A bifacial solar cell includes a silicon substrate; an emitter layer; a plurality of first electrodes locally on the emitter layer; a first aluminum oxide layer on the emitter layer; a first silicon oxide layer between the first aluminum oxide layer and the emitter layer; a first anti-reflection layer on the first aluminum oxide layer; a back surface field layer on the silicon substrate; a second aluminum oxide layer on the silicon substrate; a second silicon oxide layer between the second aluminum oxide layer and the silicon substrate; a second anti-reflection layer on the second aluminum oxide layer; and a plurality of second electrodes respectively on the back surface field layers through the second anti-reflection layer, the second aluminum oxide layer and the second silicon oxide layer.
1. A bifacial solar cell comprising:
an n type silicon substrate;
a p type emitter layer positioned at a first surface of the n type silicon substrate;
a plurality of first electrodes locally positioned on the p type emitter layer and electrically connected to the p type emitter layer;
a first aluminum oxide layer positioned on the p type emitter layer;
a first silicon oxide layer formed at an interface between the first aluminum oxide layer and the p type emitter layer, the first silicon oxide layer having a thickness of about 1 nm to 3 nm;
a first anti-reflection layer positioned on the first aluminum oxide layer and containing silicon nitride (SiN x );
a back surface field layer positioned on a rear surface of the n type silicon substrate;
a second aluminum oxide layer on the rear surface of the n type silicon substrate;
a second silicon oxide layer formed at an interface between the second aluminum oxide layer and the rear surface of the n type silicon substrate, the second silicon oxide layer having a thickness of about 1 nm to 3 nm;
a second anti-reflection layer positioned on the second aluminum oxide layer and containing silicon nitride (SiN x ); and
a plurality of second electrodes directly contacting the back surface field layer through the second anti-reflection layer, the second aluminum oxide layer and the second silicon oxide layer,
wherein the plurality of first electrodes and the plurality of second electrodes include silver (Ag), the plurality of first electrodes further include aluminum (Al), and the plurality of second electrodes do not include aluminum (Al),
wherein the plurality of first electrodes are formed of a first conductive paste including a glass frit and a mixture (Ag:Al) of silver (Ag) and aluminum (Al), and the plurality of second electrodes are formed of a second conductive paste including a glass frit and silver (Ag), and
wherein the p type emitter layer includes a first doped region, which is lightly doped with impurities of the p type, and a second doped region formed locally, which is more heavily doped than the first doped region with impurities of the p type.
2. The bifacial solar cell of claim 1 , wherein each of the first aluminum oxide layer and the second aluminum oxide layer has a refractive index of about 1.55 to 1.7.
3. The bifacial solar cell of claim 1 , wherein each of the first aluminum oxide layer and the second aluminum oxide layer has a thickness of about 5 nm to 30 nm.
4. The bifacial solar cell of claim 1 , wherein a width of the back surface field layer is equal to or less than a width of a second electrode of the plurality of second electrodes.
5. The bifacial solar cell of claim 1 , wherein a width of the back surface field layer is greater than a width of a second electrode of the plurality of second electrodes.
6. The bifacial solar cell of claim 1 , wherein each of the first anti-reflection layer and the second anti-reflection layer has a refractive index of about 1.9 to 2.3.
7. The bifacial solar cell of claim 1 , wherein each of the first anti-reflection layer and the second anti-reflection layer has a thickness of about 50 nm to 100 nm.
8. The bifacial solar cell of claim 1 , wherein the plurality of first electrodes are formed to be parallel to each other with a certain width and the plurality of second electrodes are formed to be parallel to each other with a certain width.
9. The bifacial solar cell of claim 1 , wherein the second doped region is formed at the same location of the n type silicon substrate as the plurality of first electrodes.
10. The bifacial solar cell of claim 9 , wherein a width of the second doped region is equal to or less than a width of each first electrode.
11. The bifacial solar cell of claim 9 , wherein a width of the second doped region is greater than a width of each first electrode.
12. The bifacial solar cell of claim 9 , wherein the first doped region has a surface resistivity of about 80 Ω/sq to 200 Ω/sq.
13. The bifacial solar cell of claim 9 , wherein the second doped region has a surface resistivity of about 30 Ω/sq to 80 Ω/sq.
14. The bifacial solar cell of claim 1 , wherein then type silicon substrate has a front textured surface and a rear textured surface.