Charge Transport by Superexchange in Molecular Host-Guest Systems

Area of Science:

• Materials Science
• Organic Electronics
• Quantum Chemistry

Background:

• Charge transport in disordered organic semiconductors is typically modeled as incoherent hopping between localized states.
• Organic light-emitting diodes (OLEDs) rely on efficient charge transport within multicomponent host-guest emissive layers.
• Existing models may not fully capture the nuances of charge dynamics in complex organic semiconductor systems.

Purpose of the Study:

• To investigate the role of molecular superexchange in charge transport within OLED host-guest systems.
• To demonstrate how coherent charge transfer mechanisms can enhance transport properties.
• To explore the impact of superexchange on emitter-to-emitter hopping and percolation pathways.

Main Methods:

• Utilized multiscale ab initio based modeling.
• Focused on multicomponent emissive host-guest layers characteristic of OLEDs.
• Analyzed charge transport dynamics under varying guest concentrations and trap state depths.

Main Results:

• Demonstrated that molecular superexchange significantly enhances charge transport.
• Showed increased emitter-to-emitter hopping rates, especially when emitters act as deep trap states.
• Identified the formation of percolation paths for charge transport at low guest concentrations due to superexchange.

Conclusions:

• Coherent charge transport via molecular superexchange is a crucial mechanism in organic semiconductors.
• Superexchange offers a pathway to improve charge mobility and device efficiency in OLEDs.
• This finding challenges the solely incoherent hopping paradigm and opens new avenues for material design.