Van Der Waals Hybrid Perovskite of High Optical Quality by Chemical Vapor Deposition

Abstract

Among different structures, two extreme cases are of special interest: (1) when m goes to infinity, a complete 3D structure is formed due to the absence of larger alkyl amine ligands, e.g., CH 3 NH 3 PbI 3 ; [4] (2) when m goes to 1, smaller alkyl groups are absent and a complete 2D structure is formed where each single layer of lead halide octahedrons is separated by large alkyl groups, i.e., (RNH 3 ) 2 PbX 4 . [5] A finite m value which exceeds unity will lead to multilayers of lead halide octahedrons in each individual inorganic slab, e.g., (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 3 Pb 4 I 13 . [8] At present, most of the successful devices are based on 3D perovskites, e.g., CH 3 NH 3 PbX 3 , whose long carrier recombination lifetime, long diffusion length, and high carrier mobility make them promising for photovoltaic applications. [3] In comparison, 2D perovskites will not only inherit most of the aforementioned advantages of 3D perovskites but also possess the superiorities of other 2D materials (transitional metal dichalcogenides (TMDCs) and graphene), e.g., high in-plane carrier mobility [9] and easiness in exfoliation or transfer. [10,11] These advantages make them competitive candidates for high-speed transistors, heterostructures, or planar photodetectors. Figure 1b showed the polyhedron model of a typical 2D perovskite (C 4 H 9 NH 3 ) 2 PbI 4 where each layer of inorganic octahedrons (drawn grey) is sandwiched between two layers of organic butylamine ligands. As illustrated in Figure 1c, this unique AB stacking of organic-inorganic layers provides a natural quantum well structure where charge carriers are localized within inorganic layers due to the insulating organic ligands. The dielectric confinement and quantum confinement effect both enhance the charge carrier localization such that exciton binding energy amounts to several hundred meV, leading to observable excitonic effect even at room temperature. [10,[12][13][14] In addition, when integrated with 3D perovskites, 2D perovskites serve as protection layers and enhances the moisture stability of the system. [8] These promising properties have attracted intensive investigations into (RNH 3 ) 2 PbX 4 with various organic ligands (R ranging from C 4 H 9  to C 12 H 25  and other aromatic compounds) [13,[15][16][17] and halide elements (usually Br and I). [15,17] The great potential of (RNH 3 ) 2 PbX 4 is being rapidly revealed, as witnessed by its recent success in solar cells, light-emitting diodes (LEDs), and photodetectors. [8,9,18,19] 2D hybrid perovksite (RNH 3 ) 2 PbX 4 materials not only serve as ideal platforms to study fundamental physics such as polariton dynamics but also show promise for optoelectronic and electro-optic applications. However, for the preparation of high optical quality crystals, mechanical exfoliation has to be applied in the past. In this work, the vapor phase growth of single crystalline (C 4 H 9 NH 3 ) 2 PbI 4 flakes with high optical quality is reported. Individual single crystalline domains show lateral size about 5-10 µm w...

Merits and Challenges of Ruddlesden–Popper Soft Halide Perovskites in Electro‐Optics and Optoelectronics

“…Structural phase transitions of (C 4 H 9 NH 3 ) 2 PbI 4 were found to be stopped by substrate interactions . For example, exfoliated (C 4 H 9 NH 3 ) 2 PbI 4 monolayers were transferred to the SiO 2 surface, part of the transferred flakes stayed in the high‐temperature phase until liquid‐helium temperature, whereas without enough substrate interference, the (C 4 H 9 NH 3 ) 2 PbI 4 crystal would undergo a normal phase transition at about 235 K (see Figure i) . In vapor‐synthesized single‐crystalline (C 4 H 9 NH 3 ) 2 PbI 4 flakes, not only was the structural phase transition stopped, but the electron–phonon interaction was also suppressed because of the reduced flake thickness .…”

Band‐Edge Exciton Fine Structure and Exciton Recombination Dynamics in Single Crystals of Layered Hybrid Perovskites

“…They can be easily grown by both solution methods and vapor transport methods at low temperature, [14][15][16][17] with a tunable bulk direct bandgap. As a consequence of the dielectric and quantum confinement effect, they show strongly bound and stable excitons at room temperature.…”

Ruddlesden–Popper Perovskite for Stable Solar Cells

“…In 2D Ruddlesden–Popper Perovskite, n values influence directly semiconductor characteristics of provskite films (e.g., exciton binding energy, band gap, and carrier mobility). In the most of studies, researchers assumed to the existence of a certain n ‐value in the films . However, recent papers have showed that the 2D Ruddlesden–Popper perovskite films comprised multiple perovskite phases, even though the films were intended to be prepared as a single‐phase .…”

“…In order to achieve a greater PCE based on 2D Ruddlesden–Popper perovskite, Tsai et al . employed a hot‐casting technique to fabricate the 2D layered perovskite thin films (See Figure for the configuration and performance).…”

“…Because the L cation serves as a spacer among the lead halide octahedral planes at various n values, 2D Ruddlesden–Popper type perovskites possess the adjustable semiconductor properties . Simultaneously, a variety of film‐forming methods, including spin coating, hot casting, dipping, chemical vapor deposition, have been applied to enhance the PCE of Ruddlesden–Popper perovskites devices, and the highest efficiency has exceeded 13% . Recently, based on the 2D–3D heterostructured lead halide perovskites, Snaith et al.…”