Intrinsically distinct hole and electron transport in conjugated polymers controlled by intra and intermolecular interactions

TL;DR

This study isolates intrinsic factors affecting hole and electron transport in conjugated polymers, revealing how intra- and inter-molecular interactions distinctly influence charge mobility and enabling prediction of transport properties from optical characteristics.

Contribution

It demonstrates the fundamental role of ground-state intra- and inter-molecular coupling in selectively enhancing charge transport in conjugated polymers.

Findings

Holes mainly involve inter-chain interactions with H-type coupling.

Electrons primarily involve intra-chain interactions with J-type coupling.

Charge transfer state presence correlates with charge mobility.

Abstract

It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole transport within the same film microstructure of a model copolymer semiconductor. Relatively, holes predominantly bleach inter-chain interactions with H-type electronic coupling character, while electrons' relaxation more strongly involves intra-chain interactions with J-type character. Holes and electrons mobility correlates with the presence of a charge transfer state, while their ratio is a function of the relative content of intra- and inter-molecular interactions. Such fundamental observation, revealing the specific role of the ground-state intra- and inter-molecular coupling in selectively assisting charge transport, allows predicting a more favorable hole or electron transport already from screening the polymer film ground state optical properties.