Photocurrent response time

It is believed that surface localized electron-hole pairs produced under light in SC nanoparticles participate in photo-induced processes of charge transfer between nanoparticles. These processes most probably of quantum tunnel type determine photoconductivity of composite films containing SC nanoparticles in a dielectric matrix. The photocurrent response time in this case should correspond to the lifetime ip of such pairs, which is of the order nanosecond and even more [6]. This rather long ip makes photo-induced tunnel current in composite film possible. 

Within the potential range where Ru(bpy)3 remains in the aqueous phase, photocurrent responses are clearly observed with a slow rising time of the order of 10 s as shown in Fig. 14(a). According to the convention employed by these authors, positive currents correspond to the transfer of a negative charge from water to DCE. No photoresponses were observed in the absence of either the dye in the aqueous phase or TCNQ in DCE. Further analysis of the interfacial behavior of the product TCNQ revealed that the ion transfer occurred outside of the polarizable window [cf. Fig. 14(d)], confirming that these photoresponses are not affected by coupled ion-transfer processes. An earlier report also showed photoeffects for the photoreduction of the viologen under similar conditions [131]. 

Electronic Methods.—The response time of radiation detectors such as the photocell may be as low as io sec. but for high speed scanning a limit is set by the statistical fluctuations in the photocurrent. The relative fluctuations Ff are given by... 

In this section, we briefly consider the response of nanocrystalline semiconductor-electrolyte interfaces to either pulsed or periodic photoexcitation. Several points are worthy of note in this respect (a) the photocurrent rise-time in response to an illumination step is nonlinear. Further, the response is faster when the light intensity is higher, (b) The decay profiles exhibit features on rather slow time-scales extending up to several seconds, (c) The photocurrent decay transients exhibit a peaking behavior. The time at which this peak occurs varies with the square of the film thickness, d. (d) A similar pattern is also seen in IMPS data where the transit time, r, is seen to be proportional to d. ... 

Since it is important to address this issue at the earliest times following photoexcitation, measurements of transient photoconductivity in the picosecond to nanosecond regime were carried out [145,146,201,202], In response to an ultrafast light pulse (duration 25 ps), there is an initial fast photocurrent response with decay time of about 100 ps followed by a slower component with... 

To assess the suitability of the nanocrystals as optically active centers for their incorporation into optoelectronic devices, a monolayer of particles was deposited onto mercaptopropionic acid derivatized ITO substrates. Their photoelectrochemical response was assessed under conditions of illumination using LED whose peak intensity (A.pk = 470 nm) is greater than the calculated bandgap. As can be seen from the inset of Fig. 2, upon illumination of the SnS-derivatized electrode the current is observed to quickly increase and remain relatively constant during the illumination time, here 20 s, and upon switching off of the LED the current returns to its preillumination value. This photocurrent response profile is reproducible over many cycles (in a number of trials for periods in excess of an hour). An average photocurrent (current under illumination minus background current) for a number of similarly prepared electrodes has yielded values of between 6 and 8 nA cm . ... 

Figure 30. Time-dependent photocurrent response for a ITO/poly-86/Au cell with a Hg—Xe lamp (4.5 mW/cm, OV-bias).

A plot of the time constant for the photocurrent response to a step in the bias potential vs. resistance for the model system is given in Figure 7. The potential steps were kept relatively small, from pip - 50mV to pip + 50 mV, to stay in a region where photocurrent changes approximately linearly with potential across the semicon-... 

Figure 7. Time constant of sensor photocurrent response to step in bias potential vs. resistance when the lipid bilayer is replaced with standard electrical components. Cm = 1.5 nF.

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