Simultaneous Enhancement of Electron and Hole Mobility in Para-Azaquinodimethane-Derived Polymer by Individually Applying Various Additives.

Abstract

Achieving simultaneous enhancement of electron and hole mobility in organic semiconductors (OSCs) using a single additive remains a significant challenge. In this study, we present a unique additive strategy that enables concurrent improvement of both n- and p-type transport in an n-dominant ambipolar polymer incorporating para-azaquinodimethane and diketopyrrolopyrrole. By individually applying various additives including ionic, p-type, and n-type compounds, we achieve unprecedented enhancements of both electron (∼400%) and hole (∼100%) mobility. Such parallel improvement is unattainable via conventional electron transfer mechanism. We ascribe this effect to optimized film morphology, reduced activation energy, and lowered contact resistance. To further elucidate additive-induced variations in electronic structure and guide future molecular design, density functional theory calculations reveal that incorporating para-azaquinodimethane into the polymer backbone facilitates strong orbital coupling with additives. This coupling introduces additional charge transport pathways between polymer segments, enhancing both electron and hole transport along lamellar and π-π stacking directions. Our findings suggest promoting robust orbital coupling between host polymers and additives offers a promising strategy to concurrently boost electron and hole mobility in a single OSC, effectively circumventing traditional limitations associated with separate p- and n-type additives/dopants.