Modeling the P3HT microcavity reflectance spectrum: Introducing a partitioning scheme for treating large disordered...

Area of Science:

• Organic electronics
• Solid-state physics
• Spectroscopy

Background:

• Poly(thiophene) (P3HT) is a key material in organic electronics.
• Understanding light-matter interactions in P3HT films is essential for device optimization.
• Microcavity spectroscopy provides insights into exciton dynamics.

Purpose of the Study:

• To analyze the microcavity reflectivity spectrum of a thin P3HT film.
• To model light-matter interactions using theoretical frameworks.
• To elucidate the origins of spectral features in P3HT films.

Main Methods:

• Frenkel-Holstein-Tavis-Cummings Hamiltonian and Lindblad formalism for relaxation.
• Partitioning scheme for disordered P3HT chain segments (aggregate/amorphous domains).
• Analysis of free-space absorption and microcavity reflectivity spectra.

Main Results:

• Excellent agreement between measured and calculated reflectivity spectra with ensemble light-matter coupling (NgS) of 0.9 eV.
• Observation of narrow lower polariton (LP) and broad upper polariton (UP) features.
• Rabi splitting of approximately 1 eV, with weak middle polaritons attributed to vibronic coupling.

Conclusions:

• The LP feature primarily originates from aggregate P3HT domains.
• The UP feature arises from both aggregate and amorphous P3HT domains.
• Herzberg-Teller mechanism explains the appearance of bright vibronic polaritons.