PHOTOVOLTAIC CELLS WITH COPPER GRID
A photovoltaic device, such as a solar cell, having improved performance is provided. The photovoltaic device includes a copper-containing layer that contains an amount of impurities therein which is sufficient to hinder the diffusion of copper into an underlying semiconductor substrate. The copper-containing layer, which is located within a grid pattern formed on a front side surface of a semiconductor substrate, includes an electroplated copper-containing material having an impurity level of 200 ppm or greater located atop at least one metal diffusion barrier layer.
1 . A method of forming a photovoltaic device comprising:
providing a semiconductor substrate including a p-n junction with a p-type semiconductor portion and an n-type semiconductor portion one on top of the other, wherein an upper exposed surface of one of the semiconductor portions represents a front side surface of the semiconductor substrate;
forming patterned antireflective coatings on the front side surface of the semiconductor substrate to provide a grid pattern on the front side surface, said grid pattern comprising exposed portions of the front side surface of the semiconductor substrate;
forming at least one metal diffusion barrier layer on the exposed portions of the front side surface of the semiconductor substrate; and
electrodepositing a copper-containing layer having an impurity level of 200 ppm or greater atop the at least one metal diffusion barrier layer.
2 . The method of claim 1 , wherein a bottom most layer of the at least one metal diffusion barrier layer is a metal semiconductor alloy layer that is formed on the exposed portions of the front side surface of the semiconductor substrate, wherein said forming the metal semiconductor alloy layer comprises providing a metal layer and annealing.
3 . The method of claim 1 , wherein said copper-containing layer having said impurity level of 200 ppm or greater comprises copper or a copper alloy and at least impurity.
4 . The method of claim 3 , wherein said at least one impurity comprises carbon, oxygen, chloride, sulfur or any combination thereof.
5 . The method of claim 4 , wherein said at least one impurity includes a combination of carbon, oxygen, chloride and sulfur.
6 . The method of claim 5 , where said carbon impurity is present in an amount from 60 ppm to 10000 ppm, said oxygen impurity is present in an amount from 10 ppm to 10000 ppm, said chloride impurity is present in an amount from 60 ppm to 10000 ppm, and said sulfur impurity is present in an amount from 10 ppm to 10000 ppm.
7 . The method of claim 1 , wherein said electrodepositing said copper-containing layer further comprise light illumination.
8 . The method of claim 1 , wherein said electrodepositing the copper-containing layer includes providing a plating bath comprising at least one metal salt as a source of copper ions, said metal salt further including at least one impurity selected from the group consisting of carbon, oxygen, chloride and sulfur.
9 . The method of claim 1 , wherein said electrodepositing the copper-containing layer includes providing a plating bath comprising at least one metal salt as a source of copper ions and a separate impurity source, said separate impurity source including at least one impurity selected from the group consisting of carbon, oxygen, chloride and sulfur.
10 . The method of claim 1 , wherein said n-type semiconductor portion overlies said p-type semiconductor portion.
11 . The method of claim 1 , wherein said at least one metal diffusion barrier comprises a nickel layer and said copper-containing layer comprises copper and a combination of carbon, oxygen, chloride and sulfur as impurities, and wherein said nickel layer is in direct contact with the exposed portions of the front side surface of the semiconductor substrate.
12 . The method of claim 1 , wherein said at least one metal diffusion barrier layer comprises a cobalt layer and said copper-containing layer comprises copper and a combination of carbon, oxygen, chloride and sulfur as impurities, and wherein said cobalt layer is in direct contact with the exposed portions of the front side surface of the semiconductor substrate.
13 . The method of claim 1 , wherein said at least one metal diffusion barrier layer comprises a nickel layer and said copper-containing layer comprises copper and a combination of carbon, oxygen, chloride and sulfur as impurities, and wherein said nickel layer is separated at least in part from the exposed portions of the front side surface of the semiconductor substrate by a nickel silicide layer.
14 . The method of claim 1 , wherein said at least one metal diffusion barrier layer comprises a cobalt layer and said copper-containing layer comprises copper and a combination of carbon, oxygen, chloride and sulfur as impurities, and wherein said cobalt layer is separated at least in part from the exposed portions of the front side surface of the semiconductor substrate by a nickel silicide layer.
15 . The method of claim 1 , wherein said photovoltaic device comprising the copper-containing layer having an impurity level of 200 ppm or greater has a lifetime that is 25% to 200% greater than an equivalent photovoltaic device including a copper-containing layer having an impurity level of below 200 ppm.