Layered lead halide perovskites have recently been heavily investigated due to their versatile structures, tunable electronic properties, and better stability compared with 3D perovskites and have also been effectively incorporated into photovoltaic and light-emitting devices. They are often prepared into thin film form by solution methods and typically contain a mixture of phases with different inorganic layer thicknesses (denoted by "n"). In addition, melt-processing has recently been introduced as an option for film deposition of n = 1 lead iodide-based perovskites. Here, we study the thermal properties of higher n (n > 1) layered perovskites in the family (β-Me-PEA) 2 MA n−1 Pb n I 3n+1 , with n = 1, 2, and 3 and where β-Me-PEA = β-methylphenethylammonium and MA = methylammonium, and reveal that they do not melt congruently. However, they can still be melt-processed in air by using a two-step process that includes a lower temperature postannealing step after the initial brief melting step. While typically higher n films contain a mixture of the different n phases, the resulting two-step melt-processed films are highly crystalline and phase pure. Optical and electrical properties of these films were further characterized by time-resolved photoluminescence and dark/illuminated transport measurements, showing the same order of magnitude single-exciton recombination rates compared to previous single crystal results and >2 orders of magnitude higher conductivity compared to conventional spin-coated films. These results offer new pathways to study the layered perovskites and to integrate them into electronic and optoelectronic devices.
Light-matter interactions can create and manipulate collective many-body phases in solids 1-3 , which are promising for the realization of emerging quantum applications. However, in most cases these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin films, exhibit such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high energy electron-hole pairs, which quickly
Light-matter interactions can create and manipulate collective many-body phases in solids1-3, which are promising for the realization of emerging quantum applications. However, in most cases these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin films, exhibit such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high energy electron-hole pairs, which quickly relax to lower energy domains and then develop a macroscopic quantum coherence through spontaneous synchronization. The excitation fluence dependence of the spectroscopic features and the population kinetics in such films unambiguously confirm all the well-known characteristics of superfluorescence. These results show that the creation and manipulation of collective coherent states in hybrid perovskites can be used as the basic building blocks for quantum applications4,5.
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