Automated laser cutter repairs solar cells
The LAZAR system combines two significant solar cell manufacturing improvements with a laser cutting technique that minimises potential shunting of solar cells as well as a corrective step to remove already existing shunts. A thermal camera identifies defective cells that can be cut out, isolated or both to improve the overall efficiency of the solar panel.
In the cutting mode, the user chooses the cutting size from a set of standard solar cells sizes, which are translated to CNC X-Y coordinates along which the laser moves. If the correction mechanism is selected, the solar cell undergoes a thermal scan to locate and evaluate the severity of existing shunts (defects). The diagnostic information is then sent to the main decision unit, which decides whether or not correction will take place. To repair the cell, the laser is focussed on the silver lining on the front face of the solar cell, grooving the silver ﬁngers and electrically isolating the shunted region from the rest of the solar cell.
The team used a commercial laser CNC machine with a simplified architecture as the majority of laser equipment for solar panels are large production systems.
The hardware frame has three metallic orthogonal axes with mounted stepper motors for automated precise smooth motion. The fibre laser choice was made to cut silicon with minimal loss or damage, and power consumption was also a major consideration. The first design was successfully tested to cut commercial standard solar cell sizes and then improved to incorporate the defect correction mechanism using the thermal camera. An alarm system was also added to the control unit for safety.
Laser cutting is widely used today as an efficient alternative to conventional mechanical methods in cutting solar cells. After research, it was found that the solar cells laser cutters only existed as large scale industrial machines. Our proposed design is the first commercial, compact, user-friendly solar cell laser cutting machine. While the fixing of shunts using laser solution was only implemented in research, LAZAR comes as the first automated machine that repairs solar cells by exploiting laser properties such as cutting precision, positional accuracy, improved edge quality and high repeatability.
The correction improved solar cell conversion efficiency by 1.465% after the shunt isolation, effectively fixing solar cells.
While many cutting operations can be completed through three cutting axes, two extra axes may be required when operating on the rear contact sides. Another improvement is to an additional mechanism which evaluates the solar cell electrical performance after cutting and correction operations take place.
The team was a runner up in the recent James Dyson innovation award.