Jun 3, 2011
Solar cell developers combine merits of nanotubes and nanoparticles
The use of TiO2 nanotubes (NTs) and nanoparticles (NPs) in dye-sensitized solar cells (DSSCs) has been widely investigated on an individual basis. Typically, NTs offer a more direct path for electron collection, while NPs provide a larger surface area and higher dye-loading capacity. By combining the merits of NTs and NPs, researchers have demonstrated that it's possible to boost the overall light conversion efficiency of DSSCs by factors of more than 100% when directly compared with bare NT-based devices.
Scientists from the Nano Tech Center at Texas Tech University and the National Renewable Energy Laboratory, both in the US, have teamed up to study TiO2 nanostructured DSSCs. The group used hydrothermal synthesis to modify the surface morphology of the NTs by infiltrating NPs onto the walls of the structure.
TiCl4 aqueous solution was employed as a precursor of TiO2 NPs and penetrates deeply inside the NTs under high pressure in an autoclave at 100 °C. The process ensures that a conformal NP porous layer is deposited on the NT walls from the opening at the top of the tube through to the bottom with high density and uniformity, as confirmed by the secondary electron microscopy (SEM) images.
This infiltration cycle can be repeated to achieve further surface enhancement through layer-by-layer deposition, and reaches saturation after several iterations.
The as-synthesized NPs take full advantage of the inner and outer space available on the NTs, and significantly enhance the available surface area, as demonstrated by more than a doubling in dye-loading capacity.
The mixed NT and NP structure combines the NP advantage of high surface area and increased light harvesting capability with the NT high electron collection efficiency. As a result, overall photon conversion efficiencies of the fabricated DSSCs are improved by factors of 152%, 107% and 49% for 8, 13, and 20 µm long NTs, respectively.
Additional information can be found in the journal Nanotechnology.
About the author
The study was conducted by researchers from the Nano Tech Center at Texas Tech University and the National Renewable Energy Laboratory (NREL), US. The work at Texas Tech was supported by the US Army CERDEC. Xuan Pan is a PhD student, Dr Changhong Chen is a research associate and Dr Zhaoyang Fan is an assistant professor. All three are based in the Department of Electrical and Computer Engineering at Texas Tech University. Dr Kai Zhu is a senior scientist at NREL. One of the research goals of the team is to investigate the properties of nanostructured materials and their applications in photovoltaics.