MULTI-JUNCTION SOLAR CELLS WITH THROUGH-VIA CONTACTS
Multi junction solar cell devices are provided in which through-wafer vias contacting the top surface eliminate the need for gridlines and enhance efficiency of epitaxially grown multi junction solar cell elements.
1 . A multi junction solar cell comprising:
an electrically conductive semiconductor substrate with at least one multi junction solar cell element formed in an epitaxial region grown thereon;
a cap region formed on top of the epitaxial region;
though-wafer vias that extend from the cap region to a back surface of the substrate;
the cap region being shaped according to a cap pattern comprising collars around the through-wafer vias;
conductive metal within the through-wafer vias and electrically connected to the collars;
an electrically insulating liner on the inner walls of the through-wafer vias insulating the substrate and the epitaxial region from the conductive metal inside the through-wafer vias that connect with the cap region; and
a back metal in ohmic contact with the back surface of the substrate, the back metal being electrically connected with the conductive metal within the through-wafer vias, and wherein the back metal is patterned with a back metal pattern.
2 . The multi junction solar cell of claim 1 , further comprising:
a patterned dielectric layer on the back surface of the substrate;
metal regions comprising contact pads on the patterned dielectric layer, wherein the contact pads are in direct electrical contact with the conductive metal inside the through-wafer vias, the contact pads are not directly electrically connected to the semiconductor substrate or to the back metal.
3 . The multi junction solar cell of claim 2 , wherein the contact pads are patterned such that multiple contact pads are electrically connected together, thereby electrically tying together multiple metal vias.
4 . The multi junction solar cell of claim 2 , wherein the back surface of the substrate comprises recesses comprising metal electrodes electrically connected to the through-wafer vias.
5 . The multi junction solar cell of claim 1 , wherein the back surface of the substrate comprises recesses comprising metal electrodes electrically connected to the through-wafer vias.
6 . The multi junction solar cell of claim 1 , comprising metal gridlines interconnect multiple cap regions.
7 . The multi junction solar cell of claim 1 , comprising top metal and gridlines electrically connected to the cap region, wherein the top metal and the gridlines are characterized by a sheet resistance less than 5 ohms/square.
8 . The multi junction solar cell of claim 1 , wherein the multi junction solar cell is characterized by a shadowing loss less than 5%, an emitter loss less than 2%, and a grid loss less than 0.1%.
9 . A multi junction solar cell comprising:
a semi-insulating semiconductor substrate having a top surface and a back surface;
an epitaxial region overlying the top surface of the substrate;
an electrically conductive semiconductor region between the top surface of the substrate and the epitaxial region;
at least one multi junction solar cell element formed in the epitaxial region;
a cap region formed 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 comprising a collar around each of the through-wafer vias;
conductive metal within each of the through-wafer vias and electrically connected to the respective collar;
an electrically insulating liner on the inner walls of each of the through-wafer vias insulating the conductive metal within each of the through-wafer vias from at least the epitaxial region and the electrically conductive semiconductor region; and
a back metal in electrical contact with the conductive metal in each of the through-wafer vias.
10 . The multi junction solar cell of claim 9 , comprising metal gridlines interconnecting multiple cap regions.
11 . The multi junction solar cell of claim 9 , comprising top metal and gridlines electrically connected to the cap region, wherein the top metal and the gridlines are characterized by a sheet resistance from 0.01 ohms/square to 1 ohm/square.
12 . The multi junction solar cell of claim 9 , wherein the multi junction solar cell is characterized by a shadowing loss less than 5%, an emitter loss less than 2%, and a grid loss less than 0.1%.
13 . A multi junction solar cell, comprising:
a substrate comprising a lower surface and an upper surface, wherein the upper surface faces the direction of incident radiation;
an epitaxial region overlying the upper surface of the substrate, wherein the epitaxial region comprises at least one sub-cell and an upper epitaxial surface;
a back metal contact disposed on the lower surface of the substrate; and
a plurality of through-vias extending from an annular cap region overlying the upper epitaxial surface to the back metal contact, wherein each of the plurality of through-vias comprises a dielectric liner on the walls of the through-via and an electrically conductive material within a central portion of the through-via;
wherein the annular cap region, the electrically conductive material within the central portion of a through-via, and the back metal contact are electrically connected.
14 . The multi junction solar cell of claim 13 , wherein the center-to-center distance between adjacent through vias is from 100 microns to 200 microns.
15 . The multi junction solar cell of claim 13 , wherein the multi junction solar cell is characterized by a shadowing loss less than 5%, an emitter loss less than 2%, and a grid loss less than 0.1%.
16 . The multi junction solar cell of claim 13 , comprising gridlines disposed on the lower surface of the substrate.
17 . The multi junction solar cell of claim 16 , wherein the gridlines electrically interconnect multiple through-vias.
18 . The multi junction solar cell of claim 13 , wherein through-vias are characterized by a resistance of less than 0.01 ohms for each via.
19 . The multi junction solar cell of claim 13 , comprising top metal and gridlines electrically connected to the cap region, wherein the top metal and the gridlines are characterized by a sheet resistance less than 5 ohms/square.
20 . The multi junction solar cell of claim 13 , comprising top metal and gridlines electrically connected to the cap region, wherein the top metal and the gridlines are characterized by a sheet resistance from 0.01 ohms/square to 1 ohm/square.