MULTI-JUNCTION SOLAR CELLS WITH THROUGH-SUBSTRATE VIAS
Multi junction solar cells and methods for making multi junction solar cells are disclosed. Back-contact-only multi junction solar cells wherein the side facing the sun, is capable of withstanding environments for use in space are disclosed.
1 . A multi junction solar cell device comprising:
an electrically conductive semiconductor substrate with at least one multi junction solar cell element formed in an epitaxial region grown thereon;
a plurality of cap regions formed on top of the epitaxial region;
a plurality of through-substrate via heads corresponding to each of the plurality of cap regions formed on a back surface of the substrate;
through-substrate vias that extend through the substrate from each of the plurality of cap regions to the corresponding through-substrate vias heads;
conductive metal within the through-substrate vias and electrically connecting each of the plurality of cap regions to the corresponding through-substrate via heads;
an electrically insulating liner disposed on the walls of each of the through-substrate vias insulating the substrate and the epitaxial region from the conductive metal inside the through-substrate vias;
an optical cover material disposed upon an optically transparent adhesive material directly above each of the plurality of through-substrate via heads; and
a back metal, patterned with a back metal pattern, in ohmic contact with the back surface of the electrically conductive semiconductor substrate, and electrically isolated from the through-substrate via heads.
2 . The multi junction solar cell device of claim 1 , comprising:
a patterned insulating layer on the back surface of the substrate; and
metal regions comprising contact pads on the patterned insulating layer such that the metal regions are in direct electrical contact to the conductive metal inside the through-substrate vias and not electrically connected directly to the semiconductor substrate or to the back metal.
3 . The multi junction solar cell device of claim 2 , wherein the contact pads are patterned to form a patterned back contact such that multiple contact pads are electrically interconnected.
4 . The multi junction solar cell device of claim 3 , wherein the patterned back contact and the back metal are patterned in an interdigitated back contact pattern.
5 . The multi junction solar cell device of claim 1 , comprising metal gridlines along cap regions that extend from exposed metal of the through-via region on the top side of the device.
6 . The multi junction solar cell device of claim 1 , wherein materials forming the device do not contain silver metal.
7 . The multi junction solar cell device of claim 1 , wherein the through-substrate via head comprises a planar metal region disposed upon a cap region defined during front-end processing such that the via metal is electrically connected to the cap region through the planar metal region.
8 . The multi junction solar cell device of claim 1 , wherein the through-substrate via head comprises:
a metal region deposited on the cap region; and
a dielectric material encircled by the cap region; wherein the dielectric material acts as an etch stop layer during etching of through-substrate vias and is removed prior to via metal deposition.
9 . A method of forming a through-substrate via head comprising:
providing a substrate having an epitaxial region grown thereon and a plurality of cap regions formed on top of the epitaxial region;
depositing a photoresist region on the plurality of cap regions;
etching a plurality of through-substrate vias from a backside of the substrate and using the photoresist region as an etch stop layer;
depositing an electrically insulating liner within each of the plurality of through-substrate vias;
removing the photoresist region to expose the plurality of cap regions; and
depositing metal within the through-substrate vias to connect the plurality of cap regions.
10 . The method of claim 9 , wherein the optical cover material is bonded to the top surface prior to a substrate thinning step.
11 . A multi junction solar cell device comprising:
a semi-insulating semiconductor substrate having a back surface;
an epitaxial region overlying the semi-insulating semiconductor substrate;
an electrically conductive semiconductor region between the substrate and the epitaxial region;
at least one multi junction solar cell element formed in the epitaxial region, the epitaxial region being grown on the electrically conductive semiconductor region;
a cap region overlying the epitaxial region;
though-wafer vias that extend from the cap region to the back surface of the substrate;
the cap region being shaped according to a cap pattern including collars around the through-wafer vias;
conductive metal within the through-wafer vias and electrically connected to the cap patterned collars;
an electrically insulating liner on the walls of the through-wafer vias insulating the conductive metal inside the through-wafer vias from at least the epitaxial region and from the conductive semiconductor region;
an optical cover material disposed upon an optically transparent adhesive material directly above the through-substrate via heads formed on top of the epitaxial region; and
a back metal on the back surface of the substrate in electrical contact with the conductive metal in the through-wafer vias.
12 . The multi junction solar cell device of claim 11 , comprising metal gridlines along cap regions that extend from exposed metal of the through-via region.
13 . The multi junction solar cell device of claim 11 , wherein materials forming the device do not contain silver metal.
14 . A multi junction solar cell device comprising:
an electrically conductive semiconductor substrate with at least one multi junction solar cell element formed in an epitaxial region grown thereon;
a plurality of cap regions formed on top of the epitaxial region;
through-substrate vias that extend from the plurality of cap regions to a back surface of the substrate;
conductive metal within the through-substrate vias and electrically connected to the plurality of cap regions;
an electrically insulating liner disposed on the walls of the through-substrate vias insulating the substrate and the epitaxial region from the conductive metal inside the through-wafer vias;
a through-substrate via head that electrically connects the conductive metal within the through-substrate vias with the plurality of cap regions, henceforth called;
a temporary carrier substrate bonded directly above the through substrate via heads formed on top of the epitaxial region; and
a back metal, patterned with a back metal pattern, in ohmic contact with the back surface of the electrically conductive semiconductor substrate, and electrically isolated from the conductive metal within the through-substrate vias.
15 . The multi junction solar cell device of claim 14 , wherein the through-substrate via head comprises a planar metal region disposed upon a cap region defined during front-end processing such that the via metal is electrically connected to the cap region through the planar metal region.
16 . The multi junction solar cell device of claim 14 , wherein the through-substrate via head comprises:
a metal region deposited on the cap region; and
a dielectric material encircled by the cap region; wherein the dielectric material acts as an etch stop layer during etching of through-substrate vias and is removed prior to via metal deposition.
17 . A method of forming a multi junction solar cell device, comprising:
providing an electrically conductive semiconductor substrate with at least one multi-junction solar cell element formed in an epitaxial region grown thereon, and a plurality of cap regions formed on top of the epitaxial region;
bonding a cover glass on top of the substrate and the plurality of cap regions;
thinning the substrate;
etching through-substrate vias from a back surface of the substrate;
forming a patterned dielectric layer on the back surface of the substrate; and
forming electrical connection between the patterned cap region and the back metal contacts pads with conductive metal inside the through-substrate vias, such that the contact pads are not directly electrically connected to the semiconductor substrate.
18 . A method of forming a multi junction solar cell device, comprising:
providing an electrically conductive semiconductor substrate with at least one multi-junction solar cell element formed in an epitaxial region grown thereon, and a patterned cap region formed on top of the epitaxial region;
bonding a polymer cover on top of the substrate and the patterned cap region;
thinning the substrate;
etching through-substrate vias from a back surface of the substrate;
forming a patterned dielectric layer on the back surface of the substrate;
forming a plurality of back metal contact pads; and
forming electrical connection between the patterned cap region and the back metal contacts pads with conductive metal inside the through-substrate vias, such that the contact pads are not directly electrically connected to the semiconductor substrate.