Terahertz complex conductivities of carriers with partial localization in doped polythiophenes

Abstract

We have investigated the complex conductivity spectra σ̃(ω) of two p-doped polythiophenes—poly(3-hexylthiophene) and poly(3,4-ethylenedioxythiophene)—with various carrier densities by using terahertz time-domain spectroscopy. The real part of σ̃(ω) is found to gradually decrease with decreasing frequency ω and to approach a finite value for ω→0 unlike the Drude conductivity behavior, suggesting that carriers in polythiophenes have a partially localized nature. By reproducing both the measured real and imaginary parts of σ̃(ω) with the Drude–Smith model, we show that carriers become less localized with increasing carrier density up to ∼1.8×1020 cm−3.

Nondestructive measurement of carrier mobility in conductive polymer PEDOT:PSS using Terahertz and infrared spectroscopy

“…The dynamics of weakly localized carriers in polypyrrole films were studied by the localization modified Drude (LMD) model [6]. Other group also investigated ion-doped conducting poly-3-hexylthiophen (P3HT) using Drude-Smith model [5]. Our results indicates that THz conductivity in PEDOT:PSS is well fitted by LMD model which indicates that PEDOT:PSS is the disordered metal near metal-insulator transition [6].…”

“…However, their carrier transport mechanisms are not fully understood. Several groups reported THz complex conductivity of the conductive polymers using THz-TDS [4,5]. Their results show the partially localized carrier behavior and very high carrier scattering rate Γ.…”

Effect of solvent on carrier transport in poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) studied by terahertz and infrared-ultraviolet spectroscopy

“…[8][9][10] These studies obtained the fitting parameters of Drude-like models for THz conductivity to determine the carrier density and mobility by assuming the effective mass m*. However, the carrier damping rate C/2p in such disordered systems is much higher than the measurable frequency range of a conventional THz-TDS system, which results in multiple solutions for the fitting without information of the background dielectric constant in the absence of carriers e bTHz in the THz region.…”

Microscopic origin of the Drude-Smith model

“…76,77 Fitting these simulations enabled Nemȇc et al to provide approximate mathematical expressions for the Drude-Smith fit parameters 76 that have since been applied to experimental data to extract meaningful physical information. 15,26,27,33,38 Complementary experimental techniques are often also used to examine the structure 11,12,15,[17][18][19][20]22,23,25,26,29,31,[33][34][35][36][37][38][39][41][42][43][44]46,47,50 and carrier transport characteristics 11,12,19,23,26,43,57 in a sample to test the fidelity of the Drude-Smith fits. Nevertheless, in the absence of a tractable derivation that shows how weak carrier confinement yields the DrudeSmith formula with well-understood fit parameters, it is difficult for the Drude-Smith model to be more than a convenient expression for linking the conductivities of similar nanosystems to one another, and to Monte Carlo simulations.…”

“…(1) was originally applied to liquid metals 7,8,49 and was later adopted for nanosystems, 9−48 where physical boundaries on the nanoscale provide a conceptually clear source of directionally biased scattering. Its use has grown in prevalence over the last few years, extending to disordered crystals, 50-53 molecular networks, [54][55][56][57][58][59][60] and highfield transport.…”