Synthesis of Two‐Dimensional Perovskite by Inverse Temperature Crystallization and Studies of Exciton States by Two‐Photon Excitation Spectroscopy

Abstract Two‐dimensional (2D) organic–inorganic hybrid perovskites (OIHPs), a natural multiple‐quantum‐well structure with quasi‐2D electronic properties, have recently emerged as a promising class of semiconducting materials for photovoltaic and optoelectronic applications. However, facile synthesis of high‐quality 2D OIHPs single crystals is still lacking. The layer dependence of the exciton binding energy of (C 4 H 9 NH 3 ) 2 PbI 4 (C4PI), a widely studied 2D OIHP, is still debated. Herein, a novel synthesis technique based on inverse temperature crystallization in a binary‐solvent system is used to prepare 2D OIHPs and a systematic study of excitonic states of the synthesized 2D OIHPs by two‐photon excitation (TPE) spectroscopy is conducted. The obtained TPE spectra indicate that the exciton binding energies are similar for C4PI nanosheets and bulk crystals with different number of layers, most likely due to the intrinsically weak interlayer coupling. Further, the dark excitonic 2 p states of (C 6 H 5 (CH 2 ) 2 NH 3 ) 2 PbI 4 (PEPI) and C4PI are also observed by TPE spectroscopy. The results provide a novel synthesis protocol and insight into exciton properties of 2D OIHPs.