Microstructural control suppresses thermal activation of electron transport at room temperature in polymer transistors

TL;DR

This study demonstrates that microstructural control through precise processing and annealing in polymer transistors can suppress thermal activation of electron transport, achieving high mobility with minimal temperature dependence at room temperature.

Contribution

It reveals that uniaxial molecular alignment and annealing within the melting endotherm enable electron delocalization and reduce energy barriers, advancing understanding of charge transport in polymer transistors.

Findings

Achieved voltage-independent mobility with vanishing activation energy above 280 K.

Demonstrated that molecular alignment and annealing improve crystalline domain size and electron delocalization.

Provided experimental and computational evidence for reduced energy barriers in aligned crystalline regions.

Abstract

Recent demonstrations of inverted thermal activation of charge mobility in polymer field-effect transistors have excited the interest in transport regimes not limited by thermal barriers. However, rationalization of the limiting factors to access such regimes is still lacking. An improved understanding in this area is critical for development of new materials, establishing processing guidelines, and broadening of the range of applications. Here we show that precise processing of a diketopyrrolopyrrole-tetrafluorobenzene-based electron transporting copolymer results in single crystal-like and voltage-independent mobility with vanishing activation energy above 280 K. Key factors are uniaxial molecular alignment and thermal annealing at temperatures within the melting endotherm of films. Experimental and computational evidence converge toward a picture of electrons being delocalized within crystalline domains of increased size. Residual energy barriers introduced by disordered regions are bypassed in the direction of molecular alignment by a more efficient interconnection of the ordered domains following the annealing process.