Patent Application
20100233838
The present application is directed to solar cell manufacturing and, more particularly, to mounting of solar cells on a flexible substrate.
Thin solar cells are fabricated by depositing layers of light absorbing semiconductor material on the surface of a semiconductor wafer and then removing the wafer. The solar cell layer stack is typically bonded to a carrier to provide support during certain manufacturing steps, including removal of the semiconductor wafer. Additional processing can be performed after removal of the semiconductor wafer such as depositing metal wiring and cutting the thin layers of solar cell material into individual solar cell chips. Each solar cell chip can be removed from the support carrier and attached to a solar array device such as a solar panel, collector, etc. The solar cell chips can be made thin enough so that they flex when attached to curved surfaces.
The layers of solar cell material are typically attached to a carrier support using an adhesive or solder. It is difficult to remove the thin solar cell chips from the support carrier after the semiconductor wafer is removed and processing of the cells is completed. The thin solar cell chips are often damaged during the support substrate removal process, which can require excessively high temperatures and/or mechanical/chemical forces to break the bond formed between the solar cells and the support carrier. Damaging solar cells during the support substrate removal process significantly reduces conventional thin film solar cell manufacturing yields.
According to one embodiment, a method of manufacturing a solar cell includes depositing a sequence of layers of semiconductor material forming at least one solar cell on a first substrate; temporarily bonding a flexible film to a support second substrate; permanently bonding the sequence of layers of semiconductor material to the flexible film so that the flexible film is interposed between the first and second substrates; thinning the first substrate while bonded to the support substrate to expose the sequence of layers of semiconductor material; and subsequently removing the support substrate from the flexible film.
According to another embodiment, a method of manufacturing a solar cell includes depositing a sequence of layers of semiconductor material forming at least one solar cell on a first substrate; attaching a flexible film to a support second substrate with a temporary adhesive; attaching the sequence of layers of semiconductor material to the flexible film with a permanent adhesive so that the flexible film is interposed between the first and second substrates; thinning the first substrate while bonded to the support substrate to expose the sequence of layers of semiconductor material; and subsequently applying an adhesive remover to holes formed through the support substrate to dissolve the temporary adhesive and remove the support substrate from the flexible film.
According to yet another embodiment, a method of manufacturing a solar cell includes depositing a sequence of layers of semiconductor material forming at least one inverted metamorphic multifunction solar cell on a first substrate; temporarily bonding a flexible film to a support second substrate; permanently bonding the sequence of layers of semiconductor material to the flexible film so that the flexible film is interposed between the first and second substrates; thinning the first substrate while bonded to the support substrate to expose the sequence of layers of semiconductor material; and subsequently removing the support substrate from the flexible film.
Of course, the present invention is not limited to the above features and advantages. Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
Details of the present invention will now be described including exemplary aspects and embodiments thereof. Referring to the drawings and the following description, like reference numbers are used to identify like or functionally similar elements, and are intended to illustrate major features of exemplary embodiments in a highly simplified diagrammatic manner. Moreover, the drawings are not intended to depict every feature of the actual embodiment nor the relative dimensions of the depicted elements, and are not drawn to scale.
With this in mind, the present application is directed to permanently bonding a thin solar cell formed on a growth substrate to one side of a flexible film and temporarily bonding the other side of the flexible film to a support substrate so that the support substrate can be easily removed from the flexible film after processing of the thin solar cell is complete. Thin solar cells manufactured in accordance with the embodiments described herein weigh less and are thus well suited for applications where weight is a concern such as space applications. In addition, the solar cells are relatively thin and thus can be readily attached to curved surfaces. Still other advantages of having thin solar cells attached to a flexible film will become readily apparent in view of the detailed description below.
The support substrate 110 provides support to the sequence of layers of semiconductor material 100 during subsequent processing step(s). This way, the growth substrate 120 on which the sequence of layers of semiconductor material 100 is deposited can be removed after attachment to the support substrate 110. The sequence of layers of semiconductor material 100 can also be segmented into individual solar cell chips (not shown in
According to one embodiment, the sequence of layers of semiconductor material 100 is deposited on the growth substrate 120 by forming a first solar subcell on the growth substrate 110 having a first band gap and forming a second solar subcell over the first solar subcell having a second band gap smaller than the first band gap. A grading interlayer is formed over the second solar subcell having a third band gap larger than the second band gap. A third solar subcell having a fourth band gap smaller than the second band gap is formed such that the third solar subcell is lattice mismatched with respect to the second solar subcell. In one embodiment, the first solar subcell is composed of an InGaAlP emitter region and an InGaAlP base region and the second solar subcell is composed of an InGaP emitter region and an InGaAs base region. The grading interlayer can be composed of InGaAlAs. Alternatively, the grading interlayer can be composed of a plurality of layers with a monotonically increasing lattice constant. Yet other layers of semiconductor material can be deposited on the growth substrate 120 to form a solar cells which is now ready for attachment to the support substrate 110.
In one embodiment, the flexible film 130 is vacuum sealed to a chuck (not shown) and the temporary adhesive 150 spun onto the film 130. The support substrate 110 is then mated with the flexible film 130 while on the chuck. Alternatively, the temporary adhesive 150 can be spun onto the support substrate 110. According to this embodiment, the holes 112 formed in the support substrate 110 are temporarily plugged so that the adhesive 150 does not escape through the holes 112. The holes 112 can be plugged by placing tape (not shown) over the side 116 of the support substrate 110 not being bonded to the flexible film 130. The tape can be removed after the support substrate 110 and flexible film 130 are brought into contact. The support substrate 110 and the flexible film 130 are then bonded together via the temporary adhesive 150 under appropriate heat and/or pressure conditions for curing the temporary adhesive 150. The growth substrate 120 with the sequence of layers of semiconductor material 100 is also prepared for bonding to the flexible film 130.
In another embodiment, the support substrate 110 does not have holes 112 formed therein and the temporary adhesive 150 is dissolved by heating the adhesive 150 to a temperature which breaks the temporary bond between the support substrate 110 and the flexible film 130. The individual solar cell chips 210 each with a layer of the flexible film 130 permanently bonded thereto can then be attached to any type of desirable surface. The solar cell chips 210 are thin and flexible and can be readily attached to flat or curved surfaces. Cover glasses (not shown) and interconnects 200 can be applied to solar cell chips 210 either before or after demounting from the support substrate 110 since the flexible film 130 provides ample support to the chips 210 during this type of processing. The flexible film 130 permanently bonded to the solar cell chips 210 can be sucked down with a vacuum to make the film 130 flat to do cover glassing and welding or soldering.
Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
