Photovoltage spectroscopy

The prototype DSCs used liquid electrolytes, typically L/I2 in an organic solvent such as propylene carbonate. The electron generation/collection problem in this cell has been discussed analytically with the help of intensity-modulated photocurrent and photovoltage spectroscopy [314]. A particularly challenging issue has been the replacement of the liquid electrolyte with a solid charge-transport material... 

In conclusion, nanorods are a potentially interesting material, but present results still do not allow understanding of whether the nanostructure leads to an improvement of the intrinsic photocatalytic behaviour, or whether other factors (accessible surface area, enhanced adsorption, etc) are responsible for the observed differences. In ZnO nanorods have been shown quite recently by surface photovoltage spectroscopy that the built-in electrical field is the main driving force for the separation of the photogenerated electron-hole pairs.191 This indicates that the nano-order influences the photophysical surface processes after photogeneration of the electron-hole pairs. A similar effect could be expected for Titania nanorods. However, present data do not support this suggestion, mainly due to the absence of adequate photo-physical and -chemical characterization of the materials and surface processes. 

Surface photovoltage spectroscopy (SPS) in Fig. 6.5 was used to determine the surface acidity of JML-1 by measuring transition of electrons between the interface and the surface. The JML-I40 calcined at 550°C exhibited two peaks at 596 nm and 677 nm, whereas the sample without calcination had only one peak at 330 nm. The peak at 330 nm is assigned to the band-band electron transition and those at 596 nm and 677 nm are attributed to the surface-related transitions. The observation of these surface-related transitions indicates the presence of positive charges on the surface of the calcined sample, suggesting that the acidity of JML-1 catalyst is resulted from a large amount of SZ acidic sites on the silica surface. 

Lenzmann F., Krueger J., Burnside S., Brooks K., Gratzel M., Gal D., Ruehle S. and Cahen D. (2001), Surface photovoltage spectroscopy of dye-sensitized solar cells with Ti02, Nb205, and SrTiOs nanocrystalline photoanodes indication for electron injection from higher excited dye states , J. Phys. Chem. B 105, 6347-6352. 

Photovoltage spectra are measured at open circuit using chopped light of low intensity. It might appear that an advantage of photovoltage spectroscopy over photocurrent spectroscopy is that no photocorrosion occurs. However, this is not necessarily correct, because anodic photocorrosion in the illuminated areas may be balanced by cathodic reduction of solution species such as oxygen or protons. 

The basic measurement technique for intensity-modulated photovoltage spectroscopy (IMVS) is the same as for IMPS. In principle, IMVS measurements can be made for any constant current condition, but in practice it is usual to make measurements under conditions where the net current is zero. In the case of a photoelectrochemical solar cell, this corresponds to the open-circuit condition, and a high impedance voltage amplifier is used to ensure that a negligible current is drawn from the illuminated device. The output of the voltage amplifier is fed to the FRA, and the remainder of the set up is the same as for IMPS (cf. Fig. 12.26). 

We will distinguish various modes. The techniques most widely used in DSSCs are intensity modulated photocurrent spectroscopy (IMPS) which is, like IPCE, concerned with electron transport under short circuit conditions Intensity modulated photovoltage spectroscopy IMVS, which probes the competition between transport and recombination at open circuit and electrical impedance spectroscopy (EIS), which probes the bias-dependent electrical response, analogous to dark-current transients. Other variants, such as frequency-resolved transmittance, the frequency domain analogs of transient absorption, have been developed [50]. The techniques and... 

G. Schlichthorl, S. Y. Huang, J. Sprague et al.. Band edge movement and recombination kinetics in dye-sensitized nanocrystalline Ti02 solar cells a study by intensity modulated photovoltage spectroscopy, J. Phys. Chem. B 1997, 101(41), 8141-8155. 

Table 5-41. Other spectroscopic methods Multiwavelength analysis, NMR, raman spectroscopy, and surface photovoltage spectroscopy. ...

A cost effective experimental setup for optical modulettion experiments, recently built in our laboratory. Is shown in Fig. 8 (57). Similar setup was recently reported by Tian et al. (58). Experiments performed with this system include photoreflectance (PR), electrolyte electroreflectance (EER), surface photovoltage spectroscopy (SPV), 1st. and 2nd. harmonics photoinduced current-voltage characteristics, spectral response and d.c. current-voltage characteristics. One can switch electronically between experiments and perform any number of techniques without moving the cell or removing the electrode from the electrolyte. A variable neutral... 

A variance that usually appears in the literature as Surtece Photovoltage Spectroscopy (21) uses either a vibrating metal electrode in close proximity to the surface of the semiconductor (Kelvin probe), or a semitransparent metal electrode with a modulated light source to make contact with the semiconductor, and monitors the spectral response of the photovoltage with subband gap illumination. This technique can also be viewed as a non-contact technique that can be used for in situ characterization during device fabrication. 

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