Investigating Excited State Coherence and Coupling in Engineered Spin-Cast Superlattices of 2D Halide Perovskites

Hybrid organic-inorganic perovskites (HOIPs) are low-cost and rapidly developing materials with many unexplored avenues of generating multifunctionality. Recently, several reports have shown coherent optical phenomena in colloidal perovskite superlattice structures and phonon-coupling behavior in the carrier dynamics of 2D-phase perovskites. Although typical spin-coated films have poor crystallographic orientation, we present single crystalline-like and highly-oriented spin-coated 2D-phase perovskites, i.e. superlattices, and their resultant coherent excited states. Using X-Ray Reflectometry measurements, we identified the well-defined layered structure of 2D-phase superlattice perovskite structures. This is demonstrated with several chemical variations, including a ferroelectric phase by selection of a fluorinated cation in the A-site. The resulting coherent phenomenon emergent in these confined and ordered structures are studied through temperature dependent and time-resolved photoluminescence, the electron-phonon coupling effects on decay dynamics in transient absorption with polarized pump and probe, and photoinduced Raman spectroscopy. Then we incorporated the engineered ferroelectric HOIP superlattice thin film into a ferromagnetic/ferroelectric interfacial materials system and as the light-emitting layer of an LED. Finally, we report the optical-magnetic coupling behavior, as characterized by Polarized Neutron Reflectometry, using this dually light-emitting and ferroelectric superlattice. This work develops a superlattice 2D-HOIP yielding ferroelectricity which provides the fundamental platform to explore multifunctional coupling behavior towards a new-generation of spin-related optoelectronic devices.