Photocurrent produced by light

Figure 2. Voltage spectra of photocurrent produced by light scat-tered from solutions of polydisperse PS in cyclohexane at 37°C. Concentration = 10 mg/mL, Scattering angle 6 = 40°, (--------) = sample...

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. ...

The efficiency of PEC is directly related to the magnitude of the photocurrent produced by exposure to light. Clearly, doubling the efficiency or photocurrent halves the area of PEC required to produce a given mass of gas. 

Grider has studied photoemission from copper with adsorbed Br, F, ion, thiourea, and pyridine. He proposed that the major effect attributable to adsorption of halide ions and thiourea was partial relaxation of the conservation of electron momentum parallel to the surface. In the case of R4N ion adsorption, the structure of the yield ratio of photocurrents produced by p-and -polarized light shifted with photon energy, and this was explained by an increase in the local density of electrons near the surface due to the adsorption, which can cause scattering effects. Pyridine, upon adsorption, similarly affected the yield ratio structure at bulk concentrations >10 M, but a clear understanding of this result remains to be attained. Grider et also have provided evidence that partial relaxation of parallel momentum conservation occurs for in situ photoemission from a single-crystal copper... 

It is difficult to measure metal/polymer Schottky energy barriers smaller than about 0.5 eV using internal pholoemission. Small Schotiky energy barriers lead to thermal emission currents produced by the absorption of light in the metal which are difficult to separate from true photocurrents 134]. If the structure is cooled to try to improve this contrast, it is often found that the significant decrease in the electrical transport properties of the polymer [27 [ makes it difficult to measure the internal photoemission current. To overcome this limitation, internal photoemission and built-in potential measurements are combined to measure small Schottky energy barriers, as described below. 

Sulfur-doped highly ordered Ti02 nanotube arrays, produced by annealing in a flow of H2S at 380 °C, were also reported to show higher photobehavior (photocurrent) under visible light irradiation up to 650 nm. ... 

Evidence indicates that the slow process or processes may be associated with the surface. For example Heiland (47) has found that the irradiation of zinc oxide in a vacuum by light or electrons produces a photocurrent which remains stable, even after the irradiation has ceased, until oxygen is allowed to reach the sample. 

Also frequently used is the photocurrent response at a given potential and light condition (intensity and wavelength). The photocurrent obtained with illumination of the n-type hematite used as anodes are directly proportional to the amount of dihydrogen that can be produced by reduction of protons in the electrolyte. 

Fig. 27. Top left image of the device. Inset luminescence image of microwires. Top right I-V curves of microwires produced by slow evaporation (red line) and dip-and-pull approach (black line). Bottom left schematic diagram of the device used for the detection of light. Bottom right photocurrent of the device (excitation wavelength 450 nm), which can be switched on/off rapidly by illumination under voltage bias of 0.5 V. Reproduced with the permission of the Royal Society of Chemistry 244).

Since protection of electrodes against corrosion in the photoelectrolysis cells is a question of vital importance, many attempts have been made to use protective films of different nature (metals, conductive polymers, or stable semiconductors, eg., oxides). Of these, semiconductive films are less effective since they often cause deterioration in the characteristics of the electrode to be protected (laying aside heterojunction photoelectrodes specially formed with semiconducting layers of different nature [42]). When metals are used as continuous protecting film (and not catalytical "islands" discussed above), a Schottky barrier is formed at the metal/semiconductor interface. The other interface, i.e., metal/electrolyte solution is as if connected in series to the former and is feeded with photocurrent produced in the Schottky diode upon illuminating the semiconductor (through the metal film). So, the structure under discussion is but a combination of the "solar cell" and "electrolyzer" within the photoelectrode Unfortunately, light is partly lost due to absorption by the metal film. 

Photoconductivity is a typical phenomenon for many organic semiconductors. When a photoconductor is illuminated by light, which it is able to absorb, charge carriers are produced and consequently the conductivity of the material increases [198]. Several processes are responsible for the magnitude of a photocurrent within an organic solid [199, 200] ... 

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