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The wide bandgap p-type metal pseudohalide semiconductor copper(I) thiocyanate (CuSCN) can serve as a transparent hole transport layer in various opto-electronic applications such as perovsksite and organic solar cells and light-emitting diodes. The material deposits as one-dimensional CuSCN nanorod arrays, which are advantageous due to their high surface area and good charge transport properties. However, the growth of high-quality epitaxial CuSCN nanorods has remained a challenge. Here, we introduce a low cost and highly scalable room temperature procedure for producing epitaxial CuSCN nanorods on Au(111) by an electrochemical method. Epitaxial CuSCN grows on Au(111) with a high degree of in-plane as well as out-of-plane order with +0.22% coincidence site lattice mismatch. The phase of CuSCN that deposits is a function of the Cu 2+ /SCN − ratio in the deposition bath. A pure rhombohedral material deposits at higher SCN − concentrations, whereas a mixture of rhombohedral and hexagonal phases deposits at lower SCN − concentrations. A Au/epitaxial CuSCN/Ag diode has a diode quality factor of 1.4, whereas a diode produced with polycrystalline CuSCN has a diode quality factor of 2.1. A highly ordered foil of CuSCN was produced by epitaxial lift-off following a triiodide etch of the thin Au substrate. The 400 nm-thick CuSCN foil had an average 94% transmittance in the visible range and a 3.85 eV direct bandgap.

The expansion of future optoelectronic materials into transparent flexible electronics, perovskite, organic, and tandem photovoltaics depends on the development of high-performance p-type materials with optical transparency. We introduce the epitaxial growth of γ-CuI, a wide band gap p-type semiconductor with the zinc blende structure, on single crystalline Si(111) using a simple, cost-effective, room-temperature electrochemical method. The deposited epitaxial film grows with a high degree of in-plane and out-of-plane order, templated by the Si(111) substrate. A deposition mechanism is proposed, in which epitaxial CuI seed crystals are nucleated on the freshly etched n-Si(111) surface, followed by the simultaneous oxidation of Si to form a thin layer of SiO x and the lateral overgrowth of the CuI seeds into a continuous film. The rectifying p-CuI/SiO x /n-Si heterojunction diode shows an ideality factor of 1.5, a built-in voltage of 0.67 V, and a barrier height of 0.91 eV. The epitaxial CuI film has been epitaxially lifted off by chemical etching to produce textured CuI foils with an out-of-plane and in-plane order that mimics that of single crystals.

Functional self-assembled monolayers (SAMs) of thiols on single-crystal metals provide two-dimensional (2D) soft templates for the highly ordered growth of crystalline materials. An epitaxial Cu(111) film is electrodeposited on a SAM of the amino acid l-cysteine on Au(111). Epitaxy is confirmed, with Cu(111) following the Au(111) in-plane and out-of-plane orientations with a small amount of twinned [511] orientation, which is shown by X-ray analysis. The mismatch between Cu(111) and the Au(111) substrate is −11.37%. This mismatch is lowered to −0.29% by forming a coincident site lattice in which nine unit meshes of Cu coincide with eight unit meshes of Au. Defect-mediated and coordination-controlled electrodeposition mechanisms are illustrated as two possible deposition mechanisms. The carboxylic (−COOH) and amine (−NH2) functional groups of the l-cysteine molecule are shown to be crucial for the epitaxy of Cu because a 1-butanethiol SAM on Au(111) which has no functional groups yields a textured film with no in-plane order. The (√3 × √3)R30° surface structure of l-cysteine SAM and the c(4 × 2) surface structure of 1-butanethiol SAM on Au(111) are discussed. A 3D model of the Cu lattice on the l-cysteine SAM on Au(111) is proposed. A possible coordination to Cu is shown, which facilitates the epitaxial nucleation and 2D growth of Cu. The Cu(111) films have potential as a substrate for catalysts for CO2 reduction, photovoltaic devices, spintronic devices, and high-temperature superconductors. Direct epitaxial lift-off of the Cu film without etching gives a single-crystal-like Cu(111) foil. The Cu(111) foil exhibits a low resistivity of 3.75 × 10–8 Ω·m and good bending stability, showing only a 12% increase in resistance after 104 bending cycles. Cu(111) foils can be utilized as inexpensive, highly ordered, and conductive substrates for flexible electronics such as wearable solar cells, sensors, and flexible displays. Here, we show an example by electrodepositing epitaxial cuprous oxide on a Cu(111) foil.

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