Solar cell and method for fabricating the same

1. A solar cell comprising:

an n-type semiconductor layer;

a p-type semiconductor layer;

a p-side electrode layer;

an n-side electrode; and

a ZnO transparent electrode layer; wherein

the n-type semiconductor layer is in contact with the p-type semiconductor layer;

the p-type semiconductor layer is interposed between the p-side electrode layer and the n-type semiconductor layer;

the n-type semiconductor layer is interposed between the n-side electrode layer and the p-type semiconductor layer;

the n-side electrode layer covers a part of the upper surface of the n-type semiconductor layer;

the n-side electrode layer formed of Ag x Au 1-x ;

x represents a value of not less than 0.1 and not more than 0.5;

the ZnO transparent electrode layer is formed on the upper surface of the n-side electrode layer;

the ZnO transparent electrode layer is composed of a plurality of ZnO columnar particles,

each ZnO columnar particle has a longitudinal direction substantially parallel to a normal line of the ZnO transparent electrode layer; and

the cross-sectional area of each ZnO columnar particles that appears by cutting the ZnO columnar particles perpendicularly to the longitudinal direction increases from the upper surface of the n-side electrode layer to the upper surface of the ZnO transparent electrode layer.

2. The solar cell according to claim 1 , wherein

a ratio of S2/S1 is not less than 1.21 and not more than 2.25;

S1 is a cross-sectional area at the bottom end of the ZnO columnar particle which is in contact with the upper surface of the n-side electrode layer; and

S2 is a cross-sectional area at the upper end of the ZnO columnar particle located at the upper surface of the ZnO transparent electrode layer.

3. The solar cell according to claim 1 further comprising an anti-reflection film,

the anti-reflection film covers the other part of the upper surface of the n-type semiconductor layer.

4. A method for generating an electric power using a solar cell, the method comprising steps of:

a step (A) of preparing the solar cell comprising:

an n-type semiconductor layer;

a p-type semiconductor layer;

a p-side electrode layer;

an n-side electrode; and

a ZnO transparent electrode layer; wherein

the n-type semiconductor layer is in contact with the p-type semiconductor layer;

the p-type semiconductor layer is interposed between the p-side electrode layer and the n-type semiconductor layer;

the n-type semiconductor layer is interposed between the n-side electrode layer and the p-type semiconductor layer;

the n-side electrode layer covers a part of the upper surface of the n-type semiconductor layer;

the n-side electrode layer formed of Ag x Au 1-x ;

x represents a value of not less than 0.1 and not more than 0.5;

the ZnO transparent electrode layer is formed on the upper surface of the n-side electrode layer;

the ZnO transparent electrode layer is composed of a plurality of ZnO columnar particles,

each ZnO columnar particle has a longitudinal direction substantially parallel to a normal line of the ZnO transparent electrode layer; and

the cross-sectional area of each ZnO columnar particles that appears by cutting the ZnO columnar particles perpendicularly to the longitudinal direction increases from the upper surface of the n-side electrode layer to the upper surface of the ZnO transparent electrode layer, and

a step (B) of irradiating the n-type semiconductor layer and the p-type semiconductor layer with sunlight through the ZnO transparent electrode layer so as to generate a voltage difference between the p-side electrode layer and the n-side electrode layer.

5. A method for fabricating a solar cell, the method comprising steps of:

a step (a) of preparing a electric power generation element comprising an n-type semiconductor layer, a p-type semiconductor layer, and a p-side electrode layer; wherein

the n-type semiconductor layer is in contact with the p-type semiconductor layer; and

the p-type semiconductor layer is interposed between the p-side electrode layer and the n-type semiconductor layer;

a step (b) of forming an n-side electrode layer consisting of Ag x Au 1-x on an upper surface of the n-type semiconductor layer; wherein

x represents a value of not less than 0.1 and not more than 0.5; and

the n-side electrode layer covers a part of the upper surface of the n-type semiconductor layer; and

a step (c) of forming a ZnO transparent electrode layer on an upper surface of the n-side electrode layer by a chemical bath deposition method; wherein

the ZnO transparent electrode layer is composed of a plurality of ZnO columnar particles;

each ZnO columnar particle has a longitudinal direction substantially parallel to a normal line of the ZnO transparent electrode layer; and

the cross-sectional area of each ZnO columnar particles that appears by cutting the ZnO columnar particles perpendicularly to the longitudinal direction increases from the upper surface of the n-side electrode layer to the upper surface of the ZnO transparent electrode layer.

6. The method according to claim 5 , wherein

a ratio of S2/S1 is not less than 1.21 and not more than 2.25; wherein

S1 is a cross-sectional area at the bottom end of the ZnO columnar particle which is in contact with the upper surface of the n-side electrode layer; and

S2 is a cross-sectional area at the upper end of the ZnO columnar particle located at the upper surface of the ZnO transparent electrode layer.

7. The method according to claim 5 , wherein

in the step (c), the upper surface of the n-side electrode layer is brought into contact with a mixture of 0.1M Zn (NO 3 ) 2 and 0.1M hexamethylene tetramine.

8. The method according to claim 5 further comprising:

a step (d) of forming an anti-reflection layer on the other part of the upper surface of the n-type semiconductor layer after the step (c).