Molecular Packing Motifs Determine Charge-Transfer and Carrier Dynamics in Molecular Heterosystems: the Case of Pentacene - Perfluoropentacene

TL;DR

This study investigates how molecular packing motifs in pentacene-perfluoropentacene heterostructures influence charge transfer and carrier dynamics, revealing the importance of molecular orientation on optical properties and exciton behavior.

Contribution

It provides new insights into the relationship between packing motifs and optical/electronic properties in molecular heterostructures, highlighting the role of molecular alignment.

Findings

Interface-specific luminescence channels at 1.4 and 1.5 eV depend on molecular alignment.

Molecular packing influences exciton dissociation and charge transfer efficiency.

Different carrier injection channels are identified in heterostructures versus unitary films.

Abstract

The great majority of electronic and optoelectronic devices depends on interfaces between n-type and p-type semiconductors. Finding such matching donor-acceptor systems in molecular crystals remains a challenging endeavor. Structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties: large exciton binding energies may favor bound electron-hole pairs rather than charge separation by exciton dissociation, and free, band-like transport is challenging to achieve as hopping commonly dominates charge motion. Structurally well-defined pentacene-perfluoropentacene heterostructures in different polymorphs and molecular orientations are model systems to study the relation of packing motif and optical properties. These heterosystems feature two characteristic interface-specific luminescence channels at around 1.4 and 1.5 eV. Their relative emission strength strongly depends on the molecular alignment of the respective donor and acceptor molecules. Evaluating their dynamics in comparison with the corresponding unitary films reveals the role of singlet-triplet intersystem crossing and different channels for carrier injection into the interface-specific resonances.