Esatto: Technology Chefs Cook up Higher Performance
In addition to market demand and government incentives, extremely advanced technologies are required to support the steadily decreasing price of power generated by photovoltaic (PV) cells. One of the most crucial technologies is the metallization on the two sides of the wafer to conduct the electrons, that is, electric power, out of the cell. This is mostly done with screen printing, where a conductive paste is forced through the openings of a fabric (called a screen) to establish contact with the wafer.
In principle, screen printed wires are designed and realized to achieve a very low electrical resistance to allow the current to flow more freely (exactly as happens with a water duct: it is easier for water to flow through a larger duct than through a narrower one). However, large metal wires occupy more area on the front of the wafer, and since they are made with silver, which is not transparent to light, part of the cell is shadowed by the metal from the sun, thus reducing the amount of electricity produced. The solution is apparently easy: very thin but very tall wires preserve the current-carrying capacity while reducing the shadows cast on the cell surface. Unfortunately this is not easy to do with standard screen printing equipment.
Now, researchers in Applied Materials’ Baccini group have developed a method that allows printing two or more layers of silver paste one on top of each other. This method uses a technology called Esatto. Simply stated, Esatto technology allows printing a layer of any material on top of any other with high accuracy and reliability. Sounds easy? Now, think about doing this on 1,500 PV cells per hour, 24/7, and with 15 micron alignment error margin — at the most. To achieve such precision, Esatto technology is a blend of state-of-the-art screen printing equipment, high precision mechanical parts, dedicated vision systems, and software algorithms. Not just that, obtaining the desired result requires the choice of the “right” paste and of the “right” screen. Read, Applied Materials Introduces Multiple Printing Capability for Producing Higher Efficiency Solar Cells news release to learn more.
Researchers are working as chefs in controlling the process by choosing and tuning all the technological ingredients, but the result is amazing. Tall but thin lines are generated with unprecedented repeatability and accuracy. Thanks to this technology, cell manufacturers are squeezing more power from their cells: for example, cell efficiency can rise from 16% (typical for a mainstream multi-crystalline solar cell) to 16.5%. And, Esatto technology can be used to implement other enhanced solutions, like emerging “selective emitters.” Stay tuned.