The onset wavelengths of the surface photovoltage (SPV) in dye-sensitized solar cells (DSSCs) with different mesoporous, wide-band gap electron conductor anode materials, viz., TiO 2 (anatase), Nb 2 O 5 (amorphous and crystalline), and SrTiO 3 , using the same Ru bis-bipyridyl dye for all experiments, are different. We find a clear dependence of these onset wavelengths on the conduction band edge energies (E CB ) of these oxides. This is manifested in a blue-shift for cells with Nb 2 O 5 and SrTiO 3 compared to those with TiO 2 . The E CB levels of Nb 2 O 5 and SrTiO 3 are known to be some 200-250 meV closer to the vacuum level than that of our anatase films, while there is no significant difference between the optical absorption spectra of the dye on the various films. We, therefore, suggest that the blue shift is due to electron injection from excited-state dye levels above the LUMO into Nb 2 O 5 and SrTiO 3 . Such injection comes about because, in contrast to what is the case for anatase, the LUMO of the adsorbed dye in the solution is below the E CB of these semiconductors, necessitating the involvement of higher vibrational and/or electronic levels of the dye, with the former being more likely than the latter. While for Nb 2 O 5 hot electron injection has been proposed earlier, on the basis of flash photolysis experiments, this is the first evidence for such ballistic electron-transfer involving SrTiO 3 , a material very similar to anatase but with a significantly smaller electron affinity. Additional features in the SPV spectra of SrTiO 3 and amorphous Nb 2 O 5 (but not in those of crystalline Nb 2 O 5 ) can be understood in terms of hole injection from the dye into the oxide via intraband gap surface states.

Nanocrystalline titanium dioxide colloids have been synthesized using a sol-gel technique followed by growth under hydrothermal conditions in a basic environment at temperatures between 190 and 270 °C. Thin films have been made from aqueous suspensions of these colloids. X-ray analysis showed the colloids to be primarily the anatase crystal phase. Scanning electron microscopy (SEM) revealed a predominantly rodlike particle morphology after growth at lower temperatures and the formation of principally truncated tetragonal or tetrahydral bipyramidal nanocrystallites following growth at higher temperatures. The rodlike particles self-organize into regular cubic arrays with the long axis of the rods aligned perpendicular to the film surface. This self-organization is dependent upon the base used in colloidal synthesis and also upon the dielectric constant of the medium used during film formation.

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350-450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.

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Organic halide salt passivation is considered to be an essential strategy to reduce defects in state-of-the-art perovskite solar cells (PSCs). This strategy, however, suffers from the inevitable formation of in-plane favored two-dimensional (2D) perovskite layers with impaired charge transport, especially under thermal conditions, impeding photovoltaic performance and device scale-up. To overcome this limitation, we studied the energy barrier of 2D perovskite formation from ortho-, meta- and para-isomers of (phenylene)di(ethylammonium) iodide (PDEAI2) that were designed for tailored defect passivation. Treatment with the most sterically hindered ortho-isomer not only prevents the formation of surficial 2D perovskite film, even at elevated temperatures, but also maximizes the passivation effect on both shallow- and deep-level defects. The ensuing PSCs achieve an efficiency of 23.9% with long-term operational stability (over 1000 h). Importantly, a record efficiency of 21.4% for the perovskite module with an active area of 26 cm2 was achieved.

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For the first time we have characterized a micromotor driven by a piezoelectric PZT (PbZr x Ti 1-x O 3 ) thin film. Sputter and sol-gel techniques have been applied for the deposition of the PZT films onto a silicon stator membrane, which was 20 to 30 µm thick and had a diameter of 4 mm. The amplitudes of the membrane deflections have been measured by means of laser interferometry. They are as large as 800 nm/V at the first resonance (26 kHz), and 60 nm/V at 1 Hz. This is one order of magnitude larger than previously reported for a ZnO activated device of similar geometry. The operation of the motor was obtained at 1 to 3 V rms , with speeds of up to 200 rpm at 1.1 V rms and torques of 35 nN·m at 2.5 V rms and 1 mN force between rotor and stator. In comparison with the conceptually identical ZnO version published by Racine et al. this is an improvement by a factor of 3 in speed per volt. Taking into account the linear increase of the torque with the stator vibration frequency, the torque per voltage is a factor two higher. A long time test of 100 h showed no degradation of the motor performance.

The microstructure and preferred orientations of rapid thermally annealed Pb(Zr,,53,Tio.4,)03 films, deposited on Pt/Ti/SiO,/Si electrode/substrates by solution-gel spinning, have been investigated using analytical and high-resolution electron microscopy and X-ray diffraction. The temperature of pyrolysis of the PZT films was found to influence the preferred orientation of the film: lower temperatures (350°C) favored a (111) orientation, whereas higher temperatures (420°C) favored a (100) orientation. Excess Pb was used to control the A-site stoichiometry of the film particularly at the film surface where Pb-deficient crystals could often be observed. The absence of these crystals was shown to be correlated with an improvement in the dielectric response.