This Application claims priority of Taiwan Patent Application No. 099141425, filed on Nov. 30, 2010, the entirety of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to an apparatus for film deposition, and in particular relates to an apparatus for chemical bath deposition.
2. Description of the Related Art
Development in the solar cell industry is driven by global environmental concerns and rising raw material prices. Among the various solar cells developed, dye-sensitized solar cell (DSSC) is advantageous as it can be fabricated with relatively lower costs due to its simpler fabrication process and ability for large area fabrication.
In a solar cell, a buffer layer plays an important role, because it is used as an n-type material and it protects the absorption layer of the solar cell. Therefore, it is important to fabricate a high quality buffer layer to improve the photoelectric conversion efficiency of solar cells.
Techniques for deposition of the buffer layer include: sputtering, vacuum evaporation, chemical bath deposition (CBD), spray pyrolysis, in which chemical bath deposition (CBD), is a widely used method due to its simple process and required low cost equipment. However, the conventional CBD process consumes a large amount of chemicals, and results in a large amount of waste.
Thus, there is a need to provide a chemical bat deposition apparatus with a simple process, using fewer chemicals.
The invention provides an apparatus for chemical bath deposition, comprising: a first cover and a second cover, wherein the first cover and the second cover are disposed opposite to each other, and the first cover has at least two holes; and a spacer disposed between the first cover and the second cover, wherein the first cover, the spacer and the second cover form a film deposition space.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
Referring to
In order to improve the seal-tightness between the first cover 21 and the second cover 22, the edge of first cover 21 or the second cover 22 has a groove (not shown in
The function of the first cover 21 is to reduce the evaporation loss of the solution. The first cover 21 has at least two holes 24, and one hole 24a is used as a solution inlet, and the other hole 24b is used as a solution outlet. When the solution is prepared to be filled into the solution inlet 24a, the solution outlet 24b is opened to balance the pressure in the film deposition space 25 to help the injection of solution. The holes have a diameter of about 3-5 mm. Note that the diameter may not be too large in order to avoid evaporation of the solution and degradation of film quality.
The first cover 21 has good corrosion resistance, and acid/base resistance, and is made of material such as aluminum alloy, glass, quartz, aluminum oxide or polymer, wherein the polymer comprises poly vinly chloride (PVC), polytetrafluoroethylene (PTFE) or poly propylene (PP). In one embodiment, the material of the first cover 21 is preferred to be polytetrafluoroethylene (PTFE). Because PTFE has low surface energy, a film would not likely form on the PTFE following the deposition process. Thus, after the deposition process, the first cover 21 made of PTFE, would be easy to wash.
Additionally, the first cover 21 also provides a pressure to the second cover 22, and the pressure prevents the solution from leaking out therefrom, to improve the seal-tightness of the first cover 21 and the second cover 22. The spacer 23 is used to seal the first cover 21 and the second cover 22, and thus the seal-tightness of the spacer 23 my also be improved by the pressure which is provided by the first cover 21.
The second cover 22 may be a substrate for film deposition, and the material of the second cover comprises glass, stainless steel or polyimide (PI). Moreover, a substrate for film deposition may be disposed on the inner surface of the first cover 21, while the second cover 22 is another substrate for film deposition, wherein the two substrates for film deposition may be disposed simultaneously. Note that the substrate for film deposition may be the second cover or further be disposed on the inner surface of the first cover, and those skilled in the art may adjust the arrangement of the substrate according to actual application needs.
The function of the spacer 23 is to seal the first cover 21 and the second cover 22, and the spacer 23 has good elastic property, good acid/base resistance, and low surface energy. The material of the spacer 23 comprises rubber, silicone or polytetrafluoroethylene (PTFE). In one embodiment, an O-ring with a diameter of about 60 mm-200 mm and a thickness of about 2 mm-15 mm is used as the spacer 23.
Note that the height of the solution for film deposition filled in the film deposition space 25 is determined by the height of the spacer 23. In general, the height of the spacer 23 is about 2 mm-10 mm. Thus, waste is reduced due to the reduced heights.
Referring to
Note that because the second cover 22 itself is a substrate for film deposition and the heater 26 is directly disposed below the second cover 22, the substrate for film deposition is heated directly. In the conventional techniques, the solution rather than the substrate is heated. Thus, the advantages of the apparatus of the invention are to save energy and reduce film deposition time.
Additionally, the apparatus of the invention further comprises a magnetic material in the first cover 21. When the first cover 21 is disposed on the heater 26, the magnetic material of the first cover 21 may be attracted by the heater 26 (made of magnetic material) to provide an additional pressure. The additionally pressure may improve the seal-tightness between the first cover 21 and the second cover 22 and prevent the solution from leaking.
Furthermore, referring to
Referring to
In the film deposition process, the solution is injected from the hole 24, and a desired thickness of film is obtained by controlling the time and temperature of the film deposition process. After the deposition process, a washing process is conducted by injecting air, argon, nitrogen or de-ionized water from the inlet 24a into the space 25 to wash the first cover 21 and the second cover 22. The waste solution is then exhausted from the outlet 24b. The simple washing process is provided to reduce cost.
Additionally, before conducting the above-mentioned film deposition process, the surface composition or the surface morphology of the substrate may be changed by a specific compound. For example, before fabricating the buffer layer of CIGS cell, the substrate is etched by the bromine water to change the surface morphology thereof, or the substrate is dipped into a potassium cyanate (KCN) solution to change the surface composition thereof. Thus, the toxic bromine water and the toxic potassium cyanate (KCN) solution are limited in the small sized film deposition space 25 by the apparatus of the invention. Thus, the use of the toxic material is reduced.
In prior art, a crucible is often used as a solution container, and the film is not only grown on a substrate but also on the crucible. Thus, the crucible is needed to be washed after every cycle of the film deposition process. Note that the invention provides an apparatus formed by the first cover, the second cover and the spacer without the crucible, and the film is only grown on the substrate for film deposition (such as the second cover). Thus, the utilization rate of the solution is improved, and the use of the solution is reduced and no additional washing crucible process is needed.
Therefore, the apparatus for CBD of the invention has several advantages as follows.
(1) By the design of the first cover, the second cover and the spacer, the utilization degree of the solution is improved, the use of the solution is reduced and waste is reduced.
(2) The substrate for film deposition is heated directly to save energy and reduce film deposition time.
(3) The first cover or the second cover is used as a container rather than the crucible to simplify the washing process and reduce time and cost.
0.00185 M of cadmium sulfate (CdSO4), 1.5 M of ammonia (NH4OH) and 0.075 M of thiourea ((NH2)2CS) were mixed together to prepare a solution for film deposition.
The apparatus 20 is shown in
The film deposition process is described as follows:
(1) a second cover (glass substrate) 22 was disposed on a heater 26;
(2) a spacer 23 and the second cover 21 (made of PTFE) were cover on the second cover 22;
(3) a solution for film deposition was injected from a hole 24 into a film deposition space 25;
(4) the solution was heated at 70° C. for 20 minutes to obtain a cadmium sulfide (CdS) film with a thickness of 80 mm, or at 70° C. for 40 minutes to obtain a cadmium sulfide (CdS) film with a thickness of 100 mm; and
(5) After the film deposition process, a washing process was conducted, and de-ionized water was injected into the space 25 through an inlet 24a and was exhausted through outlet 24b to wash the apparatus 20.
Example 2 is similar with Example 1, with the difference being that a shaking device (YSC. Company) 27 was added in Example 2.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Number | Date | Country | Kind |
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TW099141425 | Nov 2010 | TW | national |