VLS Homoepitaxy of Lead Iodide Nanowires for Hybrid Perovskite Conversion

Abstract

Controlled fabrication of lead halide-based perovskite (LHP) nanostructures provides a new methodology for exploiting the excellent optoelectronic properties of the material. Here, we report the vapor–liquid–solid (VLS) growth of a highly uniform and dense array of [0001]-oriented PbI2 nanowires using PbI2 thin film as the epitaxial substrate layer. We show that reducing the lattice mismatch of the van der Waals epitaxial PbI2 substrate layer is necessary to accommodate the aligned nanowire growth. Our proposed layer growth model suggests that the nanowire growth is stabilized by maintaining the {0001} liquid–solid interface, which stems from the nucleation on the PbI2 substrate layer. We also demonstrate that the strain-induced nanowire deflection after conversion into CH3NH3PbI3 depends on the transfer sequence and conversion time. These findings provide a general opportunity to design and fabricate nanostructures, such as heterojunctions or superstructures for future device applications, rationally based on lead halide or LHP nanowires.

Orientation-Dependent Conversion of VLS-Grown Lead Iodide Nanowires into Organic-Inorganic Hybrid Perovskites

“…Thus, the difference in the degree of perovskite conversion between type A and B might be related to the accessibility of gaseous MAI onto the surface of nanowire sidewalls, necessitating the evaluation of MAI affinity to the exposed PbI 2 surface facets since they must intercalate through the crystal layers. In our previous study, we reported that the [0001]-oriented PbI 2 nanowires show three-fold symmetric sidewalls (i.e., truncated hexagons), which are primarily comprised of {1010}-type facets [33]. In accordance with this knowledge, we note that the type A nanowires observed in this work generally exhibited "tapered oscillatory" morphology, suggesting that the original {1010} sidewalls are multi-faceted into other planes [49].…”

“…Anisotropic van der Waals layered semiconductors, such as germanium (II) sulfide were also demonstrated to grow via VLS mechanism, as reported by Sutter et al [30]. Our previous study showed that lead iodide (PbI 2 ), another van der Waals type material system, can homoepitaxially grow on the PbI 2 substrate layers pre-deposited on the muscovite mica surface [33]. These results emphasize the VLS mechanism as a universal approach to fabricate intrinsically two-dimensional van der Waals type crystals into one-dimensional nanowire structures, which may open up the new methodology to modulate their physical properties.…”

“…It is noteworthy that no signature of 1D anisotropic growth was observed when PbI 2 was deposited on the bare c-sapphire substrate without Sn particles (Supplementary Figure S3). This indicates that the 1D nanowire growth via precursor evaporation is promoted only when the Pb-Sn alloying occurs in the presence of Sn source (i.e., nanoparticles) unless excess Pb exists on the substrate by thermal evaporation or sputtering [32,33]. We also note that the as-grown PbI 2 nanowires are primarily classified into two types with distinct morphology and orientation, as highlighted by red and green colors in Figure 1a.…”

“…Both PbI 2 nanowire growth and perovskite conversion were carried out in a homebuilt chemical vapor deposition (CVD) tube furnace system, as described elsewhere [33] and illustrated in the Supplementary Figure S1. First, Sn powders (Sigma Aldrich, St. Louis, Mo, USA, <150 nm in particle size, ≥99%) of 2.5 mg were dispersed in methanol (Duksan Reagents, Ansan, South Korea) in a vial and sonicated for 60 min to prepare a Sn suspension.…”

“…[23][24][25][26][27]. Recently, the application of VLS mechanism has been extended to the low-dimensional growth of other material systems, specifically layered semiconductors such as transition metal dichalcogenides (TMDs) [28,29], group IV chalcogenides [30,31], and metal halides [32,33]. Eda et al reported the growth of twodimensional (2D) molybdenum disulfide (MoS 2 ) nanoribbons via the VLS method using molten Na-Mo-O droplet particles as the catalyst for crawling growth on the substrate [28].…”