Electron Transfer Enhanced by a Minimal Energetic Driving Force at the Organic-Semiconductor Interface

Area of Science:

• Materials Science
• Organic Electronics
• Photochemistry

Background:

• Efficient optoelectronic devices like organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs) require minimized energetic driving forces for electron transfer.
• Understanding charge-transfer (CT) state dynamics at interfaces is crucial for correlating energetics, electron-transfer efficiency, and device performance.

Purpose of the Study:

• Investigate electron transfer from charge-transfer (CT) states to triplet excited states (T1) in upconversion OLEDs.
• Analyze the relationship between CT interaction, energetic driving force, and electron transfer efficiency.
• Develop novel donor-acceptor combinations for efficient OLEDs.

Main Methods:

• Studied 45 material combinations in upconversion OLEDs.
• Analyzed CT emission and singlet excited-state emission from triplet-triplet annihilation via the dark T1.
• Extracted energetics and electron-transfer efficiencies.
• Applied Marcus theory to explain electron transfer dynamics.

Main Results:

• CT→T1 electron transfer is enhanced by stronger CT interaction and minimal energetic driving force (<0.1 eV).
• Marcus theory with small reorganization energy (<0.1 eV) explains the observed electron transfer.
• A novel donor-acceptor combination resulted in efficient blue emission with a low turn-on voltage (1.57 V).

Conclusions:

• Controlling interfacial CT states is essential for developing efficient optoelectronic devices with minimal energy loss.
• The findings provide a pathway for designing high-performance OLEDs by optimizing CT state dynamics.
• This research contributes to the advancement of energy-efficient organic electronic devices.