May 22, 2008
Silicon quantum dot/crystalline silicon solar cells
“Third-generation” thin-film solar cells are targeting significant increases in energy conversion efficiency. One of the research subjects in our group is concentrating on “all-silicon” tandem solar cells because silicon is a non-toxic and abundant material. In these cells high energy bandgap cells are stacked on top of lower-bandgap devices (see figure).
The silicon bandgap is controlled by quantum confinement of carriers in artificial semiconductor quantum dots, which behave like individual atoms. If they are close enough to interact, atomic-like energy levels broaden out into bands analogous to the conduction and valence bands of a bulk semiconductor. This gives rise to an amorphous-type semiconductor material with electrical and optical properties that may be tuned by adjusting the dot size, density and host material.
In a recent paper about quantum dot/crystalline silicon solar cells published in Nanotechnology it was found that silicon quantum dots surrounded by the 2 nm thick insulating oxide matrix with additional phosphorus doping play an important role in carrier transport. An oxide film on crystalline silicon does not show a device property, unless an ultra-thin oxide layer (<3 nm) in a metal–insulator semiconductor solar cell is used. The photo-generated carriers in the silicon quantum dot/silicon device are transported through silicon quantum dots or trap-assisted tunnelling via defects in the SiO2 matrix until carriers reach the device electrodes.
Successful fabrication of the silicon quantum dot/silicon photovoltaic devices is an encouraging step towards the realization of all-silicon tandem solar cells based on silicon quantum dot materials.
About the author
Eun-Chel Cho is a research fellow at the Photovoltaics Centre of Excellence, University of New South Wales. Sangwook Park and Xiaojing Hao are PhD students supervised by Cho and Green. Dengyuan Song is a postdoctoral research fellow. Gavin Conibeer is a deputy director at the Centre. Sang-Cheol Park is a member of research staff in the Samsung Advanced Institute of Technology. Martin A Green is a professor and executive research director in the Centre.