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Laser cutting in solar manufacturing

Laser processing established itself as a mainstream technology in the manufacturing of industrial standard solar cells. Various process steps are suitable for laser processing and have been commonly used in the past, such as via drilling, laser edge isolation, and the laser doped selective emitter process.

Today, the laser contact opening (LCO) process to structure the backside passivation layer is a key step to enable the production of passivated emitter rear cells (PERC). Moreover, cell cutting into two halves by laser is another technology gaining more and more interest because of its ability to increase the module power output significantly. InnoLas, a pioneer in laser processing for the photovoltaic (PV) industry since 2003, developed a fully automated cell cutting solution combining a laser grooving process with an integrated soft breaking and handling automation.

Electrical losses in solar cell modules

Increasing cell efficiency is one way to reduce the cost of solar power. The reduction of the cell-to-module (C2M) losses during module assembly presents another strategy which allows a significant increase of PV module power output by integrating only one additional process step.

solar cell

Solar cell cut into two halves

The device-inherent resistivity together with the high photo-induced current of the solar cells within one string is causing significant electrical losses when cell-to-cell interconnection takes place during the stringing process. This represents one of the main contributors to electrical performance and has therefore a high impact onto later module efficiency.

cell to cell losses

Cell to module losses

When using half or quarter cells instead of full cells, the impact of the cell resistivity in one string can be lowered due to the reduction of the photo-induced current per unit cell. As a result of German research institutes, the output power of half-cell modules increases up to 10-15W, driven by significantly higher Isc and FF. A real-world outdoor measurement carried out over a period of six months in Germany using half-cell modules confirmed a + 3% higher average module power yield in comparison to standard modules and represents a strong argument of using cell cutting to reduce C2M losses.

Process and tool solutions for cell cutting

Today cell cutting is typically done by laser processing due its low cost and high precision. Though there are different approaches for cutting a solar cell into halves, the most common way is to groove it with a laser from the back side about one third of the wafer thickness and break it along the kerf. Cutting through the solar cell entirely by laser would be an alternative, but may cause shunting of the solar cell, e.g. through metallic residues remaining along the edge of the cut or damage to the p-n junction of the solar cell. Breaking of the grooved solar cell requires a small additional handling step, but is superior since it can avoid the shunting effect.

InnoLas developed an integrated solution based on its new ILM-2 laser machine and handling platform for an advanced precise and high- aspect ratio laser grooving process together with a soft breaking method. The machine package, which is optimized for lowest cost of ownership, represents the first fully automated cell cutting equipment running in high-volume production in the market. With its modular concept it can be used as a stand-alone or in line system. The flexibility to employ different laser sources and different automation concepts allows for a perfect adaption to the various requirements of today’s solar cell and module lines.

solar production machine

ILM-2 production machine

Electrical losses are a major restraint for the achievable power output of industrial solar cell modules. Using half or quarter solar cells helps to increase the module output power by about 3% compared to the power output of standard full cell modules. This leads to an increasing demand for cell cutting solutions in the PV market. The novel ILM-2 platform designed by InnoLas Solutions is an equipment package combining a laser grooving process with an integrated soft breaking and handling automation.

Written by Ernst Hartmannsgruber, Director of Sales and Marketing at InnoLas Solutions GmbH

Labels: solar cell manufacturing,backside passivation,laser contact opening,PERC,Innolas

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