TUNNELING-JUNCTION SOLAR CELL WITH SHALLOW COUNTER DOPING LAYER IN THE SUBSTRATE

1 . A method for fabricating a tunneling junction solar cell, comprising:

obtaining a base layer for the solar cell, wherein the base layer includes a shallow counter doping layer having a conduction doping type that is opposite to a remainder of the base layer;

forming an emitter layer adjacent to the shallow counter doping layer, wherein the emitter layer has a bandgap that is wider than that of the base layer;

forming a surface field layer;

forming a front-side electrode; and

forming a back-side electrode.

2 . The method of claim 1 , wherein the base layer comprises at least one of:

a mono-crystalline silicon wafer; and

an epitaxially grown crystalline-Si (c-Si) thin film.

3 . The method of claim 1 , wherein the shallow counter doping layer has a graded doping concentration, and where a peak value of the graded doping ranges between 1×10 18 /cm 3 and 5×10 20 /cm 3 .

4 . The method of claim 1 , wherein the shallow counter doping layer has a thickness that is less than 300 nm.

5 . The method of claim 1 , wherein the shallow counter doping layer is formed using at least one of:

doping silicate glass by thermal drive-in of dopants;

doping a-Si by thermal drive-in of dopants;

doping multi-crystalline Si by thermal drive-in of dopants;

ion implantation; and

epitaxially growing a layer of doped c-Si.

6 . The method of claim 1 , further comprising at least one of:

forming a first quantum-tunneling-barrier (QTB) layer between the base layer and the emitter layer; and

forming a second QTB layer between the base layer and the surface field layer.

7 . The method of claim 6 , wherein the first and/or the second QTB layers comprise at least one of:

silicon oxide (SiO x );

hydrogenated SiO x ;

silicon nitride (SiN x );

hydrogenated SiN x ;

aluminum oxide (AlO x );

silicon oxynitride (SiON);

hydrogenated SiON; and

one or more wide bandgap semiconductor materials.

8 . The method of claim 6 , wherein the first and/or the second QTB layers have a thickness between 1 and 50 angstroms.

9 . The method of claim 6 , wherein the first and/or the second QTB layers are formed using at least one of the following techniques:

thermal oxidation;

atomic layer deposition;

wet or steam oxidation;

low-pressure radical oxidation; and

plasma-enhanced chemical-vapor deposition (PECVD).

10 . The method of claim 1 , wherein the emitter layer and/or the surface field layer comprise at least one of:

amorphous-Si (a-Si);

polycrystalline Si; and

one or more wide bandgap semiconductor materials.

11 . The method of claim 10 , wherein the emitter layer and/or the surface field layer comprise a graded-doped amorphous-Si (a-Si) layer with a doping concentration ranging between 1×10 15 /cm 3 and 5×10 20 /cm 3 .

12 . The method of claim 1 , wherein the emitter layer is situated at a front side of the base layer facing the incident sunlight.

13 . The method of claim 1 , wherein the emitter layer is situated at a back side of the base layer facing away from the incident sunlight.

14 . A tunneling junction solar cell, comprising:

a base layer, wherein the base layer includes a shallow counter doping layer having a conduction doping type that is opposite to a remainder of the base layer;

an emitter layer situated adjacent to the shallow counter doping layer, wherein the emitter layer has a bandgap that is wider than that of the base layer;

a surface field layer situated adjacent to a side of the base layer opposite to the shallow counter doping layer;

a front-side electrode; and

a back-side electrode.

15 . The solar cell of claim 14 , wherein the base layer comprises at least one of:

a mono-crystalline silicon wafer;

an epitaxially grown crystalline-Si (c-Si) thin film; and

an epitaxially grown crystalline-Si (c-Si) thin film with graded doping.

16 . The solar cell of claim 14 , wherein the shallow counter doping layer has a graded doping concentration, and where a peak value of the graded doping ranges between 1×10 18 /cm 3 and 5×10 20 /cm 3 .

17 . The solar cell of claim 14 , wherein the shallow counter doping layer has a thickness that is less than 300 nm.

18 . The solar cell of claim 14 , wherein the shallow counter doping layer is formed using at least one of:

doping silicate glass by thermal drive-in of dopants;

doping a-Si by thermal drive-in of dopants;

doping multi-crystalline Si by thermal drive-in of dopants;

ion implantation; and

epitaxially growing a layer of doped c-Si.

19 . The solar cell of claim 14 , further comprising at least one of:

a first quantum-tunneling-barrier (QTB) layer between the base layer and the emitter layer; and

a second QTB layer between the base layer and the surface field layer.

20 . The solar cell of claim 19 , wherein the first and/or the second QTB layers comprise at least one of:

silicon oxide (SiO x );

hydrogenated SiO x ;

silicon nitride (SiN x );

hydrogenated SiN x ;

aluminum oxide (AlO x );

silicon oxynitride (SiON);

hydrogenated SiON; and

one or more wide bandgap semiconductor materials.

21 . The solar cell of claim 19 , wherein the first and/or the second QTB layers have a thickness between 1 and 50 angstroms.

22 . The solar cell of claim 19 , wherein the first and/or the second QTB layers are formed using at least one of the following techniques:

thermal oxidation;

atomic layer deposition;

wet or steam oxidation;

low-pressure radical oxidation; and

plasma-enhanced chemical-vapor deposition (PECVD).

23 . The solar cell of claim 14 , wherein the emitter layer and/or the surface field layer comprise at least one of:

amorphous-Si (a-Si);

polycrystalline Si; and

one or more wide bandgap semiconductor materials.

24 . The solar cell of claim 23 , wherein the emitter and/or the surface field layer comprise a graded-doped amorphous-Si (a-Si) layer with a doping concentration ranging between 1×10 15 /cm 3 and 5×10 20 /cm 3 .

25 . The solar cell of claim 14 , wherein the emitter layer is situated at a front side of the base layer facing the incident sunlight.

26 . The solar cell of claim 14 , wherein the emitter layer is situated at a back side of the base layer facing away from the incident sunlight.