Low‐Dimensional Single‐Cation Formamidinium Lead Halide Perovskites (FA_m+2Pb_mBr_3m+2): From Synthesis to Rewritable Phase‐Change Memory Film

Abstract

Synthesis of 2D perovskites often demands long and bulky organic spacer cations, but they hamper optoelectronic properties of the resulting 2D perovskites. Novel low‐dimensional single‐cation perovskites with a general formula of FAm+2PbmBr3m+2 are prepared by using a quenching‐assisted solution process, which leads to the wide dimensional control over 1D FA3PbBr5 (m = 1), 2D FAm+2PbmBr3m+2 (m ≥ 2), and 3D FAPbX3 (m = ∞) perovskites simply by changing the composition of precursors. In this case, formamidinium (FA) acts as both an A‐site cation and spacer cation in FAm+2PbmBr3m+2. Unlike conventional 2D perovskites, FAm+2PbmBr3m+2 perovskites have (110) orientation. PVDF (poly(vinylidene fluoride)) preferentially stabilizes the low‐dimensional FAm+2PbmBr3m+2 phases, which is utilized to fabricate the stable FAm+2PbmBr3m+2‐PVDF composite films. The phase transitions from 1D and 2D to 3D are investigated in response to various stimuli, including humidity, ultraviolet, oxygen, and solvents, are exploited for rewritable phase‐change memory films.

High-Temperature Phase Transition with Switchable Dielectric Behavior and Significant Photoluminescence Changes in a Zero-Dimensional Hybrid SbBr6 Perovskite

“…According to this formula, cycles at 6 K, this reversible phase transition has the characteristic of a first-order phase transition. 4,[8][9][10][11]13,14,18,21 In addition, it can be observed from the thermogravimetry differential thermal analysis (TG-DTA) curve (Figure 1b) that the decomposition temperature of compound 1 reaches 505 K, which is much higher than the reversible phase transition temperature. It is an honor that the phase transition temperature of compound 1 has been higher than many reported organic−inorganic hybrid perovskites, such as [(CH 3 ) 3 NOH] 2 BiCl 5 (183.5 K) 2 3 and [(CH 2 ) 4 N-(CH 2 ) 4 ] 2 [MnBr 4 ] (327 K).…”

“…By using a similar heating operation method, we can further calculate Δ H = 2.256 kJ·mol –1 , Δ S = 7.643 J·mol –1 ·K –1 and N = 2.508. Combined with the thermal hysteresis effect between heating and cooling cycles at 6 K, this reversible phase transition has the characteristic of a first-order phase transition. ,− ,,,, …”

Optoelectronic Properties of Polyvinylidene Fluoride Films Embedded with FAPbBr3 Nanocrystals Affected by Carrier Kinetics

“…Recently, an alternative approach was developed to increase the perovskite stability. In this approach, perovskite nanocrystals (NCs) are embedded in a polymeric matrix or hard porous template so as to eliminate the interference of oxygen and moisture, which can protect the perovskite material and maintain its stability for a long time. − For example, Zhong et al performed in situ fabrication of MAPbX 3 NC-embedded polyvinylidene fluoride (PVDF) composite films, which were brightly luminescent and color-tunable. Yang et al.…”

Photoinduced Transition from Quasi-Two-Dimensional Ruddlesden–Popper to Three-Dimensional Halide Perovskites for the Optical Writing of Multicolor and Light-Erasable Images

“…This has allowed us to create high-resolution multicolor microimages on the n = 3 quasi-2D perovskite thin films using a two-photon direct laser writing method by controlling the irradiation dose and exposure time. These images can be considered as examples of high-capacity optical data storage and could meet the demands of information encryption technology, which significantly exceeds previous works on halide perovskites in terms of DPI. − Moreover, a simple projection UV lithography has been applied to the n = 2 quasi-2D perovskite films to demonstrate light-erasable luminescent labels, which may provide secure items with an advanced level of protection and accelerate the potential progress in anticounterfeiting. A further increase in resolution can be achieved by integration of the quasi-2D perovskites with various optically resonant nanostructures localizing and amplifying light at the nanoscale. − …”