Understanding the doping dependence of the conductivity of conjugated polymers: Dominant role of the increasing density of states and growing delocalization

Abstract

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Doping, density of states, and conductivity in polypyrrole and poly(p-phenylene vinylene)

“…In this work the difference between FeCl 3 and PF 6 doped OC 1 C 10 -PPV and PF 6 doped PPy, as a function of doping level is investigated in detail by studying both the electrochemical gated transistor (EGT) characteristics and temperature dependence of conductivity using a precise calibration of the amounts of doping. The higher DOS per unit volume for PF 6 doped PPy compared to doped OC 1 C 10 -PPV and the occupation of the energy states near the Fermi level explain the observed difference in conductivity behavior.…”

“…For example, polyalkylthiophenes (PAT) and poly[2-methoxy-5-(3 ′ ,7 ′ dimethyloctyoxy)-pphenylene vinylene (OC 1 C 10 -PPV), 3 that have been frequently used in polymeric transistors and polymeric light emitting diodes, respectively, remain as insulators even at the highest doping levels (with dopants like FeCl 3 ). 4,5,6 To explain the transport data in conducting polymers in general, key ingredients are the crystalline coherence length (a few nanometers), the volume fraction of crystallinity (> 50%), the doping level, the interchain transfer integral, the energy dependence of the density of states, the extent of disorder in the material, charge repulsion and polaronic effects. 7,8,9,10,11 The relevant values of the transfer integral, the spread in its mean value due to disorder and of the Coulomb correlations are usually all around 0.1 eV or less, which is close to the thermal energy at 300 K. A systematic study of the evolution of density of states (DOS) and charge transport as a function of well controlled doping level is still lacking in several conducting polymers.…”

Charge-carrier concentration dependence of the hopping mobility in organic materials with Gaussian disorder

“…IV for the case of a Gaussian DOS. Furthermore, we show that in the models proposed by Arkhipov et al 17 and Martens et al 22 the treatment of percolation is quantitatively not quite correct. In Secs.…”

“…Martens et al 22 have recently formulated a model for an arbitrary DOS that uses the approach introduced by Mott for hopping in a uniform DOS. 24 It is assumed that the conductivity, expressed as…”

“…To this end, we make a comparison between the results obtained from five semianalytical models, the Monte Carlo results from Bässler, 7 and the Master Equation results reported by Pasveer et al 16 The latter work is used as a benchmark. We discuss the semianalytical models presented by Arkhipov et al 17 and Roichman and Tessler, 18 already mentioned and we apply three other general models to the specific case of a Gaussian DOS: ͑i͒ the model introduced by Movaghar and Schirmacher, 20 which involves a modified effective medium approximation, ͑ii͒ a percolation model, in the form used earlier by Vissenberg and Matters for the case of an exponential DOS, 21 ͑iii͒ a model given recently by Martens et al 22 The latter two models are based on formalisms introduced by Ambegoakar et al 23 and by Mott,24 respectively.…”