TANDEM SOLAR CELL WITH IMPROVED TUNNEL JUNCTION

1 . A method for fabricating a photovoltaic device, comprising:

forming a light-absorbing semiconductor structure on a transmissive substrate including a first doped layer;

forming an intrinsic layer on the first doped layer, wherein the intrinsic layer includes an amorphous material;

treating the intrinsic layer with a plasma to form seed sites; and

forming a first tunnel junction layer on the intrinsic layer by growing microcrystals from the seed sites.

2 . The method as recited in claim 1 , wherein the first tunnel junction layer includes one of a P-type layer and an N-type layer.

3 . The method as recited in claim 1 , wherein the intrinsic layer includes amorphous silicon and the first tunnel junction layer includes microcrystalline silicon.

4 . The method as recited in claim 1 , wherein the transmissive substrate includes a transparent conductor formed thereon.

5 . The method as recited in claim 1 , wherein treating includes treating the intrinsic layer with a hydrogen plasma.

6 . The method as recited in claim 1 , further comprising providing an increased dopant concentration for the first tunnel junction layer to improve conductivity.

7 . The method as recited in claim 1 , wherein the seed sites enable the formation of a microcrystalline phase for the first and second tunnel junction layers.

8 . The method as recited in claim 1 , further comprising forming one or more additional light-absorbing semiconductor structures on the first tunnel junction layer.

9 . The method as recited in claim 8 , wherein the one or more additional light-absorbing semiconductor structures includes additional tandem cells.

10 . A method for fabricating a photovoltaic device, comprising:

forming a first photovoltaic cell by:

forming a transparent conductor on a transmissive substrate;

forming a first doped layer on the transparent conductor;

forming an intrinsic layer on the first doped layer, wherein the intrinsic layer includes an amorphous material;

treating the intrinsic layer with a plasma to form seed sites;

forming a first tunnel junction layer on the intrinsic layer by growing microcrystals from the seed sites;

forming a second photovoltaic cell by:

forming a second tunnel junction layer having an opposite polarity from the first tunnel junction layer, a corresponding intrinsic layer formed from a material having a different band gap from the first cell and a second doped layer formed on the corresponding intrinsic layer.

11 . The method as recited in claim 10 , wherein the intrinsic layer of the first photovoltaic cell includes amorphous silicon and the first tunnel junction layer includes microcrystalline silicon.

12 . The method as recited in claim 10 , wherein treating includes treating the intrinsic layer with a hydrogen plasma.

13 . The method as recited in claim 10 , wherein the seed sites enable the formation of a microcrystalline phase for the first and second tunnel junction layers.

14 . The method as recited in claim 10 , further comprising forming one or more additional tandem cells on the second photovoltaic cell.

15 . The method as recited in claim 14 , further comprising treating an intrinsic layer of at least one other additional tandem cell with a plasma to form seed sites

16 . The method as recited in claim 14 , further comprising providing increasing band gaps for tandem cells as a function of distance from incident radiation.

17 . The method as recited in claim 10 , further comprising providing an increased dopant concentration for the first tunnel junction layer to improve conductivity.

18 .- 25 . (canceled)