Quantifying Charge Carrier Localization in PBTTT Using Thermoelectric and Spectroscopic Techniques

Shawn A Gregory; Amalie Atassi; James F Ponder Jr; Guillaume Freychet; Gregory M Su; John R Reynolds; Mark D Losego; Shannon K Yee

doi:10.1021/acs.jpcc.3c01152

Quantifying Charge Carrier Localization in PBTTT Using Thermoelectric and Spectroscopic Techniques

J Phys Chem C Nanomater Interfaces. 2023 Jun 14;127(25):12206-12217. doi: 10.1021/acs.jpcc.3c01152. eCollection 2023 Jun 29.

Authors

Shawn A Gregory¹, Amalie Atassi¹, James F Ponder Jr², Guillaume Freychet³, Gregory M Su^{4

5}, John R Reynolds^{1

6}, Mark D Losego¹, Shannon K Yee²

Affiliations

¹ School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
² George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
³ NSLS-II, Brookhaven National Laboratory, Upton, New York 11973, United States.
⁴ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
⁵ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
⁶ School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.

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.