Abstract: A photovoltaic cell comprising a thin semiconductor lamina is described; the lamina is formed by cleaving from a donor wafer while the wafer is bonded to a receiver element which provides mechanical support. Thus fabrication steps performed following cleaving are advantageously performed at temperatures that will not damage the receiver element. By fabricating a cell comprising an MIS-type tunnel diode, rather than a conventional p-n diode, a high-temperature doping step may be avoided.

Abstract: Low-relief texture can be created by applying and firing frit paste on a silicon surface. Where frit contacts the surface at high temperature, it etches silicon, dissolving silicon in the softened glass frit. The result is a series of small, randomly located pits, which produce a near-Lambertian surface, suitable for use in a photovoltaic cell. This texturing method consumes little silicon, and is advantageously used in a photovoltaic cell in which a thin silicon lamina comprises the base region of the cell. When the lamina is formed by implanting ions in a donor wafer to form a cleave plane and cleaving the lamina from the donor wafer at the cleave plane, the ion implantation step will serve to translate texture formed at a first surface to the cleave plane, and thus to the second, opposing surface following cleaving. Low-relief texture formed by other methods can be translated from the first surface to the second surface in this way as well.

Abstract: In some embodiments, a method of forming a photovoltaic cell includes (1) forming a cleave plane in a donor body so as to define a lamina to be bonded to a receiver element and exfoliated from the donor body; (2) prior to bonding, pre-heating the donor body without the receiver element to a temperature of greater than about 200° C. for a first time period that is less than a time period required for exfoliation of the lamina from the donor body; (3) cooling the donor body after pre-heating the donor body; (4) bonding the donor body to the receiver element; and (5) heating the bonded donor body and receiver element for a second time period so as to complete the exfoliation of the lamina from the donor body. Numerous other aspects are provided.

Abstract: Ion implanters are especially suited to meet process dose and energy demands associated with fabricating photovoltaic devices by ion implantation followed by cleaving.

Abstract: A method for forming a photovoltaic cell is disclosed which comprises the steps of providing a semiconductor donor body having a first surface and a second surface opposite the first surface, cleaving a first portion from the first surface of the semiconductor donor body to form a first lamina of semiconductor material, wherein the first lamina of semiconductor material has a first lamina thickness, and cleaving a second portion from the second surface of the semiconductor donor body to form a second lamina of semiconductor material, wherein the second lamina of semiconductor material has a second lamina thickness.

Abstract: In aspects of the present invention, a lamina is formed having opposing first and second surfaces. Heavily doped contact regions extend from the first surface to the second surface. Generally the lamina is formed by affixing a semiconductor donor body to a receiver element, then cleaving the lamina from the semiconductor donor body wherein the lamina remains affixed to the receiver element. In the present invention, the heavily doped contact regions are formed by doping the semiconductor donor body before cleaving of the lamina. A photovoltaic cell comprising the lamina is then fabricated. By forming the heavily doped contact regions before bonding to the receiver element and cleaving, post-bonding high-temperature steps can be avoided, which may be advantageous.

Abstract: It is advantageous to create texture at the surface of a photovoltaic cell to reduce reflection and increase travel length of light within the cell. A method is disclosed to create texture at the surface of a silicon body by reacting a silicide-forming metal at the surface, where the silicide-silicon interface is non-planar, then stripping the silicide, leaving behind a textured surface. Depending on the metal and the conditions of silicide formation, the resulting surface may be faceted. The peak-to-valley height of this texturing will generally be between about 300 and about 5000 angstroms, which is well-suited for use in photovoltaic cells comprising a thin silicon lamina.

Abstract: In aspects of the present invention, a method is disclosed to form a lamina having opposing first and second surfaces. Heavily doped contact regions extend from the first surface to the second surface. Generally the lamina is formed by affixing a semiconductor donor body to a receiver element, then cleaving the lamina from the semiconductor donor body wherein the lamina remains affixed to the receiver element. In the present invention, the heavily doped contact regions are formed by doping the semiconductor donor body before cleaving of the lamina. A photovoltaic cell comprising the lamina is then fabricated. By forming the heavily doped contact regions before bonding to the receiver element and cleaving, post-bonding high-temperature steps can be avoided, which may be advantageous.

Abstract: Methods for bonding a donor wafer to a receiver element and transferring a lamina from the donor wafer to the receiver element are disclosed herein. The donor wafer may be, for example, a monocrystalline silicon wafer with a thickness of from about 300 microns to about 1000 microns, and the lamina may be may be less than 100 microns thick. The receiver element may be composed of, for example, metal or glass, and the receiver element may have dissimilar thermal expansion properties from the lamina. Although the lamina and the receiver element may have dissimilar thermal expansion properties, the methods disclosed herein maintain the integrity of the bond between the lamina and the receiver element.

Abstract: A photovoltaic device is disclosed herein that, in various aspects, includes a conductive layer, and a substantially crystalline lamina with a first surface oriented toward the conductive layer and a second surface oriented away from the conductive layer. The lamina thickness is within the range between about 0.2 microns and about 50 microns. An aperture passes through the lamina from the first surface to the second surface. A connector in electrical communication with the conductive layer is disposed through the aperture. Methods of manufacture of the photovoltaic devise are also disclosed.

Abstract: Ion implanters are especially suited to meet process dose and energy demands associated with fabricating photovoltaic devices by ion implantation followed by cleaving.

Abstract: Ion implanters incorporating multibeam ion sources are used to meet process dose and energy demands associated with fabricating a thin lamina for use in photovoltaic devices. The thin lamina are formed by ion implantation followed by cleaving.

Abstract: 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.

Abstract: Fabrication of a photovoltaic cell comprising a thin semiconductor lamina may require additional processing after the semiconductor lamina is bonded to a receiver. To minimize high-temperature steps after bonding, the p?n junction is formed at the back of the cell, at the bonded surface. In some embodiments, the front surface of the semiconductor lamina is not doped or is locally doped using low-temperature methods. The base resistivity of the photovoltaic cell may be reduced, allowing a front surface field to be reduced or omitted.

Abstract: 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.

Abstract: A very thin photovoltaic cell is formed by implanting gas ions below the surface of a donor body such as a semiconductor wafer. Ion implantation defines a cleave plane, and a subsequent step exfoliates a thin lamina from the wafer at the cleave plane. A photovoltaic cell, or all or a portion of the base or emitter of a photovoltaic cell, is formed within the lamina. In preferred embodiments, the wafer is affixed to a receiver before the cleaving step. Electrical contact can be formed to both surfaces of the lamina, or to one surface only.

Abstract: A novel surface texturing provides improved light-trapping characteristics for photovoltaic cells. The surface is asymmetric and includes shallow slopes at between about 5 and about 30 degrees from horizontal as well as steeper slopes at about 70 degrees or more from horizontal. It is advantageously used as either the front or back surface of a thin semiconductor lamina, for example between about 1 and about 20 microns thick, which comprises at least the base or emitter of a photovoltaic cell. In embodiments of the present invention, the shallow slopes are formed using imprint photolithography.

Abstract: A donor semiconductor wafer is processed to define a cleave plane, then affixed to a discrete receiver element, which may be glass, metal or a metal compound, plastic, or semiconductor. A semiconductor lamina is cleaved from the donor wafer at the cleave plane. A photovoltaic assembly is fabricated comprising the semiconductor lamina and the receiver element. The photovoltaic assembly comprises a photovoltaic cell. After fabrication, the photovoltaic assembly can be inspected for defects and tested for performance, and select photovoltaic assemblies can be assembled into a completed photovoltaic module.

Abstract: A semiconductor donor body is affixed to a receiver element, and a thin semiconductor lamina is cleaved from the donor body, remaining affixed to the receiver element. A photovoltaic assembly is fabricated which includes the lamina and the receiver element, wherein a photovoltaic cell comprises the lamina. The bond between the semiconductor donor body and the receiver element must survive processing to complete the cell, as well as eventual assembly, transport, and operation in a finished photovoltaic module. It has been found that inclusion of a conductive layer such as titanium or aluminum aids bonding between the semiconductor donor body and the receiver element. In some embodiments, the conductive layer may also serve as an electrical contact and/or as a reflective layer.

Abstract: A very thin photovoltaic cell is formed by implanting gas ions below the surface of a donor body such as a semiconductor wafer. Ion implantation defines a cleave plane, and a subsequent step exfoliates a thin lamina from the wafer at the cleave plane. A photovoltaic cell, or all or a portion of the base or emitter of a photovoltaic cell, is formed within the lamina. In preferred embodiments, the wafer is affixed to a receiver before the cleaving step. Electrical contact can be formed to both surfaces of the lamina, or to one surface only.