Role of carrier density and disorder on anisotropic charge transport in polypyrrole

Abstract

Polypyrrole (PPy) has been synthesized electrochemically on platinum substrate by varying synthesis temperature and dopant concentration. The charge transport in PPy has been investigated as a function of temperature for both in-plane and out-of-plane geometry in a wide temperature range of 5 K–300 K. The charge transport showed strong anisotropy and various mechanisms were used to explain the transport. The conductivity ratio, σr = σ(300 K)/σ(5 K) is calculated for each sample to quantify the relative disorder. At all the temperatures, the conductivity values for in-plane transport are found to be more for PPy synthesized at lower temperature, while the behavior is found to be different for out-of-plane transport. The carrier density is found to play a crucial role in case of in-plane transport. An effort has been made to correlate charge transport to morphology by analyzing temperature and frequency dependence of conductivity. Charge transport in lateral direction is found to be dominated by hopping whereas tunneling mechanisms are dominated in vertical direction. Parameters such as density of states at the Fermi level [N(EF)], average hopping distance (R), and average hopping energy (W) have been estimated for each samples in both geometry.

Chemical synthesis and charge transport mechanism in solution processed flexible polypyrrole films

“…Strong temperature dependence of electrical conductivity observed in these PPy films can be used for making of precise temperature sensors. The observed trend appears similar to those reported earlier for PPy [27][28][29] as well as for other conducting polymers [36][37][38]. It has been observed from Fig.…”

“…(4) are used to estimate density of states at Fermi level. Density of states at Fermi level for PPy pellet and film is $ 7.88 Â 10 21 and 1.65 Â 10 20 cm À 3 eV À 1 respectively and are in good agreement with reported earlier for PPy [26][27][28][29] and other π-conjugated materials [36][37][38]. Apart from these the conduction behavior of PPy samples is further analyzed in terms of average hopping distance (R) and average hopping energy (W) as given by [32] …”

“…In this study, it is assumed that r will be equal to the pyrrole monomer dimensions of $ 3 Å because the electrons are always at least delocalized to the extent of π-orbitals on the monomer units [28,39]. The characteristic temperature T 0 evaluated from slope of Fig.…”

“…It is worthwhile to study and understand charge transport properties in these PPy films before their potential use in precisely controlled device applications. Despite of a large number of studies, charge transport mechanism in conducting polymers (CPs) still remains a topic of discussion and research [24][25][26][27][28][29]. This is probably due to the different type of structural and electronic defects as well as lack of long range ordering, which arises during synthesis.…”

Impedance measurements in undoped and doped regioregular poly(3-hexylthiophene)

“…Apart from these, charge carrier density, trap density, molecular weight, etc. also observed to have important roles [15,16]. All these factors control and limit the mobility in disordered semiconducting polymers.…”