Photocurrent vs. time

FIG. 50 Photocurrent vs. time at —0.6 V for 50-layer MEH-PPV LS films (different time scales). 

Figure 9. Short-circuited photocurrent vs. time for a monolayer of ZnTOAPP (ZnTOAPP.SA, 1 4) directly on a SnOt OTE (0.1U KCl, pH 7.0, 0.05M HSQ, Ns purged)...

Figure 7. Comparison between the experimental photocurrent vs. time profile and the cathodic equivalent of Equation 22 (a) —0.95 V (NHE) (b—facing page,) —1.15 V (NHE) (c—facing page,) —1.36 V (NHE)...

Figure 5. Photocurrent vs. time interferogram of the foam film...

Fig. 21. Short-circuit photocurrent vs. time for bare and polypvrrol-coated n-GaAs electrodes in...

Figure 7 Photocurrent vs. time mterferogram of thinning of the emulsion film of sodium dodecyl sulfate. The photomicrograph depicts...

The exciton migration within aggregates of cyanine dyes and the possibility of oxygen diffusion into the porous dye film result in a bulk generation of photocurrent [80]. Photoholes produced due to the oxidation of excitons by molecular oxygen diffuse to the back contact. The diffusion coefficient of charge carriers in dye layer (Dc) can be evaluated from the potential-step chronoamperometric measurements in the indifferent electrolyte. Considering dye film as a thin-layer cell, the current vs. time dependence can be described as follows [81] ... 

Fig. 105. Plot of photocurrent relaxation time, x, following a ns light pulse vs. total load resistance flload (= Rm + Roul), where ROM = fJ,cries + /iL, showing linearity expected at small values of fl)Dad. Inset shows the plot at values of ftload approaching zero.

Time-resolved measurements of electron transfer times for quantum well photoelectrodes which can be compared with hot electron relaxation times, have not yet been reported. Only some excitation spectra, i.e. photocurrent vs. photon energy for MQWs and single quantum wells (SQWs), have been published so far [2]. In both cases, the photocurrent spectra show distinct structures corresponding to transitions between the hole and electron wells as shown for SQW electrodes in Fig. 9.32. The... 

When Rm is at least three orders of magnitude larger than Ref the fast transient can be considered as almost instantaneous and that term can be eliminated from the expression. Near I pipr HI responds with the same time constant as Vt to a step in bias potential (Equation 8). lo is the measured alternating photocurrent amplitude immediately after distribution of the step in potential across the capacitances. If is the measured alternating photocurrent amplitude after complete dissipation of the potential across the membrane capacitance. When In(If - II ) is plotted vs. time, the slope is equal to -I/12 (Equation 9). can then be calculated from Equation 6. 

Figure 11.4. Double-logarithmic plot of the photocurrent / versus time t at various electric fields for the carbazole trimer (63) (a) 4.6 X 10 V/cm, (b) 2.4 x 10 V/cm, (c) 0.6 x 10 V/cm temperature 303 K. Inset linear plot of /photo vs. time for a field of 4.6 X 10 V/cm.

Figure 5.38 illustrates the experimental setup for water photoelectrolysis measurements with the nanotuhe arrays used as the photoanodes from which oxygen is evolved. The 1-V characteristics of 400 nm long short titania nanotuhe array electrodes, photocurrent density vs. potential, measured in IM KOH electrolyte as a function of anodization hath temperature under UV (320-400 nm, lOOmW/cm ) illumination are shown in Fig. 5.39. The samples were fabricated using a HF electrolyte. At 1.5V the photocurrent density of the 5°C anodized sample is more than three times the value for the sample anodized at 50°C. The lower anodization temperature also increases the slope of the photocurrent—potential characteristic. On seeing the photoresponse of a 10 V 5°C anodized sample to monochromatic 337 nm 2.7 mW/cm illumination, it was found that at high anodic polarization, greater than IV, the quantum efficiency is larger than 90%.

The surface of a carbon electrode was at first coated with a thin film of an anionic polymer such as sodium poly(styrene-sulfonate) 95) or nafion 96) (thickness thousand A) then the cationic Ru(bpy)2+ was adsorbed in the anionic layer electrostatically. The modification was also made by coating water insoluble polymer pendant Ru(bpy)2 + ( ) from its DMF solution 97). These Ru(bpy) +/polymer modified electrode gave a photoresponse in the MV2+ solution with the Pt counter electrode 95-97) The time-current behaviours induced by irradiation and cutoff of the light under argon are shown in Fig. 28. It is interesting to see that the direction of the photocurrent reversed at the electrode potential of ca. 0.4 V (vs. Ag—AgCl) under... 

Fig. 4.9. (a, top) The 8iph/iph vs. v 1 dependence for W03 electrode sensitized by Dye II in monomeric form ( ) partially aggregated by coprecipitation with PD IV (O). The excitation wavelength 560 nm. / = 20 s. The total surface concentration of Dye II 10 8 mol cm 2. Electrolyte 0.25 M Na2S04. (b, bottom) The potential-time programme and corresponding photocurrent-time curves used for x evaluation. Hatched areas indicate the exposure periods. 

Figure 8.27 illustrates the theoretical electron density profiles and photocurrent transients calculated by Solbrand et al. The transients exhibit a maximum at a time fpeak = d2/6D. The inset in Fig. 8.26 shows that a plot of fpeak VS. d2 is linear as predicted (the authors use W rather than d to denote the film thickness), and the slope of the plot gives a value of 1.5 x 10-scm-2s-1 for the electron diffusion coefficient. 

Kontani et al. (1995, 1996) measured hole mobilities of vapor-deposited TiOPc. The transit times were derived from photocurrent transients in double logarithmic representation. In agreement with the work of Ioannidis and cowoikers with ClAlPc, the results showed that the mobilities were strongly dependent on the substrate temperature during the vapor deposition. For substrate temperatures between -160 to 160 C, the room temperature mobility increased from 6.0 x 10-6 to 8.0 x 10-5 cn /Vs. The authors attributed this to an increase in film crystallinity. Films prepared at low temperatures were largely amorphous while those prepared at high temperatures were mainly polyciystalline. 

Kepler et al. (1995) measured electron and hole mobilities of tris(8-hydroxyquinoline)aluminum (Alq). Alq is of interest for electroluminescent devices. The photocurrent transients for both carriers were highly dispersive. Transit times could be resolved only from double logarithmic transients. The electron mobilities were approximately two orders of magnitude higher than hole mobilities. Figure 46 compares the room temperature electron and hole mobilities. The dashed line represents electron mobilities reported by Hosokawa et al. (1994). At 4 x 105 V/cm, the electron and hole mobilities are 1.4 x 10-6 cm2/Vs and 2.0 x 10-8 cm2 Vs. The activation energy for the electron mobility was reported as 0.56 eV. Later results of Lin et al. (1996) were in excellent agreement with the hole mobilities reported by Kepler et al. 

Figure 26. Transient photocurrent data plotted in semilogarithmic format for n-WSe2 in 1.0 M KI at —0.30 V (vs. SCE) showing the rapid decay component at short times. (Reproduced with permission from Ref. [113].)...

Figure 6.11 Photocurrent, liphl as a function of time t for the laser-induced deposition of Zn in the system p-type Si (100)/O.l M ZnS04, at A = - 1.15V vs. SCE, A = 647 nm, power density 110 mWcm" 16.1221.

Fig. 43. Complex plane IMPS plot for 14 micron thick nanoporous GaP layer on n-GaP under depletion conditions (potential 2.5V vs. SCE) in acid electrolyte (pH = 1.0). Illumination from the electrolyte side 350 nm). The steady state photocurrent efficiency is unity. The transit time r d) derived from a> i is 5 10-3 s ...

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