Silicon-based double-sided organic / inorganic heterojunction solar cell and preparation method thereof

Abstract

The present application provides a silicon-based bifacial organic / inorganic heterojunction solar cell and its preparation method, relating to the field of solar cell technology. The silicon-based bifacial organic / inorganic heterojunction solar cell comprises a stacked positive metal electrode layer, a wetting additive protective layer, a PEDOT:PSS hole transport layer, a first intrinsic amorphous silicon passivation layer, an n-type silicon substrate layer, a second intrinsic amorphous silicon passivation layer, an n-type amorphous silicon doped layer, a transparent conductive oxide layer, and a back metal electrode layer. This can improve the efficiency of the solar cell.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a silicon-based double-sided organic / inorganic heterojunction solar cell and a preparation method thereof. Background Art

[0002] At present, crystalline silicon solar cells account for more than 85% of the market share of mass-produced solar cells. Bifacial cells have been mass-produced, which reduces the waste of substrate silicon wafers, fully utilizes sunlight, and has great potential for application in photovoltaic building integration.

[0003] How to improve the efficiency of bifacial cells has become a research hotspot for scientific research institutes and photovoltaic companies around the world. Summary of the Invention

[0004] The embodiments of the present application provide a silicon-based double-sided organic / inorganic heterojunction solar cell and a preparation method thereof, which can improve the efficiency of the solar cell.

[0005] The embodiment of the present application is implemented as follows:

[0006] In a first aspect, an embodiment of the present application provides a silicon-based double-sided organic / inorganic heterojunction solar cell, comprising a positive metal electrode layer, a wetting additive protective layer, a PEDOT:PSS hole transport layer, a first intrinsic amorphous silicon passivation layer, an n-type silicon substrate layer, a second intrinsic amorphous silicon passivation layer, an n-type amorphous silicon doping layer, a transparent conductive oxide layer, and a back metal electrode layer stacked in sequence.

[0007] In the above technical solution, the main component of the PEDOT:PSS hole transport layer is (3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), which serves as a window layer for incident light in solar cells. Its energy band gap is adjustable, which can excite more photogenerated carriers and reduce the parasitic absorption of incident light. Secondly, the PEDOT:PSS hole transport layer has a relatively high mobility and can efficiently transport hole carriers, hindering the passage of electron carriers, playing a selective transport role and improving the efficiency of solar cells. In addition, the raw materials of the PEDOT:PSS hole transport layer are relatively cheap and suitable for large-scale mass production. In addition, the wetting additive protective layer can increase the wettability of the PEDOT:PSS hole transport layer and the n-type silicon substrate layer, making the contact between the two closer and stronger, reducing the contact resistance of the metal electrode, and improving the efficiency of the solar cell.

[0008] In one possible embodiment, the wetting additive protective layer contains aluminum metal particles and fluoride ionomer.

[0009] In this technical solution, the fluoride ion polymer forms chemical bonds that enhance the adhesion between the PEDOT:PSS hole transport layer and the first intrinsic amorphous silicon passivation layer. Furthermore, the aluminum metal particles increase the surface activity of the metal and raise the surface temperature, thereby increasing the tensile strength of the screen-printed low-temperature silver paste. The protective layer of wetting additives containing the aluminum metal particles and fluoride ion polymer creates a tighter and more secure contact between the PEDOT:PSS hole transport layer and the n-type silicon substrate, reducing the contact resistance of the metal electrodes and improving the efficiency of the solar cell.

[0010] In one possible embodiment, the particle size of the aluminum metal particles is 800-1000 nm.

[0011] In the above technical solution, aluminum metal particles within this particle size range are more conducive to increasing the surface activity energy of the metal, thereby making the contact between the PEDOT:PSS hole transport layer and the n-type silicon substrate layer tighter and firmer, thereby improving the efficiency of the solar cell.

[0012] In one possible embodiment, the fluorine ion polymer is selected from any one of polyhexafluoropropylene and polytetrafluoroethylene.

[0013] In the above technical solution, polyhexafluoropropylene and polytetrafluoroethylene have chemical bonds, which are stronger than the intermolecular forces and can better increase the adhesion between the PEDOT:PSS hole transport layer and the first intrinsic amorphous silicon passivation layer.

[0014] In one possible embodiment, the thickness of the wetting additive protective layer is 10-30 μm.

[0015] In the above technical solution, the thickness of the wetting additive protective layer is set to 10~30 μm, which can not only better ensure the function of increasing the wettability of the PEDOT:PSS hole transport layer and the n-type silicon substrate layer, but also avoid the thickness being too thick to affect the cell efficiency of the solar cell.

[0016] In one possible embodiment, both the front metal electrode layer and the back metal electrode layer contain Cu.

[0017] In the above technical solution, both the positive metal electrode layer and the back metal electrode layer contain Cu, so that the positive metal electrode layer and the back metal electrode layer have good electrical conductivity and can increase the carrier collection rate.

[0018] In one possible embodiment, the positive metal electrode layer further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn and Ag;

[0019] And / or, the back metal electrode layer further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn and Ag.

[0020] In the above technical solution, the front metal electrode layer further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn, and Ag. These metal elements are used together with Cu, which can reduce costs compared to using Cu alone, while also ensuring conductivity and battery efficiency. In addition, the back metal electrode layer further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn, and Ag. These metal elements are used together with Cu, which can reduce costs compared to using Cu alone, while also ensuring conductivity and battery efficiency.

[0021] In one possible embodiment, the thickness of the PEDOT:PSS hole transport layer is 300-500 nm.

[0022] In the above technical solution, the thickness of the PEDOT:PSS hole transport layer is set to 300~500nm, so that the PEDOT:PSS hole transport layer has a higher mobility and improves the efficiency of the solar cell.

[0023] In a second aspect, the present invention provides a method for preparing a silicon-based bifacial organic / inorganic heterojunction solar cell according to the first aspect, comprising:

[0024] forming a first intrinsic amorphous silicon passivation layer and a second intrinsic amorphous silicon passivation layer on two opposite surfaces of the n-type silicon substrate layer;

[0025] forming a PEDOT:PSS hole transport layer on the first intrinsic amorphous silicon passivation layer, and forming an n-type amorphous silicon doping layer on the surface of the second intrinsic amorphous silicon passivation layer;

[0026] forming a wetting additive protective layer on the surface of the PEDOT:PSS hole transport layer and forming a transparent conductive oxide layer on the surface of the n-type amorphous silicon doped layer;

[0027] A positive metal electrode layer is formed on the surface of the wetting additive protection layer, and a back metal electrode layer is formed on the surface of the transparent conductive oxide layer.

[0028] In the above technical solution, the method for preparing silicon-based double-sided organic / inorganic heterojunction solar cells is suitable for industrial production, and the prepared silicon-based double-sided organic / inorganic heterojunction solar cells have high cell efficiency.

[0029] In a possible implementation, the first intrinsic amorphous silicon passivation layer and the second intrinsic amorphous silicon passivation layer are both deposited using a mixture of SiH 4 and H 2 as source gases, with a volume ratio of SiH 4 to H 2 being 2-4:1.

[0030] In the above technical solution, a mixture of SiH4 and H2 with a volume ratio of 2 to 4:1 is used as a gas source for deposition to obtain a first intrinsic amorphous silicon passivation layer and a second intrinsic amorphous silicon passivation layer, which can saturate the dangling bonds and crystal defects of the n-type silicon substrate layer and improve the open circuit voltage and battery efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 This is a schematic structural diagram of a silicon-based double-sided organic / inorganic heterojunction solar cell provided in an embodiment of the present application.

[0033] Icon: 100-Silicon-based double-sided organic / inorganic heterojunction solar cell; 10-positive metal electrode layer; 20-wetting additive protective layer; 30-PEDOT:PSS hole transport layer; 40-first intrinsic amorphous silicon passivation layer; 50-n-type silicon substrate layer; 60-second intrinsic amorphous silicon passivation layer; 70-n-type amorphous silicon doping layer; 80-transparent conductive oxide layer; 90-back metal electrode layer. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0036] In the description of this application, it should be noted that the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0037] The present invention provides a silicon-based double-sided organic / inorganic heterojunction solar cell 100 and a method for manufacturing the same. Figure 1 , Figure 1FIG. 1 shows a schematic structural diagram of a silicon-based double-sided organic / inorganic heterojunction solar cell 100 .

[0038] The silicon-based bifacial organic / inorganic heterojunction solar cell 100 includes a stacked positive metal electrode layer 10, a wetting additive protective layer 20, a PEDOT:PSS hole transport layer 30, a first intrinsic amorphous silicon passivation layer 40, an n-type silicon substrate layer 50, a second intrinsic amorphous silicon passivation layer 60, an n-type amorphous silicon doped layer 70, a transparent conductive oxide layer 80, and a back metal electrode layer 90. It should be noted that the n-type silicon substrate layer 50 can be n-type polycrystalline silicon or n-type single crystal silicon. Exemplarily, the thickness of the n-type silicon substrate layer 50 is 80-120 μm.

[0039] In addition, the material of the transparent conductive oxide layer 80 can be optionally indium tin oxide (ITO) or aluminum-doped zinc oxide (AZO).

[0040] Among them, the main component of the PEDOT:PSS hole transport layer 30 is (3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), which serves as a window layer for incident light in the solar cell. Its energy band gap is adjustable, which can excite more photogenerated carriers and reduce the parasitic absorption of the incident light. Secondly, the PEDOT:PSS hole transport layer 30 has a relatively high mobility and can efficiently transport hole carriers, hindering the passage of electron carriers, playing a selective transport role, and improving the efficiency of the solar cell. Exemplarily, the thickness of the PEDOT:PSS hole transport layer 30 is 300~500nm, for example, it can be 300nm, 350nm, 400nm, 450nm or 500nm. This thickness gives the PEDOT:PSS hole transport layer 30 a higher mobility, improving the efficiency of the solar cell.

[0041] The wetting additive protective layer 20 can increase the wettability of the PEDOT:PSS hole transport layer 30 and the n-type silicon substrate layer 50, making the contact between the two closer and stronger, reducing the contact resistance of the metal electrodes, and improving the efficiency of the solar cell.

[0042] In one possible embodiment, the wetting additive protective layer 20 contains aluminum metal particles and fluoride ion polymers. Fluoride ion polymers have chemical bonds that can increase the adhesion between the PEDOT:PSS hole transport layer 30 and the first intrinsic amorphous silicon passivation layer 40; in addition, aluminum metal particles can increase the surface activity of the metal and increase the surface temperature, which is beneficial to increase the tension of the screen-printed low-temperature silver paste. The wetting additive protective layer 20 containing aluminum metal particles and fluoride ion polymers makes the contact between the PEDOT:PSS hole transport layer 30 and the n-type silicon substrate layer 50 tighter and firmer, reduces the contact resistance of the metal electrode, and improves the efficiency of the solar cell. It should be noted that as long as the wetting additive protective layer 20 contains aluminum metal particles and fluoride ion polymers, the efficiency of the solar cell can be improved. The specific ratio of aluminum metal particles and fluoride ion polymers is not limited in the embodiments of the present application.

[0043] Exemplarily, the thickness of the wetting additive protective layer 20 is 10-30 μm. Setting the thickness of the wetting additive protective layer 20 to 10-30 μm effectively ensures the wettability of the PEDOT:PSS hole transport layer 30 and the n-type silicon substrate layer 50 while preventing excessive thickness from affecting the solar cell efficiency. Optionally, the thickness of the wetting additive protective layer 20 is any one of 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm, or a range between any two of these.

[0044] Optionally, the aluminum metal particles have a particle size of 800-1000 nm, for example, any one of 800 nm, 850 nm, 900 nm, 950 nm, and 1000 nm, or any two thereof. Aluminum metal particles within this particle size range are more conducive to increasing the surface activity of the metal, thereby ensuring a tighter and more secure contact between the PEDOT:PSS hole transport layer 30 and the n-type silicon substrate layer 50, thereby improving the efficiency of the solar cell.

[0045] For example, the fluorine ion polymer is selected from polyhexafluoropropylene and polytetrafluoroethylene. Polyhexafluoropropylene and polytetrafluoroethylene have chemical bonds, which are stronger than intermolecular forces and can better increase the adhesion between the PEDOT:PSS hole transport layer 30 and the first intrinsic amorphous silicon passivation layer 40.

[0046] Furthermore, in one possible embodiment, both the positive metal electrode layer 10 and the back metal electrode layer 90 contain Cu. This configuration ensures that the positive metal electrode layer 10 and the back metal electrode layer 90 have good conductivity and can increase the carrier collection rate. For example, the height of the positive metal electrode layer 10 and the back metal electrode layer 90 is 20-30 μm and the width is 40-80 μm.

[0047] Optionally, the positive metal electrode layer 10 further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn, and Ag. Using these metal elements together with Cu can reduce costs compared to using Cu alone while also ensuring conductivity and battery efficiency.

[0048] Optionally, the back metal electrode layer 90 further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn, and Ag. Using these metal elements together with Cu can reduce costs compared to using Cu alone while also ensuring conductivity and battery efficiency.

[0049] To improve the open-circuit voltage and cell efficiency of solar cells, in one possible embodiment, the first intrinsic amorphous silicon passivation layer 40 and the second intrinsic amorphous silicon passivation layer 60 are both deposited using a mixture of SiH4 and H2 as the source gas, with the volume ratio of SiH4 to H2 being 2-4:1. Exemplarily, the deposition method is plasma-enhanced chemical vapor deposition (PECVD). Exemplarily, the thickness of the first intrinsic amorphous silicon passivation layer 40 is 10-20 nm, and the thickness of the second intrinsic amorphous silicon passivation layer 60 is 5-10 nm. Such a thickness setting is more conducive to improving the cell efficiency of the solar cell.

[0050] The present embodiment further provides a method for preparing a silicon-based bifacial organic / inorganic heterojunction solar cell 100, which comprises:

[0051] (1) A first intrinsic amorphous silicon passivation layer 40 and a second intrinsic amorphous silicon passivation layer 60 are formed on two opposite surfaces of the n-type silicon substrate layer 50 .

[0052] Exemplarily, the n-type silicon substrate layer 50 is placed in a PECVD film forming device, into which SiH4 and H2 gas sources with a volume ratio of 2 to 4:1 are introduced, and a first intrinsic amorphous silicon passivation layer 40 and a second intrinsic amorphous silicon passivation layer 60 are respectively deposited on two opposite surfaces of the n-type silicon substrate layer 50.

[0053] For example, before forming the first intrinsic amorphous silicon passivation layer 40 and the second intrinsic amorphous silicon passivation layer 60, the n-type silicon substrate layer 50 is first cleaned and textured, wherein the n-type single crystal silicon substrate layer is formed with a surface textured structure pyramid shape on the n-type silicon substrate layer 50 using a NaOH solution, and the n-type polycrystalline silicon substrate layer is formed with a surface textured structure pyramid shape on the n-type silicon substrate layer using a HCl / HNO3 solution.

[0054] (2) A PEDOT:PSS hole transport layer 30 is formed on the surface of the first intrinsic amorphous silicon passivation layer 40 ; and an n-type amorphous silicon doping layer 70 is formed on the surface of the second intrinsic amorphous silicon passivation layer 60 .

[0055] For example, an inkjet device may be used to spray PEDOT:PSS onto the surface of the first intrinsic amorphous silicon passivation layer 40 to form the PEDOT:PSS hole transport layer 30 .

[0056] Exemplarily, PH3 and SiH4 source gases are deposited on the surface of the second intrinsic amorphous silicon passivation layer 60 at a volume ratio of 4:1 through a PECVD device to form an n-type amorphous silicon doping layer 70 .

[0057] (3) A wetting additive protection layer 20 is formed on the surface of the PEDOT:PSS hole transport layer 30 , and a transparent conductive oxide layer is formed on the surface of the n-type amorphous silicon doped layer 70 .

[0058] For example, the wetting additive may be sprayed onto the surface of the PEDOT:PSS hole transport layer 30 in a spraying manner to form the wetting additive protection layer 20 .

[0059] For example, a transparent conductive oxide layer may be formed on the surface of the n-type amorphous silicon doped layer 70 by magnetron sputtering.

[0060] (4) A front metal electrode layer 10 is formed on the surface of the wetting additive protection layer 20, and a back metal electrode layer 90 is formed on the surface of the transparent conductive oxide layer.

[0061] Exemplarily, both the front metal electrode layer 10 and the back metal electrode layer 90 can be formed by screen printing.

[0062] The silicon-based bifacial organic / inorganic heterojunction solar cell 100 of the present application is further described in detail below with reference to embodiments.

[0063] Example 1

[0064] The present embodiment provides a silicon-based bifacial organic / inorganic heterojunction solar cell 100, which includes a positive metal electrode layer 10, a wetting additive protective layer 20, a PEDOT:PSS hole transport layer 30, a first intrinsic amorphous silicon passivation layer 40, an n-type silicon substrate layer 50, a second intrinsic amorphous silicon passivation layer 60, an n-type amorphous silicon doping layer 70, a transparent conductive oxide layer 80, and a back metal electrode layer 90, which are stacked in sequence. The wetting additive protective layer 20 has a thickness of 20 μm and contains aluminum metal particles and polyhexafluoropropylene in a weight ratio of 1:3, wherein the particle size of the aluminum metal particles is 900 nm. Furthermore, both the first intrinsic amorphous silicon passivation layer 40 and the second intrinsic amorphous silicon passivation layer 60 are deposited using a mixture of SiH4 and H2 as the source gas, with the volume ratio of SiH4 to H2 being 4:1. Both the positive metal electrode and the back metal electrode are Cu.

[0065] Example 2

[0066] The structures of the silicon-based bifacial organic / inorganic heterojunction solar cell 100 of this embodiment are substantially the same as those of the first embodiment, with the only difference being that the weight ratio of the aluminum metal particles to the polyhexafluoropropylene in the second embodiment is 3:1.

[0067] Example 3

[0068] The structures of the silicon-based bifacial organic / inorganic heterojunction solar cell 100 of this embodiment are basically the same as those of Example 1. The only difference is that the first intrinsic amorphous silicon passivation layer 40 and the second intrinsic amorphous silicon passivation layer 60 in Example 3 are both deposited using a mixture of SiH4 and H2 as the gas source, and the volume ratio of SiH4 to H2 is 2:1.

[0069] Example 4

[0070] The structures of the silicon-based bifacial organic / inorganic heterojunction solar cell 100 of this embodiment are substantially the same as those of the first embodiment, with the only difference being that the front metal electrode and the back metal electrode in the fourth embodiment are both formed of Cu and Ti.

[0071] Example 5

[0072] The structures of the silicon-based bifacial organic / inorganic heterojunction solar cell 100 of this embodiment are substantially the same as those of the first embodiment, with the only difference being that the front metal electrode and the back metal electrode in the fifth embodiment are both formed of Cu and Al.

[0073] Comparative Example 1

[0074] The solar cell of this comparative example has substantially the same structure as the silicon-based bifacial organic / inorganic heterojunction solar cell 100 of Example 1, with the only difference being that the wetting additive protection layer 20 is not provided in Comparative Example 1.

[0075] Comparative Example 2

[0076] The structure of the solar cell of this comparative example is basically the same as that of the silicon-based double-sided organic / inorganic heterojunction solar cell 100 of Example 1. The only difference is that the hole transport layer of Comparative Example 2 uses cadmium sulfide (CdS) as the raw material.

[0077] Test example

[0078] The conversion efficiency of the silicon-based bifacial organic / inorganic heterojunction solar cells 100 prepared in Examples 1 to 5 and the solar cells prepared in Comparative Examples 1 and 2 was tested using a Halm online IV test system under the conditions of 25°C, AM 1.5, and 1 standard sun. The results are shown in Table 1.

[0079] Table 1 Test results of conversion efficiency of solar cells in Examples 1 to 5 and Comparative Examples 1 to 2

[0080]

[0081] The results in Table 1 show that Example 1 significantly improves battery efficiency by including an additional wetting additive protective layer 20 compared to Comparative Example 1. Furthermore, Example 1 significantly improves battery efficiency by including a PEDOT:PSS hole transport layer 30 compared to Comparative Example 2.

[0082] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A silicon-based double-sided organic / inorganic heterojunction solar cell, characterized in that: It includes a positive metal electrode layer, an infiltration additive protection layer, a PEDOT:PSS hole transport layer, a first intrinsic amorphous silicon passivation layer, an n-type silicon substrate layer, a second intrinsic amorphous silicon passivation layer, an n-type amorphous silicon doping layer, a transparent conductive oxide layer and a back metal electrode layer stacked in sequence; The wetting additive protective layer contains aluminum metal particles and polyhexafluoropropylene.

2. The silicon-based double-sided organic / inorganic heterojunction solar cell according to claim 1, characterized in that: The particle size of the aluminum metal particles is 800-1000 nm.

3. The silicon-based double-sided organic / inorganic heterojunction solar cell according to claim 1 or 2, characterized in that: The thickness of the wetting additive protective layer is 10 to 30 μm.

4. The silicon-based double-sided organic / inorganic heterojunction solar cell according to claim 1 or 2, characterized in that: The front metal electrode layer and the back metal electrode layer both contain Cu.

5. The silicon-based double-sided organic / inorganic heterojunction solar cell according to claim 4, characterized in that: The positive metal electrode layer further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn and Ag; And / or, the back metal electrode layer further contains at least one of Mo, W, Ti, Ni, Al, Mg, Ta, Sn and Ag.

6. The silicon-based double-sided organic / inorganic heterojunction solar cell according to claim 1 or 2, characterized in that: The thickness of the PEDOT:PSS hole transport layer is 300-500 nm.

7. A method for preparing a silicon-based double-sided organic / inorganic heterojunction solar cell according to any one of claims 1 to 6, characterized in that: include: forming the first intrinsic amorphous silicon passivation layer and the second intrinsic amorphous silicon passivation layer on two opposite surfaces of the n-type silicon substrate layer respectively; forming the PEDOT:PSS hole transport layer on the first intrinsic amorphous silicon passivation layer, and forming the n-type amorphous silicon doping layer on the surface of the second intrinsic amorphous silicon passivation layer; forming the wetting additive protection layer on the surface of the PEDOT:PSS hole transport layer, and forming the transparent conductive oxide layer on the surface of the n-type amorphous silicon doped layer; The front metal electrode layer is formed on the surface of the wetting additive protection layer, and the back metal electrode layer is formed on the surface of the transparent conductive oxide layer.

8. The method for preparing a silicon-based double-sided organic / inorganic heterojunction solar cell according to claim 7, characterized in that: The first intrinsic amorphous silicon passivation layer and the second intrinsic amorphous silicon passivation layer are both deposited using a mixture of SiH4 and H2 as source gases, and the volume ratio of the SiH4 to the H2 is 2 to 4:1.

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