Photovoltaic device and method for manufacturing the same
Disclosed is a method for manufacturing a photovoltaic device. The method comprising: forming a first electrode on a substrate; forming a first unit cell comprising an intrinsic semiconductor layer on the first electrode; forming an intermediate reflector on the first unit cell, and the intermediate reflector comprising a plurality of sub-layers stacked alternately by changing a flow rate of non-silicon based source gas; forming a second unit cell comprising an intrinsic semiconductor layer on the intermediate reflector; and forming a second electrode on the second unit cell.
1. A photovoltaic device comprising:
a substrate;
a first electrode placed on the substrate;
a first unit cell placed on the first electrode and comprising an intrinsic semiconductor layer;
an intermediate reflector placed on the first unit cell and comprising a plurality of sub-layers stacked alternately, and the plurality of sub-layers having different crystal volume fractions from each other;
a second unit cell placed on the intermediate reflector and comprising an intrinsic semiconductor layer; and
a second electrode placed on the second unit cell.
2. The photovoltaic device according to claim 1 , wherein the intermediate reflector is profiled such that concentrations of a non-silicon based element included in the sub-layers increase the farther the concentrations of the non-silicon based element are from a light incident side of the photovoltaic device.
3. The photovoltaic device according to claim 1 , wherein the intermediate reflector includes a hydrogenated n-type nano-crystalline silicon oxide, a hydrogenated n-type nano-crystalline silicon carbide, or a hydrogenated n-type nano-crystalline silicon nitride.
4. The photovoltaic device according to claim 1 , wherein the unit cell which is closest to a light incident side of the photovoltaic device comprises an n-type semiconductor layer including a hydrogenated n-type nano-crystalline silicon, and the intermediate reflector in contact with the n-type semiconductor layer includes an n-type nano-crystalline silicon based material.
5. The photovoltaic device according to claim 1 , wherein the plurality of sub-layers comprise at least one pair of a first sub-layer and a second sub-layer, and wherein a thickness ratio between the first sub-layer and the second sub-layer in each of the pairs is constant.
6. The photovoltaic device according to claim 1 , wherein the plurality of sub-layers comprise a first sub-layer and a second sub-layer, and wherein one of either the first sub-layer or second sub-layer has a larger crystal volume fraction comprising crystalline silicon grains than the other sub-layer.
7. The photovoltaic device according to claim 1 , wherein the plurality of sub-layer comprise a first sub-layer and a second sub-layer, and wherein one of either the first sub-layer or the second sub-layer has a greater crystal volume fraction than the other sub-layer.
8. The photovoltaic device according to claim 1 , wherein the plurality of sub-layers comprise a first sub-layer and a second sub-layer, and wherein one of either the first sub-layer or second sub-layer has a larger crystal volume fraction comprising crystalline silicon grains, and wherein a diameter of the crystalline silicon grains is greater than or equal to 3 nm and less than or equal to 10 nm.
9. The photovoltaic device according to claim 1 , wherein a thickness of the intermediate reflector is greater than or equal to 30 nm and less than or equal to 200 nm.
10. The photovoltaic device according to claim 1 , wherein the plurality of sub-layers comprise a first sub-layer and a second sub-layer, and thicknesses of the first sub-layer and the second layer are greater than or equal to 10 nm and less than or equal to 50 nm.
11. The photovoltaic device according to claim 1 , wherein the number of the sub-layers included in the intermediate reflector is greater than or equal to three.
12. The photovoltaic device according to claim 1 , wherein a refractive index of the intermediate reflector is greater than or equal to 1.7 and less than or equal to 2.2 in a wavelength range from 500 nm to 700 nm.
13. The photovoltaic device according to claim 1 , wherein an average content of a non-silicon based element included in the intermediate reflector is greater than or equal to 10 atomic % and less than or equal to 30 atomic %.
14. The photovoltaic device according to claim 1 , wherein an average hydrogen content of the intermediate reflector is greater than or equal to 10 atomic % and less than or equal to 25 atomic %.
15. The photovoltaic device according to claim 1 , wherein an average crystal volume fraction of the intermediate reflector is greater than or equal to 4% and less than or equal to 30%.
16. The photovoltaic device according to claim 1 , wherein the unit cell which is closest to a light incident side of the photovoltaic device comprises a p-type semiconductor layer and an intrinsic semiconductor layer, and the intermediate reflector contacts with the intrinsic semiconductor layer of the unit cell which is closest to the light incident side of the photovoltaic device.
17. The photovoltaic device according to claim 1 , wherein, when a nominal operating cell temperature of the photovoltaic device is greater than or equal to 35 degrees Celsius, and a short circuit current of the unit cell that is closest to a light incident side of the photovoltaic device, is less than or equal to that of the other unit cell.
18. The photovoltaic device according to claim 1 , wherein, when nominal operating cell temperature of the photovoltaic device is less than 35 degrees Celsius, and a short circuit current of one unit cell, which is closest to a light incident side of the photovoltaic device, is greater than or equal to that of the other unit cell.
19. The photovoltaic device according to claim 1 , wherein the plurality of sub-layers comprise a first sub-layer and a second sub-layer, and one of either the first sub-layer or the second sub-layer comprises a hydrogenated n-type nano-crystalline silicon oxynitride (n-nc-SiON:H), and the other comprises a hydrogenated n-type nano-crystalline silicon oxide (n-nc-SiO:H).
20. The photovoltaic device according to claim 1 , wherein the plurality of sub-layers comprises a first sub-layer, a second sub-layer, and a third sub-layer.
21. The photovoltaic device according to claim 20 , wherein the first sub-layer includes a hydrogenated n-type nano-crystalline silicon oxynitride (n-nc-SiON:H), the second sub- layer includes a hydrogenated n-type nano-crystalline silicon oxide (n-nc-SiO:H), and the third sub-layer includes a hydrogenated n-type nano-crystalline silicon (n-nc-Si:H).
22. A photovoltaic device comprising:
a substrate;
a first electrode placed on the substrate;
a first unit cell placed on the first electrode and comprising an intrinsic semiconductor layer;
an intermediate reflector placed on the first unit cell and comprising a plurality of sub-layers stacked alternately, and the plurality of sub-layers having different crystal volume fractions from each other;
a second unit cell placed on the intermediate reflector and comprising an intrinsic semiconductor layer; and
a second electrode placed on the second unit cell,
wherein the plurality of sub-layers stacked alternately comprise a first layer formed at a first flow rate α of a non-silicon based source gas and a second layer formed at a second flow rate β of the non-silicon based source gas, wherein the first flow rate α is greater than the second flow rate β, and the first layer is disposed between the first unit cell and the second layer.