A solar cell is discussed. The solar cell includes a substrate of a first conductive type, an emitter region which is positioned at a front surface of the substrate and has a second conductive type different from the first conductive type, a front passivation region including a plurality of layers which are sequentially positioned on the emitter region, a back passivation region which is positioned on a back surface opposite the front surface of the substrate and includes three layers, a plurality of front electrodes which pass through the front passivation region and are connected to the emitter region, and at least one back electrode which passes through the back passivation region and is connected to the substrate.
1. A solar cell comprising:
a substrate of a first conductive type;
an emitter region which is positioned at a front surface of the substrate and has a second conductive type different from the first conductive type;
a front passivation region including a plurality of layers which are sequentially positioned on the emitter region;
a back passivation region which is positioned on a back surface opposite the front surface of the substrate and includes three layers;
a front electrode part which passes through the front passivation region and is connected to the emitter region; and
a back electrode part which continuously covers an entire back surface of the back passivation region, passes through the back passivation region and is connected to the substrate,
wherein the plurality of layers of the front passivation region include:
a silicon oxide layer which is positioned on the emitter region and is formed of silicon oxide;
an aluminum oxide layer which is positioned on the silicon oxide layer and is formed of aluminum oxide; and
a silicon nitride layer which is positioned on the aluminum oxide layer and is formed of silicon nitride,
wherein the aluminum oxide layer is positioned between the silicon oxide layer and the silicon nitride layer,
wherein the three layers of the back passivation region include:
a first back passivation layer which is positioned on the back surface of the substrate and is formed of silicon oxide;
a second back passivation layer which is positioned on the first back passivation layer and is formed of silicon nitride; and
a third back passivation layer which is positioned on the second back passivation layer and is formed of aluminum oxide,
wherein the second back passivation layer is positioned between the first back passivation layer and the third back passivation layer,
wherein the back electrode part includes a back electrode having a plurality of contact portions which locally abut the back surface of the substrate,
wherein the solar cell further comprises a plurality of back surface field regions respectively positioned at the back surface of the substrate abutting the plurality of contact portions,
wherein the first back passivation layer is directly on the plurality of back surface field regions, the second back passivation layer is directly on the first back passivation layer, and the third back passivation layer is directly on the second back passivation layer,
wherein the third back passivation layer is formed as an outermost layer of the three layers of the back passivation region, and
wherein the plurality of layers of the front passivation region including the silicon oxide layer, the aluminum oxide layer, and the silicon nitride layer sequentially positioned on the front surface of the substrate, and the three layers of the back passivation region including the first back passivation layer, the second back passivation layer, and third back passivation layer sequentially positioned on the back surface of the substrate, are asymmetrical to each other.
2. The solar cell of claim 1 , wherein the first back passivation layer has a thickness of 5 nm to 30 nm, and the third back passivation layer has a thickness of 5 nm to 20 nm.
3. The solar cell of claim 2 , wherein the first back passivation layer and the third back passivation layer have the same thickness.
4. The solar cell of claim 1 , wherein a thickness of the second back passivation layer is greater than a thickness of the first back passivation layer and a thickness of the third back passivation layer.
5. The solar cell of claim 4 , wherein each of the first back passivation layer and the third back passivation layer has the thickness of about 10 nm, and the second back passivation layer has the thickness of about 90 nm.
6. The solar cell of claim 1 , wherein the first back passivation layer has a thickness of 5 nm to 30 nm, the second back passivation layer has a thickness of 10 nm to 200 nm, and the third back passivation layer has a thickness of 5 nm to 20 nm.
7. The solar cell of claim 1 , wherein the aluminum oxide layer has a thickness of 5 nm to 20 nm, and the silicon nitride layer has a thickness of 10 nm to 200 nm.
8. The solar cell of claim 7 , wherein a thickness of the silicon nitride layer is greater than a thickness of the aluminum oxide layer.
9. The solar cell of claim 8 , wherein the silicon nitride layer has the thickness of about 90 nm, and the aluminum oxide layer has the thickness of about 10 nm.
10. The solar cell of claim 1 , wherein the silicon oxide layer has a thickness of 5 nm to 30 nm.
11. The solar cell of claim 10 , wherein each of the silicon oxide layer and the aluminum oxide layer has a thickness of about 10 nm, and the silicon nitride layer has a thickness of about 90 nm.
12. The solar cell of claim 1 , wherein the silicon oxide layer and the first back passivation layer have the same thickness.
13. The solar cell of claim 1 , wherein the first conductive type is an n-type, and the second conductive type is a p-type.
14. The solar cell of claim 1 , wherein the aluminum oxide layer and the third back passivation layer have the same thickness.
15. The solar cell of claim 1 , wherein the front electrode part includes a plurality of front electrodes and a plurality of front bus bars connected to the plurality of front electrodes at crossings of the plurality of front electrodes and the plurality of front bus bars.
16. The solar cell of claim 1 , wherein the front electrode part has a lattice shape on the front surface of the substrate.
17. The solar cell of claim 1 , wherein the back electrode part further includes a plurality of back bus bars connected to the back electrode.
18. The solar cell of claim 17 , wherein the back electrode covers a back surface of the third back passivation layer except in a formation area of the plurality of back bus bars.
19. The solar cell of claim 1 , wherein the plurality of back surface field regions are not positioned at the back surface of the substrate between the adjacent contact portions.
20. The solar cell of claim 1 , wherein the back electrode is connected to the plurality of back surface field regions through the plurality of contact portions.