Photocurrents irradiation intensity

Indeed, when using ( )/( ) couples, mass transport limitations are evident from the lack of linearity of the photocurrent versus incident power plots (Fig. 17.33) in the presence of a spacer, the photocurrent density produced by the cobalt-mediated cell is very close to the iodide/iodine system at low irradiation intensities (0.018 and... 

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. 

It is good to realize that we have normalized the irradiation intensity and the photocurrent to particles per second per unit area. In this way the IMPS impedance and admittance are dimensionless. 

Applying the boundary conditions Eqs (48) and (49), the electron transport Eq. (47), can be solved in the frequency domain and the harmonic photocurrent, driven by the harmonic oscillation of the irradiation intensity, reads... 

Figure 6.1 Steady-state photocurrent in an a-As2Se3 sample at 700 nm illumination with approximate intensity of lO photons/cm /s as a function of inverse temperature (curve 1). Also shown is the effect induced hy laser irradiation (A = 633 nm) at 7 = 100 K (curve 2).

Figure 18 Stability test carried out with two sealed DSSCs over 7000 hr of continuous illumination with visible light (polycarbonate 395-nm cutoff filter) at 1000 W/m2 light intensity. The photocurrent and voltage drop measured across an external load resistor of 10 ft are plotted as a function of irradiation time. Cell 1 (solid line) was continuously illuminated at 35°C the same for cell 2 (broken line) except that it was operated for a 700-hr period at 75°C and for 1000 hr at an open circuit. (From Ref. 153.)...

Unprimed, solid-line curves are photocurrent (left-hand scale) and primed, dotted-line curves are emission intensity (right-hand scale) monitored at Kmax 600 nm. Curves A and A result from excitation at 501.7-nm, 23°C Curves B and B from 514.5-nm, 23< C Curves C and C , 49°C and 501.7-nm excitation Curves D and D 86°C, 514.5-nm irradiation. Note that the ordinate of Curve D has been expanded by a factor of 10. Equivalent numbers of 501.7- and 514.5-nm photons were used to excite the photoelectrode in identical geometric configurations. The exposed electrode area is 0.41 cm2, corresponding to an estimated x for 501.7-nm excitation at 23°C and +0.7 V vs. Ag (PRE) of 0.50, uncorrected for solution absorbance and reflectance losses (9). 

The results imply that the diffusion coefficient represents the thermally activated transport of electrons through the particle network. Indeed, these and subsequent studies have been interpreted with models that involve trapping of conduction band electrons or electron hopping between trap sites [158, 159]. An unexpected feature of the diffusion constants reported by Cao et al. is that they are dependent on the incident irradiance. The photocurrent rise times display a power law dependence on light intensity with a slope of -0.7. The data could be simulated if the diffusion constant was assumed to be second order in the electron concentration, D oc n. The molecular origin of this behavior is not well understood and continues to be an active area of study [157, 159]. 

Totally absorbing material is heated by incident irradiation (bolometer). A relationship between intensity and temperature effects exists. Since temperature measurement are very sensitive, this effect is used to determine intensities. Semiconductor detectors either use the internal or external photoeffect [117,118]. In a photodiode, an incident photon causes a photocurrent by charge separation. It can be amplified and depends linearly on the number of incident photons. 

Rg. 4.32. Irradiation set-up in wiiich the photoreaction is controlled by spectroscopy. The intensity of the radiation source is monitored by a physical device measuring photocurrent... 

Vol. 1, Sect. 5.6). Its intensity profile /(homodyne spectroscopy. The different fi equency contributions inside the line profile I (co) interfere, giving rise to beat signals at many different frequencies coi - cok < Aco [929]. If a photodetector is irradiated by the attenuated laser beam, the frequency distribution of the photocurrent (7.68) can be measured with an electronic spectrum analyzer. This yields, according to the discussion above, the spectral profile of the incident light. In the case of narrow spectral linewidths this correlation technique represents the most accurate measurement for line profiles [940]. 

---