Infoscience

Journal article

Investigation on the dynamics of electron transport and recombination in TiO2 nanotube/nanoparticle composite electrodes for dye-sensitized solar cells

In this work, the fabrication and characterization are reported of dye-sensitized solar cells based on TiO2 nanotube/nanoparticle (NT/NP) composite electrodes. TiO2 nanotubes were prepd. by anodization of Ti foil in an org. electrolyte. The nanotubes were chem. sepd. from the foil, ground and added to a TiO2 nanoparticle paste, from which composite NT/NP electrodes were fabricated. In the composite TiO2 films the nanotubes existed in bundles with a length of a few micrometers. By optimizing the amt. of NT in the paste, dye-sensitized solar cells with an efficiency of 5.6% were obtained, a 10% improvement in comparison to solar cells with pure NP electrodes. By increasing the fraction of NT in the electrode the c.d. increased by 20% (from 11.1-13.3 mA cm-2), but the open circuit voltage decreased from 0.78-0.73 V. Electron transport, lifetime and extn. studies were performed to investigate this behavior. A higher fraction of NT in the paste led to more and deeper traps in the resulting composite electrodes. Nevertheless, faster electron transport under short-circuit conditions was found with increased NT content, but the electron lifetime was not improved. The electron diffusion length calcd. for short-circuit conditions was increased 3-fold in composite electrodes with an optimized NT fraction. The charge collection efficiency was more than 90% over a wide range of light intensities, leading to improved solar cell performance.

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