The rapid increase in the use of electricity for various electronic goods will lead to a rise in global electricity consumption. At the same time, prices for the dwindling resources of petroleum and natural gas are climbing. This indicates that renewable energy, such as solar energy, has a bright future.
A significant challenge faced by the solar energy industry is its high cost of generation. The conventional techniques that are used in the production of solar cells are making this form of energy expensive to produce. According to experts in this field, development of grid parity (the point at which photovoltaic electricity is equal to or cheaper than grid power) will be achieved in a few years though. This means that the costs and opportunities in the grid will be equal for solar electricity and conventionally generated electricity. Therefore, the industry demands novel manufacturing techniques that can lead to faster and cheaper production of solar cells.
Lasers are already being used in the production of solar cells and have proved to be an ideal tool, but there is still considerable room for process optimisation. A team of researchers from the Fraunhofer Institute for Laser Technology (ILT) in Aachen, Germany have developed laser technologies that are expected to allow faster, better and cheaper production of solar cells in the future. The team has demonstrated that the laser system developed can drill holes efficiently into the silicon wafers to produce solar cells, thereby optimising manufacturing time and costs.
The ILT laser system drills more than 3000 holes within one second. Since it is not possible to move the laser source at this speed, the experts have developed optimised manufacturing systems that guide and focus the light beam at the required points. The tiny holes drilled in the silicon wafer have a diameter of around 50 micrometres. Previously, the electrical contacts were arranged on the top of the cells. Now, 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. This increases the energy yield.
The major goal is to increase the efficiency of the cells by 20% in industrially produced emitter wrap-through (EWT) cells, with a yield of one-third more than classic silicon cells. The design principle itself remains unchanged wherein the semiconductor layer, light particles, or photons, produce negative electrons and positive holes, each of which then wanders to the oppositely poled electrodes. The contacts for anodes and cathodes in the EWT cells are all on the back, there is no shading caused by the electrodes, and the degree of efficiency increases.
With this technique, it may one day be possible to use unpurified ‘dirty’ silicon to manufacture solar cells that have poorer electrical properties, but are cheaper to obtain.
ILT is also cooperating in the 6 million Euro project ‘Solasys – Next Generation Solar Cell and Module Laser Processing Systems’ along with an international research team. This project aims to develop new technologies for the manufacturing of solar cells that will allow production to be optimised in the future.
In addition to gradually improving the manufacturing technology, the physicists and engineers in Aachen are working with solar cell developers on new engineering and design alternatives. The team is also experimenting with various laser sources and optical systems. The ultimate goal is to increase the performance of the laser to drill 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.
For more information on Frost & Sullivan’s technical or market analysis, please contact Patrick Cairns on [email protected].
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, [email protected], www.frost.com
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