Characterization of solid-state dye-sensitized solar cells utilizing high absorption coefficient metal-free organic dyes
ABSTRACT Solid-state dye-sensitized solar cells were fabricated using the organic hole-transporting medium (HTM) 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), and three organic indoline-based sensitizer dyes with high molar extinction coefficients. The cells were characterized by several techniques, including spectral response measurements, photovoltage decay transients, intensity modulated photovoltage spectroscopy (IMVS), and charge extraction. The differences in apparent electron lifetime observed for cells fabricated using the three dyes are attributed in part to changes in the surface dipole potential at the TiO2/spiro-MeOTAD interface, which shift the TiO2 conduction band energy relative to the Fermi level of the HTM. These energy shifts influence both the open circuit voltage (as a result of changes in free electron density) and the short circuit current (as a consequence of changes in the overlap between the dye LUMO level and the conduction band). A self-consistent approach was used to derive the positions of the conduction band relative to the spiro-MeOTAD redox Fermi level for cells fabricated using the three dyes. The analysis also provided estimates of the free electron lifetime in spiro-MeOTAD cells. In order to evaluate the possible contribution of the adsorbed dyes to the observed changes in surface dipole potential, their dipole moments were estimated using ab initio density functional theory (DFT) calculations. Comparison of the calculated dipole contributions with the experimentally measured shifts in conduction band energy revealed that other factors such as proton adsorption may be predominant in determining the surface dipole potential.
SourceAvailable from: Jianjian Lin[Show abstract] [Hide abstract]
ABSTRACT: Three-dimensional (3D) hierarchical nanoscale architectures comprised of building blocks, with specifically engineered morphologies, are expected to play important roles in the fabrication of 'next generation' microelectronic and optoelectronic devices due to their high surface-to-volume ratio as well as opto-electronic properties. Herein, a series of well-defined 3D hierarchical rutile TiO 2 architectures (HRT) were successfully prepared using a facile hydrothermal method without any surfactant or template, simply by changing the concentration of hydrochloric acid used in the synthesis. The production of these materials provides, to the best of our knowledge, the first identified example of a ledgewise growth mechanism in a rutile TiO 2 structure. Also for the first time, a Dye-sensitized Solar Cell (DSC) combining a HRT is reported in conjunction with a high-extinction-coefficient metal-free organic sensitizer (D149), achieving a conversion efficiency of 5.5%, which is superior to ones employing P25 (4.5%), comparable to state-of-the-art commercial transparent titania anatase paste (5.8%). Further to this, an overall conversion efficiency 8.6% was achieved when HRT was used as the light scattering layer, a considerable improvement over the commercial transparent/reflector titania anatase paste (7.6%), a significantly smaller gap in performance than has been seen previously. T he design and growth of inorganic nanostructures with well-controlled sizes and morphologies have been the focus of intensive research in recent years due to their wide ranging applications. TiO 2 is a functional material used in many ways, such as in photocatalysis, photoelectrochemical solar energy conversion 1 , and Li-ion batteries 2 . The properties and applications of TiO 2 are generally correlated to crystal phase, dimensions, morphology, and surface properties. As such, rationally designed and controlled nanostructured TiO 2 has attracted great interest 3,4Scientific Reports 08/2014; 4. DOI:10.1038/srep05769 · 5.08 Impact Factor
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ABSTRACT: A ruthenium polypyridyl dye containing a hexasulfanyl-styryl modified bipyridyl group as ancillary ligand, coded TG6, is investigated as a sensitizer for ZnO-based dye-sensitized solar cells (DSSCs). The advantages of this dye are a broad wavelength absorption spectrum, a large loading in ZnO photoelectrodes, a significantly larger extinction coefficient compared to more classical Ru-polypyridyl dyes and the formation of less agglomerate in the pores of the ZnO layers. TG6 has been used to sensitize ZnO nanorod particle layers of high structural quality and ZnO layers made of sub-micrometer spheres composed of aggregated nanocristallites and that develop an internal surface area. The latter are highly light-scattering in the visible wavelength region but more difficult to sensitize correctly. The TG6 dye has been compared with the metal-free D149 dye and has been shown more efficient photoconversion. The best performances have been obtained by combining TG6 with the nanorod layer, the optimal power conversion efficiency being measured at 5.30% in that case. The cells have been investigated by impedance spectroscopy over a large applied voltage range. We especially show that the sub-micrometer sphere layers exhibit a less conductivity and a less charge collection efficiency as compared to the nanorod particle ones.ACS Applied Materials & Interfaces 12/2014; DOI:10.1021/am5068645 · 5.90 Impact Factor
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ABSTRACT: The photo behaviour of indoline dye D149 on different metal oxide nanoparticles in functioning solar cells is investigated by time-resolved studies in the time range from 100 fs to several ns. The cells are also characterized by standard photovoltaic measurements. The electron injection is found to occur on the time scales from <200 fs to several tens of ps. Locally excited (LE) and charge transfer (CT) excited states of the dye are identified to participate in the electron injection and dye deactivation mechanisms. The dependence of the ultrafast dynamics on the coadsorbent concentration and energy density of the pump pulse indicates the important role of excited state self-quenching. A decrease in the photocurrent of the cells upon aging (very fast for ZnO and slower for TiO2 nanoparticles) is found to be correlated with the transient absorption kinetics, with a probable explanation suggested as electrolyte-induced dye rearrangement and aggregate formation.Dyes and Pigments 02/2015; 113:692-701. DOI:10.1016/j.dyepig.2014.10.008 · 3.47 Impact Factor