Fig. 2
Excitation spectra of the THz extinction based on various 2D perovskites. a Photoluminescence spectra of the 2D perovskites used in this work and the associated UV–vis absorption (black curves). b Schematic depicting the measurement concept. The 2D perovskite samples were photoexcited using a filtered halogen lamp. c Transmission spectra of the silicon/perovskite samples for n = 1 layer (green), n = 2 layer (yellow), and n = 3 layer (red) 2D perovskites. The strong absorption of THz radiation occurs in the same narrow-band optical range as the photoluminescence spectra in a. d An expanded view of the device showing multiple 2D perovskites layers forming a superlattice. The schematic shows two possible mechanisms for exciton dissociation into free carriers. Mechanism A: excitons that are normally confined to the lead-halide plane, exhibit overlapping wavefunctions in the superlattice and tunnel into the silicon substrate, where they can dissociate thereby contributing to the THz absorption. Mechanism B: excitons diffuse through edge states (grain boundaries) where they dissociate into free carriers38. These free carriers could diffuse to the underlying silicon through the voids in the polycrystalline films
