TWI395338B - Thin film solar cells having a paticular back electrode and manufacturing method thereof - Google Patents

Description

Thin film solar cell with special back electrode structure and manufacturing method thereof

The invention relates to a thin film solar cell having a special back electrode structure and a method for fabricating the same, wherein the back electrode layer of the thin film solar cell is formed by sequentially introducing a first metal layer, an interposer and a second metal layer.

In the 1970s, the first solar cells developed by Bell Labs in the United States gradually developed. With the development of solar cells, there are many types of solar cells today, typically crystalline germanium solar cells, polycrystalline germanium solar cells, amorphous germanium solar cells, compound solar cells, dye-sensitized solar cells, and the like. The solar cell is mainly a P/N junction semiconductor structure that utilizes a photovoltaic effect to directly convert light energy into electrical energy. In recent years, thin film laminated solar cells have become the trend of development in response to the demand for thinning of solar cells. The biggest advantage of thin film laminated solar cells is that the production cost is low, but the problems of efficiency and stability have yet to be improved.

Please refer to FIG. 1 , which is a conventional thin film solar cell structure, and the conventional thin film solar cell 10 includes a substrate 11 , a front electrode layer 12 , a light absorbing layer 13 and a back electrode layer 14 which are sequentially stacked, wherein The composition of the back electrode layer 14 further includes a transparent conductive layer (GZO) 141, a silver (Ag) metal layer 142, and a titanium (Ti) metal film 145 which are sequentially stacked. However, in the material of the above-mentioned conventional back electrode layer 14, the film thickness of silver is the highest compared with the film thickness ratio of the transparent conductive material GZO and the metal Ti, that is, the film thickness of GZO and Ti is 800 Å, respectively. ) with 150 Å (Å), and the film thickness of silver must be 2100 Å (Å) to maintain a higher reflectivity of the back electrode layer. Since the film thickness of the silver introduced into the back electrode layer 14 is relatively high, the manufacturing cost of the entire thin film solar cell is relatively increased, which is unfavorable for mass production, and it is necessary to improve it.

In order to solve the above-mentioned prior art, the present invention provides a special back-up. The thin-film solar cell of the pole structure comprises a substrate, a front electrode layer, a light absorbing layer and a back electrode layer which are sequentially stacked, wherein the back electrode layer further comprises a transparent conductive layer, a first metal layer and an interposer which are sequentially formed by stacking And a second metal layer and a metal film, wherein the interposer has a resistivity value greater than 1 micro ohm-cm (μΩ-cm) to provide a conductive barrier between the first metal layer and the second metal layer.

Therefore, the main object of the present invention is to provide a thin film solar cell having a special back electrode structure, wherein the first metal layer, the interposer layer and the second metal layer are formed to provide a light reflectance of the back electrode layer of 98%. the above.

Another object of the present invention is to provide a thin film solar cell having a special back electrode structure, wherein the structure formed by the first metal layer, the interposer layer and the second metal layer can greatly reduce the introduction cost of the back electrode layer.

In addition, the present invention further provides a method for fabricating a thin film solar cell having a special back electrode structure, comprising the steps of: providing a substrate; forming a front electrode layer on the substrate; forming a light absorbing layer on the front electrode layer; and forming a back electrode The layer is in the light absorbing layer, wherein the back electrode layer is sequentially introduced with a transparent conductive layer, a first metal layer, an interposer, a second metal layer and a metal film, wherein the interposer has a resistivity value greater than 1 micro ohm-cm ( μΩ-cm) to provide a conductive barrier between the first metal layer and the second metal layer.

Therefore, the main object of the present invention is to provide a method for fabricating a thin film solar cell having a special back electrode structure, wherein the back electrode layer structure formed by sequentially introducing the first metal layer, the interposer layer and the second metal layer can make the light The reflectance is over 98%.

Another object of the present invention is to provide a method for fabricating a thin film solar cell having a special back electrode structure, wherein the back electrode layer structure formed by sequentially introducing the first metal layer, the interposer layer and the second metal layer can greatly reduce the back electrode The import cost of the layer.

The present invention discloses a thin film solar cell having a special back electrode structure and a manufacturing method thereof, wherein the principle and basic functions of the solar power generation utilized have been Usually the knowledge can be understood, so the description below will not be fully described. At the same time, the drawings referred to in the following texts express the structural schematics related to the features of the present invention, and need not be completely drawn according to the actual size, which is first described.

First, please refer to FIG. 2, which is a thin film solar cell structure mainly comprising a substrate 21, a front electrode layer 22 and a light absorbing layer which are sequentially stacked according to a preferred embodiment of the present invention. And the back electrode layer 24, wherein the back electrode layer 24 further comprises a transparent conductive layer 241, a first metal layer 242, an interposer 243, a second metal layer 244 and a metal film 245 formed by sequentially stacking, wherein the interposer 243 A resistivity value greater than 1 micro ohm-cm (μΩ-cm) is provided to provide a conductive barrier between the first metal layer 242 and the second metal layer 244.

In the above embodiment, the metal thin film 245 may be one of titanium (Ti), nickel vanadium alloy (Ni-V), nickel titanium alloy (Ni-Ti), and nickel cadmium alloy (Ni-Cd), etc., in this embodiment. In the example, Ti is used and the metal thin film Ti has a thickness of 150 Å. The front electrode layer 22 is a transparent conductive oxide (TCO). The light absorbing layer 23 is an amorphous germanium (a-Si). The transparent conductive layer 241 of the back electrode layer 24 is gallium zinc oxide (GZO), and the transparent conductive layer GZO has a thickness of 800 Å. The first metal layer 242 of the back electrode layer 24 is silver (Ag), and the first metal layer Ag has a thickness of between 300 Å and 2100 Å. The interposer layer 243 of the back electrode layer 24 is a transparent conductive oxide (TCO) or a metal. In the present embodiment, a TCO is used and the interposer TCO has a thickness of 100 Å. The second metal layer 244 of the back electrode layer 24 may be one of aluminum (Al), copper (Cu), and gold (Au). In the present embodiment, Al is used and the second metal layer A1 has a thickness of 300 Å. (Å) to between 2100 angstroms (Å).

In the above embodiment, the sheet resistance of the interposer TCO can be adjusted to form a desired conductive barrier, thereby improving the light reflectance of the back electrode layer to 98% or more. For experimental data on conductive barriers, please refer to Table 1 below.

From the combination of the above various film layers, it can be found that in order to maintain a high reflectance of the back electrode layer, the conventional thin film solar cell must maintain the thickness of the silver film of the back electrode layer at 2100 Å (as shown in Table 1). As a result, the manufacturing cost of the entire thin film solar cell is relatively increased, which is disadvantageous for mass production. However, according to the special back electrode structure of the present invention, the specifications of the experimental group number 5, 6, and 7 are taken as an example, and the thickness of the silver film is only 300 Å (about one-seventh of the standard value of the conventional silver film), and then transparent conductive The GZO film thickness of the layer is 100Å and the thickness of the aluminum film of the second metal layer is 1000Å, 1500Å or 2100Å. By controlling the film thickness ratio of the three stacked materials Ag/GZO/Al, the light reflectance of the back electrode layer can reach 98% or more. . In other words, using the lower cost material GZO and aluminum, and controlling the film thickness of GZO and aluminum within a certain range, the amount of silver film used can be greatly reduced (only 300Å), but the conventional use of pure silver can be achieved. The high cost can be achieved with high cost.

Next, please refer to the 3A, 3B, and 3C diagrams, and then explain the relationship between the reflectance and the spectrum, and use the pure aluminum, pure silver and the special stack structure Ag/GZO/Al standard film thickness 2100 of the present invention. Å sterling silver exhibits a change in reflectivity for thin film solar cells with different spectra. The X axis is the spectral wavelength, the unit is nanometer (nm), the Y axis is the reflectance, and the unit is percentage (%).

In Fig. 3A, the benefit comparison between pure aluminum with different film thicknesses and pure silver with a standard film thickness of 2100 Å is introduced in the back electrode layer, wherein the left-hand relationship diagram is used to indicate the thin film solar energy before baking. The unit cell and the right-hand diagram are used to represent the baked thin film solar module. It can be found from Fig. 3A that the reflectivity of the back electrode layer only with pure aluminum is inferior to the introduction of pure silver, that is, the film thickness of the introduced pure aluminum changes from 500 Å to 2100 Å, and the reflectance of the back electrode layer to most spectral wavelengths. Compared with the introduction of standard silver film with a thickness of 2100 Å, the reflectivity is generally poor, and the reflectivity of the back electrode layer is not good, so the photoelectric conversion efficiency of the thin film solar cell is negatively affected. Therefore, pure aluminum cannot directly replace the increase in the reflectivity of pure silver in the back electrode layer.

In Figure 3B, the benefit of comparing only the pure silver with different film thicknesses into the standard silver film with a thickness of 2100 Å is introduced in the back electrode layer. The left-hand relationship diagram is used to indicate the thin film solar power before baking. The unit cell and the right-hand relationship diagram are used to represent the baked thin film solar power module. It can be seen from Fig. 3B that the reflectance of the back electrode layer introduced with pure silver will be inferior with the thickness of the silver film, especially when the film thickness of the introduced pure silver is less than 900 Å, compared with the introduction of the standard film. In the case of 2100 Å thick silver, the decrease in the light reflectance of the back electrode layer is greatly degraded as the wavelength of the spectrum decreases. Therefore, if it is necessary to maintain the reflectivity of the back electrode layer with acceptable benefits, the film thickness of pure silver must be at least higher than 900 Å.

In Figure 3C, a comparison of the benefits of introducing a special stack structure Ag/GZO/Al control of the present invention into a standard film thickness of 2100 Å of pure silver in the back electrode layer, wherein the left hand side relationship diagram is used to indicate before baking The thin film solar cell unit cell, and the right hand side relationship diagram is used to indicate the baked thin film solar power module. It can be found from Fig. 3C that the reflectivity of the back electrode layer introduced into the special stack structure Ag/GZO/Al is completely inferior to that of the standard silver film of 2100 Å, which is the stack structure Ag/GZO/Al (film thickness). 300 Å, 100 Å, 1000 Å to 2100 Å, respectively, have excellent reflectivity for most spectral wavelengths, so such a stacked structure Ag/GZO/Al has a positive effect on the photoelectric conversion efficiency of thin film solar cells. Therefore, the special stack structure Ag/GZO/Al of the present invention can directly replace the standard film thickness of 2100 Å of pure silver in the back electrode layer. The effect of the rate of incidence, which in turn reduces the use rate of pure silver by 66%, can effectively reduce the introduction cost of the back electrode layer. In addition to the reduction in process cost, from the power generation of the entire thin film solar cell, the special stack structure Ag/GZO of the present invention used in the back electrode layer is compared to the use of a standard film thickness of 2100 Å of pure silver in the back electrode layer. /Al further enables the power generation of the entire thin film solar cell to be approximately the same as that of a thin film solar cell using a standard film thickness of 2100 Å sterling silver.

In addition, the present invention provides another preferred embodiment, which is a method for fabricating a thin film solar cell having a special back electrode structure, comprising the following steps:

(1) A substrate 21 is provided.

(2) The front electrode layer 22 is formed on the above substrate 21.

(3) forming the light absorbing layer 23 on the front electrode layer 22, and (4) forming the back electrode layer 24 on the light absorbing layer 23, wherein the back electrode layer 24 is sequentially introduced with the transparent conductive layer 241 and the first metal layer 242. The interposer 243, the second metal layer 244, and the metal film 245, wherein the interposer 243 has a resistivity value greater than 1 micro ohm-cm (μΩ-cm) to provide the first metal layer 242 and the second metal layer 244. Conductive barrier between.

In the above method embodiment, the metal film 245 may be one of titanium (Ti), nickel vanadium alloy (Ni-V), nickel titanium alloy (Ni-Ti), and nickel cadmium alloy (Ni-Cd). Ti is used in the embodiment and the metal thin film Ti has a thickness of 150 Å. The front electrode layer 22 is a transparent conductive oxide (TCO). The light absorbing layer 23 is an amorphous germanium (a-Si). The transparent conductive layer 241 of the back electrode layer 24 is gallium zinc oxide (GZO), and the transparent conductive layer GZO has a thickness of 800 Å. The first metal layer 242 of the back electrode layer 24 is silver (Ag), and the first metal layer Ag has a thickness of between 300 Å and 2100 Å. The interposer layer 243 of the back electrode layer 24 is a transparent conductive oxide (TCO) or a metal. In the present embodiment, a TCO is used and the interposer TCO has a thickness of 100 Å. The second metal layer 244 of the back electrode layer 24 may be one of aluminum (Al), copper (Cu), and gold (Au). In the present embodiment, Al is used and the second metal layer A1 has a thickness of 300 Å. (Å) to 2100 angstroms (Å) between.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the invention. The above description is intended to be apparent to those skilled in the art, and the equivalents and modifications may be included in the scope of the invention.

10 (prior art), 20‧ ‧ thin film solar cells

11 (previous technology), 21‧‧‧ substrate

12 (prior art), 22‧‧‧ front electrode layer

13 (prior art), 23‧‧ ‧ light absorbing layer

14 (prior art), 24‧‧ ‧ back electrode layer

141 (prior art), 241‧‧ ‧ transparent conductive layer

142 (prior art), 242‧‧‧ first metal layer

243‧‧‧Intermediary

244‧‧‧Second metal layer

145 (prior art), 245‧‧‧ metal film

Figure 1 is a schematic view showing a conventional thin film solar cell structure.

Figure 2 is a schematic view of a thin film solar cell structure in accordance with a preferred embodiment of the present invention.

Fig. 3A shows the relationship between the reflectance and the spectrum. The pure aluminum is compared with the standard film thickness of the pure film used for the back electrode layer, and the reflectance changes are exhibited for the thin film solar cell with different spectra.

Fig. 3B is a graph showing the relationship between the reflectance and the spectrum. The pure silver is compared with the standard film thickness of the pure film used for the back electrode layer, and the reflectance changes are exhibited for the thin film solar cell with different spectra.

Fig. 3C is a graph showing the relationship between reflectance and spectrum. The silver/gallium zinc oxide/aluminum standard film thickness of different thicknesses used in the back electrode layer of the present embodiment is compared with that of different spectra. Thin film solar cells exhibit a change in reflectivity.

20‧‧‧Thin solar cells

21‧‧‧Substrate

22‧‧‧ front electrode layer

23‧‧‧Light absorbing layer

24‧‧‧ back electrode layer

241‧‧‧Transparent conductive layer

242‧‧‧First metal layer

243‧‧‧Intermediary

244‧‧‧Second metal layer

245‧‧‧Metal film

Claims (26)

A thin film solar cell having a special back electrode structure, comprising a substrate, a front electrode layer, a light absorbing layer and a back electrode layer, which are sequentially stacked, wherein the back electrode layer further comprises a stack formed in sequence a transparent conductive layer, a first metal layer, an interposer, a second metal layer, and a metal film; wherein the interposer has a thickness smaller than a thickness of the first metal layer and the second metal layer. A thin film solar cell having a special back electrode structure according to the first aspect of the patent application, wherein the metal film is selected from the group consisting of titanium (Ti), nickel vanadium alloy (Ni-V), nickel titanium alloy (Ni-Ti), and A group of nickel-cadmium alloys (Ni-Cd). A thin film solar cell having a special back electrode structure according to the first aspect of the patent application, wherein the front electrode layer is a transparent conductive oxide (TCO). A thin film solar cell having a special back electrode structure according to the first aspect of the patent application, wherein the light absorbing layer is an amorphous germanium (a-Si). A thin film solar cell having a special back electrode structure according to claim 1, wherein the transparent conductive layer of the back electrode layer is gallium zinc oxide (GZO). A thin film solar cell having a special back electrode structure according to claim 1, wherein the first metal layer of the back electrode layer is silver (Ag). A thin film solar cell having a special back electrode structure according to claim 1, wherein the interposer layer of the back electrode layer is a transparent conductive oxide (TCO) or a metal. A thin film solar cell having a special back electrode structure according to claim 1, wherein the second metal layer of the back electrode layer is selected from the group consisting of aluminum (Al), copper (Cu), and gold (Au). Group. A thin film solar cell having a special back electrode structure according to the first aspect of the patent application, wherein the transparent conductive layer has a thickness of 800 Å. A thin film solar cell having a special back electrode structure according to claim 1, wherein the first metal layer has a thickness of between 300 Å and 2100 Å. A thin film solar cell having a special back electrode structure according to the first aspect of the patent application, wherein the interposer has a thickness of 100 Å. A thin film solar cell having a special back electrode structure according to claim 1, wherein the two metal layers have a thickness of between 300 Å and 2100 Å. A thin film solar cell having a special back electrode structure according to the second aspect of the patent application, wherein the metal film has a thickness of 150 Å. A method for fabricating a thin film solar cell having a special back electrode structure, comprising: providing a substrate; forming a front electrode layer on the substrate; forming a light absorbing layer on the front electrode layer; and forming a back electrode layer on the light absorbing layer The back electrode layer is sequentially introduced with a transparent conductive layer, a first metal layer, an interposer, a second metal layer and a metal film; wherein the interposer has a thickness smaller than the first metal layer and The thickness of the second metal layer. A method for fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the metal film is selected from the group consisting of titanium (Ti), nickel vanadium alloy (Ni-V), and nickel titanium alloy (Ni- Group of Ti) and nickel-cadmium alloys (Ni-Cd). A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the front electrode layer is a transparent conductive oxide (TCO). A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the light absorbing layer is an amorphous germanium (a-Si). A method for fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the transparent conductive layer of the back electrode layer is gallium zinc oxide (GZO). A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the first metal layer of the back electrode layer is silver (Ag). A method for fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the interposer layer of the back electrode layer is a transparent conductive oxide (TCO) or a metal. A method for fabricating a thin film solar cell having a special back electrode structure according to claim 14 wherein the second metal layer of the back electrode layer is selected from the group consisting of aluminum (Al), copper (Cu), and gold (Au). The group formed. A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 of the patent application, wherein the transparent conductive layer has a thickness of 800A. A thin film solar cell having a special back electrode structure according to claim 1, wherein the first metal layer has a thickness of between 300 Å and 2100 Å. A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 of the patent application, wherein the interposer has a thickness of 100A. A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 of the patent application, wherein the two metal layers have a thickness of between 300 A and 2100 A. A method of fabricating a thin film solar cell having a special back electrode structure according to claim 14 of the patent application, wherein the metal film has a thickness of 150A.