Electrodeposition of Epitaxial Lead Iodide and Conversion to Textured Methylammonium Lead Iodide Perovskite

Applications for lead iodide, such as lasing, luminescence, radiation detection, and as a precursor for methylammonium lead iodide perovskite photovoltaic cells, require highly ordered crystalline thin films. Here, an electrochemical synthesis route is introduced that yields textured and epitaxial films of lead iodide at room temperature by reducing molecular iodine to iodide ions in the presence of lead ions. Lead iodide grows with a [0001] fiber texture on polycrystalline substrates such as fluorine-doped tin oxide. On single-crystal Au(100), Au(111), and Au(110) the out-of-plane orientation of lead iodide is also [0001], but the in-plane orientation is controlled by the single-crystal substrate. The epitaxial lead iodide on single-crystal gold is converted to textured methylammonium lead iodide perovskite with a preferred [110] orientation via methylammonium iodide vapor-assisted chemical transformation of the solid

Epitaxial Electrodeposition of Methylammonium Lead Iodide Perovskites

An electrochemical/chemical route is introduced to deposit both textured and epitaxial films of methylammonium lead iodide (MAPbI₃) perovskites. The perovskite films are produced by chemical conversion of lead dioxide films that have been electrodeposited as either textured or epitaxial films onto [111]-textured Au and [100] and [111] single-crystal Au substrates. The epitaxial relationships for the MAPbI₃ films are MAPbI₃(001)­[010]∥PbO₂(100)⟨001⟩ and MAPbI₃(110)­[111]∥PbO₂(100)⟨001⟩ regardless of the Au substrate orientation, because the in-plane order of the converted film is controlled by the epitaxial PbO₂ precursor film. The textured and epitaxial MAPbI₃ films both have trap densities lower than and photoluminescence intensities higher than those of polycrystalline films produced by spin coating

Preparation of Bi-Based Ternary Oxide Photoanodes BiVO₄, Bi₂WO₆, and Bi₂Mo₃O₁₂ Using Dendritic Bi Metal Electrodes

The major limitation to investigating a variety of ternary oxides for use in solar energy conversion is the lack of synthesis methods to prepare them as high-quality electrodes. In this study, we demonstrate that Bi-based n-type ternary oxides, BiVO₄, Bi₂WO₆, and Bi₂Mo₃O₁₂, can be prepared as high-quality polycrystalline electrodes by mild chemical and thermal treatments of electrodeposited dendritic Bi films. The resulting oxide films have good coverage, adhesion, and electrical continuity, allowing for facile and accurate evaluation of these compounds for use in solar water oxidation. In particular, the BiVO₄ electrode retained the porosity and nanocrystallinity of the original dendritic Bi film. This feature increased the electron–hole separation yield, making this compound more favorable for use as a photoanode in a photoelectrochemical cell

Nanometer-Thick Gold on Silicon as a Proxy for Single-Crystal Gold for the Electrodeposition of Epitaxial Cuprous Oxide Thin Films

Single-crystal Au is an excellent substrate for electrochemical epitaxial growth due to its chemical inertness, but the high cost of bulk Au single crystals prohibits their use in practical applications. Here, we show that ultrathin epitaxial films of Au electrodeposited onto Si(111), Si(100), and Si(110) wafers can serve as an inexpensive proxy for bulk single-crystal Au for the deposition of epitaxial films of cuprous oxide (Cu₂O). The Au films range in thickness from 7.7 nm for a film deposited for 5 min to 28.3 nm for a film deposited for 30 min. The film thicknesses are measured by low-angle X-ray reflectivity and X-ray Laue oscillations. High-resolution TEM shows that there is not an interfacial SiO_<i>x</i> layer between the Si and Au. The Au films deposited on the Si(111) substrates are smoother and have lower mosaic spread than those deposited onto Si(100) and Si(110). The mosaic spread of the Au(111) layer on Si(111) is only 0.15° for a 28.3 nm thick film. Au films deposited onto degenerate Si(111) exhibit ohmic behavior, whereas Au films deposited onto n-type Si(111) with a resistivity of 1.15 Ω·cm are rectifying with a barrier height of 0.85 eV. The Au and the Cu₂O follow the out-of-plane and in-plane orientations of the Si substrates, as determined by X-ray pole figures. The Au and Cu₂O films deposited on Si(100) and Si(110) are both twinned. The films grown on Si(100) have twins with a [221] orientation, and the films grown on Si(110) have twins with a [411] orientation. An interface model is proposed for all Si orientations, in which the −24.9% mismatch for the Au/Si system is reduced to only +0.13% by a coincident site lattice in which 4 unit meshes of Au coincide with 3 unit meshes of Si. Although this study only considers the deposition of epitaxial Cu₂O films on electrodeposited Au/Si, the thin Au films should serve as high-quality substrates for the deposition of a wide variety of epitaxial materials