TRUMPF lasers expand possibilities in solar cell manufacturing // TRUMPF at the 27th European Photovoltaic Solar Energy Conference, Frankfurt, September 25 to 28, 2012; Hall 3.0, Booth B7

Ditzingen, September 25, 2012 - The photovoltaics industry is facing a challenge: on the one hand, it is under pressure to deliver ever greater solar cell efficiency; on the other hand, it has to reduce process costs and devise ever more efficient manufacturing processes. At the 27th European Photovoltaic Solar Energy Conference (EUPVSEC), TRUMPF is presenting innovative micro-processing lasers from the TruMicro Series which open up new opportunities in the production process for manufacturers of solar cells and of solar cell production equipment and machinery.

Green lasers such as the TruMicro 7240 are used for doping processes, during which the laser generates higher doping concentrations locally on the solar cell in order to improve the mobility of the free charge carriers, especially in the area around the contact fingers. Ultra-short pulse lasers from the TruMicro Series 5000 are highly suited to patterning processes on thin-film solar cells. With their excellent beam quality and high average power, they significantly reduce the costs per watt of solar cell output. In order to protect thin-film modules against external influences, especially moisture, roughly one centimeter is removed from the edge of the system of layers and the exposed area is then laminated with film. This protects the solar modules against corrosion and short circuits over the long run. The tool of choice for this application is the TruMicro 7050, which is able to reliably and quickly process large areas while delivering top quality.

Selective emitter
The efficiency of solar cells can be increased by means of extensive light doping of the emitter between the contact fingers and selective heavy doping directly beneath the contact fingers. Working with a laser enables the gentle, defect-free, and extremely precise diffusion of a phosphorus doping profile into the solar cell layer next to the surface. This emitter layer is just a few micrometers thick and is negatively doped. When light hits the solar cell, electron-hole pairs are generated throughout the solar cell and separated by the electric field at the p-n junction. The photoelectronically generated current is discharged via metal contacts. This allows the doping with phosphorus atoms to be increased locally and the conductivity between wafer and contact fingers to rise. A heavily doped emitter reduces contact resistance at the negative pole and increases the recombination probability of the charge carriers. The result is a big improvement in efficiency. To achieve these results, TRUMPF offers the TruMicro 7240 green-wavelength nanosecond laser, which has an average power of around 300 watts.

Patterning
The patterning of thin-film cells made of Cu(In,Ga)(S,Se)2 - or CI(G)S for short - makes especially high demands of the laser process. This is where the picosecond lasers of the TruMicro Series 5000 come in. Thanks to their ultra-short pulses, they ablate material without heating the area around the process to any significant degree. This prevents cracks, melting, and layers detaching. TRUMPF offers the TruMicro Series 5000 with wavelengths of 1030 nanometers for texturing molybdenum and 515 nanometers for processing photoactive material and patterning front contacts. Of all the picosecond lasers with up to 100 watt output power currently available, the TruMicro Series 5000 is the best value for money and has the lowest running costs.

Edge deletion
In order to protect thin-film modules against external influences, especially moisture, roughly one centimeter is removed from the edge of the system of layers and the exposed area is then laminated with film. This protects the solar modules against corrosion and short circuits over the long run. Lasers are the ideal tool for this application. The properties that make lasers so suited to patterning can be carried over to full ablation by increasing average power. A high layer stripping rate of 50 cm2/s and more enables cycle times of 30 seconds to be obtained in production for typical module sizes. The TruMicro 7050 is perfect for this application as it is capable of reliably and safely processing large formats. The micro-processing laser generates pulses lasting 30 nanoseconds at an average power of 750 watts.

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Source: Trumpf GmbH + Co. KG/4-traders.com