Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
1999-03-26
2001-10-02
Pyon, Harold (Department: 1772)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S255000, C136S256000
Reexamination Certificate
active
06297443
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP98/00556 which has an International filing date of Feb. 12, 1998 which designated the United States of America.
1. Technical Field
The present invention relates generally to improvement in conversion efficiency of a thin film photoelectric converter, and particularly to improvement in photoelectric conversion efficiency of a polycrystalline thin film photoelectric conversion layer.
2. Background Art
Important factors concerning photoelectric materials for a photoelectric converter include an effective range of sensible wavelengths, light absorption coefficient, carrier mobility, lifetime of minority carriers and so on, all of which are important parameters of physical properties for improved efficiency of photoelectric converter. In the thin film photoelectric converter, absorption coefficient is particularly important. When a photoelectric conversion layer is formed of a thin film, light absorption is insufficient in longer wavelength range where absorption coefficient is low. Thus, an amount of photoelectric conversion is limited by the thickness of the photoelectric conversion layer. Therefore, a thin film photoelectric converter having high sensitivity and a high absorption coefficient in longer wavelength range is needed.
Recently, thin film photoelectric materials have been developed which are sensitive to light of a wide range of wavelengths and typically used in thin film polycrystalline silicon solar cells. In a thin film photoelectric material, however, the longer the wavelength of light, the smaller the absorption coefficient of the photoelectric material, and light absorption of the thin film as a whole is limited by the film thickness. Therefore, effective photoelectric conversion is difficult to be achieved over an entire range of sensible light wavelengths.
In view of the foregoing, an object of the present invention is to provide a thin film photoelectric converter capable of generating a large photoelectric current by producing a light scattering structure for preventing incident light escaping from the photoelectric conversion layer.
DISCLOSURE OF THE INVENTION
A thin film photoelectric converter of the present invention includes a substantially polycrystalline photoelectric conversion layer having first and second main surfaces and a metal thin film covering the second main surface; the polycrystalline photoelectric conversion layer being formed of a substantially polycrystalline silicon thin film with an average thickness in the range from 0.5 to 20 &mgr;m; at least the first main surface of the polycrystalline photoelectric conversion layer having a textured surface structure, and the textured structure having fine unevenness of which level differences are smaller than half of the average thickness of the polycrystalline photoelectric conversion layer and substantially in the range from 0.05 to 3 &mgr;m.
Preferably, crystallographic <110> direction of most crystal grains included in the polycrystalline photoelectric conversion layer is approximately parallel with a deviation angle less than 15° to the thickness direction of the polycrystalline photoelectric conversion layer.
Further, preferably the second main surface of the polycrystalline photoelectric conversion layer also has a textured surface structure and the textured structure has fine unevenness with level differences smaller than half of the thickness of polycrystalline photoelectric conversion layer and substantially in the range from 0.05 to 3 &mgr;m.
Still further, the polycrystalline photoelectric conversion layer is preferably formed of polycrystalline silicon of which crystallized volume fraction is 80% or larger, with hydrogen content of at least 0.1 atomic % and at most 30 atomic %.
Still further, at least a surface of the metal thin film facing the second main surface of the polycrystalline photoelectric conversion layer is preferably formed of a material selected from the group consisting of Ag, Au, Cu, Al and Pt, or an alloy including the same.
Still further, preferably, a transparent conductive or a transparent semiconductive buffer layer having a thickness in the range from 0.05 to 0.15 &mgr;m is interposed between the metal thin film and the polycrystalline photoelectric conversion layer.
Still further, the thin film photoelectric converter may include an amorphous photoelectric conversion layer of a substantially amorphous silicon thin film deposited on the first main surface of the polycrystalline photoelectric conversion layer.
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Nakajima, Akihiko et al.Solar Energy Materials and Solar Cells, vol. 48, pp. 287-294, (1997).
Nakajima Akihiko
Suzuki Takayuki
Yamamoto Kenji
Yoshimi Masashi
Birch & Stewart Kolasch & Birch, LLP
Kaneka Corporation
Miggins Michael C.
Pyon Harold
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