2D Hybrid Halide Perovskites: Synthesis, Properties, and Applications

Abstract

The hybrid organic-inorganic halide perovskites have emerged as one class of most promising light-harvesting materials for the next-generation solar cells because of their exceptional optoelectronic properties and low-temperature solution processability that allows for large-scale fabrication. [1-14] The hybrid halide perovskites are one class of semiconductors in a formula of ABX 3 that comprises a network of corner-sharing BX 6 octahedra. In this structure, A is an organic cation such as methylammonium (MA: CH 3 NH þ 3); B is a divalent metal cation such as Pb 2þ and Sn 2þ , located in the center; and X is a monovalent anion such as Cl À , Br À , and I À. These structural and compositional features determine their exceptional optoelectronic properties such as tunable bandgaps, [6-11] high absorption coefficient, [7-9,12-14] long carrier diffusion length [14-17] and lifetime, [6,17-23] low trap density, [16,17] and high carrier mobility. [7,8,14,17,24-27] Just in the past few years, the power conversion efficiency (PCE) of these halide perovskites solar cells at labscale testing has increased from 3.8% to 25.2% (in the perovskite/silicon tandem device). [28] Despite promising applications of halide perovskites in the photovoltaic industry, there are still several major challenges that inhibit their large-scale industrial applications. [29-32] These challenges include poor stability in ambient conditions, particularly in the moisture environment, and the demand for lead-free perovskites. For instance, ðMAÞPbI 3 will degrade into MAI and PbI 2 in ambient conditions in which the water molecules will facilitate the degradation process, sharply dropping perovskite thin film absorption in a matter of days. [33] Although encapsulation can mitigate the degradation from water molecules, [34] the hybrid perovskites were considered as intrinsically unstable in the long term due to unfavorable formation enthalpies. [35,36] 2D hybrid perovskites (2DHPs) offer a promising solution to overcome this instability issue. [37-47] The 2D nature refers to the layer structure of corner-sharing inorganic octahedra. These inorganic metal halide layers are interdigitated between bulky organic molecules such as butylammonium (BA: CH 3 ðCH 2 Þ 3 NH þ 3). The bulky organic molecules are bonded to the inorganic octahedra via hydrogen bonds, causing the large hydrophobic chain to orient away from the inorganic perovskite layers. This configuration forms organic bilayers that separate neighboring sheets, creating a repeating pattern of organic and inorganic layers that define the 2DHP crystal structure, see Figure 1. 2DHPs demonstrate some advantageous materials properties compared to the 3D hybrid perovskites (3DHPs), including high materials stability and robustness in the presence of water, [39,50] reasonable performance, and cheap solution processability. [37,51-54] Moreover, the interchangeability of the large organic cations and the control of layer dimensionality allow for greater tunability and flexibility of the physical and optoelect...

Rational alloying of secondary and aromatic ammonium cations in a metal-halide perovskite toward crystal-array photodetection

“…Generally, the members of this class adopt a basic formula of (A′) 2 (A) n−1 M n X 3n+1 , where A′ is an organic "spacer" cation between inorganic perovskite sheets, A is a "perovskiter" cation inside the MX 6 octahedral cavity, M is a divalent metal cation and X is a halide. From a structural perspective, the abundant incorporation of A and A′ cations into 2D hybrid perovskites endows them with infinite structural diversity, opening up a new pathway to largely enrich this family toward high-performance optoelectronic devices [11][12][13][14]. Among them, the choice of the A′-site spacing cation is not restricted by the tolerance factor, which allows for the accommodation of large components of alkylamines and aromatic amines [15].…”

Discovery of Lead-Free Hybrid Organic/Inorganic Perovskites Using Metaheuristic-Driven DFT Calculations

“…Out of 42 divalent cations, only Sn 2+ - and Ge 2+ -containing HOIPs with a single exception (no. 18) are found in Table , which partially supports the credibility of our search protocol because B-site cations such as Sn 2+ and Ge 2+ have long been studied as potential alternatives to lead-based HOIPs. − The final compounds listed in Table includes ABX 3 , A 2 BX 4 , and A 3 B 2 X 7 structures (These structures are already known in different chemical compositions. − ). In particular, both the 2D structures such as A 2 BX 4 ( n = 1) and A 3 B 2 X 7 ( n = 2) are known as the Ruddlesden–Popper phase ( n is the number of octahedron layers). − However, the familiar compositions for A 2 BX 4 structure, (MA,AD,FA) 2 (Sn,Ge)­(Cl,Br,I) 4 , were systematically avoided during the NAGA-II and -III implementations as already clarified above, but the composition for the other structures were free to be chosen.…”

Phonon Analysis of 2D Organic‐Halide Perovskites in the Low‐ and Mid‐IR Region

“…[2] Over a decade afterwards, while vigorous academic and industrial research is still focusing on of advanced material researches, in particular for their potential for optoelectronic applications. [6][7][8][9] If such materials are to be integrated in optoelectronic devices, studying their vibrational properties is of vital importance as the latter ones can and will also affect the electronic properties through, for example, electron-phonon coupling, thermal expansion of the crystal, or changes in specific heat. Though inelastic neutron scattering is generally considered as the most comprehensive experimental technique to quantitatively explore phonon dynamics over the whole Brillouin zone, it cannot be performed in simple laboratory settings, typically requiring access to large-scale facilities.…”