PHOTOVOLTAIC CELL WITH SEMICONDUCTOR FINGERS
A photovoltaic cell has a semiconductor substrate formed from semiconductor material doped by a first dopant type, and a doped region over at least a portion of the substrate. The doped region is doped by a second dopant type that is opposite to that of the first dopant type to form an emitter. Moreover, the doped region is doped to a region dopant level. In addition to the substrate and emitter, the cell also has a plurality of semiconductor fingers formed on the emitter, a plurality of busbars formed from a conductor and intersecting the plurality of semiconductor fingers, and a plurality of tabs soldered to the busbars. The fingers are doped by the second dopant type to have a second dopant level, which is greater than the region dopant level.
1 . A photovoltaic cell comprising:
a semiconductor substrate formed from semiconductor material doped by a first dopant type;
an oppositely doped region on at least a portion of the substrate, the oppositely doped region being doped by a second dopant type that is opposite to that of the first dopant type to form an emitter, the doped region being doped to a region dopant level;
a plurality of semiconductor fingers formed on the emitter, the fingers being doped by the second dopant type to have a second dopant level, the second dopant level being greater than the region dopant level;
a plurality of busbars formed from a conductor and intersecting the plurality of semiconductor fingers; and
a plurality of tabs soldered to the busbars.
2 . The photovoltaic cell as defined by claim 1 wherein a plurality of the busbars are spaced between about 1 and 10 millimeters apart.
3 . The photovoltaic cell as defined by claim 1 wherein a plurality of the fingers have average width of less than about 95 microns.
4 . The photovoltaic cell as defined by claim 3 wherein a plurality of the busbars have a width of between about 100 and 500 microns.
5 . The photovoltaic cell as defined by claim 1 wherein the substrate has a front side and an opposed back side, the front side including the emitter, busbars and fingers, the backside having a layer of insulator and a layer of conductive material, the layer of insulator being between the substrate and conductive material.
6 . The photovoltaic cell as defined by claim 1 wherein a plurality of the fingers are substantially free of the conductor.
7 . A method of forming a photovoltaic cell, the method comprising:
providing a semiconductor substrate;
adding semiconductor material to the substrate to form a plurality of semiconductor fingers and a plurality of interface sites, the fingers and interface sites being doped by a given dopant type to have a given dopant level;
adding dopant material to the substrate, the dopant material being the given dopant type and doping the substrate at a lower dopant level than the given dopant level;
adding a plurality of busbars to the plurality of interface sites, the busbars being formed from a conductor and intersecting a plurality of the fingers; and
securing tabs to at least some of the busbars.
8 . The method as defined by claim 7 wherein adding busbars comprises adding an array of pads to form a plurality of discontinuous busbars.
9 . The method as defined by claim 8 wherein securing comprises soldering tabs to the pads.
10 . The method as defined by claim 7 wherein a plurality of the tabs each has a plurality of spaced apart soldering sites along its respective busbar.
11 . The method as defined by claim 7 further comprising:
heating the substrate both to form an emitter on the substrate and to integrate the fingers with the substrate.
12 . A photovoltaic cell comprising:
a semiconductor substrate having an emitter with a top region doped to a first level by a given dopant type;
a plurality of semiconductor fingers generally integrated into the emitter and formed from semiconductor material, the fingers being doped by the given dopant type to have a second dopant level, the second dopant level being greater than the first dopant level;
a plurality of interface sites formed from semiconductor material and doped by the given dopant type to have the second dopant level;
a plurality of the busbars formed on the interface sites and being spaced between about 1 and 10 millimeters apart.
13 . The photovoltaic cell as defined by claim 12 wherein a plurality of the fingers have an average width of less than about 95 microns.
14 . The photovoltaic cell as defined by claim 12 wherein the substrate comprises polysilicon.
15 . The photovoltaic cell as defined by claim 12 wherein the busbars consist essentially of a conductor, the photovoltaic cell further comprising:
a plurality of tabs soldered to the busbars.
16 . The photovoltaic cell as defined by claim 15 wherein a plurality of the fingers are substantially free of the conductor.
17 . The photovoltaic cell as defined by claim 15 wherein the conductor comprises silver.
18 . The photovoltaic cell as defined by claim 12 wherein a plurality of the busbars are spaced less than or equal to about 10 millimeters apart
19 . A photovoltaic cell comprising:
a semiconductor substrate formed from semiconductor material and having an emitter with a layer doped by a given dopant type to have a first dopant level; and
a plurality of semiconductor fingers formed on the emitter layer doped by the given dopant type, the fingers being doped by the given dopant type to have a second dopant level, the second dopant level being greater than the first dopant level,
a plurality of the semiconductor fingers consisting essentially of doped semiconductor material.
20 . The photovoltaic cell as defined by claim 19 further comprising a plurality of interface sites on the emitter, and a plurality of busbars formed from a conductor on the interface sites, the interface sites being formed from semiconductor material doped by the given dopant type to the second dopant level.
21 . The photovoltaic cell as defined by claim 20 wherein the fingers are free of conductor material that conducts between any of the busbars.
22 . The photovoltaic cell as defined by claim 20 wherein the plurality of busbars consist essentially of the conductor.