KR20130070696A - Solar cell having layer for diffusion barrier - Google Patents

Abstract

PURPOSE: A solar cell including a diffusion barrier is provided to increase energy conversion efficiency, by preventing impurity from being diffused to a bottom electrode. CONSTITUTION: A diffusion barrier (20) is formed on a bottom substrate (10). A bottom electrode (30) is formed on the diffusion barrier. A p type light absorption layer is formed on the bottom electrode. An n type buffer layer is formed on the light absorption layer. A top electrode is formed on a transparent window.

Description

SOLAR CELL HAVING LAYER FOR DIFFUSION BARRIER}

The present invention relates to a solar cell comprising a diffusion barrier.

Traditional methods of collecting energy using fossil fuels are slowly reaching their limits due to global warming, depletion of fuel resources, and environmental pollution. Particularly in the case of petroleum fuels, the prognosis is that the forecast will reveal the floor within a very short period of time, albeit slightly different.

In addition, the energy-climate treaty, represented by the Kyoto Protocol, forcibly requires the reduction of carbon dioxide emissions resulting from the burning of fossil fuels. Therefore, it is clear that it will be restricted by the current use of fossil fuels, as well as the current contracting countries, and in the future to all countries around the world.

The most representative energy source used to replace fossil fuels is nuclear power. Nuclear power generation is an energetic alternative energy source that can substitute for fossil fuels such as petroleum, because it generates a large amount of energy that can be collected per unit weight of uranium or plutonium as a raw material and does not generate greenhouse gases such as carbon dioxide. I have received.

However, the explosion of the Chernobyl nuclear power plant in Sri Lanka and the Fukushima Nuclear Power Plant in Japan caused by the Great East Japan Earthquake has led to a reexamination of the safety of nuclear power, which has been regarded as an infinite clean energy source. As a result, The introduction of energy is desperately needed more than ever.

Hydrogen power may be used as an energy source that is widely used as other alternative energy, but the use of hydroelectric power may be limited because it is influenced by topographic and climatic factors. In addition, other alternative energy sources are also difficult to use as alternative means of fossil fuels because of the limited amount of power generation or the limited use area.

However, solar cells can be used anywhere as long as only a reasonable amount of sunlight is ensured, and the power generation capacity and equipment scale are almost linearly proportional to each other. Therefore, when the solar cells are used for small capacity such as home use, the solar cells are installed by installing a small area on the roof of a building. The advantage of this is that not only is its use globally, but its research is also increasing.

Solar cells are based on the principle of semiconductors. When a light having a certain energy level or more is irradiated to a pn-junction semiconductor, the electrons of the semiconductor are excited as freely movable electrons to form a pair of electrons and holes (EHP ) Is generated. The generated electrons and holes move to the electrode located on the opposite side to generate an electromotive force.

In the first type of the solar cell, a p-type semiconductor is formed by doping an impurity (B) into a silicon substrate, and then another impurity (P) is doped thereon to convert a part of the layer into an n-type semiconductor. It is a silicon-based solar cell, often referred to as a first-generation solar cell.

The silicon-based solar cell has the highest degree of commercialization because it has a relatively high energy conversion efficiency and a high cell conversion efficiency (ratio of conversion efficiency at the time of mass production to the highest energy conversion efficiency of the laboratory). However, in order to manufacture the silicon-based solar cell module, a complicated process step such as manufacturing an ingot from a raw material and making the ingot into a wafer and then manufacturing and modifying the cell must be performed, and a bulk material is used , There is a problem that the material consumption is increased and the manufacturing cost is high.

In order to solve the disadvantages of such a silicon solar cell, a so-called thin film solar cell called a second generation solar cell has been proposed. Since the thin film solar cell is manufactured by stacking the thin film layers sequentially required on the substrate, instead of manufacturing the solar cell by the above-described process, the process is simple, and the thin film solar cell has an advantage that the material cost is low.

However, in many cases, the energy conversion efficiency is not high compared to the silicon-based solar cell, and thus many obstacles to commercialization have been developed. However, solar cells having some high energy conversion efficiency have been developed and commercialized.

One of them is CI (G) S-based solar cell, which is copper (Cu), indium (In), germanium (Ge) (germanium may not be included. Is called CIS) and CI (G) S compound semiconductors containing selenium (Se).

Since the semiconductor contains three or four elements, the width of the bandgap can be controlled by controlling the content of the element, thereby increasing the energy conversion efficiency. Occasionally, selenium (Se) is replaced with sulfur (S) or selenium (Se) with sulfur (S). In the present invention, all of these cases are regarded as CI (G) S solar cells.

The CIGS (when germanium is included) solar cell has a lower substrate on the lowermost layer, and a lower electrode used as an electrode is formed on the lower substrate. On the lower electrode, a light absorption layer (CIGS) as a p-type semiconductor, a buffer layer (for example, CdS) as a n-type semiconductor, a transparent window, and an upper electrode are sequentially formed.

Meanwhile, glass was used as the lower substrate. Na is contained in the glass, and Na is known to diffuse into the CIGS layer to increase the open voltage and fidelity of the solar cell. However, the appropriate amount of Na may improve the efficiency of the solar cell, but in the case of excessive diffusion, there is a problem of lowering the efficiency of the solar cell.

Recently, many attempts have been made to use flexible substrates instead of glass substrates that are expensive, low in mass production, and can only be used in standardized form. Flexible substrates are cheaper than glass, and can be manufactured in a roll-to-roll manner, and can be processed in various forms, so that not only a building integrated module (BIPV) but also aerospace can be used. It can be used for purposes. As the flexible substrate, a metal plate such as stainless steel, an aluminum foil, a polyimide film, or a plastic-based substrate is used. In the case of such a flexible substrate, many impurities, including Fe, are included, and these impurities are diffused to the lower electrode or the CIGS layer, causing a problem of lowering the efficiency of the solar cell.

In the case of using a glass substrate, in order to suppress excessive diffusion of Na and suppressing diffusion of impurities in the flexible substrate, a technique of forming a diffusion barrier film made of a layer has been conventionally applied.

However, as the thickness of the solar cell, the weight reduction, etc., the thickness of the diffusion barrier film becomes very thin, a new problem arises that the effective diffusion prevention effect can not be secured in the case of the single layer diffusion barrier film. .

The present invention relates to a solar cell including a diffusion barrier having an excellent diffusion barrier effect between the lower substrate and the lower electrode.

One aspect of the invention the lower substrate; A diffusion barrier formed on the lower substrate; A lower electrode formed on the diffusion barrier layer; A p-type light absorption layer formed on the lower electrode; An n-type buffer layer formed on the light absorption layer; A transparent window formed on the buffer layer; And an upper electrode formed on the transparent window, wherein the diffusion barrier provides a solar cell having an area ratio of 40 to 90% of the lower substrate.

The solar cell of the present invention can effectively prevent the diffusion of impurities contained in the lower substrate to the lower electrode can be expected to improve the efficiency.

1 is a schematic diagram showing an embodiment of a lower substrate on which a diffusion barrier and a lower electrode of the present invention are formed.
FIG. 2 is a perspective view illustrating the lower substrate of the embodiment shown in FIG. 1.
3 is a schematic diagram showing another embodiment of the lower substrate on which the diffusion barrier and the lower electrode of the present invention are formed.
4 is a perspective view illustrating a lower substrate of another embodiment shown in FIG. 3.
5 is a schematic view showing an example of the solar cell of the present invention.
6 is a schematic view showing another example of the solar cell of the present invention.

Hereinafter, the present invention will be described in detail.

One aspect of the invention the lower substrate; A diffusion barrier formed on the lower substrate; A lower electrode formed on the diffusion barrier layer; A p-type light absorption layer formed on the lower electrode; An n-type buffer layer formed on the light absorption layer; A transparent window formed on the buffer layer; And an upper electrode formed on the transparent window, wherein the diffusion barrier provides a solar cell having an area ratio of 40 to 90% of the lower substrate.

In general, a solar cell includes a lower electrode on a lower substrate and a lower electrode, and includes a diffusion barrier layer that suppresses diffusion of impurities such as Na and Fe existing in the lower substrate to the lower electrode. do.

However, the diffusion barrier does not completely suppress impurities diffused from the lower substrate. That is, some of the impurity atoms pass through the diffusion barrier layer and are transferred to the lower electrode. For example, the existing diffusion barrier film is in contact with the lower substrate or the lower electrode at an area ratio of 100%. At this time, assuming that 100 impurity atoms diffuse from the lower substrate to the lower electrode, all 100 impurity atoms are lower electrodes. To spread. However, in the present invention, it is intended to improve the diffusion prevention effect by reducing the area of the diffusion barrier. In other words, by reducing the area of the diffusion barrier, the surface of the diffusion barrier is in contact with the lower substrate and the lower electrode, thereby eliminating passages through which impurities can diffuse. For example, if the area of the diffusion barrier is 70%, since only 70 passages for impurity atoms can be generated, the diffusion of impurity atoms can be effectively reduced.

For this diffusion prevention effect, the area ratio of the diffusion barrier is preferably 90% or less than that of the lower substrate. As described above, by reducing the area of the diffusion barrier, the movement path of the impurity atoms can be removed, and the diffusion prevention effect can be improved. For this effect, it is preferable that the diffusion barrier has as small an area as possible, but if the area is excessively reduced, it may be difficult to support the lower electrode formed on the diffusion barrier, and the diffusion barrier may not be formed when the lower electrode is coated. Since the lower electrode may be coated on a region that does not have a diffusion barrier effect, the area ratio of the diffusion barrier layer is preferably 40% or more. Therefore, the diffusion barrier layer preferably has an area ratio of 40 to 90% of the lower substrate or the lower electrode. The area ratio of the diffusion barrier is more preferably in the range of 60 to 85%, even more preferably in the range of 70 to 80%.

1 is a schematic diagram showing an embodiment of a lower substrate on which a diffusion barrier film and a lower electrode of the present invention are formed, and FIG. 2 is a perspective view showing a lower substrate according to the embodiment. EMBODIMENT OF THE INVENTION Hereinafter, one Embodiment of this invention solar cell is described with reference to FIGS. 1 and 2 illustrate an example of the present invention, but are not necessarily limited thereto.

As can be seen in Figures 1 and 2, the solar cell substrate 100 according to an embodiment of the present invention is a diffusion barrier 20 having a form of a layer (layer) between the lower substrate 10 and the lower electrode 30. Is formed, and holes 22 are formed in the film. As such, by forming the hole 22, the area of the diffusion barrier film 20 is reduced to effectively suppress diffusion of impurities such as Na and Fe of the lower substrate 10 into the lower electrode 30. In this case, the hole 22 may have a variety of shapes and positions, and the hole 22 is not particularly limited thereto. FIG. 2 illustrates a solar cell substrate 100 including a diffusion barrier film 20 including a hole 22 having a circular columnar shape as an example. However, it may have a polygonal shape as well as such a circular shape. However, in order to form the diffusion barrier 20 easily, the diffusion barrier 20 preferably has a circular or rectangular shape. The above-mentioned solar cell substrate means a lower substrate on which a diffusion barrier and a lower electrode are formed.

On the other hand, in order to improve the diffusion prevention effect, the average thickness of the diffusion barrier is preferably 10nm ~ 10㎛. If less than 10nm, since impurities can easily penetrate the diffusion barrier, the effect of preventing diffusion of impurities may be lowered. If it exceeds 10㎛, production efficiency may be reduced due to an increase in process time and process cost. Therefore, the average thickness of the diffusion barrier film preferably has a range of 10 nm to 10 μm, more preferably 50 nm to 5 μm, and even more preferably 100 nm to 2 μm.

3 is a schematic diagram showing another embodiment of the lower substrate on which the diffusion barrier film and the lower electrode of the present invention are formed, and FIG. 4 is a perspective view showing the lower substrate according to the other embodiment. As shown in Figures 3 and 4, the solar cell of the present invention may be provided with a diffusion barrier of a different form from the above-described embodiment. Hereinafter, another embodiment of the solar cell of the present invention will be described with reference to FIGS. 3 and 4. 3 and 4 also show an example of the present invention, but are not necessarily limited thereto.

As can be seen in Figures 3 and 4, the diffusion barrier 20 according to another embodiment of the present invention may itself be in the shape of a cylinder or polygonal pillar, it is preferable that the pillar 20a is one or more. In other words, the diffusion barrier 20 may be formed in such a form, and thus, the diffusion barrier may be improved by reducing the area ratio. The diffusion barrier of this type also preferably has a thickness in the range of 10 nm to 10 μm for the reasons described above.

On the other hand, it is preferable that the above-mentioned holes (holes) and pillars have an average width of 20 to 500 nm. If the average width of the hole is less than 20 nm, the area reduction rate may be reduced, and the diffusion prevention effect may be reduced. If the average width is more than 500 nm, durability may occur and damage may occur due to external impact. On the other hand, if the average width of the pillar is less than 20nm may cause a problem in durability and may be damaged by an external impact. In addition, since the process of controlling the width of the column extremely fine is not easy in the process, the manufacturing cost may increase. In the case where the average width of the pillar exceeds 500 nm, the area is increased, so that the diffusion preventing effect can be reduced. Therefore, the average width of the holes and the pillars is preferably in the range of 20 to 500 nm, more preferably in the range of 20 to 300 nm, even more preferably in the range of 50 to 200 nm.

If a plurality of holes or pillars is provided, it is preferable that the interval between each other, that is, the average interval between the holes or pillars, is 1 to 100 nm. When the average spacing between the holes is less than 1 nm, the second diffusion barrier layer or the electrode may penetrate into the holes during coating of the electrode in a later process, thereby preventing diffusion. If it exceeds 100 nm, the trapping effect of impurities may be reduced. On the contrary, when the average distance between the pillars is less than 1 nm, the trapping effect of impurities may be lowered, and the diffusion preventing effect may be reduced. If the thickness exceeds 100 nm, the electrode may penetrate between the pillars during electrode coating in a later process, and diffusion prevention may not be achieved. Therefore, it is preferable that the average interval between holes or pillars is 1-100 nm, It is more preferable to have a range of 1-50 nm, It is still more preferable to have a range of 1-10 nm.

On the other hand, the diffusion barrier is preferably one selected from the group consisting of ZnO, ITO, FTO and AZO, more preferably, the diffusion barrier is ZnO for easy formation.

The method for forming the diffusion barrier as described above is not particularly limited, but as an example, the following Chemical Vapor Deposition (CVD) method may be used. Diethylzinc (Zn (C ₂ H ₅ ) ₂ ) and oxygen gas at a ratio of 1: 300 in the chamber at 350-500 ° C. and 0.3-0.4 torr vacuum pressure were applied vertically. A growing ZnO diffusion barrier film can be obtained. At this time, when the precursor gas is supplied such that the pressure rises to 2 to 5 Torr while maintaining a constant temperature range and the ratio of the precursor, the ZnO diffusion barrier film grows at a rate of about 10 nm per minute. In addition, it is possible to control the width of the diffusion barrier film in the range of 40nm ~ 140nm through temperature control, the width becomes narrower as the temperature is increased. On the other hand, in addition to the temperature control as described above, it can be controlled to the level to obtain the width by controlling other conditions such as pressure or the ratio of the precursor alone or in combination.

Meanwhile, the lower substrate may be made of not only glass but also a flexible substrate. The flexible substrate includes all metal materials (stainless steel, aluminum foil, Fe-Ni-based metal plates, Fe-Cu-based metal plates, etc.), plastic-based materials such as polyimide, and the like.

5 is a schematic diagram showing an example of the solar cell of the present invention, Figure 6 is a schematic diagram showing another example of the solar cell of the present invention. Hereinafter, the solar cell of the present invention will be described with reference to FIGS. 5 and 6. 5 and 6 illustrate an example of the present invention, but are not necessarily limited thereto.

As shown in Figures 5 and 6, the present invention is a lower substrate (10); A diffusion barrier film 20 formed on the lower substrate 10; A lower electrode 30 formed on the diffusion barrier film 20; A p-type light absorption layer 200 formed on the lower electrode 30; An n-type buffer layer 300 formed on the light absorption layer 200; A transparent window 400 formed on the buffer layer 300; And an upper electrode 500 formed on the transparent window 400.

5 and 6 show that the holes 22 are formed in the diffusion barrier film 20 as shown in FIGS. 1 and 3, respectively, or the diffusion barrier film 20 includes the solar cell substrate 100 having a pillar 20a shape. As the solar cell 1000 is illustrated, an improvement in efficiency can be expected through the impurity diffusion suppressing effect as described above.

On the other hand, depending on the type of solar cell to be implemented, the material of the light absorption layer, the buffer layer, etc. may vary. However, as an example, the CIGS solar cell may include CIGS as the light absorption layer, CdS as the n-type semiconductor, and ZnO as the transparent window. Meanwhile, as mentioned above, the lower substrate may be one selected from the group consisting of glass, stainless steel, aluminum foil, Fe—Ni-based metal, Fe—Cu-based metal, and polyimide. In addition, the transparent window or the upper electrode can be preferably applied to the present invention as long as it is commonly used in the art, the type is not particularly limited.

10: lower substrate 20: diffusion barrier
20a: pillar 22: hole
30: lower electrode 100: solar cell substrate
200: light absorbing layer 300: buffer layer
400: transparent window 500: upper electrode
1000: solar cell

Claims (11)

A lower substrate;
A diffusion barrier formed on the lower substrate;
A lower electrode formed on the diffusion barrier layer;
A p-type light absorption layer formed on the lower electrode;
An n-type buffer layer formed on the light absorption layer;
A transparent window formed on the buffer layer; And
An upper electrode formed on the transparent window,
The diffusion barrier is a solar cell having an area ratio of 40 to 90% of the lower substrate.
The method according to claim 1,
The diffusion barrier is in the form of a layer (layer), a hole is formed in the film, the hole comprises a circular or polygonal form of a solar cell.
The method according to claim 1,
The diffusion barrier has a shape of a cylinder or a polygonal column, wherein the cylinder or polygonal column comprises at least one.
The method according to claim 1,
The average thickness of the diffusion barrier film is a solar cell comprising 10nm ~ 10㎛.
The method according to claim 2,
The solar cell comprising an average width of the hole is 20 ~ 500nm.
The method according to claim 3,
The solar cell comprising an average width of the pillar is 20 ~ 500nm.
The method according to claim 2,
The average interval between the holes (hole) is a solar cell comprising a 1 ~ 100nm.
The method according to claim 3,
The average interval between the pillar is a solar cell comprising 1 ~ 100nm.
The method according to claim 1,
The diffusion barrier is a solar cell, characterized in that at least one selected from the group consisting of ZnO, ITO, FTO and AZO.
The method according to claim 1,
The lower substrate is a solar cell, characterized in that one selected from the group consisting of glass, stainless steel, aluminum foil, Fe-Ni-based metals, Fe-Cu-based metals, polyimide.
The method according to claim 1,
The light absorption layer is CIGS, the buffer layer is CdS, the transparent window is a solar cell, characterized in that the ZnO.

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