Charge trap-controlled

Fig. 3.29(b) shows the published J-V curves of an Al/OCiCio/ITO diode by Jain et al. [40], [OCiCio is poly(2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene vinylene).] In this paper [40] Jain et al. attributed the extremely fast rise of the hole current at low voltages to Shockley like current due to the forward biased Al Schottky contact. In their later paper [56] Jain et al. showed that by including the PFE they can fit the theory of bulk limited trap controlled space charge currents with the same experimental results (see Fig. 3.29(b)). Jain et al. [40] suggested that PFE induces the high injection effect earlier, which presumably makes the Schottky barrier at the Al contact small. 

Because adsorption equilibria can produce a substantially different population at the semiconductor-liquid interface than is present in solution, interfacial charge trapping can produce specific activation of the better adsorbate from a mixture. Thus adsorption pre-equilibria are likely to be important in controlling the relative rates of photooxidation of competing substrates on semiconductor surfaces. Because adsorption equilibria can be influenced by the addition of very small amounts of cosolvent additives, higher reactivity [36] and higher selectivity can often be simulta-... 

Thus, the band positions of the irradiated semiconductor are key thermodynamic variables for in the control of the observed redox chemistry resulting from photo-catalyzed single-electron transfer (charge trapping) across the semiconductor-electrolyte interface. Whether oxygenation, rearrangement, isomerization, or other consequences follow this initial electron transfer seems to be controlled by surface effects on the relative rates of reaction. 

The presence of alkali metal ions is crucial for the stabilization of excess charge trapped within the nanopartides. Intercalation of metal ions within the nanoparticle thus becomes a limiting factor as the rate of transport of these ions becomes slower in thicker metal oxide films. This in turn controls the rate of coloration and recovery of the electrochromic effects. Limited efforts have also been made to employ mixed Ti02/W03 [145], WO3/V2O5 [146], and WO3/M0O3 [147] systems to enhance the efficiency of electrochromic effects. The beneficial aspect of these nanostructured semiconductor films in electrochromic devices is yet to be explored in a systematic way. 

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