Secondary Exciplex by Electromer Mediated Charge Transfer for Multiband Electroluminescence

Area of Science:

• Organic electronics
• Polymer science
• Optoelectronics

Background:

• Charge-transfer states, known as exciplexes, are well-understood in organic semiconductor heterojunctions.
• Electromer states, distinct from exciplexes, can form in specific polymeric molecules with folded chains.

Purpose of the Study:

• To investigate the interaction between exciplex and electromer states in polymer blends.
• To identify and characterize a novel electrically excited state resulting from this interaction.
• To explore the implications for broadband light emission in organic optoelectronics.

Main Methods:

• Fabrication of a blend film using poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylene-diamine) (PFB) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT).
• Analysis of the electroluminescence spectrum to resolve different emission bands.

Main Results:

• Observation of an indirect optoelectronic mechanism mediated by electromers, leading to the formation of a secondary exciplex.
• Resolution of four distinct emission bands: excitons, electromers, primary exciplexes, and secondary exciplexes.
• Broad electroluminescence spectrum spanning from 500 nm (green) to 900 nm (near-infrared), with a full bandwidth of 400 nm.

Conclusions:

• The interaction between exciplex and electromer states creates a secondary exciplex, expanding the understanding of excited states in organic semiconductors.
• This electromer-mediated heterojunction mechanism facilitates broadband light emission, crucial for advanced optoelectronic devices.
• The findings are significant for the development of polymeric optoelectronics and broadband light-emitting devices.