Photocurrent generation

MFEs on the photocurrents of the modified electrode with nanoclusters of the mixture of C qN and MePH were examined to verify the photocurrent generation mechanism. In the presence of a magnetic field, the photocurrents clearly increased. 

The efficiency of the photocurrent generation in practical photogalvanic cells is generally low, since it is limited by short lifetimes of the excited dyes, parasitic electron transfer reactions, etc. 

Gao, F. G., A. J. Bard, and L. D. Kispert. 2000. Photocurrent generated on a carotenoid-sensitized Ti02 nanocrystalline mesoporous electrode. J. Photochem. Photobiol. A 130 49-56. 

An example is shown in Fig. 8.9, where the photocurrent generated in n-type semiconducting WO3 is plotted for three different wavelengths... 

Quantum dots (QDs) on various matrices has been extensively studied for their promising optoelectronic applications. To enhance the photocurrent generated by... 

Fig. 5.41 Photocurrent generated from 6 pm long nanotube-arrays...

ZnS-CdS (bandgap = 2.3-2.4 eV) composite semiconductor photoelectrodes show a broad spectral response and n-type behavior, with saturation of the anodic photocurrent upon increasing anodic potential making the system suitable for use as a photoelectrochemical cell photoanode [72], Nanostructured ZnS-CdS thin film electrodes show that anodic photocurrent saturation can be attained with the application of a small, 0.1 V, bias [73], while hydrogen evolution is observed at the Pt cathode. The performance of the ZnS-CdS photoanodes appear strongly dependent upon the method of film preparation [72,73], with Zn rich films demonstrating superior photocurrent generation, and stability, in comparison to Cd rich films. 

Fig. 7 FESEM images of titania nanocoil produced by anodic oxidation (a). The cartoon shows schematically the photocurrent generated by light irradiation of nanocoil containing a catalyst particle (b) and the associated magnetic field (c). Source Centi and Perathoner. ...

Fig. 4 Schematic illustration of the processes leading to photocurrent generation in organic solar cells, (a) Photon absorption in Step 1 leads to excitons that may diffuse in Step 2 to the donor/ acceptor (D/A) interface. Quenching of the exciton at the D/A interface in Step 3 leads to formation of the charge-transfer (CT) state. Note that processes analogous to Steps 1-3 may also occur in the acceptor material, (b) Charge separation in Step 4 leads to free polarons that are transported through the organic layers and collected at the electrodes in Steps 5 and 6, respectively, (c) The equilibria involved in Steps 1-4- strongly influence device efficiency...

Photocurrent generation, involving the CT state, has often been treated [106, 107, 143-145] according to the Onsager-Braun model [146, 147], to describe the field dependence for charge separation and charge recombination from the CT state. The... 

Mihailetchi VD, Koster LJA, Hummelen JC, Blom PWM (2004) Photocurrent generation in polymer-fullerene bulk heterojunctions. Phys Rev Lett 93 216601... 

Photocurrent generation was observed after illumination of the cell with ZnO electrode see for instance. Refs 166-169. 

The photocurrent generated by a Chi a multilayer in contact with an aqueous electrolyte without any added redox agents has been measured as a function of pH of the solution (67). 

Takahashi and co-workers (69,70,71) reported both cathodic and anodic photocurrents in addition to corresponding positive and negative photovoltages at solvent-evaporated films of a Chl-oxidant mixture and a Chl-reductant mixture, respectively, on platinum electrodes. Various redox species were examined, respectively, as a donor or acceptor added in an aqueous electrolyte (69). In a typical experiment (71), NAD and Fe(CN)g, each dissolved in a neutral electrolyte solution, were employed as an acceptor for a photocathode and a donor for a photoanode, respectively, and the photoreduction of NAD at a Chl-naphthoquinone-coated cathode and the photooxidation of Fe(CN)J at a Chl-anthrahydroquinone-coated anode were performed under either short circuit conditions or potentiostatic conditions. The reduction of NAD at the photocathode was demonstrated as a model for the photosynthetic system I. In their studies, the photoactive species was attributed to the composite of Chl-oxidant or -reductant (70). A p-type semiconductor model was proposed as the mechanism for photocurrent generation at the Chi photocathode (71). 

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. 

Tetraphenylporphine (TPP) and other metal porphyrine derivatives coated on platinum (87,88,89) or gold (89,90) electrodes have been investigated in photoelectrochemical modes. Photocurrents reported are cathodic or anodic, depending on the pH as well as the composition of the electrolyte employed. Photocurrent quantum efficiencies of 2% (89) to 7% (87) were reported in systems using water itself or methylviologen as the redox species in aqueous electrolyte. Photocurrent generation at Zn-TPP-coated metal cathodes (89) was interpreted in terms of a rectifying effect of the Schottky barrier formed at a metal-p-type... 

Accordingly, such factors as molecular configuration or surface concentration of Chi and thickness of the layer significantly affect the efficiency of photocurrent generation in electrochemical systems. 

---