Lasers Make Solar Cells Competitive
For centuries we have been using fossil fuels for industrial and domestic purposes. Most of us consider fossil fuels cheap. But now we are realizing the “real” costs of using fossil fuels. It is destroying our environment and making us pay in other terms. Another problem we are facing is, what were luxuries for the previous generation have become the necessities for current generation. We are using lots of gadgets such as computers, cell phones, iPhones and kitchen and home appliances. They all run on electricity. It is now clear that most of us will be driving electric cars in future. So the problem will be compounded by our growing energy needs. According to the newest forecast from the World Energy Council (WEC) global electricity requirements will double in the next 40 years. At the same time, we know that prices for the dwindling resources of petroleum and natural gas are mounting.
We are trying to shift to other alternative sources of energy but they are still in transitional phase. We know that solar energy is a good source of energy and at the same time it is clean and green too. But the price of solar panels still resides heavily on a common man’s pocket. Government has to step in and subsidize the cost of solar energy if it has to be used for domestic purposes. A lot of R & D work is taking place at various laboratories of the world.
“Laser 2009” is organized in Munich from June 15 to June 18. Researchers from the Fraunhofer Institute for Laser Technology (ILT) in Aachen, Germany, will be demonstrating how laser technology can contribute to optimizing the manufacturing costs and efficiency of solar cells.
At Laser 2009, the researchers will demonstrate how the ILT laser system drills more than 3,000 holes within one second. The scientists have developed optimized manufacturing systems to guide and focus the light beam at the required points.
Dr. Arnold Gillner, who is the head of the microtechnology department at the Fraunhofer Institute for Laser Technology in Aachen, Germany, explained, “We are currently experimenting with various laser sources and optical systems. Our goal is to increase the performance to 10,000 holes a second. This is the speed that must be reached in order to drill 10,000 to 20,000 holes into a wafer within the cycle time of the production machines.”
Here it is to be noted that drilling holes into silicon cells is only one of the many laser applications in solar cell manufacturing that is being developed. There is another EU project underway. This is called Solasys, Next Generation Solar Cell and Module Laser Processing Systems. Here an international research team is presently working on new technologies that will optimize the production in the future. ILT in Aachen is coordinating this six million euro project. Here researchers are paying close attention to the various aspects of manufacturing of solar cells and they are considering how to minimize the loss of material and reduce the cost of production.
According to Gillner they are trying to make certain processes such as the doping of semiconductors, the drilling and the surface structuring of silicon, the edge isolation of the cells, and the soldering of the modules more economical. Gillner coins a term “selective laser soldering.” “Selective laser soldering” makes it possible to improve the rejection rates and quality of the contacting, and these lead to reducing manufacturing costs. When panels are conventionally designed the electrodes are mechanically pressed onto the cells, and then heated in an oven. During this process silicon cells often break making it a primary cost factor in production. But when “selective laser soldering” is used the contacts are pressed on to the cells with compressed air and then soldered with the laser. This makes the mechanical stress zero and the temperature can be precisely regulated. This path leads towards optimal contacts and almost no rejects.
In the nutshell we can say that this research team is working on a technology that will allow faster, better, and cheaper production of solar cells in the future. Dr. Arnold Gillner elaborates, “Lasers work quickly, precisely, and without contact. In other words, they are an ideal tool for manufacturing fragile solar cells. In fact, lasers are already being used in production today, but there is still considerable room for process optimization.”
What magic can these tiny holes perform? They can lead to design alternatives! Though the holes in the wafer are only 50 micrometers in diameters they can open new possibilities for solar manufacturers. Gillner explains, “Previously, the electrical contacts were arranged on the top of the cells. The holes make it possible to move the contacts to the back, with the advantage that the electrodes, which currently act as a dark grid to absorb light, disappear. And so the energy yield increases. The goal is a degree of efficiency of 20 percent% in industrially-produced emitter wrap-through (EWT) cells, with a yield of one-third more than classic silicon cells.”
The rise of laser technology in solar technology is just taking baby steps and it is still learning to walk and run. “Lasers simplify and optimize the manufacture of classic silicon and thin-film cells, and they allow the development of new design alternatives,” Gillner continues. “And so laser technology is making an important contribution towards allowing renewable energy sources to penetrate further into the energy market.”