Laser Grooved Buried Contacts

LASER GROOVED BURIED CONTACTS

The opaque front side contacts on a conventional crystalline solar cell prevent light from falling on a significant fraction of the (potentially) active surface area. It is possible to bury the contacts in the surface of the silcon, reducing the obscuration area. 

Laser Grooved Buried Contacts (LGBC) is a technique to reduce front-side shadowing by fingers and busbars. A laser is used to cut grooves are made in the wafer surface. The silicon is doped n++ below the grooves. Metal is selectively plated in the grooves by electroless deposition (in place of the regular screen-printed silver paste).
Metallised fingers are only 25-30mm wide (compared to 90-150mm wide for screen printed fingers): reduced shadowing, larger open area
Fingers have good conductivity, low contact resistance and low contact recombination.
An IR or green ns-pulsed laser is appropriate for this application
Throughput of 300+ wafers per MSV-Wx module per hour is possible

 A 1um laser is used to generate 20-30um wide and deep trenches on ~ 2-3mm pitch. Heavy doping is generated in the region of these trenches which are subsequently filled with metal. The relatively deep and narrow trench gives a good contact area with a small surface area, reducing obscuration. Additionally, this type of contacting scheme also has electrical advantages leading to very high efficiency solar cells. LGBC is often used with concentrator PV cells.

For generation of LGBC a 1um laser is favoured, the laser head is kept stationary and the wafer positioned by an (x,y) stage. Such control of stages, combined with alignment by vision systems is a key M-Solv strength.