Patent Application
20110252853
1. Field of the Invention
The present invention relates generally to a method and an apparatus for compacting a copper/indium/gallium/selenium (CIGS) thin film, and more particularly, to a method and an apparatus for compacting a CIGS light absorbing layer of a solar cell in a non-vacuum environment.
2. The Prior Arts
Recently, the oil price remains at a high level, and the environmental protection becomes more concerned all over the world. Correspondingly, many countries have put their efforts for developing renewable energies including solar cell technology. Among many kinds of solar cells, the silicon solar cells are featured with higher photoelectric conversion efficiency, and the technology thereof has been well established. However, the further application of the silicon solar cells is very much restricted by the insufficient supply of the raw material, i.e., silicon wafers. Therefore, thin film solar modules are more and more concerned and developed in commercial applications since they only use 1/100 of the raw materials in comparison with crystallized silicon solar cells. Typically, according to raw materials, thin film solar modules can be classified into three categories, including amorphous silicon, CIGS, and cadmium telluride (CdTe). It is well known that the CIGS thin film has the highest photoelectric conversion efficiency among these thin films. For example, a CIGS solar cell had achieved a conversion efficiency up to 20%, and a CIGS thin film solar module had already achieved a conversion efficiency up to 14% during the past two years.
Conventional methods for fabricating CIGS solar cells are typically categorized into vacuum processing and non-vacuum processing. In a vacuum processing, a sputtering process or a co-evaporation process is typically employed. Unfortunately, the vacuum processing requires expansive processing equipment and is featured with a low material utilization. On the contrary, the non-vacuum processing, e.g., printing or electrodeposition process is still remained in the experimental stage, and not yet as mature as to be mass production.
A well-known problem of the non-vacuum processing is that non-compact CIGS thin film is difficult to get larger grains. As a result, too much grain boundaries retard absorbing the sunlight. Accordingly, a CIGS solar cell with non-compact CIGS thin absorbing layer will cause a lower conversion efficiency.
A primary objective of the present invention is to provide a method and an apparatus to compact a CIGS thin film in a non-vacuum environment.
According to the present invention, a substrate having a CIGS light absorbing layer configured thereon is processed with a soft baking process. Then, a pneumatic cylinder is designed to drive a roller which is linked to a holder. When the pneumatic cylinder applies a pressing force to the holder, the holder with the roller will press downward onto the CIGS light absorbing layer. The substrate is then moved back and forth to compact the CIGS light absorbing layer uniformly.
In accordance with the present invention, the diameter of the roller and the pressing force applied by the roller must be controlled within specific ranges for achieving a better compacting performance. Preferably, a hard coating layer is coated on an outer surface of the roller for protecting the outer surface of the roller.
The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawing, in which:
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawing illustrates embodiments of the invention and, together with the description, serves to explain the principles of the invention.
The CIGS thin film 50 is obtained from a deposited CIGS slurry or ink containing CIGS material, and processed with a soft baking process. Such a CIGS thin film has a relatively low densification.
In operation, the pneumatic cylinder 10 is adjusted to provide a suitable air pressure. Then, the pneumatic cylinder 10 drives the holder 20 to downward apply a pressing force on the substrate 40 having the CIGS thin film 50 configured thereon. Then, the substrate 40 is laterally moved forth and back, so that the roller 30 uniformly rolls on the substrate to compact the CIGS thin film 50.
However, it should be noted that the pressure applied by the roller 30 on the CIGS thin film 50 should be controlled within a certain range. If the pressure is too high, the substrate 40 on which the CIGS thin film 50 is configured may be damaged. Preferably, the pressure provided by the pneumatic cylinder is lower than an upper threshold, about 3 kg/cm2. Further, on another hand, if the pressure is too low, the holder 20 cannot be driven to rise or fall, and therefore the roller 30 is incapable of applying the pressure onto the CIGS thin film 50. Therefore, the pressure is preferred to be higher than a lower threshold, about 0.2 kg/cm2.
Further, the diameter of the roller 30 should be controlled within a suitable range. If the diameter of the roller 30 is too large, the uniformity of compacting performance may decay. If the diameter of the roller 30 is too small, too much rollers 30 have to be used for uniformly compacting the CIGS thin film 50. According to the embodiment of the present invention, the diameter of the roller 30 is preferably controlled in a range of 0.5 cm to 10 cm.
In addition, in order to improve the abrasion resistance of the outer surface of the roller 30, the outer surface of the roller 30 can be processed with a thermal treatment to avoid damaged caused by broken glass. Alternatively, the roller 30 may further include a hard coating layer provided on the outer surface of the roller 30 for protecting the outer surface of the roller 30. The thermal treatment on the outer surface of the roller 30 or the hard coating layer provided on the outer surface of the roller 30 is adapted for avoiding adverse affection caused by sharp stuff or broken chips. Preferably, the hard coating layer is made of electroplated chromium or tungsten. Alternatively, the outer surface of the roller 30 can also be covered with a ceramic material, such as carborundum, diamond like carbon (DLC), or diamond. According to a further aspect of the embodiment, the roller 30 can be made of ceramic. In such a way, the roller 30 with better hardness won't be damaged by any sharp stuff or broken chips.
In summary, the present invention provides a method and an apparatus to compact a CIGS thin film in a non-vacuum environment. According to the present invention, a roller is employed to uniformly roll on the CIGS thin film configured on the substrate for improving the densification of the CIGS thin film, thus providing a solution to a well-known problem as discussed with respect to the conventional technology.
Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.
