Molecular Interactions and Ordering in Electrically Doped Polymers: Blends of PBTTT and F₄TCNQ

Abstract

Identifying how small molecular acceptors pack with polymer donors in thin and thick (bulk) films is critical to understanding the nature of electrical doping by charge transfer. In this study, the packing structure of the molecular acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ) with the semiconducting polymer poly­(2,5-bis­(3-tetradecylthiophen-2-yl)­thieno­[3,2-b]­thiophene) (PBTTT-C14) is examined. A combination of solid-state NMR, synchrotron X-ray scattering, and optical spectroscopy was used to determine the packing motif for blends of PBTTT-C14 and F4TCNQ in thin and bulk films. These results indicate that F4TCNQ and PBTTT-C14 order in a cofacial arrangement where charge transfer is near 100% efficient in the solid state. These results provide crucial insights into the structures and compositions of ordered domains in doped semiconducting polymers and suggest a model for the microstructure where the location of the molecular acceptors are correlated rather than randomly dispersed.

Anion-induced N-doping of naphthalenediimide polymer semiconductor in organic thin-film transistors

“…30 The root mean square surface roughness (RMS) of the un-doped film was 1.40 nm. In contrast to reports where dopant phase-segregated from the host, 58,59 TBAF doped P(NDI2OD-T2) showed no obvious phaseseparated domains formed by the dopant. Films doped with 0.025 and 0.25 eq.…”

Comparison of solution-mixed and sequentially processed P3HT:F4TCNQ films: effect of doping-induced aggregation on film morphology

“…This is the typical method of preparing polymer:F4TCNQ films in the literature. 4,5,8,13,14,18,19,25,33,34 Fig . 1c shows UV-vis-NIR spectra of films prepared using the mixed solution method at doping levels between 0.5 and 17 mol% F4TCNQ.…”

“…Several groups have noted that doping often results in drastically reduced solubility of polymers; as a result, mixed polymer:dopant solutions must be kept at high temperatures and dilute concentrations, and tend to rapidly aggregate, forming gels or large particles. 4,33,34 Unfortunately, increasing solution temperatures to prevent aggregation has been shown to reduce doping efficiency. 6 Such behavior is far too capricious for industrial applications.…”

High Conductivity in Molecularly p‐Doped Diketopyrrolopyrrole‐Based Polymer: The Impact of a High Dopant Strength and Good Structural Order

“…To date, the molecular doping of small-molecule semiconductors and relatively electron-rich polymers has been studied intensively. It was demonstrated that doping of P3HT [12] and PBTTT [13] by F4TCNQ leads to a dramatic increase in the conductivity from 10 −6 S cm −1 for neat polymers up to 1-2 S cm −1 for optimally doped polymers. The high efficiency of the doping process in these cases is due to a large driving force of the charge transfer process [14,15] as the lowest unoccupied molecular orbital (LUMO) level of the dopant (−5.24 eV) lies much below the highest occupied molecular orbital (HOMO) levels of polythiophenes (−4.8 to −5.1 eV).…”