1. Field of Invention
The invention relates to a solar cell structure and the fabricating method thereof. In particular, the invention relates to a thin-film solar cell structure that uses a chemical thin film as its absorbing layer and the fabricating method thereof.
2. Related Art
In recent years, the solar energy industry gradually turns its research emphasis from conventional wafer manufacturing to thin films. Compound thin films, in particular, receive particular attention. Compound thin film solar cells compared with wafer solar cells have many advantages, such as higher conversion efficiency, lower cost, wider absorbing range, more flexible, and possible for large area applications. Among various chemical compounds, copper indium gallium selenium (CIGS) materials have a wide absorbing spectrum. They can absorb more solar power to increase the conversion efficiency.
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In summary, the prior art always has the problem that the power conversion efficiency is affected by the interface trap density. Therefore, it is desirable to provide a better solution.
In view of the foregoing, the specification discloses a thin film solar cell structure and the fabricating method thereof.
One embodiment of the disclosed thin film solar cell structure includes: a substrate, a metal layer, an absorbing layer, and a passivation layer. The metal layer is formed on the substrate. The absorbing layer is formed on the metal layer. The passivation layer is formed on the absorbing layer. The surface electric field of the passivation layer passivates the absorbing layer.
Another embodiment of the disclosed thin film solar cell structure also includes: a substrate, a metal layer, an absorbing layer, and a passivation layer. The metal layer is formed on the substrate. The absorbing layer is formed on the metal layer. The passivation layer is formed on the metal layer and contacts at least one side of the absorbing layer. The surface electric field of the passivation layer passivates the absorbing layer.
The disclosed fabricating method of thin film solar cells includes the steps of: providing a substrate; forming a metal layer on the substrate; forming an absorbing layer on the metal layer; and forming a passivation layer on the absorbing layer, with the surface electric field of the passivation layer passivating the absorbing layer.
The disclosed structure and fabricating method differ from the prior art in the following. By embedding the passivation layer in the thin film solar cell, the passivation layer is in contact with the absorbing layer. The surface electric field of the passivation layer thus reduces the interface trap density of the absorbing layer.
The invention achieves the goal of increasing power conversion efficiency and protecting the absorbing layer.
The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:
The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.
We first describe the structure of the disclosed thin film solar cell.
The metal layer 22 forms on the substrate 21. In practice, the metal layer 22 is grown on the substrate 21 by sputtering Mo onto the substrate 21, and is used as a back electrode layer for conducting electricity. In addition, the metal layer 22 can also be formed by depositing a layer of Mo using electron-beam evaporation (EBE) and connected to the positive electrode.
The absorbing layer 23 forms on the metal layer 22. The material of the absorbing layer 23 is such compound as copper indium gallium selenium (CIGS), copper indium selenium (CIS), or copper gallium selenium (CGS). The absorbing layer 23 can be formed on the metal layer 22 by co-evaporation, sputtering, or printing. The absorbing layer 23 is P-type. In practice, the CIGS thin film can be formed using the vacuum process of four-element co-evaporation or the combination of sputtering and selenium. In particular, co-evaporation can freely control the composition and energy gap of the thin film in order to make high-efficiency thin film solar cells. However, it is harder to control and more difficult in producing large-area products. For the combination of sputtering and selenium, one has to be careful in processing special gas (e.g., HSe).
Since CIS can form a thin film between 350° C. to 550° C. Therefore, when using CIS as the absorbing layer 23, one can use the cheaper soda-lime glass as the substrate 21.
The passivation layer 24 forms on the absorbing layer 23. The passivation layer 24 carries sufficient positive or negative fixed charges to form a surface electric field in order to passivate the absorbing layer 23. The passivation refers to the action of filling defects in the absorbing layer 23. For example, the absorbing layer 23 after laser cutting produces an interface trap density that affects power conversion efficiency. In practice, the passivation layer 24 can be grown from Al2O3 by atomic layer deposition (ALD), low pressure chemical vapor deposition (LPCVD), sputtering, or sol-gel. The growth thickness is pervious to light (e.g., the growth thickness can between 30 nm and 100 nm). As a result, the negative fixed charges on Al2O3 produces a surface electric field so that there is less surface binding on the absorbing layer 23, rendering a better passivation effect. It should be noted that the invention is not restricted to the above-mentioned thickness of the passivation layer 24. Moreover, Al2O3 can enclose the absorbing layer 23 or even grow on the metal layer 22, in contact with at least one side of the absorbing layer 23. The details will be described later. Besides, the passivation layer 24 prevents moisture and oxygen from directly contacting the absorbing layer. The absorbing layer 23 is thus free from deterioration in power conversion efficiency due to moisture and oxygen.
Besides, step 240 can be further followed by the step of growing a coating layer of CdS, ZnS, or ZnO on the passivation layer 24 (step 250). The coating layer and the passivation layer 24 are both N-type in order to form a P—N junction with the P-type absorbing layer 23. In practice, since CdS contains poisonous cadmium, one can use ZnS instead.
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In summary, the invention differs from the prior art in that a passivation layer 24 is embedded in the thin film solar cell 20 to be in contact with the absorbing layer 23. The surface electric field of the passivation layer 24 reduces the interface trap density of the absorbing layer 23. This disclosed technique solves problems existing in the prior art and increase the power conversion efficiency as well as protect the absorbing layer.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.
Number | Date | Country | Kind |
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099124643 | Jul 2010 | TW | national |