Dye-Sensitized Solar Cells Based on Oriented TiO₂ Nanotube Arrays: Transport, Trapping, and Transfer of Electrons

Abstract

Dye-sensitized solar cells fabricated using ordered arrays of titania nanotubes (tube lengths 5, 10, and 20 microm) grown on titanium have been characterized by a range of experimental methods. The collection efficiency for photoinjected electrons in the cells is close to 100% under short circuit conditions, even for a 20 microm thick nanotube array. Transport, trapping, and back transfer of electrons in the nanotube cells have been studied in detail by a range of complementary experimental techniques. Analysis of the experimental results has shown that the electron diffusion length (which depends on the diffusion coefficient and lifetime of the photoinjected electrons) is of the order of 100 microm in the titania nanotube cells. This is consistent with the observation that the collection efficiency for electrons is close to 100%, even for the thickest (20 microm) nanotube films used in the study. The study revealed a substantial discrepancy between the shapes of the electron trap distributions measured experimentally using charge extraction techniques and those inferred indirectly from transient current and voltage measurements. The discrepancy is resolved by introduction of a numerical factor to account for non-ideal thermodynamic behavior of free electrons in the nanostructured titania.

Electron Transport in Dye-Sensitized Solar Cells Based on ZnO Nanotubes: Evidence for Highly Efficient Charge Collection and Exceptionally Rapid Dynamics

“…For nt-ZnO R is 0.06, yielding a T 0 ∼ 5000 K. Interestingly, similar values of T 0 (5500 K) have recently been reported for TiO 2 nanotube photoanodes. 25,35 Further interpretation of the capacitance of ZnO nanotube arrays is not straightforward, since the active layer is relatively thin and the degree of doping is unknown. For example, one can not fully discard the possibility that a depletion layer is formed in the surface of the ZnO layer as observed in thicker ZnO pillars.…”

Facile Synthesis of Highly Efficient One-Dimensional Plasmonic Photocatalysts through Ag@Cu2O Core–Shell Heteronanowires

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] An important application of 1D nanostructures is in photocatalytic degradation of organic pollutants, and recent decades have witnessed an exponential growth in the design and fabrication of highly efficient and active photocatalysts due to the growing awareness of environmental pollution issues and safety considerations. Various semiconducting nano-photocatalysts, especially metal oxide semiconductors such as TiO 2 and ZnO, are being extensively investigated.…”

Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO4

“…A possible reason for the contrary conclusions is that the reaction selectivity on different facets is also affected by adsorption/desorption behaviours of reactant molecules and reaction intermediates on different facets 33,34 . A semiconductor with 1-D nanostructure and different crystal orientations has been proposed to lead to more efficient separation of electrons and holes with respect to the bulk material to explain the increased solar energy conversion efficiency [35][36][37][38][39] , though experimental evidence on the separation of electrons and holes on different crystal facets remains elusive.…”