| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Monday Sessions |
| Session EN-MoA |
| Session: | Excitonic and Third Generation Solar Cells |
| Presenter: | G. Butail, Rensselaer Polytechnic Institute |
| Authors: | G. Butail, Rensselaer Polytechnic Institute P. Gopal, Rensselaer Polytechnic Institute M. Raddiar, Rensselaer Polytechnic Institute R. Teki, Rensselaer Polytechnic Institute N. Ravishankar, Rensselaer Polytechnic Institute G. Ramanath, Rensselaer Polytechnic Institute |
| Correspondent: | Click to Email |
Titania is a promising photocatalyst used in a variety of photovoltaic, optoelectronic and biofiltering applications. There is great interest in synthesizing high surface area titania nanostructures by inexpensive means for low-cost power generation, among which titania nanotubes offer higher efficiencies because of unidirectional charge transport and low scattering losses. Here we demonstrate, for the first time, the formation of branched titania nanotubes using potentiostatic anodization of titanium thin films. The realization of branched titania nanotubes provides a means to tune the electronic properties of titania and to functionalize them with multi-sized quantum dots and other metallic/semiconducting nanostructures.
Experimental analysis show anodization diameter to be a linear function of applied voltage. We exploit the relationship between the anodization voltage and nanotube diameter to obtain and control the extent of branching and tune branch diameters between 30 to 110 nm. Branching achieved through single step voltage induced anodization offers the added advantage of control of point of branching depending on rate of anodization at each voltage. We also evaluate the morphology and the optical properties of branched titania nanotubes and compare their light-harvesting efficiency with unbranched nanotubes in dye-sensitized solar cells. We specifically compare branched titania nanotubes formed by ramping down the voltage from 60 to 33 V and compare the them with titania nanotubes formed at 60 V and 33 V. Preliminary results show a 33% increase in active surface area of branched titania nanotubes as compared to unbranched nanotubes formed at 60 V which is further confirmed through BET analysis.
Application of straight (unbranched) titania nanotubes for fabrication of dye-sensitized solar cells using a rutheim based dye (N719) results in an efficiency of 0.58±0.2% with short circuit current density of 6.3±1.0 mA/cm2 and fill factor of 22.4±0.2. Use of branched titania nanotubes of same thickness under same conditions reports an efficiency of 1.04±0.1% with increase in short circuit current density to 9.1±0.8 mA/cm2 and a fill factor of 23.7±0.1%. A two-fold enhancement of photovoltaic efficiency of branched samples as compared to straight nanotubes correlates well to the difference in surface area and optical properties of the two structures.