Migration of Charge-Transfer States at Organic Semiconductor Heterojunctions

Area of Science:

• Organic electronics
• Semiconductor physics
• Photophysics

Background:

• Charge-transfer (CT) states at organic donor-acceptor (D-A) heterojunctions are vital for optoelectronic devices.
• The migration and diffusion length (L_D) of these CT states are not well understood.
• Factors influencing CT state L_D require elucidation for device optimization.

Purpose of the Study:

• To measure the CT state diffusion length (L_D) in various D-A mixtures.
• To investigate the impact of mixture composition and molecular structure on CT state migration.
• To establish a correlation between CT state L_D and charge carrier mobility.

Main Methods:

• Utilized photoluminescence quenching to measure CT state L_D.
• Examined several D-A semiconductor mixtures with varying compositions.
• Analyzed charge carrier mobility alongside CT state migration.

Main Results:

• CT state L_D was found to be approximately 5 nm in equal D-A mixtures, irrespective of CT energy or molecular structure.
• CT state L_D demonstrated strong dependence on the mixture composition.
• A significant correlation was observed between CT state L_D and the slowest charge carrier mobility.

Conclusions:

• CT state migration in bulk heterojunctions can be tuned by controlling mixture composition.
• Charge carrier mobility is a key factor determining CT state diffusion length.
• These findings provide insights for optimizing organic photovoltaic and light-emitting devices and understanding interfacial excited state transport.