Bifacial solar cell

1. A bifacial solar cell comprising:

a substrate;

an emitter portion formed on a first surface of the substrate;

a first insulating layer formed on the emitter portion;

a plurality of first electrodes contacting the emitter portion through the first insulating layer and extended in a first direction;

a plurality of first current collectors extended in a second direction crossing the first direction, wherein the plurality of first current collectors are electrically and physically connected to the plurality of first electrodes;

a second insulating layer formed on a second surface of the substrate;

a back surface field formed on the second surface of the substrate, and having an impurity concentration that is higher than an impurity concentration of the substrate;

a plurality of second electrodes contacting the back surface field through the second insulating layer and extended in the first direction; and

a plurality of second current collectors extended in the second direction, wherein the plurality of second current collectors are electrically and physically connected to the plurality of second electrodes,

wherein a number of the plurality of second electrodes is different from a number of the plurality of first electrodes,

wherein two neighboring first electrodes among the plurality of first electrodes are spaced apart from each other by a first pitch P 1 , and two neighboring second electrodes among the plurality of second electrodes are spaced apart from each other by a second pitch P 2 , and

wherein the second pitch P 2 is smaller than the first pitch P 1 .

2. The bifacial solar cell of claim 1 , wherein a central line of each of the plurality of second electrodes in a width direction is positioned not to conform to a central line of each of the plurality of first electrodes in the width direction.

3. The bifacial solar cell of claim 1 , wherein a ratio n of the first pitch P 1 and the second pitch P 2 satisfies an equation: 0.1<n<1, where n=P 2 /P 1 .

4. The bifacial solar cell of claim 1 , wherein each of the plurality of first electrodes has a line width of less than 60 μm and a thickness of at least 10 μm.

5. The bifacial solar cell of claim 1 , wherein each of the plurality of second electrodes has a line width of less than 70 μm and a thickness of at least 10 μm.

6. The bifacial solar cell of claim 1 , wherein the substrate is formed of n conductive type silicon, and the emitter portion is of a p conductive type.

7. The bifacial solar cell of claim 6 , wherein the emitter portion is formed of a p conductive type silicon.

8. The bifacial solar cell of claim 1 , wherein the first insulating layer includes at least one of a silicon nitride layer, a silicon oxide layer, or an aluminum oxide layer.

9. The bifacial solar cell of claim 1 , wherein the second insulating layer includes at least one of a silicon nitride layer, a silicon oxide layer, or an aluminum oxide layer.

10. The bifacial solar cell of claim 1 , wherein two neighboring second electrodes among the plurality of second electrodes are aligned within a spacing of two neighboring first electrodes among the plurality of first electrodes when viewing a side view of the bifacial solar cell.

11. The bifacial solar cell of claim 1 , wherein the plurality of first electrodes directly contact the emitter portion through openings of the first insulating layer.

12. The bifacial solar cell of claim 1 , wherein the plurality of second electrodes directly contact the back surface field through openings of the second insulating layer.

13. The bifacial solar cell of claim 1 , wherein the substrate is a silicon substrate.