THIN FILM COATING PINNING ARRANGEMENT
In one aspect of the present invention, a photovoltaic cell for use in a solar collector is described. The photovoltaic cell includes two electrically conductive layers that are positioned on a surface of a semiconductor substrate. The first conductive layer is adhered to and in direct contact with a surface of the semiconductor substrate. The second conductive layer has a different composition from and is substantially more electrically conductive than the first conductive layer. There are multiple spaced apart pinning regions that are distributed through an interface between the first and second conductive layers. The pinning regions, help locally anchor the two layers. Some aspects of the present invention relate to the use of pinning regions in other types of optical or electrical components.
1 . A photovoltaic cell comprising:
a semiconductor substrate that includes a first surface;
a first electrically conductive layer that is adhered to the first surface of the semiconductor substrate;
a second electrically conductive layer that is adhered to, has a different composition from and is substantially more electrically conductive than the first conductive layer; and
a multiplicity of spaced apart pinning regions that are distributed at the interface between the first and second conductive layers, wherein the pinning regions locally anchor the first conductive layer to the second conductive layer and wherein the adhesive strength of the pinning regions to the second conductive layer is greater than the adhesive strength of the first conductive layer to the second conductive layer.
2 . A photovoltaic cell as recited in claim 1 , wherein the centers of the pinning regions are spaced apart by a distance d, the distance d being less than approximately an estimated minimum size of a buckling feature in the interface when the interface lacks pinning regions.
3 . A photovoltaic cell as recited in claim 1 wherein the pinning regions occupy less than 5% of the interface between the first layer and the second layer.
4 . A photovoltaic cell as recited in claim 1 , wherein the pinning regions are defined by adhesive pinning elements positioned between the first layer and the second layer and the adhesive pinning elements are made of one selected from the group consisting of titanium, chrome, nickel, nickel chrome alloy, glass and polymer.
5 . A photovoltaic cell as recited in claim 1 , wherein the pinning regions are defined by adhesive pinning elements positioned between the first layer and the second layer and the adhesive pinning elements are deposited using one selected from the group consisting of spraying, electroplating, vapor deposition, electron beam deposition, sputtering, screen printing, electroless plating, and chemical deposition.
6 . A photovoltaic cell as recited in claim 1 , wherein the pinning regions are formed by treating selected areas of the first layer such that the adhesive properties of the selected areas are substantially greater than in adjacent untreated areas.
7 . A photovoltaic cell as recited in claim 1 , wherein the spacing between the pinning regions is based at least in part on one selected from the group consisting of: 1) the stiffness of the second conductive layer, the strength of adhesion between the first and second conductive layers and an estimation of force that may be applied to the second conductive layer; and 2) a minimum radius of a circular buckle a m , a m being based at least partly on the following:
a
m
=
1.106
h
f
E
f
σ
m
,
wherein h f is the thickness of a buckling layer, E f is the in-plane Young's modulus of the buckling layer and σ m is the mismatch stress in the buckling layer, the buckling layer being selected from the group consisting of the first conductive layer and the second conductive layer.
8 . A photovoltaic cell as recited in claim 1 wherein the pinning regions are substantially less electrically conductive than the first and second conductive layers.
9 . A photovoltaic cell as recited in claim 1 wherein:
the second conductive layer is formed from silver,
the first conductive layer is formed from aluminum; and
the semiconductor substrate is formed from doped silicon.
10 . A photovoltaic cell as recited in claim 1 wherein adjacent pinning regions of the multiplicity of pinning regions are substantially uniformly spaced apart.
11 . A photovoltaic cell as recited in claim 1 wherein adhesive pinning elements define the pinning regions and the pinning elements are formed on and extend out of a surface of the first conductive layer, there being gaps between the pinning elements that are filled with portions of the second layer.
12 . A photovoltaic cell as recited in claim 1 wherein the pinning regions are arranged at a periphery of the photovoltaic cell.
13 . A photovoltaic cell as recited in claim 1 wherein the thickness of each of the first and second conductive layers is approximately between 1 and 35 μm;
14 . A method of forming a photovoltaic cell, the method comprising:
applying a first conductive layer on a semiconductor substrate, wherein the first conductive layer is formed from a first electrically conductive material;
forming at least one pinning element along the first conductive layer; and
applying a second conductive layer on the at least one pinning element in the semiconductor substrate, wherein the second conductive layer is formed from a second electrically conductive material that is different from and is substantially more conductive than the first electrically conductive material, wherein the at least one pinning element locally anchors the first conductive layer to the second conductive layer.
15 . A method as recited in claim 14 , further comprising:
after applying the first conductive layer on the semiconductor substrate, spraying a material onto the first conductive layer to form a plurality of the pinning elements, wherein the spraying is performed such that the plurality of pinning elements are physically isolated from one another and are spaced apart, wherein applying the second layer over the pinning elements involves filling in gaps between the pinning elements with the second conductive layer.
16 . A method as recited in claim 14 , further comprising:
determining a minimum size for a buckling feature at an interface between the first and second layers when the interface lacks any pinning elements; and
forming a plurality the pinning elements, wherein the pinning elements are spaced apart to help minimize a likelihood of buckling at the interface between the first and second layers and wherein the spacing of the pinning elements is based on the determining operation.
17 . A component, comprising:
a substrate;
a thin film coating that is adhered to and in direct contact with a first surface of the substrate; and
a multiplicity of spaced apart pinning regions that are distributed through an interface between the substrate and the thin film coating, the pinning regions locally anchoring the substrate to the thin film coating, the adhesive strength of the pinning regions to the substrate being greater than the adhesive strength of the thin film coating to the substrate, wherein the interface is suitable for one selected from the group consisting of: 1) transmitting optical energy; 2) reflecting optical energy; 3) transmitting electrical energy; 4) transmitting electromagnetic energy; and 5) reflecting electromagnetic energy.
18 . A component as recited in claim 17 wherein the thin film coating is reflective for infrared wavelengths and transmissive for visible wavelengths.
19 . A solar receiver for use in a solar energy collector, comprising:
a photovoltaic cell; and
a component as recited in claim 17 wherein the component is a protective layer that covers the photovoltaic cell.
20 . A component as recited in claim 17 wherein the pinning regions are one selected from the group consisting of 1) substantially less reflective than adjacent regions; and 2) substantially less transmissive than adjacent regions.