Plexciton Dynamics in Au-Hybrid CsPbBr₃ Perovskite Nanoplatelets

Interaction of polar excitations in quantum size particles and localized surface plasmons in metallic nanoparticles results in formation of a quasi-particle called plexciton, a coupled exciton-plasmon polariton. We report observation of thickness dependent plexcitons in Au-hybrid CsPbBr₃ nanoplatelets (NPls) using optical spectroscopic measurements. Our results suggest that the greater quantum and dielectric confinement leads to extremely large exciton binding energies in thin CsPbBr₃ NPls, enhancing the Fröhlich interaction. In effect, exciton-phonon scattering phenomenon dominates the exciton decay dynamics in thin NPls. Surprisingly, the exciton-phonon scattering vanishes completely on Au-incorporation in thin CsPbBr₃ NPls, directing the formation of strong plexcitons by coupling between the localized surface plasmons of Au and the confined excitons in thin NPls. Here the plasmon induced electric field propagates through the NPls, thus altering the dielectric field strengths responsible for such elevated exciton binding energy and introducing additional screening effects to the excitons. In turn, the exciton binding energy reduces significantly, hindering the exciton-phonon interaction. Moreover, the weakened exciton binding energy extends the exciton lifetime and increases the free carrier yield, which shows a clear thickness dependence, highlighting their promising applications in nonlinear optoelectronics.