Enhancing Organic Semiconductor-Surface Plasmon Polariton Coupling with Molecular Orientation

Area of Science:

• Optoelectronics
• Materials Science
• Plasmonics

Background:

• Surface plasmon polaritons (SPPs) enhance light-molecule coupling in organic optoelectronic devices.
• SPP electric field enhancement is anisotropic, favoring perpendicular molecular orientation for maximal benefit.
• Controlling molecular orientation is crucial for optimizing device performance.

Purpose of the Study:

• To demonstrate the orientation dependence of SPP dispersion and photoluminescence.
• To investigate SPP-mediated light-molecule coupling at a model gold/small-molecule interface.
• To quantify the impact of molecular orientation on SPP properties.

Main Methods:

• Fabrication of p-SIDT(FBTTh2)2 thin films with controlled molecular orientations (in-plane vs. mixed in-plane/out-of-plane) using diiodooctane.
• Characterization using momentum-resolved reflectometry to study SPP dispersion.
• Measurement of momentum-resolved photoluminescence to quantify light-molecule coupling.

Main Results:

• Achieved distinct molecular orientations: purely in-plane or a 50/50 mix of in-plane/out-of-plane.
• Observed increased SPP momentum for out-of-plane oriented molecules.
• Demonstrated a 2-fold enhancement in photoluminescence intensity for systems with out-of-plane oriented transition dipoles.

Conclusions:

• Molecular orientation significantly impacts SPP dispersion and light-molecule coupling.
• Perpendicular molecular orientation leads to enhanced photoluminescence in organic optoelectronic devices.
• Results provide critical insights for designing and analyzing high-performance organic optoelectronics.