Solar cell

1. A solar cell comprising:

a photoelectric conversion unit comprising a semiconductor substrate, a tunneling layer on the semiconductor substrate, and a first conductive type region and a second conductive type region formed on the tunneling layer at a same side of the semiconductor substrate, wherein each of the first and second conductive type regions includes a semiconductor material;

electrodes formed on the photoelectric conversion unit and comprising an adhesive layer directly formed on the respective first and second conductive type regions and an electrode layer formed on the adhesive layer,

wherein the adhesive layer comprises a metal of titanium (Ti) or tungsten (W),

wherein the electrode layer comprises:

a first electrode layer disposed on the adhesive layer and comprising at least one of copper (Cu), aluminum (Al), silver (Ag), gold (Au), and alloys thereof, and

a second electrode layer on the first electrode layer and comprising at least one of tin (Sn) and a nickel (Ni)-vanadium (V) alloy,

wherein the second electrode layer is an outermost layer of the electrode layer,

wherein the tunneling layer comprises an oxide, and each of the first and second conductive type regions comprises a polycrystalline semiconductor, and

wherein a coefficient of thermal expansion of the adhesive layer is greater than coefficients of thermal expansion of both the first conductive type region and the second conductive type region and is less than a coefficient of thermal expansion of the first electrode layer; and

a barrier region is disposed between the first and second conductive type regions and on the tunneling layer,

wherein the first and second conductive type regions and the barrier region are formed on the same plane and in alignment with each other.

2. The solar cell according to claim 1 , wherein the adhesive layer has transparency.

3. The solar cell according to claim 2 , wherein the adhesive layer has a smaller thickness than each of the first and second electrode layers of the electrode layer.

4. The solar cell according to claim 3 , wherein the first electrode layer comprises a reflective material.

5. The solar cell according to claim 4 , wherein the first electrode layer has a thickness of 50 nm to 300 nm.

6. The solar cell according to claim 5 , wherein the second electrode layer is formed by sputtering and has a thickness of 50 nm to 300 nm.

7. The solar cell according to claim 4 , wherein the second electrode layer is connected to a ribbon.

8. The solar cell according to claim 1 , wherein the adhesive layer has a thickness of 50 nm or less.

9. The solar cell according to claim 1 , wherein the semiconductor substrate or the first conductive type region and the second conductive type region comprise silicon (Si).

10. A solar cell module comprising:

a plurality of solar cells, each solar cell comprising a semiconductor substrate, a tunneling layer on the semiconductor substrate, and a first conductive type region and a second conductive type region formed on the tunneling layer at a same side of the semiconductor substrate;

electrodes respectively formed on the first conductive type region and the second conductive type region,

wherein the electrodes include an adhesive layer formed on the respective first and second conductive type regions, a first electrode layer disposed on the adhesive layer, and a second electrode layer disposed on the first electrode layer;

a ribbon directly connected to the second electrode layer with a conductive film or a paste so that the plurality of solar cells are connected;

a front substrate on a second side of the plurality of solar cells;

a back sheet on a first side of the plurality of solar cells;

a first sealant between the plurality of solar cells and the back sheet;

a second sealant between the plurality of solar cells and the back sheet,

wherein the second electrode layer is an outermost layer of the electrodes,

wherein the tunneling layer comprises an oxide, and each of the first and second conductive type regions comprises a polycrystalline semiconductor, and

wherein a coefficient of thermal expansion of the adhesive layer is greater than coefficients of thermal expansion of both the first conductive type region and the second conductive type region and is less than a coefficient of thermal expansion of the first electrode layer; and

a barrier region is disposed between the first and second conductive type regions and on the tunneling layer,

wherein the first and second conductive type regions and the barrier region are formed on the same plane and in alignment with each other.

11. The solar cell module according to claim 10 , wherein the adhesive layer comprises a metal of titanium (Ti) or tungsten (W).

12. The solar cell module according to claim 11 , wherein the adhesive layer has a thickness of 50 nm or less.

13. The solar cell module according to claim 11 , wherein the first electrode layer comprises at least one of copper (Cu), aluminum (Al), silver (Ag), gold (Au), and alloys thereof.

14. The solar cell module according to claim 13 , wherein the first electrode layer has a thickness of 100 nm to 300 nm.

15. The solar cell module according to claim 13 , wherein the second electrode layer comprises at least one of tin (Sn) and a nickel (Ni)-vanadium (V) alloy.

16. The solar cell module according to claim 13 , wherein the second electrode layer has a thickness of 100 nm to 300 nm.

17. The solar cell module according to claim 16 , wherein the electrodes have a thickness of 650 nm or less.