METHOD TO MITIGATE SHUNT FORMATION IN A PHOTOVOLTAIC CELL COMPRISING A THIN LAMINA
A photovoltaic cell can be formed from a thin semiconductor lamina cleaved from a substantially crystalline wafer. Shunts may inadvertently be formed through such a lamina, compromising device performance. By physically severing the lamina into a plurality of segments, the segments of the lamina preferably electrically connected in series, loss of efficiency due to shunt formation may be substantially reduced. In some embodiments, adjacent laminae are connected in series into strings, and the strings are connected in parallel to compensate for the reduction in current caused by severing the lamina into segments.
1 . A method to form a photovoltaic module, the method comprising:
forming a substantially crystalline semiconductor lamina affixed to a receiver element; and
severing the affixed semiconductor lamina into a plurality of segments, each segment remaining affixed to the receiver element, wherein each segment is a portion of a photovoltaic cell, and wherein the segments of the plurality are electrically connected in series.
2 . The method of claim 1 wherein the semiconductor lamina has a thickness, measured perpendicular to the receiver element, between about 0.5 and 50 microns.
3 . The method of claim 1 wherein, before the severing step, the semiconductor lamina has a width, measured parallel to the receiver element, less than about 300 mm.
4 . The method of claim 1 wherein the semiconductor lamina has an average crystal size of at least 1000 angstroms.
5 . The method of claim 1 wherein the semiconductor lamina is at least 80 percent crystalline.
6 . The method of claim 1 wherein the semiconductor lamina consists essentially of silicon.
7 . The method of claim 1 wherein the step of severing the semiconductor lamina into a plurality of segments comprises scribing the semiconductor lamina with a laser.
8 . The method of claim 1 wherein the semiconductor lamina is severed into at least 4 segments.
9 . The method of claim 8 wherein the semiconductor lamina is severed into at least 10 segments.
10 . The method of claim 1 wherein the step of forming a substantially crystalline semiconductor lamina affixed to a receiver element comprises:
defining a cleave plane in a semiconductor donor wafer;
affixing the donor wafer to the receiver element at a first surface of the donor wafer; and
cleaving the semiconductor lamina from the semiconductor donor wafer along the cleave plane.
11 . The method of claim 10 further comprising, before the affixing step, doping at least a portion of the first surface of the donor wafer.
12 . A photovoltaic module comprising:
a substantially crystalline semiconductor lamina, the semiconductor lamina severed into at least two physically separate segments, each segment of the semiconductor lamina permanently affixed to the same receiver element and remaining in its original orientation before severing,
wherein the semiconductor lamina has a width measured parallel to the receiver element no more than about 300 mm,
wherein each segment comprises at least a portion of a photovoltaic cell, and wherein the at least two physically separate segments are electrically connected in series.
13 . The photovoltaic module of claim 12 wherein the semiconductor lamina consists essentially of monocrystalline semiconductor material.
14 . The photovoltaic module of claim 12 wherein the semiconductor lamina has a thickness, measured normal to the receiver element, of between about 0.2 and about 100 microns.
15 . The photovoltaic module of claim 14 wherein the thickness of the semiconductor lamina is between about 0.5 and about 20 microns.
16 . The photovoltaic module of claim 12 wherein the lamina is severed into at least 10 physically separate segments.
17 . The photovoltaic module of claim 12 wherein the semiconductor lamina consists essentially of silicon.
18 . A method for forming a photovoltaic module, the method comprising:
defining a cleave plane in a first semiconductor donor wafer;
affixing the first donor wafer to a first receiver element;
cleaving a first semiconductor lamina from the first donor wafer along the cleave plane, wherein the first donor wafer remains affixed to the first receiver element; and
severing the first semiconductor lamina into a first plurality of segments, wherein each segment remains affixed to the first receiver element, and wherein, in the completed photovoltaic module, each segment is at least a portion of a photovoltaic cell.
19 . The method of claim 18 wherein the semiconductor lamina has a thickness between about 0.5 and about 20 microns.
20 . The method of claim 18 wherein the semiconductor lamina is at least 80 percent crystalline.
21 . The method of claim 20 wherein the semiconductor lamina is monocrystalline semiconductor material.
22 . The method of claim 20 wherein the average crystal size of the semiconductor lamina is at least 1000 angstroms.
23 . The method of claim 18 wherein the step of defining a cleave plane in a semiconductor donor wafer comprises implanting one or more species of gas ions into the semiconductor donor wafer.
24 . The method of claim 18 wherein the step of severing the first semiconductor lamina into a plurality of first segments is performed by laser scribing.
25 . The method of claim 18 wherein, in the completed photovoltaic module, the segments of the first plurality are electrically connected in series.