SummaryDye-sensitized solar cells (DSCs) provide a promising third-generation photovoltaic concept based on the spectral sensitization of a wide-bandgap metal oxide. Although the nanocrystalline TiO2 photoelectrode of a DSC consists of sintered nanoparticles, there are few studies on the nanoscale properties. We focus on the microscopic work function and surface photovoltage (SPV) determination of TiO2 photoelectrodes using Kelvin probe force microscopy in combination with a tunable illumination system. A comparison of the surface potentials for TiO2 photoelectrodes sensitized with two different dyes, i.e., the standard dye N719 and a copper(I) bis(imine) complex, reveals an inverse orientation of the surface dipole. A higher surface potential was determined for an N719 photoelectrode. The surface potential increase due to the surface dipole correlates with a higher DSC performance. Concluding from this, microscopic surface potential variations, attributed to the complex nanostructure of the photoelectrode, influence the DSC performance. For both bare and sensitized TiO2 photoelectrodes, the measurements reveal microscopic inhomogeneities of more than 100 mV in the work function and show recombination time differences at different locations. The bandgap of 3.2 eV, determined by SPV spectroscopy, remained constant throughout the TiO2 layer. The effect of the built-in potential on the DSC performance at the TiO2/SnO2:F interface, investigated on a nanometer scale by KPFM measurements under visible light illumination, has not been resolved so far.

Several Scanning Probe Microscopy (SPM) methods allow to image dopant profiles in a range from 10 14 cm-3 to 10 19 cm-3 on semiconducting samples. In our work we present Scanning Capacitance Force Microscopy (SCFM) and Kelvin Probe Force Microscopy (KPFM) experiments performed on cross sections of silicon (Si) and silicon carbide (SiC) power devices and epitaxially grown calibration layers. The KPFM signals show under illumination a reduced influence on surface defect states. In addition results from numerical simulation of these microscope methods are discussed.

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Sensitized mesoporous titania is of increasing interest for catalysis and photovoltaic devices such as dye-sensitized solar cells (DSCs). For photovoltaic applications, the catalytic properties of TiO2 can cause degradation of the dyes during device fabrication. This is especially the case if natural sensitizers are used. We addressed this issue by fabrication of carotenoic acid sensitized solar cells under inert and ambient assembly conditions. The DSCs were investigated by currentvoltage and quantum efficiency measurements. Further characterization of the cells was made using impedance spectroscopy. The conversion efficiency of the DSCs prepared under inert conditions improved by at least 25% and the devices showed an enhanced reproducibility. The improvement of the DSCs correlated with the conversion efficiency of the sensitizers under inert conditions. We conclude that the photocatalytic bleaching depends on the electron injection efficiency of the sensitizer. Hence carotenoic acids support their own degradation. However, the photocatalytic decomposition of the sensitizers can be avoided by fabrication of the DSCs under inert conditions.