No. 78: The future of solar cell (August 30, 2011)

Currently, silicon solar cell and compound solar cell are the two major solar cells. Silicon solar cells are produced by Sharp, Kyocera, Mitsubishi Electric, and Sanyo Electric. There are two kinds of silicon solar cells: crystalline silicon cell and amorphous silicon cell. The former provides high conversion efficiency between 15-20%, but it is costly. The latter is reasonable in price and easy to mass produce, but its conversion efficiency is about 9%. Compound solar cells are produced by Honda and Showa Shell Sekiyu. They have the ability to use lights of various wavelengths rather effectively, but they need rare metals.

The solar cell has been increasing the performance thanks to the improvement of its materials and structure. For example, Sanyo Electric’s “HIT”, made up of crystalline silicon cell and amorphous silicon cell, provides conversion efficiency of 21.6%, the world’s highest level. According to the road map of the development of solar cells drawn by the New Energy and Industrial Technology Development Organization (NEDO), photovoltaic generation cost is scheduled to decrease in incremental steps from 23 yen per kW, 14 yen per kW, and to 7 yen per kW by 2050.

A Toyota Technological Institute professor predicts that the generation cost of silicon solar cell would level off in 15-20 years. The light focusing type that collects lights using lens and mirror and the multilayer type that utilizes lights of different wavelengths will increase the presence. The NEDO and Europe started the joint research on the light focus solar cells in June this year with a view to obtaining the conversion rate of 45%.

The quantum dot type that uses particles of nano meter size is expected to replace the light focusing type in the future. Theoretically, it has the ability to provide the conversion rate of higher than 60%. Bendable organic thin film type that can be produced by applying organic semiconductor materials will follow the quantum dot type in the future. A Tokyo Institute of Technology professor emphasizes the necessity of making steady efforts because the solar cell has the possibility of increasing the performance quite rapidly in a certain stage of research and development.