Nano-Structures and Solar Cells

The foreseeable depletion of fossil fuel and the global warming caused by the carbon dioxide had led to the increasing attention of alternative renewable energy, especially photovoltaic. Therefore, crystalline Si-PV devices are quickly spreading. Unfortunately, the large consumption of Si materials hinders their vast applications. Many efforts have been switched to developing thin-film PV devices. In this talk, we will discuss the use of nano-structured semiconductors that enable the fabrication of thin-film solar cells with improved efficiency. Two types of such thin-film solar cells will be discussed, including the semiconductor-oxide sandwiched organic solar cells and Si nanowire/organic composite solar cells.
In the semiconductor-oxide sandwiched organic solar cells, we will discuss the functions of the semiconductor oxides that sandwich the organic active materials. The semiconductor oxides serve as the electron/hole blocking layers as their conduction band and valence band are properly aligned with the LUMO level and the HOMO level of the organic blends. In addition, the semiconductor oxide can better protect the organic active materials from the interaction with moisture or oxygen. Furthermore, one of the oxide layers also works as the optical spacer to increase light absorption in the organic materials. Our particular technology of using solution process to deposit those layers for sandwiched structure offers the possibility of very low-cost production of organic solar cells in the future.
For the solar cells using Si nanowires, we will discuss the combination of the nanowires with the PEDOT:PSS organic materials to form p-n junction. Compared to the planar structure of Si/organic solar cells, the Si nanowires increase the light absorption and carrier collection. Then we will particularly describe the technique of nanowire transfer technology for the possibility of fabricating Si nanowire thin-film solar cells to lower the material cost.