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Solar energy is an indispensable part of the energy mix. In order to further reduce the costs of solar power, research has to reduce production costs of PV modules and increase the efficiency of solar cells. Laser technology plays a key role in the cost-effective production of high-quality solar cells on an industrial scale. Fraunhofer ILT is developing industrial laser processes and the necessary components for an economical production process with high process efficiency.

A current focus of Fraunhofer ILT's work is in the field of organic photovoltaics, in which high-performance interconnection technologies are integrated into highly productive systems. Here, Fraunhofer ILT offers state-of-the-art coating, laser-based thin-film modification and structuring systems in a roll-to-roll process. These are characterized by particularly high flexibility and low production costs.

Coating and structuring

In organic thin-film solar cells, the researchers at Fraunhofer ILT apply contacts and semiconducting layers to a transparent film. They also use thin anti-reflective and passivation layers, which improve the optical and electrical properties and, thus, increase efficiency. These thin layers, however, must be selectively and precisely removed.

An ideal tool for this task is highly precise ultrashort pulse laser radiation that works reliably at high throughput and speeds of up to 10 m/s. With an adapted temporal and local shaping of the laser beam, USP lasers completely ablate the layers with a line width of a few micrometers without damaging the substrate or the layer underneath.

Soldering and welding of solar modules

Solar modules consist of individual solar cells that are contacted with each other for long-term stability. This is currently done using infrared soldering or so-called thermode soldering with heat and pressure, which, however, can cause the thin cells to crack. Laser soldering, on the other hand, applies energy selectively without heating the wafer too much. With two beam paths, the front and rear sides can be soldered simultaneously, resulting in process times of less than three seconds per cell. Laser beam welding reaches processing speeds ten times faster than soldering.

Film packaging

Multilayer films are required for the packaging of film-based organic solar modules in order to protect the sensitive active layers from environmental influences such as oxygen and water. The use of laser radiation as a welding tool has a major advantage over conventional fixed tools, particularly in film processes where production takes place in a roll-to-roll process.

Depending on the process requirements, the laser transmission welding or gap welding process is suitable. In addition to film laminates made from various plastics, multi-layer film laminates with barrier layers or metallic components can also be joined in this way.

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