P-type doped polymers

On the other hand, p-type doped polymers may be expected to be stable but prone to the degradative effect of counter-ions. Druy el al. [29] demonstrated the counter-ion dependence of initial electrical conductivity loss in polyacetylene where the electrical conductivities of the samples doped with I2 and CIO4 were maximally affected, due to the strong oxidizing ability of these dopants. Somewhat complementary results have also been reported by various other workers [30-32]. 

Only polarons are detected for p-type doping. The Raman spectra of the polymers doped with acceptors do not show large changes with various excitation wavelengths [72, 73, 75]. The polymer-chain structures of p-type-doped polymers are more homogeneous, and more regular arrays of polarons are formed. 

A chemical compensation process is one in which, for example, a p-type doped polymer (i.e., oxidized polymer) reacts chemically... 

In this paper, we mainly describe "in situ" experiments on n-type doped samples. A comparison is made with previous similar experiments on p-type doped polymers (8). Recent experiments performed on other conducting polymers such as polyaniline (9) are also briefly described in the last part of this paper. 

The initial discovery of the ability to dope conjugated polymers involved charge transfer redox chemistry oxidation (p-type doping) or reduction (n-type doping) [1,2], as illustrated with the following examples ... 

Optical beam induced current measurements carried out on polymer LECs indicated the same conclusion [79]. In the LEC, one carries out electrochemical redox in-situ forming an n-type doped region near one electrode and a p-type doped region near the opposite electrode [43,80]. In between, the chemical potential varies smoothly across the energy gap. 

Figure VII-5 Schematic diagram showing the operating mechanism of polymer LECs. The electrodes are labeled M, and Mj. The open circles denote oxidized species (p-type doped) the filled circles denote reduced species (n-type doped) the asterisks denote neutral electron-hole pairs, (a) The cell before applying a voltage, (b) Doping opposite sides as n-type and p-type. (c) Charge migration and radiative decay.

Redox conductivity of conducting polymers involves anion insertion associated to oxidation processes (p-type doping) and cation insertion coupled with reduction ones (n-type doping). Efficient polymer-based electronic devices require lowering of the redox potential of the involved electron transfer processes, and electrochemical reversibility is necessary to allow repetitive charge/discharge processes. In the... 

Doping of polyacetylene has been studied extensively, especially n-type doping with alkali metals and p-type doping with iodine. Since 1990, however, papers on this topic have almost ceased to appear, presumably because interest has shifted to other polymers and other properties (fluorescence for instance, which is not shown by polyacetylene). The number of papers that appeared in the 1980 s is so large as to make it impracticable to discuss the contents of each. The development of the current knowledge will be sketched and relevant contributions to the field will be mentioned where this is appropriate. 

In their neutron diffraction studies of p-type doping of PPP, Stamm and Hocker [179] have determined the setting angle (p of the chains in the pristine polymer to be 57° 3°. In this refinement, the authors started from the data by Kovacic et al. [169], but assumed a monoclinic P2i/a structure with /i=I00°. While a number of later studies by others confirm that the value of 4> is around 57°, Stamm et al. [180] find a much lower value of 45° in their electron diffraction work. The neutron study yields lateral coherence lengths L of 60 A for Kovacic PPP and 150 A for Yamamoto PPP. 

Oxidative (p-type) doping of conjugated polymers such as polyacetylene, poly(p-phenylene), polypyrrole, poly-... 

In the electrochemical sense the p-type doping reaction consists of anodic oxidation of neutral polymer chains to polycations with simultaneous insertion, to the polymer matrix, of electrolyte originating anions which preserve the electrical neutrality of the system. By symmetry, n-type doping is achieved by cathodic reduction of the polymer chains to polyanions, with... 

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