Charge transport time-resolved measurements

Traditionally, time resolved measurements are used to study the mechanisms of charge transport and recombination in semiconductor materials. 

The first step, particle formation by gas or liquid phase synthesis, leads to particles which are further functionalized at their surface to ensure colloidal stabilization and to allow charge transfer across particle—particle interfaces in the final layer. The surface and electronic properties of the particles are typically characterized by a whole set of techniques including time-resolved measurements of charge carrier transport. The best way of cost-efficient... 

The time-resolved photoconductivity measurements shown in Fig. 15 give further support for a difference in the photoinduced charge transport in the polymerized samples versus the unpolymerized samples. For the incident laser of 100 mW/cm2 and a spot size of 2.5 mm, the decay time of the photoconductivity for the unpolymerized samples is 7.4 sec, whereas the photoconductivity of the polymerized samples does not significantly drop over a 30 sec period. Also, the photoconductivity of the polymerized sample is nearly twice that of the unpolymerized samples even at the peak of the unpolymerized photoconductive response. The unnormalized values for the dark conductivity in both samples is 1.7 x 10-10 S cm-1. The photoconductivity is 5.8 x 10-11 S cm-1 for the unpolymerized sample and 1.1 x 10-10 S cm-1 for the PSLC at an optical intensity of 2 W cm-2. 

The characterisation of a DSSC device or the study of partial processes that occurs at such cells uses a series of optical and electrochemical techniques, either stationary or time-resolved. The studies cover a wide range of timescales, accompanying the wide time span of phenomena occurring in a DSSC (from fs/ps for electron injection to ms for electron transport). Optical transient absorption techniques (see Chaps. 8, 14, 15) are used in combination with transient electrical measurements to follow the appearance and disappearance of chemical species and charges on a DSSC [27]. 

In conclusion, THz time domain spectroscopy allows the simultaneous quantitative detection of real and imaginary electrical conductivity. The real component of the complex conductivity is related to the free charge carrier yield, while the imaginary component is related to the yield of bound charge pairs (excitons). Moreover, time-resolved THz measurements may provide data on charge transport along isolated polymer chains [108]. 

Light-induced electron transport in bacterial photosynthetic reaction centers leads to the creation of a charge-separated state stable for milliseconds to seconds. The structures provided by X-ray crystallography (Michel et aL, 1986 Allen et al., 1988 Deisenhofer Michel, 1989 El-Kabbani et al., 1991) constitute a unique guideline to address questions on how the function may be related to the arrangement of the cofactors and of specific amino acid residues in their vicinity. The sequence of electron transfer reactions, the identity of the reaction partners, and the reaction mechanisms have been characterized from static and time-resolved absorbance measurements (for a review, see Parson Ke, 1982). Transfer of the first electron to the primary (Q ) and secondary (Qg) quinone electron acceptors has received considerable attention, since it is associated with intraprotein protolytic reactions (for a recent review, see Okamura Feher, 1992), which have a potential role in electrostatic charge stabilization. 

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