From Excitons to Polaritons: Strong Coupling and Ultrafast Dynamics in 2D Perovskite Microcavities

Two-dimensional (2D) metal halide perovskites are promising materials for exploring strong light-matter coupling due to their large exciton binding energies and pronounced excitonic resonances. This thesis investigates the structural, optical, and dynamical properties of n = 1 butylammonium lead iodide (BA₂PbI₄) thin films and their integration into distributed Bragg reflector (DBR) microcavities.
Film morphology was optimized using solvent and additive engineering. AFM and XRD measurements showed that incorporation of 18-crown-6 significantly improved film uniformity and crystallinity. Optical spectroscopy confirmed strong excitonic absorption and narrow photoluminescence linewidths. Angle-resolved reflectivity measurements of DBR cavities revealed clear anti-crossing behaviour at room temperature, demonstrating strong coupling and exciton-polariton formation.
Low-temperature measurements identified amplified spontaneous emission (ASE) in films and bilayer structures. However, power-dependent photoluminescence studies of cavities showed no evidence of polariton condensation. Ultrafast pump-probe spectroscopy suggests that short polariton lifetimes, cavity losses, and relaxation bottlenecks limit condensation.