In Situ Grazing‐Incidence Wide‐Angle Scattering Reveals Mechanisms for Phase Distribution and Disorientation in 2D Halide Perovskite Films

Hoffman, Justin M.; Strzalka, Joseph; Flanders, Nathan C.; Hadar, Ido; Cuthriell, Shelby A.; Zhang, Qingteng; Schaller, Richard D.; Dichtel, William R.; Chen, Lin X.; Kanatzidis, Mercouri G.

doi:10.1002/adma.202002812

Cited by 96 publications

(108 citation statements)

References 46 publications

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“…Kanatzidis and co‐workers [ 98 ] divided the crystallization process of 2D perovskite into three stages: i) disordered colloidal sol–gel, ii) an oriented 3D‐like phase, and iii) oriented 2D phase. Among them, the first stage can also be called the intermediate stage, it is evident that the film forming process of 2D perovskite is closely related to the precursor.…”

Section: Crystallization Kineticsmentioning

confidence: 99%

Crystallization Kinetics in 2D Perovskite Solar Cells

Wang

Lei

et al. 2020

Advanced Energy Materials

141

124

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volatile decomposition [23] or halide segregation are often observed in hybrid perovskites under various stress conditions (light, [24] thermal, [25] and electric fields [26]); 4) spontaneous phase transition easily occurs for perovskite with unstable crystal structures, particularly for inorganic perovskite. [27-29] To improve the stability of PSCs, researchers attempted numerous methods such as encapsulation, [30] additive engineering, [31] component engineering, [32] etc. [33] However, the PSCs' stability is yet to achieve a perfect solution. Recently, researchers found that the introduction of long-chain organic cations in 3D perovskite as 2D perovskite can block water and oxygen molecules, meanwhile, generate a steric effect to prevent phase transitions, and limit ion migration. [34-36] Hence, fabricating 2D [37,38] or 2D/3D [39-43] mixed perovskite as absorbing layers are effective approaches to improve the stability of PSCs. However, the PCE of 2D PSCs remain lower than that of the 3D ones, which is mainly attributed to the introduction of organic macromolecules that blocks the effective extraction and transport of carriers. [44,45] Fortunately, 2D perovskite usually has three arrangements, namely parallel, perpendicular to the glass substrate or randomly arranged. [46] Manipulating the orientation of the crystal and the phase distribution in the 2D solution-processed perovskite can improve the efficiency and reproducibility of the device. Among them, the most desired arrangement for PSCs is the one that perpendicular to the substrate. Therefore, studying the crystallization kinetics of 2D perovskite is curial to effectively control the film forming process and adjust the crystal orientation (perpendicular to the substrate), which can effectively avoid or reduce the adverse effects of the organic molecular layer and improve device efficiency. [47,48] Nevertheless, few review articles were published on this subject. In this review, we mainly focus on the key issue for controlling crystallization kinetics and summarizing the research progress of their effects on various types of 2D PSCs. We also discuss the crystal/natural quantum well (QW) structure and the original stability for 2D PSCs in detail. Finally, remaining challenges and outlooks are presented. 2. Crystal and Natural Quantum Well Structure The material structure has a substantial impact on performance. [49-51] Properties of 2D and 3D perovskites differ 2D perovskites demonstrate higher moisture stability, oxygen content, thermal stability, and a significantly lower ion migration/phase transition occurrence in comparison to 3D perovskite. These advantages imply huge potential for 2D perovskite in commercial applications in the photovoltaic field. However, the horizontal arrangement of the organic layer severely hinders the transport of carriers, and thus, the power conversion efficiency of 2D perovskite solar cells (PSCs) is significantly lower than that of 3D. Controlling the crystallization orientation to achieve rapid carrier transport can effe...

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Section: Crystallization Kineticsmentioning

confidence: 99%

Crystallization Kinetics in 2D Perovskite Solar Cells

Wang

Lei

et al. 2020

Advanced Energy Materials

141

124

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“…Previous studies have shown that there are three stages in the film formation of 2D perovskite: initial nucleation from the sol–gel at the air/liquid interface giving an oriented 3D‐like phase, secondary nucleation on the grown 3D‐like phase and homogeneous nucleation inside the solution forming a less‐oriented 2D phase, and reorientation/rearrangement of already‐formed crystals. [ 23 ] In fact, dominating nucleation at the air/liquid interface would make the highly oriented 3D‐like perovskite seed the layered perovskites and promote the favorable out‐of‐plane orientation. [ 7 ] Oppositely, multiple nucleation events are a major cause of disorientation, [ 7 ] and the high secondary nucleation density will result in small‐grain 2D phases with substantial boundaries according to classical nucleation and growth models.…”

Section: Figurementioning

confidence: 99%

“…Both NH 4 Cl and NH 4 I x Cl 1−x -contained films express strong, sharp, and discrete Bragg spots, suggesting the directional alignment. [23,24] The absence of diffraction spots along q z between 0 and 1 Å −1 together with the clear characteristic absorption peaks of the layered perovskite (Figure S4, Supporting Information) suggests the dominated out-of-plane orientation. [25,26] The more concentrated and intense diffraction spots for the NH 4 I x Cl 1−x film demonstrate not only better crystallinity but also a higher degree of out-of-plane orientation, possibly attributed to the enhanced crystal quality and alignment.…”

mentioning

confidence: 99%

Defect Suppression in Oriented 2D Perovskite Solar Cells with Efficiency over 18% via Rerouting Crystallization Pathway

Yang

Liu

Syzgantseva

et al. 2020

Advanced Energy Materials

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sandwiched between two adjacent organic spacers result in better stability while increasing the bandgap and the exciton binding energy. [3,4] Therefore, a compromised n value around 4 is generally considered as a promising 2D perovskite composition for solar cell application. [5,6] However, the power conversion efficiencies (PCEs) of these 2D perovskite solar cells (PSCs) are substantially lower than those of the 3D PSCs mainly caused by two obstacles: i) in-plane orientation is common for 2D materials due to the minimized surface energy, while the lowconducting organic spacer layers hinder the out-of-plane transport of carriers, leading to a high degree of electrical anisotropy. [7] ii) The over-rapid kinetically controlled self-assembly of 2D perovskite nearly completes its crystallization after the spin-coating process without thermal annealing, which would generate numerous grain boundaries and defective growth. [8] Recent findings offer a range of solutions to address the problem of the highly chaotic system, such as designing new bulky organic ammoniums, [9][10][11][12] adopting the hot-casting technique, [1,6,13] decreasing the precursor supersaturation, [14,15] and applying functional additives, [16][17][18][19] which successfully promote the out-of-plane-oriented growth of 2D perovskite. However, up to now, there is still a lack of attention to the over-rapid crystallization-induced defects in those vertically oriented 2D perovskite films. According to classical nucleation and growth models, film defects are determined by nucleation, coarsening, and coalescence dynamics in establishing the final film morphology. The low nucleation density and retarded crystal growth will encourage the creation of large grains at the crystallization stage and are expected to suppress the effects of boundary defects on both charge transport and recombination kinetics. [20,21] One wellknown example is the film formation of 3D perovskite via solvent annealing. Individual nucleus-centered spots appear on the substrate due to the reduced nucleation density, and the subsequent grain coalescence forms a continuous thin film. This slow crystallization provides longer diffusion distance and self-assembly period of precursor ions/molecules than in all-solid-state thermal annealing to promote the grain growth and yield a high-quality film. [22] Therefore, regulating the nucleation and crystallization dynamics is considered a promising strategy to remove defects from vertically oriented 2D perovskite films, enabling the PCEs of 2D PSCs comparable with those of 3D PSCs.Vertically oriented 2D perovskites exhibit promising optoelectronic properties and intrinsic stability, but their photovoltaic application is still limited by the low power conversion efficiency (PCE) compared to 3D analogs. Here, a new crystallization pathway (RCP) is reported to suppress defects in vertically oriented 2D perovskite caused by its over-rapid self-assembly behavior. By controlling the specific adsorption of an ammonium halide additive on different perovs...

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“…[ 16,19–31 ] The origin of the 2D perovskite layer orientation and the crystallization kinetics were thus intensely studied using grazing‐incidence wide‐angle X‐ray scattering (GIWAXS). [ 32–36 ]…”

Section: Introductionmentioning

confidence: 99%

“…[16,[19][20][21][22][23][24][25][26][27][28][29][30][31] The origin of the 2D perovskite layer orientation and the crystallization kinetics were thus intensely studied using grazing-incidence wide-angle X-ray scattering (GIWAXS). [32][33][34][35][36] The design of perovskite-based PV and LED devices typically features either planar or bulk heterojunctions, making the crystal orientation essential in the former case and the crystal size critical in the latter case. [37] The substrate effect has been studied in great detail, particularly the aspects of charge collection properties, [38,39] induced elemental separation, [40,41] and film morphology.…”

Section: Introductionmentioning

confidence: 99%

Crystallization of 2D Hybrid Organic–Inorganic Perovskites Templated by Conductive Substrates

Kovaříček

Nádaždy

Pluhařová

et al. 2021

Adv Funct Materials

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2D hybrid organic–inorganic perovskites are valued in optoelectronic applications for their tunable bandgap and excellent moisture and irradiation stability. These properties stem from both the chemical composition and crystallinity of the layer formed. Defects in the lattice, impurities, and crystal grain boundaries generally introduce trap states and surface energy pinning, limiting the ultimate performance of the perovskite; hence, an in‐depth understanding of the crystallization process is indispensable. Here, a kinetic and thermodynamic study of 2D perovskite layer crystallization on transparent conductive substrates are provided—fluorine‐doped tin oxide and graphene. Due to markedly different surface structure and chemistry, the two substrates interact differently with the perovskite layer. A time‐resolved grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) is used to monitor the crystallization on the two substrates. Molecular dynamics simulations are employed to explain the experimental data and to rationalize the perovskite layer formation. The findings assist substrate selection based on the required film morphology, revealing the structural dynamics during the crystallization process, thus helping to tackle the technological challenges of structure formation of 2D perovskites for optoelectronic devices.

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In Situ Grazing‐Incidence Wide‐Angle Scattering Reveals Mechanisms for Phase Distribution and Disorientation in 2D Halide Perovskite Films

Cited by 96 publications

References 46 publications

Crystallization Kinetics in 2D Perovskite Solar Cells

Crystallization Kinetics in 2D Perovskite Solar Cells

Defect Suppression in Oriented 2D Perovskite Solar Cells with Efficiency over 18% via Rerouting Crystallization Pathway

Crystallization of 2D Hybrid Organic–Inorganic Perovskites Templated by Conductive Substrates

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