A solar cell is discussed. The solar cell according to an embodiment includes a substrate of a first conductive type, an emitter layer of a second conductive type opposite the first conductive type, which forms a p-n junction along with the substrate, a first anti-reflection layer on the emitter layer, a second anti-reflection layer on the first anti-reflection layer, a first electrode part connected to the emitter layer, and a second electrode part connected to the substrate. The first anti-reflection layer is formed of silicon nitride, and the second anti-reflection layer is formed of silicon oxide.
1. A solar cell comprising:
a semiconductor substrate of a first conductive type, the semiconductor substrate being a single crystal silicon substrate, and the semiconductor substrate having a textured surface;
an emitter layer of a second conductive type opposite the first conductive type, the emitter layer configured to form a p-n junction along with the semiconductor substrate, having a first part and a second part with different impurity thicknesses, and positioned on a front surface of the semiconductor substrate;
a first anti-reflection layer positioned on the emitter layer, the first anti-reflection layer being formed of silicon nitride, and the first anti-reflection layer having a first refractive index of 2.05 to 2.15 and a first thickness of 65 nm to 95 nm;
a second anti-reflection layer positioned on the first anti-reflection layer, the second anti-reflection layer being formed of silicon oxide, the second anti-reflection layer having a second refractive index of 1.5 to 1.7 and a second thickness of 80 nm to 110 nm;
a first electrode part connected to the emitter layer, and positioned on the first part of the emitter layer; and
a second electrode part connected to a back surface of the semiconductor substrate opposite the front surface of the semiconductor substrate,
wherein the second refractive index is less than the first refractive index, and the second thickness is greater than the first thickness,
wherein a first thickness of the semiconductor substrate where the first part of the emitter layer is overlapped is equal to a second thickness of the semiconductor substrate where the second part of the emitter layer is overlapped,
wherein an impurity doping thickness of the first part of the emitter layer is greater than an impurity doping thickness of the second part of the emitter layer, the impurity doping thickness of the first part of the emitter layer is 400 nm to 700 nm, and the impurity doping thickness of the second part of the emitter layer is 200 nm to 500 nm,
wherein a sheet resistance of the first part of the emitter layer is less than a sheet resistance of the second part of the emitter layer, the sheet resistance of the first part of the emitter layer is 30 Ω/sq. to 70 Ω/sq., and the sheet resistance of the second part of the emitter layer is 80 Ω/sq. to 150 Ω/sq.,
wherein an upper surface of the first part of the emitter layer is projected towards a light incident surface of the substrate,
wherein a lower surface of the first electrode part is in contact with the upper surface of the first part of the emitter layer,
wherein the first anti-reflection layer having a first portion positioned on the first part of the emitter layer and a second portion positioned on the second part of the emitter layer, the first portion of the first anti-reflection layer being formed on the first electrode part and the second portion of the first anti-reflection layer not being formed on the first electrode part,
wherein the first portion of the first anti-reflection layer is located higher than the second portion of the first anti-reflection layer, and
wherein the lower surface of the first electrode part is located higher than an upper surface of the second portion of the first anti-reflection layer.
2. The solar cell of claim 1 , wherein the first electrode part adjoins the first part of the emitter layer, and the first anti-reflection layer adjoins the second part of the emitter layer not including a dead layer.
3. The solar cell of claim 2 , wherein a first thickness of the emitter layer in the first emitter region is greater than a second thickness of the emitter layer in the second emitter region.
4. The solar cell of claim 2 , wherein a shortest distance between a surface of the semiconductor substrate and a p-n junction surface between the first part of the emitter layer and the semiconductor substrate is longer than a shortest distance between the surface of the semiconductor substrate and a p-n junction surface between the second part of the emitter layer and the semiconductor substrate.