Effect of External Electric Field on Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(bithiophene)] Chain Orderness, Morphology, and Carrier Mobility in Different Condensation Processes

Abstract

Poly[(9,-alt-co-(bithiophene)] (F8T2) is a kind of crystal and liquid-crystal conjugated polymer (CP). In this research, the effect of external electric field (EEF) on F8T2 chain orderness, morphology, and carrier mobility in different condensation processes of annealing at 130 °C (above glass-transition temperature), 200 °C (crystallization temperature), and 280 °C (liquid-crystal temperature) was investigated by UV−vis absorption spectroscopy, photoluminescence spectroscopy, Xray diffraction, atomic force microscopy, polarizing optical microscopy, transmission electron microscopy (TEM), and current density−voltage (C−V) curves. It was found that EEF could enhance F8T2 chain orderness and manipulate F8T2 chain self-assembly in all the above three types of annealed films. However, the responses of F8T2 chains to EEF were different. After applying EEF, a preferred arrangement along the EEF direction with needle-like crystals was presented in 130 °C annealed films, and ordered nanorod structures were observed in 280 °C annealed films. Meanwhile, subcrystallization with an increased crystallite size of 14.6% was also discovered in the annealed film at 200 °C. As a result, the hole mobilities of these films were improved 127% (130 °C), 367% (200 °C), and 320% (280 °C). The mechanism for both microstructure changes and hole mobility enhancement was revealed. This research sheds a new light to improve carrier mobility by utilizing EEF to control the chain-condensed state structure and film orderness. This also enlightens us to consider the relationship between external forces and chain self-assembly of CPs based on intrinsic properties of CPs and basic theory of condensed matter physics.

Effect of an External Electric Field on the Ordered Structures of Blended Donor Polymers in Solar Cells

“…However, the EEF increased the mobility of the 100% P3HT film from 0.73 × 10 –3 to 2.69 × 10 –3 cm 2 V –1 s –1 , and the growth rate was 268%. This result was consistent with the increasing trend of chain orderness in the films, indicating that charge transport in the P3HT films strongly depended on the chain-ordered structure that provided an efficient channel for charge transfer . Notably, the mobility of the PTB7/P3HT blended film (with 30% P3HT) increased from 2.72 × 10 –3 to 6.76 × 10 –3 cm 2 V –1 s –1 with the application of the EEF.…”

“…This result was consistent with the increasing trend of chain orderness in the films, indicating that charge transport in the P3HT films strongly depended on the chain-ordered structure that provided an efficient channel for charge transfer. 40 Notably, the mobility of the PTB7/P3HT blended film (with 30% P3HT) increased from 2.72 × 10 −3 to 6.76 × 10 −3 cm 2 V −1 s −1 with the application of the EEF. This mobility outperformed that of pure PTB7 (3.82 × 10 −3 cm 2 V −1 s −1 ).…”

Free-radical polymerization of 2-hydroxyethyl methacrylate (HEMA) supported by a high electric field

“…This aspect appears to be particularly interesting for polar macromolecules that can become polarized with the subsequent alignment of the molecules under the electric field. In this context, it is worth emphasizing that the strong impact of the electric field was well demonstrated in the case of the phase transformation, self-ordering, 24 or self-assembling 30,31 of different materials (including polymeric ones). Here, it is worth mentioning the interesting work by Cai et al on the reversible transformation between the two-dimensional covalent organic frameworks (2D COFs) and the self-assembled molecular networks (SAMNs) of 1,3,5-tris(4-biphenyl boronic acid)benzene (TBPBA) on a graphite surface at room temperature underneath the tip of a scanning tunneling microscope (STM).…”

Liquid–Solid Transfer Process of Ordered Structures in Efficient Polymer Photovoltaic Materials

“…Two characteristic absorption peaks were observed at 549 and 589 nm when PBDT-TTz was dissolved in CF, which red-shifted to 553 and 595 nm, respectively, when PBDT-TTz was dissolved in CB. This red-shifting phenomenon indicated that the main chain’s conjugation length for PBDT-TTz increased in CB . According to Spano’s model, the lower energy 0–0 peak (595 nm) mainly represented π–π stacking between molecular chains or between molecular chain segments, and the higher energy 0–1 peak (553 nm) represented the intrachain state .…”

“…This red-shifting phenomenon indicated that the main chain's conjugation length for PBDT-TTz increased in CB. 44 According to Spano's model, the lower energy 0−0 peak (595 nm) mainly represented π−π stacking between molecular chains or between molecular chain segments, 45 and the higher energy 0−1 peak (553 nm) represented the intrachain state. 46 In dilute solution, molecular chains are isolated from one another with no interchain interaction.…”