An solar cell is provided comprising a photoelectric conversion layer formed on a substrate formed of a semiconductor material, and a first finger electrode formed of printed conductive paste to a main surface side of the photoelectric conversion layer, wherein an average of standard deviations of heights of uneveness on a surface of the first finger electrode is 5.0 μm or less. The first finger electrode may be formed on a back surface side of the solar cell opposite to a light-receiving surface side. The substrate may be a crystalline silicon substrate. The photoelectric conversion layer may comprise the crystalline silicon substrate, an amorphous silicon layer formed on the substrate, and a transparent conductive oxide film formed on the amorphous silicon layer. The first finger electrode may be provided on the transparent conductive oxide film.
1. A solar cell comprising:
a photoelectric conversion layer including a substrate wherein the substrate formed of a semiconductor material;
a first finger electrode formed of printed conductive paste at a first main surface side of the photoelectric conversion layer, the printed conductive paste comprising conductive powder, the first finger electrode being arranged on a back surface side of the solar cell opposite to a light-receiving surface side, and
a second finger electrode formed of printed conductive paste at a second main surface side of the photoelectric conversion layer, the printed conductive paste comprising conductive powder, the second finger electrode being arranged on the light-receiving surface side of the solar cell,
wherein the first finger electrode comprises a first uneven surface on an opposite side of the first main surface of the photoelectric conversion layer and the second finger electrode comprises a second uneven surface on an opposite side of the second main surface of the photoelectric conversion layer,
an average of standard deviations of heights of unevenness on the first uneven surface of the first finger electrode is 5.0 μm or less, and
the average of the standard deviations of the heights of the unevenness on the first uneven surface of the first finger electrode is smaller than an average of standard deviations of heights of unevenness on the second uneven surface of the second finger electrode, a height of each unevenness of the first uneven surface being defined as a distance from the first main surface of the photoelectric conversion layer to the first uneven surface, a height of each unevenness of the second uneven surface being defined as a distance from the second main surface of the photoelectric conversion layer to the second uneven surface.
2. The solar cell according to claim 1 , wherein
the substrate is a crystalline silicon substrate,
the photoelectric conversion layer further comprises:
an amorphous silicon layer formed on the crystalline silicon substrate; and
a transparent conductive oxide film formed on the amorphous silicon layer and
the first finger electrode is provided on the transparent conductive oxide film.
3. The solar cell according to claim 2 , wherein
the amorphous silicon layer comprises a first amorphous silicon layer of a first conductivity type and a substantially intrinsic second amorphous silicon layer provided between the first amorphous silicon layer and the crystalline silicon substrate.
4. The solar cell according to claim 1 , wherein
the substrate is a crystalline silicon substrate,
the photoelectric conversion layer further comprises:
a first amorphous silicon layer of a first conductivity type, the first amorphous silicon layer being formed on the back surface side of the crystalline silicon substrate;
a substantially intrinsic second amorphous silicon layer provided between the first amorphous silicon layer and the crystalline silicon substrate;
a third amorphous silicon layer of a second conductivity type different from the first conductivity type,
the third amorphous silicon layer being formed on the light-receiving surface side of the crystalline silicon substrate;
a substantially intrinsic fourth amorphous silicon layer provided between the third amorphous silicon layer and the crystalline silicon substrate;
a first transparent conductive oxide film formed on the first amorphous silicon layer; and
a second transparent conductive oxide film formed on the third amorphous silicon layer, and
the first finger electrode is provided on the first transparent conductive oxide film, and the second finger electrode is provided on the second transparent conductive oxide film.
5. The solar cell according to claim 1 , wherein
an average of the standard deviations is an average obtained from 20 or more measurement samples in the first finger electrode.
6. The solar cell according to claim 1 , wherein
the printed conductive paste is low-temperature curing conductive paste.
7. The solar cell according to claim 6 , wherein
the printed conductive paste thermally cures at temperatures from 150 to 250° C.
8. The solar cell according to claim 7 , wherein
the printed conductive paste comprises silicone resin, conductive powder, thermosetting components, a curing agent, and a solvent.
9. The solar cell according to claim 8 , wherein
the thermosetting components comprises epoxy resin with an epoxy equivalent of 1000 or less and epoxy resin with an epoxy equivalent of 1500 or more.
10. The solar cell according to claim 8 , wherein
the silicone resin comprises at least one of straight silicone resins such as methyl silicone resin and methylphenyl silicone resin, and modified silicone resins modified with epoxy resin, alkyd resin, polyester, and acrylic resin.
11. The solar cell according to claim 8 , wherein
the conductive powder comprises at least one of powder of silver, copper, nickel, aluminum, copper coated with silver, aluminum coated with silver, and carbon.
12. The solar cell according to claim 8 , wherein
the thermosetting components comprises at least one of epoxy resins and blocked polyisocyanate compounds.
13. The solar cell according to claim 8 , wherein
the curing agent comprises at least one of imidazole and derivatives thereof, tertiary amines, Lewis acids containing boron fluoride, and complexes or salts thereof.
14. The solar cell according to claim 8 , wherein
the solvent comprises at least one of high-boiling solvents such as ethyl Carbitol acetate, butyl Carbitol acetate, and terpineol.
15. The solar cell according to claim 1 , wherein a first ratio of the conductive powder to the printed conductive paste for the first finger electrode is smaller than a second ratio of the conductive powder to the printed conductive paste for the second finger electrode.
16. The solar cell according to claim 15 , wherein
the first ratio is a mass ratio of a mass of the conductive powder to a mass of the printed conductive paste for the first finger electrode, and
the second ratio is a mass ratio of a mass of the conductive powder to a mass of the printed conductive paste for the second finger electrode.