Tuning interfacial charge-transfer excitons at polymer-polymer heterojunctions under hydrostatic pressure

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) is a key material in organic electronics.
• Understanding excited state dynamics in blend films is crucial for device optimization.
• Hydrostatic pressure is a tool to tune intermolecular interactions and electronic properties.

Purpose of the Study:

• To investigate the effect of hydrostatic pressure on the photoluminescence of F8BT blend thin films.
• To analyze the spectral shifts and excited state dynamics under varying pressures.
• To elucidate the relationship between intermolecular distance and exciplex emission.

Main Methods:

• Photoluminescence spectroscopy was employed.
• Blend thin films of F8BT with electron-donating copolymers were fabricated.
• Experiments were conducted under hydrostatic pressures ranging from 0.1 MPa to 8.8 GPa.

Main Results:

• The photoluminescence spectrum of F8BT exhibited a redshift of 530±60 meV with increasing pressure.
• The interfacial charge-transfer exciton redshifted by 270–370 meV.
• Despite a smaller spectral shift, excited state dynamics were enhanced, favoring exciplex emission due to reduced intermolecular distances.

Conclusions:

• Hydrostatic pressure significantly influences the photophysical properties of F8BT blend films.
• Decreasing intermolecular distances under pressure enhance excited state dynamics at the molecular heterojunction.
• Exciplex emission is favored under hydrostatic pressure due to enhanced intermolecular interactions.