Films photoelectrochemical measurements

Cathodic electrodeposition of microcrystalline cadmium-zinc selenide (Cdi i Zn i Se CZS) films has been reported from selenite and selenosulfate baths [125, 126]. When applied for CZS, the typical electrocrystallization process from acidic solutions involves the underpotential reduction of at least one of the metal ion species (the less noble zinc). However, the direct formation of the alloy in this manner is problematic, basically due to a large difference between the redox potentials of and Cd " couples [127]. In solutions containing both zinc and cadmium ions, Cd will deposit preferentially because of its more positive potential, thus leading to free CdSe phase. This is true even if the cations are complexed since the stability constants of cadmium and zinc with various complexants are similar. Notwithstanding, films electrodeposited from typical solutions have been used to study the molar fraction dependence of the CZS band gap energy in the light of photoelectrochemical measurements, along with considerations within the virtual crystal approximation [128]. 

Studies include wet-cell photoelectrochemical measurements (42,60,72,90), STM measurements on single MS particles in thin films (55,56,81), and conductivity measurements of metal chalcogenides in LB films (20,21,23). Many such studies are driven by the search for cheaper methods and materials for the fabrication of semiconductors suitable for photoelectrochemical devices. Moreover, the ability to tune optical properties via the Q-state effect and the versatility of LB fabrication make the LB films an attractive medium for semiconductor production. The photo-... 

We are primarily concerned with several typical modes of the Chi interfacial layer relevant to photoelectric and photoelectro-chemical systems. Since the Chi molecule, a surfactant pigment consisting of a partially hydrophilic porphyrin ring and a totally hydrophobic phytol chain, is insoluble in water, it is generally employed for photoelectric and photoelectrochemical measurements in the form of a solid (or quasi-solid) film deposited on an electrode surface. Such Chi films are divided into three typical modes according to molecular configuration. 

Photoelectrochemical measurements also provide an approach to the determination of electrophysical characteristics of diamond. In addition to the threshold energies of electron phototransitions, determined by the analysis of the photocurrent action spectra (Section 7), the diffusion length of minority carriers in polycrystalline diamond films was estimated (at 2 to 4 pm) by comparing light absorption spectra and open-circuit potential spectra [171],... 

J. Herrero and M. T. Gutierrez, Photoelectrochemical measurements of amorphous silicon thin films, Electrochim. Acta 36(5/6), 915, 1991. 

Limited photoelectrochemical measurements were done also on films of SnS2 nanoparticles with fullerene-like structure. 

We selected photoelectrochemical measurements as the method for evaluating the charge-separation ability, and developed an automatic semiconductor synthesis system for preparing porous thin-film photoelectrodes of various materials. The system consists of an automated liquid-handling platform, electric furnace, and... 

Figure 3-8. Schematic representation of the principle of photoelectrochemical measurements for an n-type semiconducting passive film under anodic polarization. The photon illumination forms electron and hole pairs whose charge can be consumed in the oxidation of redox couples at the surface of the film, giving rise to a photocurrent.

The photoelectrochemical properties of these films were measured using an electrolyte that consisted of 0.1 M sodium hydroxide, 0.1 M sodiumsulfideandO.01 Msulfur. Thefilmsshowedtypicalphotochemical behavior (Fig. 17). 

The photoelectrochemical response of these films was measured. As was to be expected, It and the band gap varied with film composition. 

PbO is more stable in alkaline solutions. Anodic oxidation of Pb leads to the selective growth of /I-PbO, which transforms into a-PbO in the course of prolonged polarization, as supported by X-ray diffraction studies and photoelectrochemical experiments [172]. In the presence of sulfate ions, simultaneous formation of basic lead sulfate with PbO has been observed, until the formation of 4Pb0-PbS04. At higher potentials, the oxide film in sulfate ions solution has a strong (110) orientation with microporous structure. X-ray diffractometry and photocurrent measurements have confirmed the presence of... 

Surface treatments of CD CdSe films deposited from selenosulphate/NTA solutions have a pronounced effect on various optical, electrical, and optoelectronic properties of the films, due to interaction with or modification of such surface states. Mild etching (dilute HCl) of the films reverses the direction of current flow both in CdSe/polysulphide photoelectrochemical cells [108] and in Kelvin probe surface photovoltage (SPV) measurements in air [109], These studies are discussed in more detail in Chapter 9, in Section 9.2 on photoelectrochemical cells. At this point, it is sufficient to state that the effect is believed to be due to preferential trapping of either electrons or holes at surface states that are modified by the etching process. 

Besides evaluating photoelectrodes for use in PECs, photoelectrochemical characterization can be used for other purposes. For example, photocurrent spectra of CD CdS has been used to measure the semiconductor bandgap (as f vs. hv), and agreement between the bandgap values measured by this method and by absorption spectroscopy for as-deposited and annealed films was found [78]. 

Y. Nakato H. Tsubomura, The photoelectrochemical behavior of an n-Ti02 electrode coated with a thin metal film, as revealed by measure-... 

Fig. 4. Chronoamperometric measurements of MEH-PPV (., blends of MEH-PPV Xi02 dots (—) and MEH-PPV Xi02 rods (thin solid line) in a photoelectrochemical cell. Ag/AgCl is chosen as reference electrode, while XTO and platinum as working and counter-electrode, respectively. A halogen lamp is used. Xhe films were deposited onto 1X0 and immersed into acetonitrile solution of tetrabutyl-ammonium-perchlorate 0.1 M (Petrella et al., 2004)...

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