Tuning the Mobility of Indacenodithiophene-Based Conjugated Polymers via Coplanar Backbone Engineering

Abstract

Conjugated polymers based on indacenodithiophene−benzothiadiazole (IDT−BT) have attracted great interest due to their high charge carrier mobilities while being low crystallinity (i.e., near-amorphous). They represent a promising design strategy to achieve both excellent stretchability and electrical performance. Here, we describe an approach to structural modifications of IDT−BT, namely, by introducing noncovalent interactions and substituting building blocks to promote extended coplanar backbones. We systematically investigated the effects of structural modifications on backbone conformation, polymer aggregations, and charge carrier mobilities. Among the investigated polymers, the fluorinated derivative IDT−FBT demonstrated the highest charge carrier mobility of 5.19 cm 2 /(V•s), along with low activation energy and Urbach energy, indicating its low energy disorder level. The high mobility was attributed to the higher backbone planarity reinforced by S•••F and H•••F noncovalent interactions and improved interchain interactions through strong aggregation. Our findings indicate that increasing backbone coplanarity may further improve mobility in low-crystallinity conjugated polymers.

Design Rules to Optimize the Intermolecular and Long-Range Packing of Organic Semiconductor Crystals

“…To improve the performance, we also explore the effect of selective fluorination of this material, as shown in Scheme b. Selective fluorination of conjugated organic molecules is a strategy that is used to increase backbone planarity between conjugated ring structures and thereby to enhance μ h in OSCs. − S···F and H···F noncovalent interactions are attributed to the higher backbone planarity and increased mobility in conjugated polymers and OSCs. − The presence of the fluorine could stabilize a planar syn-configuration via hydrogen bonding between the fluorine and neighboring proton or it could stabilize the anti-configuration through attractive S···F interactions. , For both configurations, we hypothesize that the attractive interaction will planarize the dihedral angle between neighboring rings and thereby increase delocalization of the polaron through the backbone and increase the μ h . The measured μ h of more than >10 cm 2 V –1 s –1 seems to validate our hypothesis but does not actually explain why the μ h increases because the fluorine stabilizes both syn- and anti-configurations.…”

Modulating Aggregation Structure and Properties of Conjugated Polymers via Ester Additives

“…High-mobility semiconductor polymers are semicrystalline, and many exhibit poor mechanical properties . Initially, researchers employed molecular design strategies to enhance the flexibility of semiconducting polymers, such as incorporating flexible nonconjugated spacers, , conjugated fused rings, , etc. However, discovering suitable materials requires iterative synthesis of polymers and device optimization.…”