Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
1999-11-05
2001-08-14
Chapman, Mark (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
Reexamination Certificate
active
06274805
ABSTRACT:
TECHNICAL FIELD
The present invention concerns a solar cell having a semiconductor layer of a chalcopyrite structure as a light absorption layer on a flexible film and, more in particular, it relates to a solar cell using a specific heat resistant polymeric film as a substrate.
BACKGROUND ART
Solar cells having amorphous silicon as a light absorption layer (amorphous silicon solar cell) have been expected as s solar cell capable of lowering the cost, which have been already put to a practical stage partially. Japanese Published Unexamined Application Hei 1-309385 discloses an amorphous silicon solar cell using a flexible film as a substrate. The solar cell has an advantageous feature, compared with existent solar cells of using glass substrate, capable of providing optional curvature by the form of the film, capable of being carried about easily by its light weight, and capable of extending application ranges.
However, since amorphous silicon involves a problem that the performance is degraded when exposed to sunlight, and a single layer amorphous silicon solar cell capable of attaining a reduced cost has a conversion efficiency of only about 6% at the highest when it is formed on a film.
On the contrary, solar cells having a semiconductor layer of a chalcopyrite structure such as Cu(In,Ga)Se
2
as a light absorption layer have been noted as the solar cells of high conversion efficiency, and research and development have been conducted vigorously for such solar cells. The layer constitution of the solar cell can include the structure, as shown in
FIG. 1
, in which a first electrode layer
2
comprising a thin film such as made of molybdenum, a p-type semiconductor layer
3
of a chalcopyrite structure, an n-type semiconductor layer
4
comprising CdS or the like and a second electrode layer comprising a thin film such as of ITO (indium/tin oxide) on a substrate
1
.
Then, Solar Energy Materials and Solar Cells, 29, 1993) 163-173 discloses a solar cell having a CuInSe
2
layer as a light absorption layer, and using a sheet of a simple noble metal such as molybdenum or titanium as a substrate. While the solar cell has a merit of being reduced in weight and having somewhat higher degree of freedom of the shape compared with the cell of using the glass substrate, it is difficult to be put into practical use since the cost for the sheet of the simple noble metal is high.
Solar Energy Materials and Solar Cells, 43 (1996) 93-98 discloses a solar cell having a CuInSe
2
layer as a light absorption layer and using a polyimide film as a substrate. In this case, when the CuInSe
2
layer is formed, it is necessary to apply a heat treatment in a hydrogen selenide atmosphere at a high temperature (400 to 600° C.) for obtaining a film of good crystallinity. In the amorphous solar cell, such a heat treatment is not conducted. In the heat treatment described above, the polyimide film suffers from warp or degradation caused by hydrogen selenide. As a result, for example, break-down caused to the CuInSe
2
layer, peeling of the CuInSe
2
layer from the molybdenum electrode or peeling of the molybdenum electrode layer from the surface of the film. So the conversion efficiency of the solar cell is lowered.
Japanese Patent Laid-Open Publication No. Hei 5-259494 discloses a solar cell having a semiconductor layer of a chalcopyrite structure as a light absorption layer, and using a polyimide film, a polyethylene tetrafluoride film, or a copolymer film of ethylene tetrafluoride and propylene hexafluoride as a substrate. Further, it discloses a method of decreasing thermal injuries to the film by applying laser annealing to the semiconductor layer of the chalcopyrite structure in a state of keeping the substrate comprising the polymeric film described above at a temperature not higher than 0° C.
However, since it is necessary to use a great amount of liquid nitrogen as a coolant for keeping the film at a temperature not higher than the 0° C., it can not be said that the method is practical since the production cost is increased.
It is a subject of the present invention to provide a solar cell having a semiconductor layer of a chalcopyrite structure as a light absorption layer and using a flexible film as a substrate, having reduced weight, a high degree of freedom for the shape and capable of suppressing the production cost while keeping a high conversion efficiency, by preventing break-down or peeling caused to the semiconductor layer of the chalcopyrite structure owing to warp caused to the flexible film upon heat treatment or during use.
DISCLOSURE OF THE INVENTION
The present invention provides a solar cell in which a semiconductor layer of a chalcopyrite structure is disposed as a light absorbing layer on the front surface of a substrate comprising a flexible film having an average value of a linear expansion coefficient in the range of 30° C. to 300° C. (hereinafter simply referred to as “linear expansion coefficient”) of from 1×10
−6
/° C. to 10×10
−6
/° C.
The linear expansion coefficient of the semiconductor layer of the chalcopyrite structure is about 9×10
−6
/° C. to 10×10
−6
° C. and, since the linear expansion coefficient of the flexible film as the substrate is substantially the same as that of the semiconductor of the chalcopyrite structure for the solar cell of the present invention, break-down and peeling less occur to the semiconductor layer of the chalcopyrite structure upon heat treatment in the step of forming the semiconductor layer of the chalcopyrite structure, upon fabrication of a film-like solar cell into a predetermined shape after completion of the lamination for each of layers and during use as a solar cell.
In the solar cell of the present invention, the flexible film as the substrate (hereinafter simply referred to as “film” or “substrate”) preferably has a tensile strength of from 20 kg/mm
2
to 80 kg/mm
2
, and an modulus of elasticity in an optional direction in parallel with the film surface of from 1,000 kg/mm
2
to 2500 kg/mm
2
and an elongation at break in an optional direction in parallel with the film surface of 5% or more.
When the substrate has a tensile strength of from 20 kg/mm
2
to 80 kg/mm
2
and a modulus of elasticity in an optional direction in parallel with the film surface of from 1,000 kg/mm
2
to 2500 kg/mm
2
, deformation and rupture of the substrate and the break-down of the semiconductor layer of the chalcopyrite structure can be prevented upon fabrication of a film-like the solar cell into a predetermined shape or upon handling during use as a solar cell. When the modulus of elasticity exceeds 2500 kg/mm
2
, the tearing strength is degraded to result in a problem upon fabrication. The modulus of elasticity is preferably from 1200 kg/mm
2
to 2500 kg/mm
2
and, particularly preferably, the modulus of elasticity is 1300 kg/mm
2
or more at least in one direction.
When the elongation at break in an optional direction in parallel with the film surface is 5% or more, the workability is improved. Films having the elongation at break of less than 5% are fragile and difficult to handle with. It is particularly preferred that the elongation at break is 10% or more.
In the solar cell of the present invention, the density of the flexible film as the substrate is preferably from 1.39 to 1.54 g/cm
3
. Since such a film having a relatively high density has excellent dimensional stability, for example, to the change of temperature and humidity, it has high characteristics as a solar cell. In addition, satisfactory characteristics as the solar cell can be kept for a long period of time with less change. The density of the flexible film can be measured, for example, by a so-called density-gradient tube method using a solvent mixture of carbon tetrachloride and toluene kept at 25° C. When the density of the aromatic polyamide film used in the embodiment of the present invention was measured, it was from 1.40 to 1.45 g/cm
3
.
In the solar cell of the present invention, the thickness of the flexible film as a subs
Nakazawa Hidenobu
Watanabe Takayuki
Asahi Kasei Kabushiki Kaisha
Chapman Mark
Pennie & Edmonds LLP
LandOfFree
Solar cell and manufacturing method thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solar cell and manufacturing method thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solar cell and manufacturing method thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2480715