Fabrication and Characterization of Dye-sensitized Solar Cells based on Anodic Titanium Oxide Nanotube Arrays Sensitized with Heteroleptic Ruthenium Dyes

Abstract

Anodic self-organized titania nanotube (TNT) arrays have a great potential as efficient electron-transport materials for dye-sensitized solar cells (DSSC). Herewith we report the photovoltaic and kinetic investigations for a series of heteroleptic ruthenium complexes (RD16-RD18) sensitized on TNT films for DSSC applications. We found that the RD16 device had an enhanced short-circuit current density (<TEX>$J_{SC}/mAcm^{-2}=15.0$</TEX>) and an efficiency of power conversion (<TEX>${\eta}=7.2%$</TEX>) greater than that of a N719 device (<TEX>${\eta}=7.1%$</TEX>) due to the increasing light-harvesting and the broadened spectral features with thiophene-based ligands. However, the device made of RD17 (adding one more hexyl chain) showed smaller <TEX>$J_{SC}(14.1mAcm^{-2})$</TEX> and poorer <TEX>${\eta}(6.8%)$</TEX> compare to those of RD16 due to smaller amount of dye-loading and less efficient electron injection for the RD17 device than for the RD16 device. For the RD18 dye (adding one more thiophene unit and one more hexyl chain), we found that the device showed even lower <TEX>$J_{SC}(13.2mAcm^{-2}) $</TEX> that led to a poorest device performance (<TEX>${\eta}=6.2%$</TEX>) for the RD18 device. These results are against to those obtained from the same dyes sensitized on <TEX>$TiO_2$</TEX> nanoparticle films and they can be rationalized according to the electron transport kinetics measured using the methods of charge extraction and transient photovoltage decays.