Conducting polymer electron affinity

Fig. 15 Simplified schematic representation of the electronic energy levels in a single-layer PLED. CB and VB are the conduction hand and valence hand, respectively, of the semiconducting polymer, which correspond to the ionization potential (IP) and electron affinity (EA) relative to vacuum level (EV). The work functions for anode (and cathode (

The ionization potential of polyphenylene is around 8 eV and it is not surprising that oxidative degradation is not a problem the undoped polymer can withstand long periods at high temperatures in air with no change in its conductivity or its ability to dope 386). However, the high oxidation potential creates two problems. Firstly, the range of dopants with sufficient electron affinity to oxidize the polymer is limited, and there are few solvents in which the oxidation can take place without destruction of the solvent. Secondly, the doped polymer is expected to be reactive towards water and this is indeed the case 386). 

Electrical conduction will occur by the hopping of either electrons or holes within these distributions of energy levels. Charge transport can be either of holes by transfer between the LUMO states or of electrons between the HOMO states. These correspond to the formation of either a radical cation by the removal of an electron to an adjacent electrode or an anion by the injection of an electron. The nature of the majority carriers will, therefore, be determined by the ionisation potentials and electron affinities of the conjugated moieties. A low ionisation potential will favour hole transport while a high electron affinity will favour electron transport. Most of the conductive polymers reported in the literature have low ionisation potentials and are hole, conductors. ... 

The reactions of organic molecules in solution are related to gas phase electron affinities and electronegativities. Anions are often intermediates in such reactions. The electron conduction of polymers is related to the electron affinities of the components. The theoretical calculations of electron affinities of aromatic hydrocarbons and the effect of substitution on electrons affinities and gas phase acidities are important to organic chemistry. Pseudo-two-dimensional Morse potentials have been used to represent the dissociation of organic molecules and their anions [18]. 

Figure 16.4. Relationship of polymer n-eleetron band structure to vacuum and various energetic parameters. g is the optical band gap, BW is the band width of the fully occupied valence band, EA is the electron affinity (measured from the bottom of the conduction band to the vacuum) and IP is the ionization potential (measured from the top of the valence band to the vacuum).

Band structure calculations have been performed with the valence effective Hamiltonian (VEH) nonempirical pseudopotential technique. The VEH method yields one-electron energies of ab initio double-zeta quality and has been demonstrated to provide accurate estimates of essential electronic properties such as ionization potentials (IP), bandwidths (BW), bandgaps (Eg), and electron affinities (EA) in the context of conducting polymers. All the calculations have been carried out using the VEH parameters previously reported for sulfur, oxygen, and nitrogen atoms and those recently obtained for carbon and hydrogen atoms,... 

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