Temporal features of the photocurrent transients

Figure 6 The temporal features of the photocurrent transients for vapor-deposited MPMP.

Yuh and Stolka (1988) described the temporal features of the photocurrent transients of TPD doped PC. The authors concluded that holes reach dynamic equilibrium within a small fraction of the transit time. A plateau in the photocurrent transient then occurs, followed by a dispersion of arrival or transit times. The dispersion was attributed to positional disorder. The results were in agreement with the simulations of Marshall (1978). A key result of the study was that W scaled with thickness as L l/2. Field-independent dispersion at very long times was attributed to fluctuations of hopping site energies. Over a wide range of fields, the mobilities were independent of thickness. 

Kanemitsu and Einami (1990) investigated the role of the polymer on hole transport in a series of 2-(p-dipropylaminophenyl)-4-(p-dimethylaminophenyl)-5-(o-chlorophenyl)-l,3-oxazole (OX) doped polymers. The polymers were a polyarylate (PA), bisphenol-A polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene) PS, poly(vinyl chloride) (PVC), polyethylene terephthalate) (PET), and poly(vinyl butyral) (PVB). The glass transition temperatures of the polymers range from 322 (PVB) to 448 K (PA). The temporal features of the photocurrent transients were strongly dependent on the polymer. Figure 76 shows the results. The field was 4.0 x H)5 V/cm and the temperature 295 K. The transients were near rectangular for PS, PET, PA, and PMMA, and highly dispersive for PVC land PVB. This was attributed to the fact... 

The temporal features of photocurrent transients of virtually all polymers and doped polymers described in the literature show (1) an initial spike of short duration, (2) a plateau of variable duration, and (3) a long tail. The initial spike has been explained as due to trapping at sites with waiting times that are comparable to the transit time (Scher, 1976) and by the thermalization of the carrier packet within the DOS (Bassler, 1993). In the plateau region, the current is independent of time, indicating the displacement of a packet of carriers with a... 

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