Ultrafast Charge-Transfer Exciton Dynamics in C₆₀ Thin Films

Area of Science:

• Materials Science
• Physical Chemistry
• Organic Electronics

Background:

• Organic molecules offer tunable optical properties for optoelectronics.
• Fundamental light-to-charge conversion mechanisms in molecular materials require further investigation.
• Fullerene (C60) thin films are promising for advanced photonic applications.

Purpose of the Study:

• Investigate the ultrafast dynamics of optically excited excitons in C60 thin films.
• Determine the influence of molecular coverage and light polarization on exciton behavior.
• Uncover the role of charge-transfer (CT) excitons in excited-state dynamics.

Main Methods:

• Time- and momentum-resolved photoemission spectroscopy.
• Femtosecond extreme ultraviolet (fs-XUV) radiation for excitation.
• Analysis of exciton cascade and valence band renormalization.

Main Results:

• Optical excitation forms charge-transfer (CT) excitons that cascade to lower-energy Frenkel-like excitons.
• Exciton number and energy are independent of molecular coverage and light polarization.
• CT and Frenkel-like exciton depopulation times vary with molecular coverage.
• CT exciton excitation efficiency is dependent on light polarization.

Conclusions:

• CT excitons play a pivotal role in the excited-state dynamics of fullerene materials.
• Molecular coverage and light polarization significantly impact exciton depopulation and excitation efficiency, respectively.
• Understanding these dynamics is key for designing next-generation optoelectronic devices.