Quantifying Charge Carrier Localization in PBTTT Using Thermoelectric and Spectroscopic Techniques

Abstract

Chemically doped poly­[2,5-bis­(3-alkylthiophen-2-yl)­thieno­[3,2-b]­thiophene] (PBTTT) shows promise for many organic electronic applications, but rationalizing its charge transport properties is challenging because conjugated polymers are inhomogeneous, with convoluted optical and solid-state transport properties. Herein, we use the semilocalized transport (SLoT) model to quantify how the charge transport properties of PBTTT change as a function of iron­(III) chloride (FeCl3) doping level. We use the SLoT model to calculate fundamental transport parameters, including the carrier density needed for metal-like electrical conductivities and the position of the Fermi energy level with respect to the transport edge. We then contextualize these parameters with other polymer-dopant systems and previous PBTTT reports. Additionally, we use grazing incidence wide-angle X-ray scattering and spectroscopic ellipsometry techniques to better characterize inhomogeneity in PBTTT. Our analyses indicate that PBTTT obtains high electrical conductivities due to its quickly rising reduced Fermi energy level, and this rise is afforded by its locally high carrier densities in highly ordered microdomains. Ultimately, this report sets a benchmark for comparing transport properties across polymer-dopant-processing systems.

Enhancing the thermoelectric performance of donor–acceptor conjugated polymers through dopant miscibility: a comparative study of fluorinated substituents and side-chain lengths

“…Doped donor–acceptor (D–A) conjugated polymers have attracted substantial attention as a highly promising class of materials for thermoelectric applications. 18–42 The inherent advantages of D–A copolymers lie in their capacity for meticulous property tailoring through the strategic manipulation of molecular structures in both donor and acceptor components. Notably, benzothiadiazole (BT) has emerged as an exemplary acceptor due to its structural rigidity and pronounced electron-withdrawing characteristics.…”