Layered Halide Perovskites: Rich Structural Chemistry and Untapped Potential in Optoelectronics

Halide perovskites have shown an immense potential as semiconductors in the past decade, exemplified by their remarkable prowess in photovoltaics, but also in other fields of optoelectronics with successful proof-of-principle demonstrations as radiation sensors, light-emitting devices and lasers. Halide perovskites hold great promise in the sense that they can match in performance the classical semiconductors, but in addition, they can exhibit unconventional behavior such as their unusual defect tolerance that derives from the dynamic nature of the crystal lattice. A specific branch of halide perovskite class of materials that have been drawn enormous attention in recent years, is the dimensionally reduced layered perovskites. Layered perovskites are produced by the incorporation of “molecular scissors” that disrupt the continuity of the inorganic lattice and produce nanoscale-sized two-dimensional sheets, periodically oriented in the form of macroscopic crystals. Layered perovskites possess all the privileges of the parent compounds, but in addition, they are subject to spatial and dielectric confinement effects, thus generating quantum phenomena within their multiple-quantum-well structure.<br/>In this talk, I will discuss the early developments in the field of layered halide perovskites and how this early work has led to the current state-of-the-art. I will outline the synthetic methods that have been utilized to obtain the materials in pure form and I will discuss the evolution of important homologous series that constitute the arch types of many related compounds. I will discuss how the optical properties of the materials vary in these systems, focusing of their ability to form stable excitonic states and the peculiar changes that occur in the spectra upon the numerous phase transitions observed in variable temperature experiments. I will conclude my talk by describing potential applications of layered perovskites that can benefit from the presence of stable excitons.<br/><br/><i>Acknowledgements</i>: CCS acknowledges the Special Account for Research Funding of the University of Crete (grants KA10330 and KA10652), the project “NANO-TANDEM” (MIS 5029191), co-financed by Greece and the European Regional Development Fund, and the Ministry of Science and Higher Education of the Russian Federation (Megagrant no. 075-15-2022-1112) for financial support.