[PV EXPO] Mitsubishi Develops Solar Cell Using TFT Material

Feb 27, 2009
Tetsuo Nozawa, Nikkei Electronics
Mitsubishi Chemical's new organic thin-film solar cell
Mitsubishi Chemical's new organic thin-film solar cell
[Click to enlarge image]
Models of materials used for the new solar cell (in the front row, from left: fullerene, precursor of BP semiconductor, and BP semiconductor). The model in the left of the back row illustrates the roll-to-roll process to produce the organic thin-film solar cell. The showpiece in the center of the back row indicates the color change that occurs when the BP semiconductor precursor is thermally converted into the BP semiconductor.
Models of materials used for the new solar cell (in the front row, from left: fullerene, precursor of BP semiconductor, and BP semiconductor). The model in the left of the back row illustrates the roll-to-roll process to produce the organic thin-film solar cell. The showpiece in the center of the back row indicates the color change that occurs when the BP semiconductor precursor is thermally converted into the BP semiconductor.
[Click to enlarge image]

Mitsubishi Chemical Corp exhibited an organic thin-film solar cell at the 2nd International Photovoltaic Power Generation Expo (PV Expo 2009).

In order to develop the new solar cell, Mitsubishi Chemical utilized an organic semiconductor material that the company developed for TFTs in 2006. At present, the solar cell has an energy conversion efficiency of 4.9% in the case of a 2mm-square cell.

"We are aiming to achieve a cell conversion efficiency of 10% (module conversion efficiency of 7%) by 2010, and 15% (module conversion efficiency of12%) by 2015," the company said.

Mitsubishi Chemical's organic thin-film solar cell currently uses a fullerene derivative as the n-type material and the company's proprietary material called "benzoporphyrin (BP)" as the p-type. The company developed BP as a material of driver TFTs for electronic paper and OLED in 2006. It decided to apply the material to solar cells because it "happened to discover that its bandgap was the perfect size for solar cells," the company said.

At present, the cell is a single-junction cell with one p-n junction. Mitsubishi Chemical intends to use the single-junction approach until the cell conversion efficiency hits 10%.

"We believe we can achieve a conversion efficiency of 10% with a single-junction cell through the optimization of elemental technologies," the company said. "We will use a tandem solar cell when we try for a cell conversion efficiency of 15%."

In addition to the development of its own solar cells, Mitsubishi Chemical plans to start designing and developing building materials made with other manufacturers' thin-film solar cells in the near future.

"We will tap the market so that it is prepared for the commercialization of our solar cells at any time," the company said.