Silicon-based dielectric stack passivation of Si-epitaxial thin-film solar cells
One embodiment of the present invention provides a solar cell. The solar cell includes a metallurgical-grade Si (MG-Si) substrate, a first layer of heavily doped crystalline-Si situated above the MG-Si substrate, a layer of lightly doped crystalline-Si situated above the first heavily doped crystalline-Si layer, a backside ohmic-contact layer situated on the backside of the MG-Si substrate, a second layer of heavily doped crystalline-Si situated above the lightly doped crystalline-Si layer, a first layer of dielectric situated above the second heavily doped crystalline-Si layer, a second layer of dielectric situated above the first dielectric layer, and front electrodes situated above the second dielectric layer.
1. A solar cell, comprising:
a metallurgical-grade Si (MG-Si) substrate;
a first heavily doped crystalline-Si layer situated above the MG-Si substrate;
a lightly doped crystalline-Si layer situated above the first heavily doped crystalline-Si layer;
a second heavily doped crystalline-Si layer situated above the lightly doped crystalline-Si layer;
front electrodes situated above the second heavily doped crystalline-Si layer;
a passivation layer situated between the second heavily doped crystalline-Si layer and the front electrodes, wherein the passivation layer passivates a surface of the second heavily doped crystalline-Si layer, wherein the passivation layer includes a three-layer dielectric stack, wherein the three-layer dielectric stack includes a SiO x N y layer in contact with the second heavily doped crystalline-Si layer, a hydrogenated SiN x layer in contact with the front electrodes, and a oxide layer situated between the SiO x N y layer and the hydrogenated SiN x layer, and wherein the SiO x N y layer relaxes interfacial stress between the second heavily doped crystalline-Si layer and the oxide layer; and
a backside ohmic-contact layer situated on the backside of the MG-Si substrate.
2. The solar cell of claim 1 , wherein the thickness of the SiO x N y layer is between 5 Å and 50 Å.
3. The solar cell of claim 1 , wherein the oxide layer comprises silicon dioxide (SiO 2 ).
4. The solar cell of claim 3 , wherein the thickness of the SiO 2 layer can be between 10 Å and 300 Å.
5. The solar cell of claim 1 , wherein the thickness of the hydrogenated SiN x layer can be between 500 Å and 1000 Å, and wherein the hydrogenated SiN x layer can serve as an anti-reflective layer.
6. The solar cell of claim 1 , wherein the front electrodes are formed using:
screen-printing and firing of Ag paste; or
aerosol printing and firing of Ag ink with glass frit.
7. The solar cell of claim 1 , wherein the first heavily doped crystalline-Si layer and the lightly doped crystalline-Si layer are p-type doped, and wherein the second heavily doped crystalline-Si layer is n-type doped.
8. The solar cell of claim 1 , wherein the first heavily doped crystalline-Si layer and the lightly doped crystalline-Si layer are deposited using a chemical-vapor-deposition (CVD) technique.
9. The solar cell of claim 1 , wherein the second heavily doped crystalline-Si layer is formed using a CVD technique.
10. The solar cell of claim 1 , wherein the second heavily doped crystalline-Si layer is formed by diffusing dopants.