This application claims the priority benefit of Taiwan application serial no. 100113232, filed on Apr. 15, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
1. Field of the Invention
The invention relates to a method of fabricating a solar cell, and more particularly to a method of fabricating a solar cell having favorable efficiency.
2. Description of Related Art
A silicon-based solar cell is a commonly used solar cell in the industry. A principle of the silicon-based solar cell is to dope a semiconductor material (i.e. silicon) with different type dopants to form a p-type semiconductor layer and an n-type semiconductor layer, and then to assemble the p-type semiconductor layer and the n-type semiconductor layer together, so as to form a p-n junction. When sunlight irradiates the semiconductor material with the p-n junction, energy carried by photons can excite electrons in the semiconductor material to generate electron-hole pairs. By respectively disposing electrodes on the p-type semiconductor layer and the n-type semiconductor layer, the electrons and the holes are all influenced by a built-in potential, wherein the holes move towards an electric field, and the electrons move towards an opposite direction, such that the solar cell is constituted.
Generally, in order to improve the electrical contact between the semiconductor layer and the electrode, a heavily doped selective emitter is formed in the lightly doped semiconductor layer. As such, series resistance is reduced, and efficiency of the solar cell is increased. However, as the heavily doped selective emitter and the lightly doped semiconductor layer are usually formed by doping with identical dopants, the difference of the conductivity therebetween is not significant. Therefore, efficiency of the solar cell is difficult to improve.
The invention is directed to a method of fabricating a solar cell, so as to form a solar cell having favorable efficiency.
A method of fabricating a solar cell is provided. A first type substrate having a first surface and a second surface is provided. A first doping process is performed on the first surface of the first type substrate by using a first dopant, so as to form a first type lightly doped layer. A second doping process is performed on a portion of the first type lightly doped layer by using a second dopant, so as to form a second type heavily doped region. A molecular weight of the second dopant is larger than a molecular weight of the first dopant, and a temperature of the first doping process is higher than a temperature of the second doping process. A first electrode is formed on the second type heavily doped region. A second electrode is formed on the second surface of the first type substrate.
Based on the above, in the method of fabricating the solar cell of the invention, the lightly doped layer is formed by using a first dopant, and the heavily doped region is formed by using a second dopant, wherein a molecular weight of the second dopant is larger than a molecular weight of the first dopant, and a temperature of the first doping process is higher than a temperature of the second doping process. As such, a heavily doped region having a shallow depth is clearly defined in the lightly doped layer, and thus a favorable ohmic contact is formed between the heavily doped region served as a selective emitter and the electrode. Therefore, the recombination rate of the electron-hole pairs in the solar cell is greatly increased and the efficiency of the solar cell is improved.
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanying figures are described in detail below.
The accompanying drawings constituting a part of this specification are incorporated herein to provide a further understanding of the invention. Here, the drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference with
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In this embodiment, a method of forming the second type heavily doped region 108 includes the following steps. First, as shown in
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In this embodiment, the mask layer 106 can be remained as an anti-reflective layer in the solar cell 100 because the material of the mask layer 106 has anti-reflective property. Alternatively, in another embodiment (not shown), after formation of the second type heavily doped region 108, the mask layer 106 without anti-reflective property can be removed, an anti-reflective layer is additionally formed on the first type lightly doped layer 104, and then the first electrode 110 and the second electrode 120 are respectively formed on the second type heavily doped region 108 and the second surface 102b of the first type substrate 102. In other words, the material of the mask layer can be selected and the anti-reflective layer is alternatively formed according to actual requirements. Moreover, the second type heavily doped region 108 can be formed by other suitable methods.
In this embodiment, the lightly doped layer and the heavily doped region are formed by using different dopants. In detail, the first dopants having a smaller molecular weight are firstly used to perform the first doping process to form the lightly doped layer, and the second dopants having a larger molecular weight are then used to perform the second doping process to form the heavily doped region in the lightly doped layer. Since the molecular weight of the second dopants is larger than the molecular weight of the first dopants, and the temperature of the first doping process is higher than the temperature of the second doping process, the heavily doped region having a shallow depth is accurately formed by the lightly doped process with the second dopants. As such, the heavily doped region having a shallow depth is clearly defined in the lightly doped layer, and thus a favorable ohmic contact is formed between the heavily doped region served as a selective emitter and the electrode. Therefore, the recombination rate of the electron-hole pairs in the solar cell is greatly increased and the efficiency of the solar cell is improved. Particularly, in this embodiment, the mask layer can be remained as an anti-reflective layer in the solar cell because the material of the mask layer has anti-reflective property, and therefore the removal process to the mask layer is not required. Accordingly, the fabricating process of the solar cell is simplified and the efficiency of the solar cell is increased.
In light of the foregoing, in the method of fabricating solar cell of the invention, the lightly doped layer is formed by using first dopants, and the heavily doped region is formed by using second dopants, wherein a molecular weight of the second dopant is larger than a molecular weight of the first dopant, and a temperature of the first doping process is higher than a temperature of the second doping process. As such, the heavily doped region having a shallow depth is clearly defined in the lightly doped layer, and thus a favorable ohmic contact is formed between the heavily doped region served as a selective emitter and the electrode. Therefore, the recombination rate of the electron-hole pairs in the solar cell is greatly increased and the efficiency of the solar cell is improved. Moreover, the method of fabricating solar cell of the invention is compatible with existing processes, and thus additional processing apparatus is not required and the cost of fabricating the solar cell is not greatly increased.
Although the invention has been described with reference to the above embodiments, it will be apparent to one of the ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed descriptions.
Number | Date | Country | Kind |
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100113232 | Apr 2011 | TW | national |