Solar cell
A solar cell is discussed. The solar cell includes a substrate having a first conductivity type and made of a crystalline semiconductor; an emitter region having a second conductivity type opposite the first conductivity type, and forming a p-n junction with the substrate; a surface field region having the first conductivity type and being separated from the emitter region; a first electrode connected to the emitter region; and a second electrode connected to the surface field region, wherein at least one of the emitter region and the surface field region includes a plurality of semiconductor portions, and at least one of the plurality of semiconductor portion is a crystalline semiconductor portion.
1. A solar cell, comprising:
a substrate having a first conductivity type and made of crystalline semiconductor;
an emitter region including a first emitter portion formed of an amorphous semiconductor and a second emitter portion formed of a crystalline semiconductor, the first emitter portion and the second emitter portion each having a second conductivity type opposite the first conductivity type and forming a p-n junction with the substrate;
a surface field region including a first surface field portion formed of an amorphous semiconductor and a second surface field portion formed of a crystalline semiconductor and being separated from the emitter region, the first surface field portion and the second surface field portion each having the first conductive type;
a first buffer region positioned between the emitter region and the substrate and between the surface field region and the substrate;
a first electrode being directly contacted with the second emitter portion of the emitter region; and
a second electrode being directly contacted with the second surface field portion of the surface field region.
2. The solar cell of claim 1 , wherein each of the first emitter portion and the first surface field portion directly contact the first buffer region.
3. The solar cell of claim 2 , wherein at least one of a surface of the second emitter portion and the second surface field portion, which is in contact with at least one of the first electrode and the second electrode is an uneven surface of a plurality of protrusions.
4. The solar cell of claim 3 , wherein the second emitter portion and the second surface field portion have surface roughness of substantially 1.5 nm to 10 nm.
5. The solar cell of claim 3 , wherein the plurality of protrusions has a maximum height of substantially 15 nm to 40 nm.
6. The solar cell of claim 1 , wherein the second emitter portion and the second surface field portion are one of microcrystalline silicon and nanocrystalline silicon.
7. The solar cell of claim 1 , wherein the first emitter portion and the first surface field portion have a thickness of about 3 nm to 10 nm.
8. The solar cell of claim 1 , wherein the second emitter portion and the second surface field portion have a thickness of about 2 nm to 25 nm.
9. The solar cell of claim 1 , wherein the second emitter portion and the second surface field portion have a crystallinity of substantially 10 vol % to 90 vol %.
10. The solar cell of claim 1 , wherein the emitter region and the surface field region are positioned on a surface of the substrate, which is opposite to an incident surface of the substrate.
11. The solar cell of claim 10 , wherein the first buffer region is further positioned on the substrate between the emitter region and the surface field region.
12. The solar cell of claim 11 , wherein the first buffer region is further positioned between the surface field region and the emitter region that are adjacent to each other.
13. The solar cell of claim 12 , wherein the emitter region is overlapped with the surface field region and the first buffer region is positioned between overlapped portions of the emitter region and the surface field region.
14. The solar cell of claim 10 , wherein the first buffer region is made of amorphous silicon.
15. The solar cell of claim 10 , further comprising a second buffer region positioned on the incident surface.
16. The solar cell of claim 15 , wherein the second buffer region is made of a same material as the first buffer region.
17. The solar cell of claim 15 , further comprising an anti-reflection layer positioned on the second buffer region.
18. The solar cell of claim 1 , wherein a thickness of the second emitter portion differs from a thickness of the second surface field portion.
19. The solar cell of claim 18 , wherein when the first conductivity type is of an n-type, the thickness of the second surface field portion is less than the thickness of the second emitter portion.
20. The solar cell of claim 1 , wherein a thickness of at least one of the second emitter portion and the second surface field portion differs from a thickness of the at least one of the first emitter portion and first surface field portion.
21. The solar cell of claim 1 , wherein the first and second electrodes are made of a transparent conductive material.
22. The solar cell of claim 21 , further comprising a third electrode and a fourth electrode positioned on the first electrode and the second electrode, respectively, and the third and fourth electrodes are made of a conductive material.
23. The solar cell of claim 1 , wherein the first and second electrodes are made of a conductive metal material.