Solar cell with electroplated metal grid
One embodiment of the present invention provides a method for fabricating solar cells. During operation, an anti-reflection layer is deposited on top of a semiconductor structure to form a photovoltaic structure, and a front-side electrode grid comprising a metal stack is formed on top of the photovoltaic structure. The metal stack comprises a metal-adhesive layer comprising Ti or Ta, and a conducting layer comprising Cu or Ag situated above the metal-adhesive layer.
1. A solar cell, comprising:
a semiconductor photovoltaic structure comprising an emitter layer positioned on a base layer; and
a first metallic grid positioned on a front side of the photovoltaic structure, wherein the first metallic grid includes:
a metal-adhesive layer which comprises Ta and is in direct contact with the emitter layer;
a Cu seed layer positioned on the metal-adhesive layer; and
an electroplated Cu layer positioned on the Cu seed layer.
2. The solar cell of claim 1 , wherein the metal-adhesive layer further comprises one or more of: Ti, Co, W, Cr, Mo, Ni, titanium nitride (TiN x ), titanium tungsten (TiW x ), titanium silicide (TiSi x ), titanium silicon nitride (TiSiN), tantalum nitride (TaN x ), tantalum silicon nitride (TaSiN x ), nickel vanadium (NiV), tungsten nitride (WN x ), and their combinations.
3. The solar cell of claim 1 , wherein the first metallic grid further comprises a soldering layer comprising Sn or Ag positioned on the electroplated Cu layer.
4. The solar cell of claim 1 , wherein the metal-adhesive layer has a thickness between 1 nm and 1000 nm.
5. The solar cell of claim 4 , wherein the metal-adhesive layer has a thickness between 5 nm and 50 nm.
6. The solar cell of claim 1 , wherein the photovoltaic structure further comprises an anti-reflection layer positioned on the emitter layer.
7. The solar cell of claim 6 , wherein the anti-reflection layer is electrically insulating, and wherein the anti-reflection layer includes a number of openings, through which the metal-adhesive layer is in direct contact with the emitter layer.
8. The solar cell of claim 7 , wherein the insulating anti-reflection layer includes at least one of:
silicon nitride (SiN x );
silicon oxide (SiO x );
titanium oxide (TiO x ); and
aluminum oxide.
9. The solar cell of claim 6 , wherein the anti-reflection layer includes a transparent conducting oxide (TCO) layer, and wherein the metal adhesive layer is in contact with the TCO layer.
10. The solar cell of claim 9 , wherein the TCO layer includes at least one of:
indium tin oxide (ITO);
aluminum zinc oxide (AZO);
gallium zinc oxide (GZO); and
tungsten doped indium oxide (IWO).
11. The solar cell of claim 1 , wherein the Cu seed layer has a thickness between 5 nm and 500 nm.
12. The solar cell of claim 1 , wherein the metal adhesive layer and the Cu seed layer are formed using a physical vapor deposition technique.
13. The solar cell of claim 12 , wherein the physical vapor deposition technique includes one of: evaporation and sputtering deposition.