III-V Compound Semiconductor Solar Cell for Terrestrial Solar Array
A concentrator photovoltaic solar cell array for terrestrial use for generating electrical power from solar radiation including a multifunction III-V compound semiconductor solar cell with material composition and bandgaps to maximize absorption in the AM1.5 spectral region, and a thickness of one micron or greater so as to be able to produce in excess of 15 watts of DC power with conversion efficiency in excess of 37%. The aggregate surface area of the grid pattern covers approximately 2 to 5% of the top cell.
1 . A concentrator photovoltaic solar cell for producing energy from the sun comprising:
a germanium substrate including a first photoactive junction and forming a bottom solar subcell;
a gallium arsenide middle cell disposed on said substrate;
an indium gallium phosphide top cell disposed over said middle cell and having a bandgap to maximize absorption in the AM1.5 spectral region; and
a surface grid disposed over said top cell and having a grid pattern which covers approximately 2.5% to 5% of the top cell surface area and adapted for conduction of the relatively high current created by the solar cell.
2 . A solar cell as claimed in claim 1 , wherein the grid pattern comprises lines having a width of 5 microns or less.
3 . A solar cell as claimed in claim 1 , wherein the grid pattern includes lines having a thickness of greater than 4 microns, and a center-to-center pitch of greater than 100 microns.
4 . A solar cell as claimed in claim 1 , wherein the grid pattern is 4-fold rotationally symmetric.
5 . A solar cell as claimed in claim 1 , wherein the grid pattern consists of a plurality of parallel grid lines covering the top surface.
6 . A solar cell as claimed in claim 1 , wherein the aggregate surface area of grid pattern covers at least 5% of the surface area of the top cell, but less than 10% of the surface area.
7 . A cell as claimed in claim 1 , wherein the solar cell, when illuminated by concentrated light by a factor in excess of 500×, has an open circuit voltage (V oc ) of at least 3.0 volts, a responsivity at short circuit at least 0.13 amps per watt, a fill factor (FF) of at least 0.70, and produces in excess of 10 watts of DC power at AM1.5 solar irradiation with conversion efficiency in excess of 35%.
8 . A solar cell as claimed in claim 3 , wherein the bandgap of the top, middle, and bottom subcells are 1.9 eV, 1.4 eV, and 0.7 eV respectively.
9 . A concentrator photovoltaic solar cell for producing energy from the sun comprising:
a bottom subcell including a first photoactive junction;
a middle cell disposed on said bottom cell and including a second photoactive junction; and
a top cell disposed over said middle cell and having a photoactive junction and bandgap to maximize absorption in the AM1.5 spectral region with a top layer sheet resistance of less than 500 ohms/square and adapted operate at an concentration level of greater than twenty suns.
10 . A solar cell as claimed in claim 9 , wherein the sheet resistance of the top cell is 250 ohms/square.
11 . A solar cell as claimed in claim 9 , further comprising tunnel diode layers disposed between subcells having a thickness adapted to support a current density through the tunnel diodes of greater than 50 amps/square centimeter.
12 . A concentrator photovoltaic solar cell for producing energy from the sun comprising:
a germanium substrate including a first photoactive junction;
a gallium arsenide middle subcell disposed on said substrate;
an indium gallium phosphide top subcell disposed over said middle cell and having a bandgap to maximize absorption in the AM1.5 spectral region and a thickness greater than 8000 Angstroms in order to carry the increased current associated with concentrated sunlight on the surface of said top cell.
13 . A solar cell as defined in claim 12 , wherein the sheet resistance is greater than 35 A/cm 2 .
14 . A solar cell as claimed in claim 12 , wherein the thickness of the semiconductor layers of the top subcell is one micron or greater.
15 . A solar cell as claimed in claim 12 , wherein the aggregate surface area coverage of the grid pattern over the top subcell is approximately 5% of the total surface area.
16 . A solar cell as claimed in claim 15 , wherein the ratio of the grid line width to the pitch is less than 4%.
17 . A solar cell as claimed in claim 16 , wherein the sheet resistance and the surface area coverage of the grid pattern are selected to maximize the fill factor.
18 . A solar cell as claimed in claim 12 , further comprising a first tunnel diode disposed between said bottom and said middle subcells, and a second tunnel diode disposed between said middle and said top subcells, capable of supporting a current density of greater than 50 amps/square centimeter.