the first passivation layer on the front surface of the silicon substrate, further comprising depositing the anti-reflection film on a front surface of the first passivation layer.

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