1. Technical Field
The disclosure relates to a thin-film photovoltaic cell. More particularly, the disclosure relates to a thin-film photovoltaic cell having a back reflector.
2. Description of Related Art
Photovoltaic cells, commonly known as solar cells, are well known devices that convert light energy into electricity. Therefore, how to increase the photoelectric conversion efficiency is always an important issue in photovoltaic system. One way is to place a back reflector beneath photoactive semiconductor layers to reflect light unabsorbed by the semiconductor layers to back through the semiconductor layers for further absorption. Accordingly, the use of a back reflector can increase the cell efficiency of the photovoltaic cells.
Accordingly, a novel back reflector is provided for photovoltaic cells. This novel back reflector is a distributed Bragg reflector (DBR) containing conductive nanostructures therein. Therefore, the resistivity of the novel DBR can be largely reduced, and the novel DBR can also serve as a metal back contact at the same time. The conductive nanostructures above can be metal nanoparticles or metal thin films distributed in the multi-layered DBR structure.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.
In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
Accordingly, the reflectance of the distributed Bragg reflector can be increased by increasing the refractive index difference between the first refractive layers 162 and the second refractive layers 164 and the pair number of the first refractive layers 162 and the second refractive layers 164. Therefore, the reflectance of the distributed Bragg reflector can be adjusted by choosing proper materials for the first refractive layers 162 and the second refractive layers 164. In addition, the required wavelength range to be reflected is dependent on the material and the thickness of the semiconductor layer 130. Generally, for single junction photovoltaic cells, the required wavelength to be reflected is about 500-800 nm. For multiple junction photovoltaic cells, the required wavelength to be reflected is about 800-1200 nm.
Possible choices for the first refractive layers 162 and the second refractive layers 164 can be silicon-based materials, III-V semiconductor materials, or II-VI semiconductor materials, for example. The silicon-based materials can be amorphous silicon, SiGe, amorphous SiGe, amorphous silicon carbide, or silicon oxide, for example. The III-V semiconductor materials can be GaN, GaP, InN, InP, GaAs, InAs, AIN, AlP, or AlAs, for example. The II-VI semiconductor materials can be ZnO, ZnTe, ZnSe, CdTe, CdSe, HgTe, ZnS, CdS, or HgS, for example.
Moreover, the distributed Bragg reflector comprises conductive nanostructures distributed in the interfaces between the first refractive layers 162 and the second refractive layers 164. The material of the conductive nanostructures can be Ag, Al, Pt, In, or Au, for example.
In
In
Next, the resistances of the distributed Bragg reflectors in
Accordingly, since the distributed Bragg reflector above contains conductive nanostructures distributed therein, the novel distributed Bragg reflector provided above can be used as a back reflector and a back metal contact at the same time.
The reader's attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, each feature disclosed is one example only of a generic series of equivalent or similar features.
This application claims priority to U.S. Provisional Application Ser. No. 61/372,101, filed Aug. 10, 2010, which is herein incorporated by reference.
Number | Date | Country | |
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61372101 | Aug 2010 | US |