Researchers Claim Advance in Si Quantum Dot PV Cell

Mar 11, 2010 21:44 Tetsuo Nozawa, Nikkei Electronics

A research group at the Tokyo Institute of Technology drastically improved a photovoltaic (PV) cell based on silicon quantum dots in terms of the open voltage (Voc) and the form factor (FF) value of current-voltage (I-V) characteristics.

The research group, which is led by Makoto Konagai, professor at the university, announced the improvement at a press conference of the Japan Society of Applied Physics March 10, 2010.

A quantum dot is a granular semiconductor whose diameter is about 10nm. A bandgap appears where the semiconductor exists, and it looks like a well shaft. The size of the bandgap can be controlled by changing the particle diameter, making it easy to constitute a multi-junction PV cell.

The research group has been engaged in the research of a PV cell element consisting of silicon quantum dots. The group employed silicon to use the plasma CVD method, which is suited for volume production. However, it has been struggling to achieve expected power generation properties.

This time, the group announced that it has developed an element with a Voc of 518mV and an FF value of 0.51 by adding oxygen to the amorphous silicon carbide (SiC) layer around silicon quantum dots to prevent the crystallization of SiC. Until now, the highest Voc of a silicon quantum dot PV cell has been 492mV, which was announced by a research group led by professor M Green at New South Wales University in Australia.

"We are aiming at the Voc of 700 to 1,000mV," the group at the Tokyo Institute of Technology said.

Also, the research group drastically enhanced the FF value from 0.25 to 0.51. Except for the short-circuit current (Isc), which is as small as 0.338mA/cm², the I-V curve looks like that of a normal PV cell.

"The Isc is small because the current is leaked to the n-type crystalline silicon layer, which is used in place of a transparent electrode," the group said.

The details of the PV cell will be presented at the 57th Spring Meeting, 2010 of the Japan Society of Applied Science, which will take place from March 17 to 20, 2010, at Tokai University.

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