Correlation of Coexistent Charge Transfer States in F₄TCNQ-Doped P3HT with Microstructure

Abstract

Understanding the interaction between organic semiconductors (OSCs) and dopants in thin films is critical for device optimization. The proclivity of a doped OSC to form free charges is predicated on the chemical and electronic interactions that occur between dopant and host. To date, doping has been assumed to occur via one of two mechanistic pathways: an integer charge transfer (ICT) between the OSC and dopant or hybridization of the frontier orbitals of both molecules to form a partial charge transfer complex (CPX). Using a combination of spectroscopies, we demonstrate that CPX and ICT states are present simultaneously in F4TCNQ-doped P3HT films and that the nature of the charge transfer interaction is strongly dependent on the local energetic environment. Our results suggest a multiphase model, where the local charge transfer mechanism is defined by the electronic driving force, governed by local microstructure in regioregular and regiorandom P3HT.

Microstructure-dependent electrochemical properties of chemical-vapor deposited poly(3,4-ethylenedioxythiophene) (PEDOT) films

“…It is well-established that the microstructure of a conductive polymer film can have impact on the relative redox properties and charge transfer, both in electrochemical systems 50 and in the solid state. 96 We are most interested in structure-property behaviors of polymer electrodes at the onset in the density of states of the polymer films and thus, focus our analysis on a small voltage window of -0.2 to 0.2 V. Wider windows and characterization of CVD PEDOT has been previously described. 62,63 Figure 14 provides the aqueous cyclic voltammograms of the three microstructure films in Figure 10, taken immediately after deposition and rinsing to remove residual oxidant.…”

The optical signatures of molecular-doping induced polarons in poly(3-hexylthiophene-2,5-diyl): individual polymer chainsversusaggregates

“…13 Consequently, implications of the presence of aggregates in solution of P3HT mixed with a dopant in solution were also investigated. [14][15][16][17] The abundance of re-P3HT aggregates in solution was reported to increase upon addition of molecular p-type dopants, with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) being the one most frequently used, and was ascribed to decreased solubility of the corresponding ionized species after ion pair (IPA) formation (doping involving integer electron transfer). 18,19 It was shown that aggregation occurs more readily for solution-mixed doping as compared to sequential doping of re-P3HT thin films.…”

Molecular Doping of PCPDT-BT Copolymers: Comparison of Molecular Complexes with and Without Integer Charge Transfer

“…For many of the complexes showing ICT, we also find one or more alternative optimized structures without ICT (the "No" cases in Table I). In other words, for the same molecular complexes, both the possibilities of ICT and non-ICT exist [17], which correspond to different local minimum structures. The results show that the optimized ICT structures can be energetically more favourable or less favourable than those without ICT.…”

“…In experiment, these two mechanisms can be distinguished using optical spectroscopy, as the electronic excitations are qualitatively different and free charges on the polymer chains show up as distinct polaron absorption features [9][10][11][12][13][14]. Also different vibrational modes exist with unique optical fingerprints in the infrared spectral range [15][16][17][18][19]. In conductivity measurements generally only a limited frac- This mechanism leads to a complex with integer charge transfer (ICT).…”