Abstract Different 2D and quasi-2D perovskite materials have demonstrated significant improvements in the device stability compared to 3D perovskites due to their increased hydrophobicity and suppressed ion migration. However, fundamental investigations of these materials have been scarce and consequently detailed understanding of the processes responsible for experimental phenomena are often lacking despite huge interest in these materials. Even more importantly, there have been a limited number of structure-property studies for different material compositions, and research is generally by trial and error rather than by design. Here we discuss different stability issues in these materials and identify questions which need to be answered to design materials with further stability improvements. 

https://www.nature.com/articles/s43246-022-00285-9.pdf

Stability of 2D and quasi-2D perovskite materials and devices

Third-order optical nonlinearities and high-order harmonics generation in Ni-doped CsPbBr3 nanocrystals using single- and two-color chirped pulses

Since its discovery, perovskite has experienced tremendous development. Furthermore, due to the outstanding stability of two-dimensional (2D) perovskites, they have been attracting increasing attention. A reduction in the dimensions of perovskites and the introduction of long organic chains yield new structures and properties. As an emerging semiconductor material with high stability, 2D perovskites have many applications in the field of optoelectronics. This review mainly describes the development and application of 2D perovskites in recent years. Firstly, we introduce the basic structure and classification of 2D perovskites. Also, we discuss the change in their characteristics and performances with a variation in the number of inorganic layers. Next, 2D perovskites are classified according to their applications in different fields. Finally, a summary and outlook based on the current development trends of 2D perovskites are presented.

Research progress on two-dimensional (2D) halide organic–inorganic hybrid perovskites

Dimensionality is the game-changer property of a material. The optical and electronic properties of a compound get dramatically influenced by confining dimensions from 3D to 2D. The bulk 3D perovskite materials have shown remarkable up-gradation in the power conversion efficiency, hence grabbing worldwide attention. But instability against moisture, temperature, and ion migration are the factors constantly back-stabbing and hindering from full-scale commercialization. 2D perovskite material has emerged as an excellent bridging entity between structural-chemical stability, and viable commercialization. Organic–inorganic 2D perovskite materials come with a layered structure in which a large organic cation layer as a spacer is sandwiched between two inorganic metal halide octahedra layers. Moreover, hydrophobic spacer cations are employed which isolate inorganic octahedral layers from water molecules. Hydrophobic spacer cations protect the authentic structure from being degraded. These layered structures occur in two phases namely the Ruddlesden–Popper phase and Dion–Jacobson phase, depending on the spacer cation types. Alternating inorganic and organic layers form multiple quantum wells naturally, along with spin–orbit-coupling gives Rashba splitting. 2D perovskite materials are coming up with interesting chemical, physical properties like exciton dynamics, charge carrier transport, and electron–phonon coupling as a result of the quantum confinement effect. Despite appreciable stability, limited charge transport and large bandgap are limiting the application of 2D perovskite materials in solar cells. These limitations can be overcome by using the concept of 2D/3D multidimensional hybrid perovskites, which includes the long-term stability of 2D perovskite and the high performance of 3D perovskite at the same time. Here in this perspective, we have given brief insight on structural versatility, synthesis techniques, some of the unique photophysical properties, potential device fabrication, and recent advancements in the 2D structure to stand against degradation. Certain shortcomings and future outlooks are also discussed to make the perspective more informative.

Progress and challenges in layered two-dimensional hybrid perovskites

Massive data processing with high computing efficiency and low operating power is required owing to the rapid development of artificial intelligence and information technology. However, the von Neumann structure computing system with the separated memory and processor can cause large energy consumption and a low running speed during massive data processing. Therefore, the brain‐inspired neuromorphic computing system is developed, that can provide hardware support for emulating biological synaptic functions and realizing highly intensive data processing with low power consumption. As a neuromorphic device, the optoelectronic synaptic device (OSD) is regarded as an ideal device to replace the von Neumann‐based computer because of its ultrafast signal transmission, large bandwidth, low energy consumption, and wireless communication. Owing to their unique optoelectronic property, metal halide perovskites (MHPs) have received growing attention as effective photosensitive materials in OSDs. Therefore, the review introduces the recent progress on OSDs based on MHPs (MHPs‐OSDs) including the structures and properties of MHPs, and the architectures and performance characteristics of MHPs‐OSDs. Furthermore, applications of MHPs‐OSDs are presented. Finally, the outlook and opportunity of MHPs‐OSDs are discussed.

Recent Developments of Optoelectronic Synaptic Devices Based on Metal Halide Perovskites

Two-dimensional (2D) halide perovskite has attracted widespread attention because of their structural diversity and adjustable material properties Their material properties are closely related to structural features, especially the inorganic layers (n) in each structural unit of 2D halide perovskite The optical properties of 2D perovskite that vary with n can be used to manufacture various optoelectronic devices This review introduces the basic structure and properties of 2D halide perovskite and then summarizes various experimental methods that can be used to directly or indirectly identify the n value, such as X-ray diffraction (XRD), grazing incidence wide-angle X-ray scattering (GIWAXS), photoluminescence spectra (PL), ultraviolet–visible spectra (UV–vis), atomic force microscopy (AFM), second harmonic generation (SHG) spectroscopy or third harmonic generation (THG) spectroscopy, etc Moreover, the existence of different n-value phases in 2D halide perovskites has been discussed in terms of the energy transfer characteristics Finally, we summarize advantages and disadvantages of characterization methods and some issues that still need to be explored in the 2D halide perovskite itself

Shouwu Yu

Papers

A review of main characterization methods for identifying two-dimensional organic–inorganic halide perovskites

Research progress on two-dimensional (2D) halide organic–inorganic hybrid perovskites