Phase-pure Cu2O Research Articles

Electrodeposition of Phase–Pure n–Type Cu2O: Role of Electrode Reactions and Local pH

Cuprous oxide (Cu2O) thin films, antithetically exhibiting n-type conductivity, were electro–deposited on Fluorine-doped Tin Oxide (FTO) coated glass substrates. Linear sweep voltammetry, chronoamperometry, and chronopotentiometry studies coupled with structural characterization of the deposit identify the occurrence of multiple reduction reactions, including “corrosion” of Cu2O to Cu. Interestingly, an underpotential conversion (negative of +0.039 V vs Ag/AgCl) of the Cu2O film to Cu islands is observed during potentiostatic deposition. The same process is also shown as a potential spike in chronopotentiometry curves, during galvanostatic deposition, at current densities that are cathodic of −0.2 mAcm−1. The reason for the formation of Cu is attributed to the decrease in local pH in the vicinity of the working electrode, whence thermodynamic conditions favor the formation of Cu. The proroguation of Cu formation is achieved by continuously stirring the solution, thereby stabilizing the pH at the electrode. Deferment of film corrosion to increasingly longer times is observed with increasing stirring rates. Mott-Schottky analysis of phase-pure films reveals the formation of degenerately doped n-type Cu2O films (n ∼1020 cm−3). The phase pure Cu2O films could be used as an electron transport layer in several photo-conversion devices and ultimately pave the way for an oxide homojunction device.

Communication—Texture and Bandgap Tuning of Phase Pure Cu2O Thin Films Grown by a Simple Potentiostatic Electrodeposition Technique

Highly textured phase pure Cu2O thin films have been grown by a simple electrodeposition technique with varying deposition voltages (−0.3 to −1.0 V). The surface morphology characterized by Scanning Electron Microscopy (SEM) revealed that the deposited thin films coherently carpet the underlying substrate and are composed of sharp faceted well-defined grains of 0.5–1.0 μm sizes. XRD analyses showed that all films are composed of polycrystalline cubic Cu2O phase only and have average crystalline domain size in the range of 30–73 nm. The preferred crystalline orientation of phase pure Cu2O films was found to be changing from (200) to (111) with increasing cathodic voltages and showed the highest (111) and (200) crystalline texture coefficient while growing at −1.0 and −0.8 V respectively. The optical bandgap of the as-grown samples was calculated in the range of 1.95–2.20 eV using UV–vis Transmission data. The performance of Cu2O/FTO photocathodes was tested by estimating LED “ON/OFF” modulated surface photovoltage into a photoelectrochemical cell at a zero bias.

Deposition and characterization of lithium doped direct current magnetron sputtered [formula omitted] films

Lithium doped cuprous oxide (Cu2O:Li) films were deposited on quartz substrates by direct current magnetron reactive co-sputtering of copper and Cu:Li targets. X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry, UV-VIS transmittance, and room temperature Hall measurements have been conducted to characterize the deposited films. SIMS revealed Li concentrations in the range 2×1018−5×1020cm−3 in the doped films. XRD confirms phase pure Cu2O for all doping concentrations. The doping concentration correlates with an increased free carrier density found from Hall effect measurements. The highest Li doping concentration results in low resistivity (4Ωcm) p-type Cu2O with acceptor concentrations up to 2×1017cm−3.

Texture and Bandgap Tuning of Phase Pure Cu2o Thin Films Grown By a Simple Potentiostatic Electrodeposition Technique

Phase pure Cu2O is one of the most desirable p-type absorber materials for ZnO based all-oxide solar cell because of its reported direct bandgap(~2.17 eV) and a suitable band alignment with n-type ZnO electrodes. Highly textured phase pure Cu2O thin films have been grown by a simple electrodeposition technique with varying cathodic potentials (-0.3 to -1.0 V) using Fluorine-doped Tin Oxide (FTO) substrates as working electrodes and a carbon rod as a counter electrode immersed in an alkaline aqueous electrolyte held at ~60 0C for 40 min. The surface morphology, structural, optical properties of the as-deposited Cu2O thin films were characterized by Scanning Electron Microscopy (SEM), Surface profiler, X-ray diffraction (XRD), and UV-Vis-NIR Spectroscopy respectively. SEM micrographs revealed that the deposited thin films coherently carpet the underlying substrate and composed of sharp faceted well-define grains having size in the range of 0.5 – 1.0 µm . XRD analyses showed that all films are composed of polycrystalline cubic Cu2O phase only and have average crystalline domain size in the range 30 – 73 nm. The preferred crystalline orientation of phase pure Cu2O films were found to be changing from (200) to (111) with increasing cathodic potentials and showed highest (111) and (200) crystalline texture coefficient while grown at -1.0 and -0.8 V respectively. The estimated optical bandgap of the as-grown samples were found in the range (2.00 – 2.20) eV consistent with the previously reported results and the variation of the optical bandgap could be attributed to the variation of the film thickness. The performance of copper oxide films was tested by estimating LED ‘ON/OFF’ modulated surface photovoltage into a photoelectrochemical cell at zero bias voltage and was found to be reasonable to integrate them into optoelectronic devices.

Morphological evolution of hexapod Cu2O microcrystals by a rapid template-free autoclaving technique

Morphologically tuned Cu2O micro-crystals were synthesized by one-pot autoclaving method at 150°C for a shorter reaction time in the presence of copper nitrate and di-methyl formamide (DMF) without using any external templating agents. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) showed the formation of phase pure Cu2O in the as-prepared samples. Morphological analysis indicated the formation of hexapod Cu2O with twenty four {111} facets at 150°C/2h. The hydrolysis product of DMF, i.e., di-methyl amine (Me2NH) and formic acid (HCOOH) played a significant role as growth controller and reducing agent, respectively for the formation of Cu2O micro-crystals. A proposed formation mechanism was illustrated.

Non-equilibrium deposition of phase pure Cu2O thin films at reduced growth temperature

Cuprous oxide (Cu2O) is actively studied as a prototypical material for energy conversion and electronic applications. Here we reduce the growth temperature of phase pure Cu2O thin films to 300 °C by intentionally controlling solely the kinetic parameter (total chamber pressure, Ptot) at fixed thermodynamic condition (0.25 mTorr pO2). A strong non-monotonic effect of Ptot on Cu-O phase formation is found using high-throughput combinatorial-pulsed laser deposition. This discovery creates new opportunities for the growth of Cu2O devices with low thermal budget and illustrates the importance of kinetic effects for the synthesis of metastable materials with useful properties.

Copper terephthalate and its thermal decomposition products

Crystalline copper terephthalate of composition Cu[C6H4(COO)2]·2H2O has been synthesized by reacting aqueous solutions of sodium terephthalate and copper sulfate, and its dehydration has been studied in the temperature range 150–300°C. The results indicate that its dehydration behavior depends on the heating rate. Slow heating (to 200°C over a period of 24 h) removes one water molecule per formula unit near 150°C and leads to the formation of an anhydrous salt and a mixture of Cu2O and CuO (a total of 12.41%) near 200°C. Heating to 300°C in 10 min leads to the formation of nearly phase-pure Cu2O.