Photocurrent, light induced

Mackor, A., Blasse, G. 1981. Visible-light induced photocurrents in SrTiOj-LaCiOj single crystalline electrodes. Chem Phys Lett 77 6-8. 

Taking a general view of the above studies, we note that Chl-coated metal (platinum) electrodes commonly function as photocathodes in acidic solutions, although the photocurrent effcien-cies tend to be lower compared to systems employing semiconductors. This cathodic photoresponse may arise from a p-type photoconduc-tive nature of a solid Chi layer and/or formation of a contact barrier at the metal-Chl interface which contributes to light-induced carrier separation and leads to photocurrent generation. 

Electroreflectance spectra were measured for n-CdSe in the liquid junction configuration, and variations of the lineshape as a function of potential were observed. As the potential was reduced below the flatband potential, the electroreflectance signals changed sign. The potential at which this change occurs correlates well with the turn-on potential for light-induced photocurrent and with the intercept of the Mott-Schottky plot. 

Recently, a new type of C-P-Q triad was reported in which the carotenoid and quinone moieties were linked to the tetraarylporphyrin via basket handle linkages between opposite aryl groups [65]. This linkage positioned the carotenoid and quinone species above and below the plane of the porphyrin, rather than to the side, as confirmed by H-NMR studies. Evidence for photoinitiated electron transfer in this molecule was provided by incorporating it into a phospholipid bilayer and detecting a light-induced photocurrent. Similar experiments had previously been reported with the other C-P-Q triads discussed above [55],... 

Let us calculate the correction to the proton polaron direct current density conditioned by light-induced transitions between the sites. This photocurrent calculation is analogous to that of the correction to the drift activation current carried out in the previous subsection [the analogy lies in the fact that operator (276) is similar to the correction to the Hamiltonian if the electric field is taken into account, with the correction being nondiagonal on the operator of the coordinate see expression (236)]. 

All light-induced processes and the resulting photocurrents are related to the transfer of minority carriers from the semiconductor to the electrolyte. The reverse process, the injection of minority carriers from a redox system into the semiconductor, is only possible with redox systems, where the standard potential is very close to the corresponding energy band of the semiconductor as illustrated in Fig. 7.32. This could be accomplished with redox systems of a fairly positive standard potential such as Ce ... 

It is unclear at this time how the light sensitivity of OTFTs compares to silicon-based TFTs, but it is certain that similar light-shielding measures must be employed. Studies in our laboratory have shown that, in addition to the photocurrents generated by incident illumination, long-lived light-induced threshold shifts can occur in pen-... 

The simplest photoelectrochemical cells consist of a semiconductor working electrode and a metal counter electrode, both of which are in contact with a redox electrolyte. In the dark, the potential difference between the two electrodes is zero. The open circuit potential difference between the two electrodes that arises from illumination of the semiconductor electrode is referred to as the photovoltage. When the semiconductor and counter electrode are short circuited, a light induced photocurrent can be measured in the external circuit. These phenomena originate from the effective separation of photogenerated electron-hole pairs in the semiconductor. In conventional photoelectrochemical studies, the interface between the flat surface of a bulk single crystalline semiconductor and the electrolyte is two dimensional, and the electrode is illuminated from the electrolyte side. However, in the last decade, research into the properties of nanoporous semiconductor electrodes interpenetrated by an electrolyte solution has expanded substantially. If a nanocrystalline electrode is prepared as a film on a transparent conducting substrate, it can be illuminated from either side. The obvious differences between a flat (two dimensional) semiconductor/ electrolyte junction and the (three dimensional) interface in a nanoporous electrode justify a separate treatment of the two cases. 

Figure 2.21 shows a schematic of the setup for simultaneous measurement of the stationary light-induced excess minority carrier microwave reflectivity and the photocurrent at the semiconductor-electrolyte contact. The sample is illuminated from the front side and photoelectrochemistry is performed using the standard... 

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