Strong coupling in organic semiconductor microcavities

Abstract

We discuss the similarities and differences between inorganic and organic semiconductor microcavities operating within the strong coupling regime and identify novel features of the organic systems that can be exploited in new structures. Experimental results for σ-conjugated poly(n-butylphenylsilane) [PBPS] based structures show a giant Rabi splitting energy of between 210 and 230 meV. PBPS represents the first of a new class of organic materials, namely the σ-conjugated polysilanes, that are well suited for strong coupling studies. The polysilanes possess large oscillator strengths, large exciton binding energies and can have relatively narrow exciton linewidths. These properties ensure large Rabi energies and allow observation at room temperature. The experimental results for both cavity reflection and emission spectra correspond well to our transfer matrix model calculations. We report the successful engineering of a flat dispersion for the lower polariton branch that results in insensitivity to emission angle for the photoluminescence emission peak. This invariance is promising for display devices that use microcavities to define colour since it ensures that there is a negligible blue-shift of the emission for off-axis viewing. As other examples of novel features that can be obtained with organic systems we describe the use of birefringent polymers to mediate multi-component polariton interactions and describe the opportunities for amplifiers based on stimulated scattering of polaritons. We also discuss prospects for inorganic/organic hybrid materials that may allow the rules that apply to matter and light to be further stretched, potentially seeding a new paradigm in optoelectronic devices.