DOUBLE-SIDED HETEROJUNCTION SOLAR CELL BASED ON THIN EPITAXIAL SILICON

1 . A method for fabricating a double-sided heterojunction solar cell, comprising:

depositing a layer of heavily doped crystalline-Si (c-Si) on the surface of a metallurgical-grade silicon (MG-Si) substrate;

epitaxially forming a layer of lightly doped c-Si on the surface of the heavily doped c-Si layer;

removing the MG-Si substrate and the heavily doped c-Si layer;

forming a front-side passivation layer on the front side of the lightly doped c-Si layer;

forming a back-side passivation layer on the back side of the lightly doped c-Si layer;

forming a front-side emitter on the front-side passivation layer;

forming a back surface field (BSF) layer on the back-side passivation layer;

forming a front-side electrode grid; and

forming a back-side electrode.

2 . The method of claim 1 , further comprising texturing at least one surface of the lightly doped c-Si layer.

3 . The method of claim 1 , wherein the MG-Si substrate is removed using one or more of the following techniques:

mechanical grinding;

chemical wet etching;

dry etching; and

chemical mechanical polishing.

4 . The method of claim 1 , further comprising forming a transparent conductive oxide (TCO) layer on the front-side emitter and/or the BSF layer.

5 . The method of claim 1 , wherein the passivation layers comprise intrinsic amorphous Si (a-Si) or silicon oxide (SiO x ).

6 . The method of claim 1 , wherein the thickness of the passivation layers is between 2 nm and 8 nm.

7 . The method of claim 1 , wherein the emitter and/or the BSF layer comprise heavily doped a-Si.

8 . The method of claim 7 , wherein the thickness of the a-Si emitter and/or the BSF layer is between 5 nm and 50 nm, and wherein the doping concentration of the heavily doped a-Si is between 1×10 17 /cm 3 and 1×10 20 /cm 3 .

9 . The method of claim 1 , wherein the lightly doped c-Si layer is deposited using a chemical-vapor-deposition (CVD) technique, wherein the thickness of the lightly doped c-Si layer is between 20 μm and 100 μm, and wherein the doping concentration for the lightly doped c-Si layer is between 1×10 15 /cm 3 and 1×10 17 /cm 3 .

10 . The method of claim 1 , wherein the lightly doped c-Si layer is n-type doped, and wherein the front-side emitter and the BSF layer are doped with different types of dopants.

11 . The method of claim 1 , wherein the heavily doped c-Si layer acts as an impurity getter layer, wherein the heavily doped c-Si layer is deposited using a chemical-vapor-deposition (CVD) technique, wherein the thickness of the heavily doped c-Si layer is between 1 μm and 5 μm, and wherein the doping concentration for the heavily doped c-Si layer is between 1×10 17 /cm 3 and 1×10 20 /cm 3 .

12 . The method of claim 1 , wherein the front-side and the back-side passivation layers are formed in one step.

13 . The method of claim 1 , wherein the front-side emitter and the BSF layer are formed in one step.

14 . A double-sided heterojunction solar cell, comprising:

a lightly doped epitaxial crystalline Si (c-Si) base layer;

a front-side passivation layer situated on the front side of the lightly doped epitaxial c-Si base layer;

a back-side passivation layer situated on the back side of the lightly doped epitaxial c-Si base layer;

a front-side emitter situated on the surface of the front-side passivation layer;

a back surface field (BSF) layer situated on the surface of the back-side passivation layer;

a front-side electrode; and

a back-side electrode.

15 . The solar cell of claim 14 , wherein at least one surface of the lightly doped epitaxial c-Si layer is textured.

16 . The solar cell of claim 14 , further comprising at least one transparent conductive oxide (TCO) layer situated on the surface of the front-side emitter and/or the surface of the BSF layer.

17 . The solar cell of claim 14 , wherein the passivation layers comprise intrinsic amorphous Si (a-Si) or silicon oxide (SiO x ).

18 . The solar cell of claim 14 , wherein the thickness of the passivation layers is between 2 nm and 8 nm.

19 . The solar cell of claim 14 , wherein the emitter and/or the BSF layer comprise heavily doped a-Si.

20 . The solar cell of claim 19 , wherein the thickness of the a-Si emitter and/or the BSF layer is between 5 nm and 50 nm, and wherein the doping concentration of the heavily doped a-Si is between 1×10 17 /cm 3 and 1×10 20 /cm 3 .

21 . The solar cell of claim 14 , wherein the lightly doped epitaxial c-Si layer is deposited using a chemical-vapor-deposition (CVD) technique, wherein the thickness of the lightly doped c-Si layer is between 20 μm and 100 μm, and wherein the doping concentration for the lightly doped c-Si layer is between 1×10 15 /cm 3 and 1×10 17 /cm 3 .

22 . The solar cell of claim 14 , wherein the lightly doped c-Si layer is n-type doped, and wherein the front-side emitter and the BSF layer are doped with different types of dopants

23 . The solar cell of claim 14 , wherein the front-side and the back-side passivation layers are formed in one step.

24 . The solar cell of claim 14 , wherein the front-side emitter and the BSF layer are formed in one step.

25 . The solar cell of claim 14 , wherein the lightly doped epitaxial c-Si layer is epitaxially grown on a metallurgical-grade Si (MG-Si) substrate, which is subsequently removed using a mechanical grinding technique.