Patent Application
20140273329
The disclosure relates most generally to solar cell devices and more particularly to methods for forming scribe lines in solar panels used to form solar cell devices.
Solar cells are photovoltaic components for direct generation of electrical current from sunlight. Due to the growing demand for clean sources of energy, the manufacture of solar cells has expanded dramatically in recent years and continues to expand. All solar cells include an absorber layer and one common absorber layer is CIGS, copper indium gallium selenide. Transparent conductive oxide, TCO, films are commonly disposed over the absorber layers in solar cells. TCO films are popular materials due to their versatility as transparent coatings and also as electrodes and function as top contacts for the solar cells.
Solar cells are often manufactured in the form of thin film solar panels. Thin film solar panels are gaining in popularity because they are less expensive to manufacture and are formed on very large substrates. These very large substrates that serve as one solar cell can have poor conversion efficiencies. Thus, multiple interconnected or separated solar cells are created from the large solar panels by separating the solar panel into efficiently sized solar cells. The solar cells are separated by scribe lines in a scribing process. Scribe lines are formed by identifying scribe line regions and removing materials from the scribe lines to separate the cells.
Improvements in scribing methods for solar panels continue to be sought.
The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not necessarily to scale. On the contrary, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. Like numerals denote like features throughout the specification and drawing.
Methods for forming scribe lines in solar panels are provided. The methods are for scribing photovoltaic structures to form monolithically integrated photovoltaic modules. Scribe lines separate the solar panels into individual solar cells and the individual solar cells are arranged in arrays in some embodiments. In other embodiments, the solar panels are scribed to create multiple solar cells that are interconnected in series. In some embodiments, groups of serially connected solar cells are connected in parallel.
Current methods for forming the scribe lines include mechanical patterning. In mechanical patterning, a stylus is used to mechanically etch micro-channels into the solar panels to form individual solar cells typically in the form of an array. Commercially used mechanical scribing methods may not create high-quality, highly defined channels and may result in film cracking which reduces the active area from which electricity is generated. The film cracking generates contaminants and often results in a decreased conversion efficiency of the solar cell.
Some laser patterning methods have also been used to form scribe lines. Such methods utilize pico-second lasers which are expensive and may undesirably create shunting between the TCO or other top electrode, and the back electrode. Current laser scribing techniques also cause thermal melting and splattering of conductive material such as TCO which can cause undesirable shorting between adjacent solar cells.
The method of the disclosure utilizes a nanosecond laser, i.e. a laser with a pulse frequency in the nanosecond range and the disclosure provides for a multiple step process for forming scribe lines on solar panels. At least one of the steps includes the use of a nanosecond laser. Nanosecond lasers are relatively inexpensive to own and operate (compared to picosecond lasers) and the methods of the disclosure provide for scribing the layers of the solar panel with virtually no cracking or particle production, eliminating common causes of cell shunting and maximizing conversion efficiency. Various embodiments of the disclosure include methods in which a first nanosecond laser cutting operation is followed by a mechanical scribing operation and other embodiments of the disclosure are methods in which a first nanosecond laser cutting operation is followed by a second nanosecond laser cutting operation. In some embodiments, the multi-step process for scribing solar panels involves more than two steps.
Various methods for forming the structure in 1C are used according to various embodiments of the disclosure as will be described below.
Shaped laser beam 24 is a nanosecond laser beam and performs a cutting operation on the structure shown in
Still referring to
The two-tiered profile of the scribe line opening 12 shown in
The nanosecond laser cutting operations utilize shaped laser beam 24 or shaped laser beam 34. In one embodiment, the shaped laser beam includes a radiation wavelength that varies from about 200 to 1100 nm in various embodiments, and in one embodiment, the laser operates with a radiation wavelength within the range of about 500-550 nm. In some embodiments, the nanosecond laser utilizes a beam with radiation having a wavelength within the range of about 200-300 nm. In another embodiment, the nanosecond laser beam is a visible light beam with a wavelength within the range of about 400-700 nm, and in another embodiment, the nanosecond laser utilizes a beam of radiation with a wavelength within the range of about 1000-1200 nm. The nanosecond laser operates using a pulse that ranges from about 0.1 ns (nanoseconds) to about 100 ns in various embodiments. In one embodiment, the nanosecond laser utilizes a pulse rate of about 0.8 to 30 ns. Various pulse energies are used for the shaped laser beam in various embodiments. In one embodiment, the pulse energy ranges from about 3 uJ (microJoules) to about 20 uJ, but other energies are used in other embodiments.
Shaped laser beams 24, 34 are shaped using various suitable means to shape the energy profiles of a laser beam across a laser beam spot.
According to the embodiment in which two nanosecond laser cutting operations are used, the beam profile and other laser beam parameters and settings are the same in each of the nanosecond laser cutting operations in some embodiments, the beam profile and other laser beam parameters and settings differ in the two nanosecond laser cutting operations.
The disclosure is not limited to the two method embodiments described herein. In other embodiments, the multi-step scribe line formation method includes additional steps. In one embodiment, two nanosecond laser scribing operations are used in conjunction with a mechanical scribing operation. The methods of the disclosure produce solar cells with minimized active area loss which increases conversion efficiency and are formed using a low-cost nanosecond laser that prevents local shunting.
According to one aspect, a method for patterning a solar cell is provided. The method comprises providing a solar panel with at least an absorber layer and a transparent conductive oxide (TCO) layer over the absorber layer and creating scribe lines in the solar panel using a multiple step process in which at least a first step of the multiple steps is a nanosecond laser cutting operation.
According to another aspect, a method for patterning a solar cell is provided. The method comprises providing a solar panel with a stack of layers including at least an absorber layer and a transparent conductive oxide (TCO) layer over the absorber layer and creating scribe lines in the solar panel by using a first nanosecond laser cutting operation that cuts through only a portion of a thickness of the stack and a second cutting step that cuts through a remaining thickness of the stack.
According to yet another aspect, a method for scribing a solar panel is provided. The method comprises: providing a thin film solar panel with a stack of layers having a thickness and including at least an absorber layer and a transparent conductive oxide (TCO) layer over the absorber layer; identifying scribe line regions of the solar cell; cutting through an upper portion of the stack of layers using a nanosecond laser cutting operation in the scribe line regions thereby leaving a lower portion of the stack of layers intact in the scribe line regions; and cutting through the lower portion of the stack of layers in the scribe line regions using one of a further nanosecond laser cutting operation and a mechanical cutting operation.
The preceding merely illustrates the principles of the disclosure. It will thus be appreciated that those of ordinary skill in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes and to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
This description of the exemplary embodiments is intended to be read in connection with the figures of the accompanying drawing, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.
Although the disclosure has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the disclosure, which may be made by those of ordinary skill in the art without departing from the scope and range of equivalents of the disclosure.
