Precise and highly technical processes are used in the manufacture of crystalline solar cells and thin-film modules as a way of reducing the cost of manufacturing, ensuring little waste in the process, increasing efficiency and improving the output of solar cells.
Increasing cell efficiency is the most effective way to reduce the cost of solar power, and PERC (passivated emitter and rear contact) is one of the technologies that meets the balance between manufacturing cost and efficiency. By incorporating lasers into the PV manufacturing process, manufacturers can lower maintenance costs and cost of ownership.
PV manufacturing platforms can be further optimized for easy integration into existing production lines and to reduce handling steps if integrated, for example, via a conveyor interface prior to a screen printer line or directly after a passivation layer deposition tool. Alternatively, it can be combined with a high-speed automation system and operated as a stand-alone tool.
The ILM-2 system from Innolas (above), for example, can be adjusted for an output of between 1,600 and 3,600 wafers per hour at an uptime of >96%. The ILM-2 has the option to use different laser sources according to the detailed process requirements.
Laser contact opening process
The laser contact opening process (LCO) opens the passivation coating of PERC solar cells by a laser lift off process. A local back surface field (BSF) and rear contacts are formed by controlling the interaction of the laser beam and the Si material at high process speed. The optimized laser and optical parameters of the system together with a new innovative dash pattern layout lead to a higher efficiency of solar cells compared to existing state of the art PERC process schemes.
Laser machining can achieve a throughput of 3600 solar cells per hour.
Previous laser processes suffered from low throughput and high cost due to limited process speeds as well as imperfect passivation layer openings. Today's PV manufacturing platforms, such as the ILM-2, comprise an improved laser and optical setup that allows control of the contact opening at the highest process speed. It enables a dashed line pattern layout enhancing the cell efficiency.
Cell cutting reduces losses
Reducing waste during the manufacturing process is another way to the costs of solar power overall. The reduction of the cell-to-module losses during module assembly presents another strategy that allows a significant increase of PV module power output by integrating only one additional process step.
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 can significantly affect later module efficiency.
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.
In a 6-month real-world outdoor measurement 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 cell-to-module losses.
Written by by Ernst Hartmannsgruber, Sales and Marketing Director at Innolas