Poly photocarriers

Despite the extensive photoconductivity data, the nature of photoexcitations in poly(phenylenevinylene), PPV, and its soluble derivatives has remained controversial. In part, the controversy arises from the conflict between the results obtained with fast time-resolved photoconductivity and those obtained by the more familiar steady-state photoconductivity the latter indicate a strong T-dependence for the np product. Recent experiments have resolved the apparent conflict [203]. The idea is rather simple If the sample is sufficiently thin that the photocarriers can be swept out before a significant fraction fall into traps, the steady-state photocurrent will provide information similar to that obtained at short times by transient photoconductivity (in the latter, sample thickness is not important since pre-trapping and trap dominated transport are separated in the time domain). 

W. Takashima, S. S. Pandey, T. Endo, M. Rikukawa, N. Tanigaki, Y. Yoshida, K. Yase and K. Kaneto. Photocarrier transports related to the morphology of regioregular poly(3-hexylthiophene) films. Thin Solid Films 393(1,2), 334-342 (2001). 

Figure 9.18 Quantum efficiency for photocarrier production in a 10-pm-thick AI/poly(3-dodecylthiophene)/AI sandwich structure as a function of electric field T = 295 K). Filled and open squares DC-measurement on a fresh sample and a sample that had been stored at 10- mbar for 1 week, respectively crosses data obtained under pulse excitation. (From Binh, N. T. et al., Synth. Met, 47, 77, 1992. With permission.)...

Photoinduced absorption studies of the oligomer have shown that the dominant long-lived photocarriers are bipolarons formed by interchain charge separation. The lifetimes of the bipolarons in poly(l-(A-carbazo-lyl)penta-5-acetoxy-l,3-diyn) are of the order of seconds at 80 K. The polymer of 1-(A-carbazolyl)-penta-l,3-diyne-5-ol, which is an intermediate compound in the synthesis of (61), has a very low band gap energy (1.6 eV) exhibits a strong non-linear optical... 

Charge carrier generation and transport in poly(3-dodecylthiophene) have been recently studied in detail [446,447], The mechanism of photocarrier generation... 

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