Fig. 2: The transmission spectra of the BIC metasurfaces before and after spin-coating of perovskite, as well as the pure perovskite film.

a Measured transmission amplitudes of BIC resonances across the frequency of perovskite phonon tuned via scaling the in-plane geometric parameters. The new parameters were derived by multiplying S with the in-plane geometric parameters. \({P}_{{\rm{xnew}}}=S{P}_{{\rm{x}}}\), \({P}_{{\rm{ynew}}}=S{P}_{{\rm{y}}}\), \({L}_{{\rm{xnew}}}=S{L}_{{\rm{x}}}\), \({L}_{{\rm{ynew}}}=S{L}_{{\rm{y}}}\), \({L}_{1{\rm{new}}}=S{L}_{1}\), \({m}_{{\rm{new}}}={Sm}\), \({w}_{{\rm{new}}}={Sw}\). b Transmission amplitude of the Au metasurface coated with an amorphous perovskite film is represented by red solid line, while that of pare Au metasurface without perovskite is represented by a red dished line. c The transmission amplitude of a MAPbI₃ film spin-coated on a quartz substrate. The arrow indicates the frequency of phonon resonance. d Transmission amplitude of Au-MAPbI₃ metasurfaces for different scaling factors shows a characteristic and anticrossing mode pattern close to the MAPbI₃ phonon. e Transmission amplitude of Au metasurface coated with a crystallized perovskite film while the resonance position of BICs is tuned to 0.95 THz, which reveals a Rabi splitting of 0.28 THz