Mitsubishi Electric announced it has achieved a photoelectric conversion efficiency rate of 18.0% in a 150mm square practical use multi-crystalline silicon solar cell, an improvement of 1.2% over previous models and the world’s highest rate to date. The company plans to present its technology at the Fukuoka 17th International Photovoltaic Science and Engineering Conference in December 2007.
To achieve the 18% rate, Mitsubishi added a low reflectivity surface texture on the multi-crystalline silicon, developed a process to print electrodes on the surface of the silicon (metallization) and reduced shade loss of the front grid electrodes. In the same surface area as previous products, the company achieved a 7% greater electric output, making the new cells suitable for small installations such as narrow roofs.
Main features of the cell include:
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. This process is based in part on the result of the NEDO (New Energy and Industrial Technology Development Organization) project for R&D of innovative next-generation photovoltaic system technology.
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.
Expanded effective electrical output surface area. Using modified screens and front metal electrodes, Mitsubishi reduced shading loss of front grid electrodes by 40% compared with its conventional cells.
The company will begin introducing this technology into mass-produced photovoltaic modules after the end of 2007. Pairing this with Mitsubishi’s power module, which has the industry’s highest energy conversion efficiency (PV-PN04F: 95.5%, PV-PN06F: 95.0% as of 31 May 2007) will increase output of solar power systems.