Chain Length Dependence of Electron Transport in an n-Type Conjugated Polymer with a Rigid-Rod Chain Topology

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• N-type conjugated polymers typically exhibit peak charge carrier mobility at moderate chain lengths (40-60 repeat units).
• Their semiflexible chain topology limits charge transport efficiency at longer lengths.

Purpose of the Study:

• To investigate the effect of rigid-rod chain topology on the electron mobility of n-type conjugated polymers.
• To understand the mechanism behind chain length-dependent charge transport in rigid-rod polymers.
• To explore the potential of rigid-rod architectures for high-performance organic electronics.

Main Methods:

• Synthesis and characterization of a model n-type conjugated polymer with a rigid-rod chain topology.
• Field-effect transistor (FET) measurements to determine charge carrier mobility and threshold voltage.
• Analysis of structural and energetic disorder as a function of polymer chain length (degree of polymerization).

Main Results:

• Electron mobility in rigid-rod polymers increased continuously without saturation, even beyond 250 repeat units.
• Reduced structural and energetic disorder were observed with increasing polymerization degree in rigid-rod polymers.
• A decrease in trap densities and trap depths was correlated with increased chain length, leading to a decay in threshold voltage.

Conclusions:

• Rigid-rod chain topology enables sustained improvement in electron transport properties with increasing polymer chain length.
• This architecture overcomes the limitations of semiflexible polymers, offering a pathway to higher mobility conjugated polymers.
• The findings highlight the critical role of polymer architecture in designing advanced organic electronic materials.