0D Perovskites: Unique Properties, Synthesis, and Their Applications

Abstract

0D perovskites have gained much attention in recent years due to their fascinating properties derived from their peculiar structure with isolated metal halide octahedra or metal halide clusters. However, the systematic discussion on the crystal and electronic structure of 0D perovskites to further understand their photophysical characteristics and the comprehensive overview of 0D perovskites for their further applications are still lacking. In this review, the unique crystal and electronic structure of 0D perovskites and their diverse properties are comprehensively analyzed, including large bandgaps, high exciton binding energy, and largely Stokes-shifted broadband emissions from self-trapped excitons. Furthermore, the photoluminescence regulation are discussed. Then, the various synthetic methods for 0D perovskite single crystals, nanocrystals, and thin films are comprehensively summarized. Finally, the emerging applications of 0D perovskites to light-emitting diodes, solar cells, detectors, and some others are illustrated, and the outlook on future research in the field is also provided.

Keywords: 0D structure; applications; optoelectronic properties; perovskites; synthetic methods.

Figure 1

Crystal structures of a) cubic 3D perovskite, b) 2D perovskite, c) 1D perovskite, and d) 0D perovskite at molecular levels. Reproduced with permission.^{[ 22 ]} Copyright 2015, Elsevier.

Figure 2

a) Views of two isolated [SnX₆]⁴⁻ species completely separated from each other by large [C₄N₂H₁₄Br]⁺ cations. b) Schematic drawing of a perfect host–guest system with the light emitting species periodically embedded in an inert matrix. a,b) Reproduced with permission.^{[ 18 ]} Copyright 2018, Royal Society of Chemistry. Crystal structure of (CH₃NH₃)₃Bi₂I₉. c) Local structure of the [Bi₂I₉]³⁻ anion. d) Cation and anion positions in the unit cell. c,d) Reproduced with permission.^{[ 25 ]} Copyright 2016, Royal Society of Chemistry. e) Unit cell of Rb₇Bi₃Cl₁₆ (pink octahedra represents the [BiCl₆]³⁻ octahedra, blue edge‐sharing dimers represents the [Bi₂Cl₁₀]⁴⁻). Reproduced with permission.^{[ 26 ]} Copyright 2019, Royal Society of Chemistry.

Figure 3

Electronic band structures of a) (C₄N₂H₁₄Br)₄SnBr₆, b) (C₄N₂H₁₄I)₄SnI₆, and c) Cs₄PbBr₆ calculated by Perdew–Burke–Ernzerhof (PBE) functionals. a‐c) Reproduced with permission.^{[ 33 ]} Copyright 2018, Royal Society of Chemistry. d) DFT‐calculated electronic band structure of EtPySbBr₆ (left). Total state density of EtPySbBr₆ and state density projected onto atomic orbitals (PDOS) of EtPy (s‐ and p‐states), Sb (s‐states), and Br (p‐states), showing Sb–Br hybridization and formation of intermediate bands (right). Reproduced with permission.^{[ 37 ]} Copyright 2018, American Chemical Society. e) Schematic illustration of the possible electronic dual‐bandgap structure for the as‐synthesized 0D Cs₄PbBr₆ perovskite NCs before and after Sn cation doping. Reproduced with permission.^{[ 38 ]} Copyright 2019, Wiley‐VCH. f) Schematic diagram showing the probable dual PL mechanism of 0D Cs₃Bi₂I₉ perovskite NCs. Reproduced with permission.^{[ 39 ]} Copyright 2018, American Chemical Society.

Figure 4

a) Schematic of typical STEs process, where GS represents ground state. FE represents free exciton state. FC represents free carrier state. STE represents self‐trapped exciton state. E _g represents bandgap energy, E _b represents exciton binding energy. E _st represents self‐trapping energy. E _d represents lattice deformation energy. E _PL represents emission energy. Reproduced with permission.^{[ 63 ]} Copyright 2019, American Chemical Society. b) Schematic of the luminescence processes in 0D perovskites, where LD represents lattice distortion. E _PL,S represents singlet state emission energy and E _PL,T represents triplet state emission energy. Reproduced with permission.^{[ 65 ]} Copyright 2021, The Royal Society of Chemistry. c) Schematic of excited state structural reorganization in (C₄N₂H₁₄Br)₄SnBr₆ pure‐halide perovskites. Reproduced with permission.^{[ 18 ]} Copyright 2018, The Royal Society of Chemistry. d) PL and PL excitation (PLE) spectra of d) Cs₄Sn(Br, I)₆ and e) Rb⁺ or K⁺ substituted compounds. d,e) Reproduced with permission.^{[ 70 ]} Copyright 2018, Wiley‐VCH. f) Excitation (monitored at 695 nm) and emission (excited at 355 nm) spectra of a Cs₂InBr₅·H₂O single crystal. g) Configurational coordinate diagram illustrating the origin of PL in Cs₂InBr₅·H₂O. f,g) Reproduced with permission.^{[ 74 ]} Copyright 2019, Wiley‐VCH. h) Steady‐state PL spectra of Rb₂InCl₅ (H₂O):Sb and Rb₃InCl₆:Sb, with the photograph of Rb₃InCl₆:Sb under UV light in the insets. i) The steady‐state PL spectra of Cs₃InCl₆:Sb and Cs₂InCl₅(H₂O):Sb. h,i) Reproduced with permission.^{[ 77 ]} Copyright 2020, Wiley‐VCH.

Figure 5

a) Crystal structure of Cs₄PbBr₆. Reproduced with permission.^{[ 30a ]} Copyright 2017, American Association for the Advancement of Science. Luminance mechanism of Cs₄PbBr₆ from b) CsPbBr₃ NC impurity phases and c) defect states. b,c) Reproduced with permission.^{[ 22 ]} Copyright 2015, Elsevier. d) Raman spectral comparison between Cs₄PbBr₆ and CsPbBr₃ at room temperature. Reproduced with permission.^{[ 83 ]} Copyright 2019, American Chemical Society. e) HRTEM image of the Cs₄PbBr₆ crystals with embedded CsPbBr₃ NCs. Reproduced with permission.^{[ 84 ]} Copyright 2018, Wiley‐VCH. f) Absorption, excitation, and PL spectra of Cs₄PbBr₆ NCs. Reproduced with permission.^{[ 29 ]} Copyright 2017, American Chemical Society. g) Blinking trace of a single Cs₄PbBr₆ NC, a typical antibunching trace with large g ²(0) value shown in the insets. h) PL lifetimes extracted from individual bursts (green and yellow) and single emitter level (blue), showing a similar decay profile. g,h) Reproduced with permission.^{[ 86 ]} Copyright 2019, Springer Nature.

Figure 6

a) Schematic illustration of cooling‐induced crystallization method to grow 0D perovskite single crystals. b) Color change of block crystals of NMPC (x = 0), NMPCB (x = 1/3), and NMPB (x = 1). Reproduced with permission.^{[ 90 ]} Copyright 2017, American Chemical Society. c) Schematic illustration of growing Cs₃Cu₂I₅ perovskite crystals via room temperature solvent evaporation crystallization method, with photographs under day light and UV lamp on the right. Reproduced with permission.^{[ 49 ]} Copyright 2020, Wiley‐VCH. d) The synthetic process of 1D and 0D tin‐based perovskites single crystals. e) Photoinduced structural transformation from 1D to 0D structure. Reproduced with permission.^{[ 89 ]} Copyright 2017, Wiley‐VCH.

Figure 7

a) Synthesis of perovskite NCs by the hot‐injection method. Reproduced with permission.^{[ 108 ]} Copyright 2020, The Royal Society of Chemistry. b) Schematic illustration of synthesis process of pure 0D Cs₄PbBr₆ NCs at room temperature, with the products images suspended in toluene solution shown in the insets. Reproduced with permission.^{[ 95 ]} Copyright 2017, Springer Science. c) Schematic illustration of room temperature antisolvent method. Reproduced with permission.^{[ 97 ]} Copyright 2020, American Chemical Society.

Figure 8

a) Schematic illustration of the one‐step spin‐coating method to prepare 0D Cs₃Sb₂I₉ film. Reproduced with permission.^{[ 100 ]} Copyright 2019, Wiley‐VCH. b) Schematic illustration of two‐step spin‐coating method to prepare 0D perovskite film.

Figure 9

a) CIE color coordinates and CCTs for 0D (C₄N₂H₁₄Br)₄SnBr₆‐based white LEDs. b) Emission spectra of the white LED at different driving currents, with a photo of this device in off and on state in the insets. a,b) Reproduced with permission.^{[ 18 ]} Copyright 2018, The Royal Society of Chemistry. c) Photograph of the UV‐pumped blue LED based on the Cs₃Cu₂I₅ phosphor. d) Schematic illustration of direct laser writing technology (top), and photographs of a patterned Cs₃Cu₂I₅/PVDF film under daylight and UV lamp (bottom). e) Photographs of a weighing paper drew by Cs₃Cu₂I₅ ink under daylight and UV lamp. c‐e) Reproduced with permission.^{[ 49 ]} Copyright 2020, Wiley‐VCH. f) PLQY, conductivity of the composite films and EQE of corresponding devices. Reproduced with permission.^{[ 111 ]} Copyright 2019, Wiley‐VCH. g) Device structure of KBr‐mixed 0D/3D perovskite LEDs. h) Capacitance–frequency plot of impedance spectroscopy carried out on each LED devices with 0D/3D: KBr v/v ratio of 100:0 (black line), 90:10 (blue line), 80:20 (green line), and 70:30 (purple line), respectively. g,h) Reproduced with permission.^{[ 112 ]} Copyright 2020, American Chemical Society.

Figure 10

a) Energy level diagram of the 0D (CH₃NH₃)₃Bi₂I₉ perovskite‐based solar cells. Reproduced with permission.^{[ 55 ]} Copyright 2016, Elsevier. b) J–V characteristic measured in the forward and backward scan direction for varying scan rates between 150 mV s⁻¹ and 1500 mV s⁻¹. Reproduced with permission.^{[ 20 ]} Copyright 2017, The Royal Society of Chemistry. c) J–V curve of (CH₃NH₃)₃Bi₂I₉‐based devices in both planar and mesoporous device architectures. Reproduced with permission.^{[ 99 ]} Copyright 2016, American Chemical Society. d) The stability comparation between the devices based on 0D MA₄PbBr₆ and 3D MAPbBr₃ under constant illumination and 65% humidity. Reproduced with permission.^{[ 117 ]} Copyright 2019, American Chemical Society. e) J–V curves of the devices using Cs_{1+ x} PbI_{3+ x} as the absorber layer. f) Light‐soaking stability measurement of the device based on Cs_1.2PbI_3.2. e,f) Reproduced with permission.^{[ 118 ]} Copyright 2019, Wiley‐VCH.

Figure 11

a) I–V characteristics of 0D Cs₃BiBr₆‐based photodetector under the dark and light illumination with different light densities. b) Photocurrent responses under various bias voltages with fixed light density of 25 mW cm⁻². a,b) Reproduced with permission.^{[ 122 ]} Copyright 2019, The Royal Society of Chemistry. c) Cross‐sectional SEM image of X‐ray detector with a device structure of glass/FTO/c‐&m‐TiO₂+Cs₂TeI₆/PTAA/Au. d) Schematic of the electrostatic‐assisted spray deposition process, with the corresponding Cs₂TeI₆ solutions and films shown aside. c,d) Reproduced with permission.^{[ 93 ]} Copyright 2018, American Chemical Society. e) ¹³⁷Cs pulse height spectra of Cs₄EuBr₆ and Cs₄EuI₆ single crystals coupled to a Hamamatsu R2059 PMT. f) The variation of scintillation light yield of Cs _n EuI_{2+ n} (n = 1, 3, and 4) with different perovskite dimension. e,f) Reproduced with permission.^{[ 35 ]} Copyright 2018, The Royal Society of Chemistry.

Figure 12

a) Schematic illustration of the LSC based on thin‐film architecture(top), and photographs of the LSC under ambient (bottom left) and one sun (100 mW cm⁻²) illumination (bottom right). b) Emission peak positions as a function of detection distance. The excitation wavelength is 400 nm. a,b) Reproduced with permission.^{[ 94 ]} Copyright 2019, Wiley‐VCH. c) Schematic of LSC prototype device composing of two silicon panels and four pieces of LSCs. Reproduced with permission.^{[ 134 ]} Copyright 2021, Elsevier. d) Schematic diagram of an electrochemical double layer capacitor based on 0D (CH₃NH₃)₃Bi₂I₉ perovskites. Reproduced with permission.^{[ 53 ]} Copyright 2017, American Chemical Society. e) Evolution of the PL spectra of Cs₄PbBr₆ microcrystal with the pump fluence ranging from 0.079 to 1.022 mJ cm⁻². f) Schematic of the optical setup for speckle‐free imaging. e,f) Reproduced with permission.^{[ 139 ]} Copyright 2019, American Chemical Society.