Precise Facet Engineering of Perovskite Single Crystals by Ligand-Mediated Strategy

Abstract

Inorganic−organic hybrid perovskite single crystals are potential materials for the application of high performance optoelectronic devices. The exposed surface of single crystals can dramatically affect the measured properties. Facet-dependent behaviors are also speculated. However, impeded by the lack of facile facet engineering strategy for inorganic−organic hybrid perovskites, the relationship between different facets and respective performance remains elusive. In this work, we present a simple approach of ligandmediated crystal growth to control the shape and the exposed facets of methylammonium lead iodide single crystals. The addition of oleylamine ligand can trigger the continuous morphological transition from dodecahedral-shaped single crystal enclosed by (100) T and ( 112) T to cubic-shaped single crystal enclosed by (110) T and (002) T while maintaining the material composition and crystalline phase. We fabricated single crystal based photodetectors and carried out the first unambiguous study on the relationship between facet structure and device performance. This report opens a new paradigm to reveal the facetdependent properties and to enhance the device performance of single crystal.

Structural and thermodynamic limits of layer thickness in 2D halide perovskites

“…This provides evidence that, in contrast to the claims in several reports (15,19), stoichiometric synthesis reactions of targeted compounds with n > 7 give samples that deviate greatly from the expected stoichiometry (because of their positive enthalpy and free energy of formation). Nevertheless, such materials do differ from the bulk 3D perovskite properties, and they lie at the broad interface between the finite n-size 2D perovskites, extended in this work to the n = 7 member, and n = ∞, where trace amounts of the spacer amine are capable of altering the bulk crystal morphology (33). Rather than 2D perovskites, these materials should perhaps be termed "quasi-2D perovskites," marking the territory defined between the crystallographically ordered 2D layers (5 nm, n = 7) on the lower end and the quantum barrier on the higher end, estimated either from the experimentally observed crystallite size (∼10 nm, "n = 15") (34) or by the quantum confinement limit of colloidal nanocrystals (12 nm, "n = 18") (35).…”

“…One of the most appealing features of 2D RP perovskites is the rational manner in which their optical properties [band gap (E g ), exciton binding energy (E b ), etc.] can be tuned as a function of n, allowing access to study their unique quasidimensional physics (33). This property derives from the inherent multiple QW-like structure, which arises from the ordered stacking of finite thickness perovskite layers alternating with organic spacers within a crystal grain, allowing for quantum properties to be obtained in a bulk material ( Fig.…”

Reduced ion migration and enhanced photoresponse in cuboid crystals of methylammonium lead iodide perovskite

“…Thus, the A c c e p t e d M a n u s c r i p t 7 presence of paired peaks might basically arise due to some symmetry breaking during the phasetransition of single crystals from cubic (Pm-3m) to tetragonal (I4/mcm) system. 22,34,35 Nonetheless, we propose the top-facet of the rhombic crystals to be mainly (200)-oriented (Figure 2d), as the relative peak intensities of {200} planes were found to be higher than that of {112} planes. Also the higher symmetry of the (200) plane compared to the (112) plane is more likely to result in a rhombus at the crystal center (Figure 2d).…”

“…19,21 In order to alter the crystal shape and the orientation of exposed facets, only a few strategies have been proposed to date. 22,23 The addition of oleylamine or increasing the concentration of iodide-ions in the precursor solution: both were shown to induce the growth of cuboid crystals with the (002) and (110) facets exposed. [22][23][24] Yet these strategies that expose the sought-after facets, entail that the crystals be grown either at relatively high temperatures (>115°C), quite above the phase-transition point of CH3NH3PbI3 (55°C), 25 or from non-stoichiometric (I-rich) precursor ratios.…”

“…This mechanism is similar to that proposed for the growth of cuboid crystals using long-chain oleylamine ligand. 22 We would also like to note that bulky DBF molecules could be less prone to intercalate into the perovskite structure rather than γ-butyrolactone (GBL) molecules, as the size of the latter can fit the perovskite inorganic cage between the octahedra (Figure S1). These growth conditions, as well as different facet orientation of the crystals, can bring unexpected ramifications in electronic behavior.…”