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Method for producing photovoltaic cell

a photovoltaic cell and cell technology, applied in the field of photovoltaic cell production, can solve the problems of increasing crystal defects, low conductivity of aluminum paste, and large internal stress in silicon substrates

Inactive Publication Date: 2011-09-01
RESONAC CORPORATION
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

This approach allows for the formation of a p-type diffusion layer without inducing internal stress or warpage in the silicon substrate, enabling the production of high-efficiency photovoltaic cells with reduced electrode thickness and expanded electrode material options, such as silver, for improved conductivity and structural integrity.

Problems solved by technology

However, aluminum paste has low conductivity, and therefore, it is generally necessary to form a thick aluminum layer of about 10 to 20 μm after sintering on the entire rear surface in order to reduce the sheet resistance.
Further, the coefficient of thermal expansion of aluminum is considerably different from the coefficient of thermal expansion of silicon, and therefore, such a difference results in generation of large internal stress in the silicon substrate during the sintering and cooling processes, which contributes to damage to a crystal grain boundary, increase in the crystal defects, and the warpage.
However, when the coating amount of the paste composition is decreased, the amount of aluminum diffused from a surface of a p-type silicon substrate into an internal portion is insufficient.
As a result, a desirable BSF (Back Surface Field) effect (an effect in which collection efficiency of generated carriers is increased due to the presence of a p+-type layer) is not achieved, resulting in the problem of a decrease in properties of a photovoltaic cell.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0074]20 g of B2O3—SiO2—R2O (R: Na, K, Li) based glass powder whose particle shape is substantially spherical, average particle diameter is 4.9 μm and softening point is 561° C. (trade name: TMX-404, manufactured by Tokan Material Technology Co., Ltd.), 0.5 g of ethylcellulose and 10 g of 2-(2-butoxyethoxy) ethyl acetate were mixed with an automatic mortar kneading machine and made into a paste to prepare a composition for forming a p-type diffusion layer.

[0075]The particle shape of the glass powder was judged by observation with a scanning electron microscope (trade name: TM-1000, manufactured by Hitachi High-Technologies Corporation). The average diameter of the glass powder was calculated with a laser diffraction particle size analyzer (measurement wave length: 632 nm, trade name: LS 13 320, manufactured by Beckman Coulter, Inc.). The softening point of the glass powder was measured according to a differential thermal analysis (DTA) curve with a Thermo Gravimetry Differential The...

example 2

[0079]A p-type diffusion layer was formed in the same manner as in Example 1, except that the glass powder was changed to B2O3—SiO2—RO (R: Mg, Ca, Sr, Ba) based glass powder whose particle shape is spherical, average particle diameter is 3.2 μm and softening point is 815° C. (trade name: TMX-603, manufactured by Tokan Material Technology Co., Ltd.). The surface at the side where the composition for forming a p-type diffusion layer was applied exhibited sheet resistance of 35 Ω / □ and the formation of a p-type diffusion layer through diffusion of B (boron).

example 3

[0080]A p-type diffusion layer was formed in the same manner as in Example 1, except that the glass powder was changed to B2O3—SiO2—RO (R: Mg, Ca, Sr, Ba) based glass powder whose particle shape is spherical, average particle diameter is 5.1 μm and softening point is 808° C. (trade name: TMX-403, manufactured by Tokan Material Technology Co., Ltd.). The surface at the side where the composition for forming a p-type diffusion layer was applied exhibited sheet resistance of 45 Ω / □ and the formation of a p-type diffusion layer through diffusion of B (boron).

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Abstract

In a method for producing a photovoltaic cell, the improvement comprising:1) coating a portion of a semiconductor substrate with a layer of a composition comprising acceptor element-containing glass particles and a dispersion medium, and2) heating the coated semiconductor substrate to a temperature sufficient to cause acceptor element diffusion from the glass particles into the semiconductor substrate so as to form an p-type diffusion region in the semiconductor substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority under 35 U.S.C. 119(e) form Provisional U.S. Patent Application No. 61 / 301,652, filed Feb. 5, 2010, and Japanese Patent Application No. 2011-005312 filed Jan. 13, 2011, the disclosure of which is incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to an improvement in a method for producing a photovoltaic cell. More specifically, the present invention relates to a technique for forming a p-type diffusion layer, which enables reduction in internal stress of silicon substrate serving as a semiconductor substrate, whereby damage to a crystal grain boundary can be suppressed and increase in crystal defects and warpage can be suppressed.[0004]2. Description of the Related Art[0005]A related art procedure of a silicon photovoltaic cell is described hereinbelow.[0006]First, in order to realize high efficiency by promoting optical confineme...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H01L31/18
CPCH01L21/2225H01L21/2255H01L31/1864Y02E10/547H01L31/022425H01L31/1804Y02P70/50
Inventor MACHII, YOUICHIYOSHIDA, MASATONOJIRI, TAKESHIOKANIWA, KAORUIWAMURO, MITSUNORIADACHI, SHUUICHIROUORITA, AKIHIROSATO, TETSUYAKIZAWA, KEIKO
Owner RESONAC CORPORATION