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Laser Applications for Silicon Solar Cells

Applications

Lasers for Silicon Photovoltaics

Laser Edge Isolation

A great engineering effort is underway to produce the next generation of Photovoltaics. The goal being to lower the cost per kWh of electricity generated by solar cells to reach a cost parity with conventional fossil fuels. In order to achieve this objective, researchers are investigating new cell manufacturing techniques to both boost efficiency and lower manufacturing costs. Laser systems and novel optical configurations play a vital role in this endeavor.

For Crystalline Silicon (c-Si), there are a number of applications where lasers improve the process quality while also improving throughput. In single-crystal silicon, the ordered nature of the atoms permits efficient electron travel through the material. Pure silicon alone does not generate a sufficient electron flow. Adding impurities into the silicon results in greatly enhance electron mobility. Typically, the silicon is doped with Phosphorous which has an extra electron in its outer valence and is called n-type. To create p-type silicon, a doping process is used to introduce Boron into the silicon. Boron lacks an electron in its outer shell which results in a 'hole'. The P-N junction created allows the silicon to act as a semiconductor with typical efficiencies of 15-18%.

Using lasers with a pulse duration below 30ns minimizes thermal affectation as compared to other long-pulse or continuous wave industrial lasers. Ultraviolet (UV) radiation typically leads to increased absorption in the material as compared to longer wavelengths, which permits higher-resolution processing. The choice of laser and wavelength is application dependant and related to the light absorption behavior of the material and to the geometry required.


Wafer cutting

In many cases, the standard wafer size of a nominal 156mm square is not ideal in for instance, concentrator applications. The wafer is downsized and sectioned to fill the area of the concentrator optics field of view. JPSA has cut Sunpower, Evergreen Solar and Suniva wafers for our customers.

silicon cutting laser silicon cutting

By optimizing the laser wavelength, power and laser beam delivery system, extremely narrow cut widths with high throughput are produced by the SuperScribe™. Typical performance is 7 micron wide cut, 150 microns deep at 150mm/sec with no microcracks. By using high performance motion stages, accuracies of +/-3 microns for the cuts are achieved. Additionally, laser dicing is a non-contact method and may be used to cut through the metal traces.


Laser Edge Isolation

To prevent recombination or current flow towards the edge of the silicon wafer, a trench is created for electrical isolation. Here, a single pass around the perifery of the focussed laser beam creates a groove with high efficiency. Typical dimensions for laser edge isolation are 30-50µm wide and 5-10µm deep.

Laser Edge Isolation Laser Edge Isolation
JPSA systems provide a variable width and a depth to meet the customer's requirements. The high-throughput isolation cuts are performed at rates up to 500mm per second with no recast. The system offers fully integrated debris control via JPSA’s vortex debris control tool. This micro precision scribing technique produces a higher quality product than what is currently available today.

Via Drilling

To minimize losses from shading of the silicon by the front metal traces, techiques such as Metal Wrap Through (MWT) or Emitter Wrap Through (EWT) are employed. For MWT, the Emitter busbar is relocated to the rear of cell with the contact fingers remain on top surface. Laser-drilled vias connect the two. For EWT, all electrical contacts are relocated on rear of cell and requires 10,000 or more laser drilled through holes.


c-silicon via drilling c-silicon via drilling
Laser Applications in Crystalline Silicon

JPSA is involved in a number of production and research applications for advanced laser techniques in c-silicon:


 

Laser Micromachining

JPSA Laser provides excimer, Diode Pumped Solid State (DPSS), and Ultrafast laser micromachining solutions for:

 


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    220 Hackett Hill Rd.
    Manchester, NH 03102 USA
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