KR101293022B1 - Substrate of photovoltaic cell - Google Patents

Abstract

The present invention relates to a solar cell substrate, wherein the solar cell substrate includes a transparent substrate and a zinc oxide (ZnO) transparent conductive thin film layer doped with a dopant formed on the transparent substrate, wherein zinc oxide (ZnO) The transparent conductive thin film layer protects the first dopant dopant layer and the first dopant dopant layer in which the light transmittance of the wavelength band having an energy level of 1.7 eV or less satisfies 80% or more, and blocks the reaction between moisture and the first dopant doped layer. And a second dopant doping layer.

Solar Cell, Substrate, Zinc Oxide, Moisture Resistance, Surface, Dopant

Description

Solar cell substrate {Substrate of photovoltaic cell}

The present invention relates to a solar cell substrate, and more particularly, to a solar cell substrate having optical and electrical properties usable for solar cells and excellent moisture resistance.

Recently, high-efficiency solar cells are being developed on a large scale as a countermeasure against environmental pollution by the Ministry of Energy and Resources. Solar cells are a key element of solar power generation that converts solar energy directly into electricity. Solar cells are now being applied to a variety of fields, from electricity, electronics, electricity to homes and buildings, and industrial development. The most basic structure of the solar cell is a diode type consisting of a pn junction, it is classified according to the materials of the light absorption layer, a silicon solar cell that uses silicon as the light absorbing layer, the light absorbing layer CIS (CuInSe ₂₎ or using the compound aspect the CdTe It is classified into a dye-sensitized solar cell in which a photosensitive dye molecule in which electrons are excited by absorbing visible light on the surface of a nanoparticle of a porous membrane and a stacked solar cell in which a plurality of amorphous silicon are stacked. In addition, solar cells are classified into bulk (including monocrystalline and polycrystalline) and thin film (amorphous and polycrystalline) solar cells.

Currently, bulk crystalline silicon solar cells using polycrystalline silicon account for more than 90% of the total market, and the unit cost of photovoltaic power generation of bulk crystalline silicon solar cells is at least three times up to ten times higher than conventional thermal, nuclear, and hydropower. expensive. This is mainly due to the high production cost of crystalline silicon solar cells using a large amount of expensive silicon raw materials and complicated manufacturing processes. In recent years, research and commercialization of amorphous silicon (a-Si: H) and microcrystalline silicon (μc-Si: H) thin film solar cells are in progress.

1 illustrates a structure of a solar cell using conventional amorphous silicon as a light absorbing layer.

As shown, the conventional amorphous silicon (eg, a-Si: H) solar cell 110 is a P-type amorphous silicon (a-Si: H) doped with a substrate 111 / transparent conductive film 112 / impurities. (113) / I-type amorphous silicon (a-Si: H) 114 that is not doped with impurity 114 / N-type amorphous silicon (a-Si: H) 115 that is doped with impurity / Back reflector ( 116). In the pin-type amorphous silicon (a-Si: H), the i-type amorphous silicon (a-Si: H) 114 which is not doped with impurities is P-type and n-type amorphous silicon (a-Si: H) doped with impurities. Depletion by the 113 and 115, the electric field is generated inside. The hole-electron pairs generated in the i-type amorphous silicon (a-Si: H) 114 by the incident light hv are respectively P-type amorphous silicon (a-Si: H) 113 by drift by the internal electric field. And n-type amorphous silicon (a-Si: H) 115 are collected to generate a current.

Microcrystalline silicon (μc-Si: H) is a boundary material between single crystal and polycrystalline silicon, and has a crystal size of several tens of nanometers to several hundreds of nanometers.At the crystal boundary between crystals, an amorphous phase is often present. Occurs. The energy bandgap of microcrystalline silicon (μc-Si: H) is about 1.6 eV, which is not much different from that of monocrystalline silicon (1.12 eV), and there is no deterioration phenomenon seen in amorphous silicon (a-Si: H) solar cells. The microcrystalline silicon (μc-Si: H) solar cell has a structure very similar to that of an amorphous silicon (a-Si: H) solar cell except for a light absorbing layer.

A single p-i-n junction thin film solar cell using amorphous silicon (a-Si: H) or microcrystalline silicon (μc-Si: H) as a light absorbing layer has low light conversion efficiency and has many limitations in actual use. Therefore, tandem or triple stacked solar cells are fabricated by stacking amorphous silicon (a-Si: H) or microcrystalline silicon (μc-Si: H) thin film solar cells in double or triple layers. This can increase the open voltage and improve the conversion efficiency of incident light by connecting the solar cells in series.

2 illustrates a structure of a conventional tandem thin film solar cell.

As shown, the conventional tandem thin film solar cell 210 is largely a substrate 211 / transparent conductive film 212 / first pn junction layer 213 / tunneling pn junction layer 214 / second and a pn junction layer 215 / back reflector 216.

In the conventional tandem thin film solar cell 210, the first pn junction layer 213 having a band gap (eg, E _g = 1.6 eV) has a smaller band gap (eg, E _g = 1.1 eV). A photon disposed above the second pn junction layer 215 and having an energy greater than 1.6 eV is absorbed in the first pn junction layer 213 and has a photon having an energy between 1.1 eV < hv <1.6 eV. The photon passes through the first pn junction layer 213 but is absorbed by the second pn junction layer 215. As the number of stacked solar cells is increased, high photoelectric conversion efficiency can be obtained.

Meanwhile, the transparent conductive film used for the solar cell is required to have high light transmittance, electrical conductivity, and light trapping effects. Particularly in the case of a tandem thin film solar cell, the transparent conductive film is required to have high light transmittance and haze value in a wide wavelength range of 350 to 1200 nm. In addition, when forming a light absorbing layer on the transparent conductive film must be equipped with durability for hydrogen plasma.

However, the transparent conductive film which is widely used for solar cells is a conductive film mainly composed of tin oxide (SnO ₂ ), which has low light transmittance in the long wavelength region (900 nm or more), which lowers the photoelectric conversion efficiency of the solar cell and also transparent conductive film. Degradation occurs in the hydrogen plasma process during coating. In addition, a transparent conductive film containing tin oxide (SnO ₂ ) as a main component has limitations in material properties such as low electrical conductivity and low transmittance of about 70%.

Currently, tin-doped indium oxide (ITO), which is mainly used as a conventional transparent conductive film, satisfies high light transmittance of 80% or more and excellent electrical conductivity of 10 ^-4 Ωcm, but indium (In), which is a main raw material, is a rare element. There are problems such as rise and high reducibility of indium (In) in the hydrogen plasma process and the accompanying chemical instability.

Therefore, research on the development of a transparent conductive film which can replace the transparent conductive film mainly composed of tin oxide (SnO ₂ ) or tin-doped indium oxide (ITO) is in progress. It is zinc oxide (ZnO) that has recently attracted attention as the most ideal material. Since zinc oxide (ZnO) is easy to doping and has a narrow conduction band, it is easy to control the electro-optic properties according to the doping material. In addition, the transparent conductive film mainly composed of zinc oxide (ZnO) is stable in the hydrogen plasma process, can be manufactured at low cost, and has high light transmittance and conductivity.

However, zinc oxide (ZnO) has a weak moisture resistance, and the electrical conductivity decreases with time. Therefore, it has a fatal drawback that can cause deterioration of solar cell performance and lifespan. In order to improve the moisture resistance of zinc oxide (ZnO), a protective coating is generally applied. However, this causes problems of additional contact resistance and cost increase due to additional processes. Meanwhile, a method of doping a dopant in zinc oxide (ZnO) has been applied, but when the dopant is overdoped, there is a problem in that moisture resistance is improved but light transmittance is lowered.

The present invention has been proposed in the above background, and an object of the present invention is to provide a solar cell substrate having excellent electrical and optical properties usable for solar cells and excellent moisture resistance.

It is an additional object of the present invention to provide a solar cell substrate having high photoelectric conversion efficiency.

In order to achieve the above object, the solar cell substrate according to an aspect of the present invention includes a transparent substrate and a zinc oxide (ZnO) transparent conductive thin film layer doped with a dopant formed on the transparent substrate, wherein the zinc oxide ( The ZnO) transparent conductive thin film layer protects the first dopant doping layer and the first dopant doping layer having a light transmittance of 80% or more at a wavelength band having an energy level of 1.7 eV or less, and reacts moisture and the first dopant doping layer. It includes a second dopant doping layer to block.

A solar cell substrate according to an additional aspect of the present invention is characterized in that a surface roughness film is formed on at least one of the transparent substrate, the first dopant doping layer, and the second dopant doping layer.

According to another additional aspect of the present invention, a solar cell substrate further includes a foreign matter elution prevention layer formed between the transparent substrate and the zinc oxide (ZnO) transparent conductive thin film layer to prevent foreign substances from eluting from the inside of the transparent substrate.

According to the above configuration, the solar cell substrate of the present invention comprises a first dopant doping layer in which a zinc oxide (ZnO) transparent conductive thin film layer satisfies 80% or more of light transmittance in a wavelength band having an energy level of 1.7 eV or less, and a first By implementing a second dopant doping layer that protects the dopant doping layer and blocks the reaction between moisture and the first dopant doping layer, it satisfies the light transmittance characteristics that can be used in the solar cell and excellent moisture resistance, There is a useful effect that can extend the life.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

FIG. 3 is a graph illustrating light transmission characteristics of wavelength-doped zinc oxide (ZnO) thin films doped with dopants, and FIG. 4 is a graph illustrating moisture resistance test results of zinc oxide (ZnO) thin films doped with dopants. 3 and 4, reference numeral 311 denotes a zinc oxide (ZnO) thin film doped with aluminum (Al) dopant of 20 mol% or more and 40 mol% or less, and 312 represents 30 mol% or more and 45 mol% or less of gallium (Ga) dopant. Doped zinc oxide (ZnO) thin film, and 313 is a zinc oxide (ZnO) thin film doped with a boron (B) dopant of 5 mol% or less.

First, the light transmission characteristics of wavelength bands of the zinc oxide (ZnO) thin films 311, 312, and 313 doped with dopants will be described.

The zinc oxide (ZnO) thin film 311 doped with aluminum (Al) dopant and the zinc oxide (ZnO) thin film 312 doped with gallium (Ga) dopant are rapidly light-transmitted in the long wavelength region of 1.7 eV or less (321). On the other hand, the zinc oxide (ZnO) thin film 313 doped with the boron (B) dopant has an excellent light transmittance of about 80% (323).

Hereinafter, the moisture resistance test results of the zinc oxide (ZnO) thin film doped with dopants will be described with reference to FIG. 4. The moisture resistance test was carried out while measuring the sheet resistance value (Ω / □) for 500 hours at a humidity of 90% and a temperature of 85 ° C.

In FIG. 4, the zinc oxide (ZnO) thin film 311 doped with aluminum (Al) dopant has a slight increase in sheet resistance (Ω / □) over time, and zinc oxide doped with gallium (Ga) dopant. The ZnO) thin film 312 has almost no change in sheet resistance (Ω / □) value over time. On the other hand, the zinc oxide (ZnO) thin film 313 doped with the boron (B) dopant has a large increase in sheet resistance (Ω / □) over time.

In the long wavelength region of 1.7 eV or less (321) shown in FIGS. 3 and 4, the results of light transmittance and moisture resistance show that the zinc oxide (ZnO) thin film doped with gallium (Ga) dopant 312 has a light transmittance. On the other hand, it is excellent in moisture resistance. The zinc oxide (ZnO) thin film 313 doped with the boron (B) dopant has excellent light transmittance but poor moisture resistance. The zinc oxide (ZnO) thin film 311 doped with aluminum (Al) dopant has better moisture resistance than the zinc oxide (ZnO) thin film 313 doped with boron (B) dopant, but is less than 1.7 eV (321). The light transmittance in the long wavelength region is poor.

FIG. 5 illustrates a structure of a solar cell substrate according to a first embodiment of the present invention, and FIG. 6 illustrates shallow donors and intrinsic defects caused by dopant doping in a zinc oxide (ZnO) transparent conductive thin film layer. Shows a shallow donor energy band.

First, as shown in FIG. 5, the solar cell substrate 510 according to the present exemplary embodiment includes a transparent substrate 511 and a zinc oxide (ZnO) transparent conductive thin film layer 512 doped with a dopant formed on the transparent substrate 511. ).

The transparent substrate 511 is not limited as long as it has excellent light transmittance and excellent mechanical properties. For example, the transparent substrate 511 is an organic film capable of thermosetting or UV curing, mainly a polymer-based material such as polyethylene terephthalate (PET), acryl, polycarbonate, and urethane acryl. It can be implemented with a rate (Urethane Acrylate), polyester (Polyester), epoxy acrylate (Epoxy Acrylate), brominated acrylate (Brominate Acrylate), polyvinyl chloride (PolyVinyl Chloride, PVC). In addition, the transparent substrate 511 may be embodied as sodaim glass (Sio2-CaO-Na2O) or aluminosilicate glass (SiO2-Al2O-Na2O) as chemically strengthened glass, and the amount of Na and Fe is adjusted to be low depending on the application. Can be done.

The dopant-doped zinc oxide (ZnO) transparent conductive thin film layer 512 flows a current generated by photoelectric conversion, and is implemented as a metal material having high conductivity and light transmittance. Since the electrical properties of zinc oxide (ZnO) are almost insulators, dopants are doped during the deposition of a zinc oxide (ZnO) thin film on the transparent substrate 511 to provide electrical conductivity.

In a preferred embodiment, the dopant-doped zinc oxide (ZnO) transparent conductive thin film layer 512 includes a first dopant doping layer 512a having a light transmittance of 80% or more in a wavelength band having an energy level of 1.7 eV or less. And a second dopant doping layer 512b that protects the first dopant doping layer 512a and blocks the reaction between moisture and the first dopant doping layer 512a.

The first dopant doping layer 512a may be formed by a slight doping of a dopant having a difference in ionic radius from zinc ions Zn ²⁺ of 1.45 times or more or 0.45 times or less to 5 mol% or less. In one example, the dopant may be implemented with any one of carbon (C), boron (B), fluorine (F), and silicon (Si). The first dopant doping layer 512a may be doped with a slight amount of the dopant to 5 mol% or less, thereby minimizing a decrease in light transmittance due to light absorption by the dopant.

In the present invention, even if a small amount of dopant is less than 5mol% in the first dopant doping layer 512a, when a dopant having a difference of 1.45 times or more from zinc ions (Zn ²⁺ ) is used, the electrical conductivity required for the solar cell may be secured. Can be. This can be confirmed through FIG. 6. As shown in FIG. 6, a size difference between a shallow donor energy band 611 and zinc ions Zn 2+ and a dopant is directly formed due to dopant doping in a zinc oxide (ZnO) transparent conductive thin film layer. Both of the shallow donor energy bands 612 due to intrinsic defects that promote the formation of the furnace are excited at room temperature close to the conduction band (CB).

In another embodiment, the first dopant doping layer 512a may be formed by a slight doping of a dopant having a valence difference of 2+ or more from zinc ions Zn ²⁺ of 5 mol% or less. This promotes the formation of energy bands in shallow donors due to the difference in the valence between zinc ions (Zn ²⁺ ) and the dopant. In one example, the dopant may be implemented by any one of ruthenium (Ru), titanium (Ti), niobium (Nb), and tin (Sn).

The second dopant doping layer 512b is implemented as being doped with a dopant including gallium (Ga). As described above in FIG. 4, the zinc oxide (ZnO) transparent conductive thin film layer doped with gallium (Ga) dopant is excellent in moisture resistance. The second dopant doping layer 512b prevents the first dopant doping layer 512a from being combined with moisture (eg, H 2 O, OH, H, etc.) to increase specific resistance. For example, the second dopant doping layer 512b may be doped with a small amount of aluminum (Al), boron (B), indium (In), or silicon (Si) together with gallium (Ga).

7 shows the structure of a solar cell substrate according to a second embodiment of the present invention.

As shown, the solar cell substrate 710 according to the present embodiment is a zinc oxide doped with a dopant including a transparent substrate 711, the first dopant doping layer 712a and the second dopant doping layer 712b. A (ZnO) transparent conductive thin film layer 712 and the foreign matter dissolution prevention film 713 may be implemented.

As illustrated, a surface roughness film having a constant surface roughness may be formed on the first dopant doping layer 712a and the second dopant doping layer 712b. In the present specification, the surface roughness film refers to a film in which nanometer-level small irregular grooves are widely distributed around the surface. The surface roughness film formed on the second dopant doping layer 712b serves to enhance the light trapping effect of the incident light passing through the transparent substrate 711. The surface roughness film formed on the first dopant doping layer 712a prevents incident light from being reflected on the surface of the transparent substrate 311 and is incident on the zinc oxide (ZnO) transparent conductive thin film layer 712 through the transparent substrate 711. It increases the light transmittance. For example, in the solar cell substrate 710 of the present invention, a surface roughness film may be formed on the surface of the transparent substrate 711.

The foreign substance leaching prevention film 713 is formed between the transparent substrate 711 and the zinc oxide (ZnO) transparent conductive thin film layer 712, and the transparent substrate 711, for example, sodaim glass (Sio2-CaO-Na 2 O) or aluminosilicate glass. This prevents elution of foreign substances, such as alkali ions such as sodium (Na +) ions, from the inside of (SiO 2 -Al 2 O—Na 2 O). Preferably, the foreign matter dissolution prevention film 713 may be implemented by any one of silicon oxide (SiO 2) or titanium oxide (TiO 2). The foreign matter dissolution prevention film 713 may be refractive index matching with the transparent substrate 711 by adjusting the film thickness. Accordingly, the foreign matter dissolution prevention film 713 may prevent the incident light from being reflected on the surface of the transparent substrate 711.

Thus far, the present specification has been described with reference to the embodiments shown in the drawings so that those skilled in the art to which the present invention pertains can easily understand and reproduce the present invention. Those skilled in the art will understand that various modifications and equivalent other embodiments are possible from the embodiments of the present invention. Accordingly, the true scope of the present invention should be determined only by the appended claims.

1 illustrates a structure of a solar cell using conventional amorphous silicon as a light absorbing layer.

2 illustrates a structure of a conventional tandem thin film solar cell.

FIG. 3 is a graph showing wavelength transmission characteristics of zinc oxide (ZnO) thin films doped with dopants. FIG.

FIG. 4 is a graph illustrating a moisture resistance test result of a zinc oxide (ZnO) thin film doped with a dopant.

5 shows a structure of a solar cell substrate according to a first embodiment of the present invention.

FIG. 6 shows energy bands of shallow donors due to dopant doping and shallow donors due to intrinsic defects in a zinc oxide (ZnO) transparent conductive thin film layer.

7 shows the structure of a solar cell substrate according to a second embodiment of the present invention.

<Description of Major Reference Marks>

510 and 710: solar cell substrate

511, 711: transparent substrate

512, 712: zinc oxide (ZnO) transparent conductive thin film layer

512a and 712a: first dopant doping layer 512b and 712b: second dopant doping layer

713: foreign substance dissolution prevention film

Claims (10)

A solar cell substrate comprising a transparent substrate and a zinc oxide (ZnO) transparent conductive thin film layer formed on the transparent substrate and doped with a dopant. The zinc oxide (ZnO) transparent conductive thin film layer, A first dopant doping layer in which light transmittance of a wavelength band having an energy level of 1.7 eV or less satisfies 80% or more; And The light transmittance of the wavelength band having an energy level of 1.7 eV or less than that of the first dopant doping layer is lower than that of the first dopant doping layer, and the electrical conductivity decreases with time due to moisture less than the first dopant doping layer. A second dopant doping layer having a wet property to protect the first dopant doping layer and to block a reaction between moisture and the first dopant doping layer; / RTI &gt; And the transparent substrate, the first dopant doping layer, and the second dopant doping layer in that order. The method of claim 1, The first dopant doping layer, A solar cell substrate comprising a dopant having a difference in ion radius from zinc ions (Zn 2+) of 1.45 times or more or 0.45 times or less. The method of claim 2, The first dopant doping layer, A solar cell substrate, wherein any one of carbon (C), boron (B), fluorine (F), and silicon (Si) is doped with a dopant. delete delete 4. The method according to any one of claims 1 to 3, The first dopant doping layer, A solar cell substrate, wherein the dopant is doped with 5 mol% or less. The method of claim 1, The second dopant doping layer, A solar cell substrate, which is doped with a dopant containing gallium (Ga). The method of claim 1, A surface roughness film is formed on at least one of the transparent substrate, the first dopant doping layer, and the second dopant doping layer. delete delete

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