February 16, 2010

Tokyo, Japan: Mitsubishi Electric Sets New PV Cell Efficiency Records

Mitsubishi Electric has achieved a photoelectric conversion efficiency of 14.8% in a 5mm x 5mm thin-film silicon photovoltaic cell. The thin-film silicon PV cell developed by Mitsubishi Electric has a triple junction structure that utilizes a majority of the solar spectrum for higher efficiency.

Mitsubishi Electric says Multi-junction layers offer an efficient way of raising conversion efficiency in thin-film silicon PV cells because each layer absorbs different wavelengths of sunlight. It is extremely difficult, however, to adjust the characteristics of each layer in the multi-junction structure, so most thin-film silicon PV cells today are only single or double layered.

Mitsubishi Electric, however, says the company has met a technological breakthrough to achieve 14.8% photoelectric conversion efficiency, according to its own evaluation, by using a triple-junction configuration in which the first layer absorbs short wavelengths and the third layer absorbs long wavelengths, thereby enabling the use of a wide solar spectrum from visible light to infrared rays.

Key technologies that help to make this possible include:

.. Semiconductor materials that tune to a particular frequency of the spectrum

.. High-quality film-deposition processing for each layer

.. Texture fabrication applied to transparent electrodes for optimal confinement of sunlight

Mitsubishi Electric has also set two world records for photoelectric conversion efficiency in polycrystalline silicon photovoltaic cells, achieved by reducing resistive loss in the cells. One of the records, which Mitsubishi Electric has now renewed for the third consecutive year, is a 19.3-percent efficiency rating for photoelectric conversion of a practically-sized polycrystalline silicon PV cell of 100 squared centimeters or larger, with the PV cell measuring approximately 15 cm x 15 cm x 200 micrometers. The rating is 0.2 points higher than the company’s previous record of 19.1 percent. The second record, achieved with the same technologies in an ultra-thin polycrystalline silicon PV cell measuring approximately 15 cm x 15 cm x 100 micrometers, is an efficiency rating of 18.1 percent, a 0.7-point improvement over the company’s previous record of 17.4 percent. The conversion efficiency rates have been confirmed by the National Institute of Advanced Industrial Science and Technology (AIST), in Japan.

Mitsubishi Electric also says the company has developed the world’s first technology to maximize output power in photovoltaic (PV) systems by incorporating a new maximum power-point tracking (MPPT) system in PV inverters. The technology, which works with a single PV inverter, achieves the maximum power point even when part of a PV array is hidden by shadow or dust.

Further details about: Mitsubishi Electric