Intensity-modulated photocurrent modulation

The combination of photocurrent measurements with photoinduced microwave conductivity measurements yields, as we have seen [Eqs. (11), (12), and (13)], the interfacial rate constants for minority carrier reactions (kn sr) as well as the surface concentration of photoinduced minority carriers (Aps) (and a series of solid-state parameters of the electrode material). Since light intensity modulation spectroscopy measurements give information on kinetic constants of electrode processes, a combination of this technique with light intensity-modulated microwave measurements should lead to information on kinetic mechanisms, especially very fast ones, which would not be accessible with conventional electrochemical techniques owing to RC restraints. Also, more specific kinetic information may become accessible for example, a distinction between different recombination processes. Potential-modulation MC techniques may, in parallel with potential-modulation electrochemical impedance measurements, provide more detailed information relevant for the interpretation and measurement of interfacial capacitance (see later discus-... 

Combination of Intensity-Modulated Photocurrent and Microwave Spectroscopy... 

Therefore intensity-modulated photocurrent Spectroscopy has been developed by Peter and co-workers as a tool for the analysis of photocurrent responses in the frequency domain.42,43 An optoacoustic coupler is... 

Intensity-modulated photocurrent spectroscopy has been used in combination with microwave reflectivity measurements to investigate hydrogen evolution at a p-type silicon45 and an n-type silicon.46 The measurement of amplitude and phase under harmonic generation of excess carriers, performed by Otaredian47 on silicon wafers in an attempt to separate bulk and surface recombination, should also be mentioned here. 

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... 

The basic experimental arrangements for photocurrent measurements under periodic square and sinusoidal light perturbation are schematically depicted in Fig. 19. In the previous section, we have already discussed experimental results based on chopped light and lock-in detection. This approach is particularly useful for measurement at a single frequency, generally above 5 Hz. At lower frequencies the performance of lock-in amplifier and mechanical choppers diminishes considerably. For rather slow dynamics, DC photocurrent transients employing optical shutters are more advisable. On the other hand, for kinetic studies of the various reaction steps under illumination, intensity modulated photocurrent spectroscopy (IMPS) has proved to be a very powerful approach [132,133,148-156]. For IMPS, the applied potential is kept constant and the light intensity is sinusoid-... 

FIG. 19 Block diagrams for photocurrent measurements with chopped light and lock-in detection (a) as well as for intensity-modulated photocurrent spectroscopy (b). (Adapted from Ref. 85.)... 

Figure 3.19 Intensity-modulated photocurrent spectroscopy, showing (a) the layout of a typical spectrometer, and (b) the response obtained AOM, acousto-optic modulator RE, reference electrode WE, working electrode CE, counter electrode FRA, frequency response analyzer...

Fig. 8.7. Experimental arrangement for intensity modulated photocurrent spectroscopy (IMPS). FRA frequency response analyser. LED light emitting diode.

L. M. Peter, J. Li, R. Peat, H. J. Lewerenz, and J. Stumper, "Frequency Response Analysis of Intensity Modulated Photocurrents at Semiconductor Electrodes," Electrochimica Acta, 35 (1990) 1657-1664. 

G. Oskam, J. C. Schmidt, and P. C. Searson, Electrical properties of n-type (111) Si in aqueous K+FeCCNjs solution. II. Intensity modulated photocurrent spectroscopy, J. Electrochem. Soc. 143, 2538, 1996. 

Investigating electron migration in nanostructured anatase Ti02 films with intensity-modulated photocurrent spectroscopy [288], it was found that, upon illumination, a fraction of the electrons accumulated in the nanostructured film is stored in deep surface states, whereas another fraction resides in the conduction band and is free to move. These data indicate that the average concentration of the excess conduction band electrons equals about one electron per nanoparticle, irrespective of the type of electrode, the film thickness, or the irradiation intensity. 

Kruger J., Plass R., Gratzel M., Cameron P. J. and Peter L. M. (2003), Charge transport and back reaction in solid-state dye-sensitized solar cells a study using intensity-modulated photovoltage and photocurrent spectroscopy , J. Phys. Chem. B 107, 7536-7539. 

Hutton R. S. and Peter L. M. (1992), Surface recombination at the n-Gai Al As-electrolyte interface—a study by intensity-modulated photocurrent spectroscopy , J. Electroanal. Chem. 330, 351-368. 

Peat R. and Peter L. M. (1987), Determination of the electron diffusion length in p-GaP by intensity-modulated photocurrent measurements with an electrolyte contact , Appl. Phys. Lett. 51, 328-330. 

Peter F.M., Li J., Peat R., Lewerenz H. J. and Stumper J. (1990b), Frequency response analysis of intensity-modulated photocurrents at semiconductor electrodes , Electrochim. Acta 35, 1657-1664. 

Peter L. M., Ponomarev E. A. and Fermin D. J. (1997), Intensity-modulated photocurrent spectroscopy reconciliation of phenomenological analysis with multistep electron-transfer mechanisms , J. Electroanal. Chem. All, 79-96. 

Ponomarev E. A. and Peter L.M. (1995), A comparison of intensity-modulated photocurrent spectroscopy and photoelectrochemical impedance spectroscopy in a... 

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