Solar cell

1. A solar cell comprising:

a substrate containing impurities of a first conductive type;

an emitter region positioned at a first surface of the substrate, the emitter region containing impurities of a second conductive type opposite the first conductive type;

a first electrode which is positioned on the first surface of the substrate and is electrically connected to the emitter region;

a back passivation layer positioned on a second surface opposite the first surface of the substrate, the back passivation layer having a plurality of holes and containing at least one of aluminum oxide (AlOx), silicon oxide (SiOx), silicon nitride (SiNx), and silicon oxynitride SiOxNy);

an adhesion enhanced layer positioned on the back passivation layer, the adhesion enhanced layer containing at least one of intrinsic amorphous silicon and intrinsic microcrystalline silicon, and having a plurality of holes; and

a second electrode which is positioned on the adhesion enhanced layer and is electrically connected to the substrate through the plurality of holes of the adhesion enhanced layer and the plurality of holes of the back passivation layer, the second electrode including a plurality of connection electrodes and a back electrode layer, the plurality of connection electrodes being positioned inside the plurality of holes of the adhesion enhanced layer and inside the plurality of holes of the back passivation layer, and the back electrode layer being positioned on the plurality of connection electrodes and the adhesion enhanced layer,

wherein the adhesion enhanced layer further includes a metal-silicon alloy layer, and

the metal-silicon alloy layer is positioned at an interface between the adhesion enhanced layer and the back electrode layer as well as at an interface between an inside surface of the plurality of holes of the adhesion enhanced layer and the plurality of connection electrodes but the metal-silicon alloy layer is not positioned at an interface between an inside surface of the plurality of holes of the back passivation layer and the plurality of connection electrodes.

2. The solar cell of claim 1 , wherein the metal-silicon alloy layer is an aluminum-silicon alloy layer.

3. The solar cell of claim 1 , wherein a thickness of the adhesion enhanced layer is about 10 nm to 100 nm.

4. The solar cell of claim 1 , wherein a refractive index of the adhesion enhanced layer is greater than a refractive index of the back passivation layer.

5. The solar cell of claim 1 , wherein a refractive index of the adhesion enhanced layer is about 3.7 to 4.2.

6. The solar cell of claim 1 , further comprising a diffusion barrier layer positioned between the back passivation layer and the adhesion enhanced layer.

7. The solar cell of claim 6 , wherein the diffusion barrier layer contains silicon nitride (SiN X ).

8. The solar cell of claim 6 , wherein a refractive index of the diffusion barrier layer is about 2.1 to 2.3.

9. The solar cell of claim 6 , wherein a thickness of the diffusion barrier layer is about 30 nm to 70 nm.

10. The solar cell of claim 1 , wherein the back passivation layer includes a plurality of layers.

11. The solar cell of claim 10 , wherein the back passivation layer includes a first passivation layer abutting on the substrate and a second passivation layer positioned on the first passivation layer.

12. The solar cell of claim 11 , wherein the first passivation layer contains aluminum oxide (AlOx), and the second passivation layer contains silicon oxide (SiOx).

13. The solar cell of claim 11 , wherein a thickness of the first passivation layer is about 5 nm to 15 nm, and a thickness of the second passivation layer is about 150 nm to 250 nm.