Controlled Deposition of Lead Iodide and Lead Chloride Thin Films by Low-Pressure Chemical Vapor Deposition

Abstract

Lead halide thin films, such as lead iodide (PbI2) and lead chloride (PbCl2), are used as precursor films for perovskite preparation, which is frequently achieved by vacuum thermal evaporation but rarely by the low-pressure chemical vapor deposition (CVD) method. Here, we report on the deposition of PbI2 and PbCl2 thin films on glass substrates by employing the low-pressure CVD method. The effect of the substrate temperature on the structure and morphology of the lead halide films is investigated. Crystalline films were realized for both lead halides, with PbI2 films showing high texture compared to the reduced texture of the PbCl2 films. Large lateral grain sizes were observed for the PbI2 films with a flat platelet grain morphology and an average grain size up to 734.2 ± 144.8 nm. PbCl2 films have columnar grains with an average grain size up to 386.7 ± 119.5 nm. The PbI2 films showed a band gap of about 2.4 eV, confirming its semiconducting properties, and the PbCl2 had a wide band gap of 4.3 eV, which shows the insulating properties of this material.

Synthesis of graphite-based lead composites and modification of their physicochemical and electrochemical properties

“…Peaks related to Pb can be distinguished in the patterns recorded for the originally obtained compound as well as for the product formed during its thermal modification at 600 °C. 41,42 It means that chemical modification in H 2 O 2 as well as heat treatment at 800 °C result in almost complete removal of lead from the investigated compounds. Contrary to the EDS surface analysis, XRD measurements revealed the presence of Pb within the originally obtained compound.…”

Optimized Substrate Orientations for Highly Uniform Metal Halide Perovskite Film Deposition

“…Despite the narrow temperature distribution, we found that the vertical substrate exhibited position-dependent thickness variations, albeit to a lesser extent than the horizontal substrate (Figure d). Observations from the vertical substrate, including low surface roughness (Figure a), low average film thickness (Figure c), and high surface coverage (Figure e), suggest that layer-by-layer growth is favored under conditions of significant mass transport limitation. , The crystal structure of PbI 2 is similar to that of two-dimensional (2D) transition metal dichalcogenides (TMDs), characterized by layered structures with weak vdW interactions. , Consequently, film formation adheres to Frank-van der Merwe (FM) type growth modes, involving the coalescence of 2D flakes through the surface diffusion of PbI 2 molecules transported from the bulk flow. This mass transport is contingent on boundary layer development, which is, in turn, influenced by the flow geometry.…”

PbI2 Nanocrystal Growth by Atomic Layer Deposition from Pb(tmhd)2 and HI

“…Thermally evaporated PbI 2 has previously been used for applications, including X-ray detection, photoemission, and photovoltaics; , however, thermal evaporation requires temperatures approaching 400 °C to vaporize the PbI 2 powder and lacks the atomic-level thickness control that is enabled by ALD processes. CVD of PbI 2 encounters similar limitations, requiring higher substrate temperatures than ALD and typically resulting in thicker films with poor control over thickness. , …”