Enhanced Electron Collection Efficiency in Dye-Sensitized Solar Cells Based on Nanostructured TiO₂ Hollow Fibers

Abstract

Nanostructured TiO 2 hollow fibers have been prepared using natural cellulose fibers as a template. This cheap and easily processed material was used to produce highly porous photoanodes incorporated in dye-sensitized solar cells and exhibited remarkably enhanced electron transport properties compared to mesoscopic films made of spherical nanoparticles. Photoinjected electron lifetime, in particular, was multiplied by 3-4 in the fiber morphology, while the electron transport rate within the fibrous photoanaode was doubled. A nearly quantitative absorbed photon-to-electrical current conversion yield exceeding 95% was achieved upon excitation at 550 nm and a photovoltaic power conversion efficiency of 7.2% reached under simulated AM 1.5 (100 mW cm -2 ) solar illumination.

Shape-tailored TiO2 nanocrystals with synergic peculiarities as building blocks for highly efficient multi-stack dye solar cells

“…However, modest PCE values have been reported to date, mainly because of the reduced internal surface area offered by photoanodes which employ nanorods or nanowires with a mean size larger than 100 nm 12,22,23 and/or the severe degradation of the original structural-morphological features of the selected anisotropic TiO 2 nanocrystals upon sintering.…”

Investigating New Materials and Architectures for Grätzel Cells

“…This process repeats, immensely increasing a photon's chance of interacting with dye. As opposed to the 1% light harvesting efficiency seen on a flat ETL, recent papers have achieved over 95% harvesting of incoming photons (Ghadiri et al, 2010). Mesoporous TiO 2 layers are effective because they allow for very dense dye adsorption, and increase the path length of light inside their porous structure.…”

“…The implication is that rough or broken TiO 2 films can still produce perfectly functional Grätzel cells. Limiting recombination is key for a solar cell -as discussed in the introduction, though open-circuit voltage (V oc ) is primarily determined by the energy difference between ETL Fermi energy upon illumination and HTL oxidation potential (Nernst potential in the case of a liquid electrolyte redox couple), recombination detracts from this value significantly (Ghadiri et al, 2010;Li et al, 2011;Peng et al, 2004;). Thus, the majority of recombination in a Grätzel cell is due to interactions between electrons in the TiO 2 semiconductor and anode material, and holes in the HTL.…”

“…the ratio of observed efficiency to theoretical max efficiency). The fill factor for the first DSSC was 0.684 (O'Regan & Grätzel, 1991), and recent cells attain values of up to 0.75 (Ghadiri et al, 2010). To give a comparison, the fill factor for an average commercial silicon cell is ~0.83, while some advanced inorganic thin-film cells have achieved almost 0.90 (Green, 1981; PVEducation.org).…”

“…One of the major detractors of voltage is recombination, the process by which excited electrons and holes recombine, giving off energy as photons. This not only detracts from current, since it means fewer electrons doing useful work, but it also lowers the observed voltage (Ghadiri et al, 2010;Ito et al, 2008;Saito et al, 2004). Because recombination causes fewer electrons to reach the anode, the Fermi energy of electrons at the anode will be decreased.…”