Mitsubishi Electric Corporation (OTC:MIELY) announced on May 31 its achievement of a world record photoelectric conversion efficiency rate of 18.0% in a 150mm square practical use multi-crystalline silicon solar cell, an improvement of 1.2% over their previous models.
They claimed to have achieved the world’s highest conversion efficiency rate of 18.0% by adding a low reflectivity surface texture on the multi-crystalline silicon as well as developing a process to print electrodes on the surface of the silicon (metallization) and reducing shade loss of front grid electrodes. In the same surface area as previous products, they have achieved a 7% greater electric output, making it suitable for even smaller installations such as narrow roofs.
In October of last year, Kyocera announced it achieved an efficiency improvement in its polycrystalline solar cells, taking them to 18.5%, although it is not clear when they will commercialize their cell. SunPower claims 22% efficiency, but for monocrystalline solar cells, which have higher efficiency than polycrystaline cells, but are more expensive. SunPower is currently in production with these 22% efficiency cells.
It may be nitpicking to argue over 0.5%, but Mitsubisihi certainly is aware of the Kyocera announcement and it is brazen of them to make this claim. I gather they are using the practical use qualifier to cover themselves as Kyocera has not announced any specific plans to commercialize their cells. In any event it is good to see that efficiencies of commercial solar cells are going up. Continuing on with Mitsubishi's press release.
Main features of cell
1. Increased light absorption using a unique Reactive Ion Etching (RIE) method
Using a nano-sized mask material, the RIE method uses highly reactive ions generated by RF plasma, letting ions precisely etch the target materials. This decreases reflectivity from the texturized surface of the multi-crystalline silicon, increasing the amount of absorbed light.
2. Suppresses reduced electrical performance in crystalline
New metal electrode material reduces metallization time by approximately half that of previous models, and sustains electrical performance of crystalline.
3. Expanded effective electrical output surface area
Using modified screens and front metal electrodes we reduced shading loss of front grid electrodes by 40% compared with our conventional cells.
They will begin introducing this technology into our mass produced photovoltaic modules after the end of 2007.