Solar cell, solar cell module, and method for manufacturing solar cell

1. A solar cell, comprising:

a silicon substrate including, in a first principal surface, a texture structure in which a plurality of pyramids are arranged in a matrix; and

a first non-crystalline silicon layer on the first principal surface of the silicon substrate, the first non-crystalline silicon layer including recesses and protrusions reflecting the texture structure, wherein:

at a valley portion in the recesses and protrusions, the first non-crystalline silicon layer includes, in stated order:

a first epitaxial layer including a crystalline region epitaxially grown on the silicon substrate;

a first amorphous layer which is a non-crystalline silicon layer on the first epitaxial layer; and

a second amorphous layer which is a non-crystalline silicon layer on the first amorphous layer,

the first amorphous layer has a density less than a density of the second amorphous layer,

the first amorphous layer and the second amorphous layer are made of a same material and have a same conductivity type, and

the first amorphous layer has a thickness less than a thickness of the second amorphous layer.

2. The solar cell according to claim 1 , wherein

the first amorphous layer has a thickness of between 1 nm and 3 nm, inclusive.

3. The solar cell according to claim 1 , wherein

the first epitaxial layer further includes a non-crystalline region.

4. The solar cell according to claim 1 , wherein

the first epitaxial layer has a density greater than the density of the first amorphous layer.

5. The solar cell according to claim 1 , wherein

in an entire region of the recesses and protrusions including the valley portion, the first non-crystalline silicon layer includes the first epitaxial layer, the first amorphous layer, and the second amorphous layer in stated order.

6. The solar cell according to claim 1 , wherein

a part of at least one of the first epitaxial layer, the first amorphous layer, and the second amorphous layer is of a conductivity type identical to a conductivity type of the silicon substrate.

7. The solar cell according to claim 1 , wherein

the silicon substrate further includes, in a second principal surface opposite to the first principal surface, a texture structure in which a plurality of pyramids are arranged in a matrix,

the solar cell further comprises;

a second non-crystalline silicon layer on the second principal surface of the silicon substrate, the second non-crystalline silicon layer including recesses and protrusions reflecting the texture structure,

at a valley portion in the recesses and protrusions, the second non-crystalline silicon layer includes, in stated order:

a second epitaxial layer including a crystalline region epitaxially grown on the silicon substrate;

a third amorphous layer which is a non-crystalline silicon layer on the second epitaxial layer; and

a fourth amorphous layer which is a non-crystalline silicon layer on the third amorphous layer, and

the third amorphous layer has a density less than a density of the fourth amorphous layer.

8. A solar cell module, comprising:

a plurality of solar cells each of which is the solar cell according to claim 1 .

9. The solar cell according to claim 1 , wherein

the first amorphous layer does not include the crystalline region.

10. The solar cell according to claim 1 , wherein

the first epitaxial layer, the first amorphous layer, and the second amorphous layer are made of the same material.