P-type Cu2O Thin Films Research Articles

Influence of pH value of precursor on growth, structural, and optical properties of Cu2O thin films grown in Mist-CVD

The Cu2O thin films were prepared from copper (II) acetylacetonate (Cu(acac)2) by the mist chemical vapor deposition (mist-CVD) method, depending on the pH value of the prepared solution. It was confirmed that the well-oriented Cu2O thin films were grown at a dominant (111) peak according to X-ray diffraction (XRD) measurement using an alkaline precursor solution. The pH of the prepared solution drastically affected the surface morphology of the Cu2O thin films, and the lowest Root Means Square (RMS) was found for pH-10 of the precursor solution. The confocal Raman spectrum confirmed the formation of the cubic Cu2O crystal structures for each pH value of the precursor solution. The very transparent Cu2O thin films that were grown. The highest transmittance, 70%, was obtained at 1100 nm from the absorption spectrum for Sample B. The optical energy band gaps of Cu2O thin films were determined using Tauc's method and found to vary within a range of 2.53 to 2.49 eV, indicating a change in the material's electronic structure. The study demonstrated the crucial role of the pH level of the prepared solution in the growth of the Cu2O thin film. Specifically, it was found that a higher pH level resulted in a greater concentration of hydroxide ions (OH−), which was a crucial factor in the growth process. These findings can be significant in using p-type Cu2O thin films prepared based on mist-CVD for optoelectronic applications.

Unveiling SiO2 nanoparticle derived from rice husk doped P-type Cu2O thin films for solar cell application

Unveiling SiO2 nanoparticle derived from rice husk doped P-type Cu2O thin films for solar cell application

Optical and Material Characteristics of MoS2/Cu2O Sensor for Detection of Lung Cancer Cell Types in Hydroplegia

In this study, n-type MoS2 monolayer flakes are grown through chemical vapor deposition (CVD), and a p-type Cu2O thin film is grown via electrochemical deposition. The crystal structure of the grown MoS2 flakes is analyzed through transmission electron microscopy. The monolayer structure of the MoS2 flakes is verified with Raman spectroscopy, multiphoton excitation microscopy, atomic force microscopy, and photoluminescence (PL) measurements. After the preliminary processing of the grown MoS2 flakes, the sample is then transferred onto a Cu2O thin film to complete a p-n heterogeneous structure. Data are confirmed via scanning electron microscopy, SHG, and Raman mapping measurements. The luminous energy gap between the two materials is examined through PL measurements. Results reveal that the thickness of the single-layer MoS2 film is 0.7 nm. PL mapping shows a micro signal generated at the 627 nm wavelength, which belongs to the B2 excitons of MoS2 and tends to increase gradually when it approaches 670 nm. Finally, the biosensor is used to detect lung cancer cell types in hydroplegia significantly reducing the current busy procedures and longer waiting time for detection. The results suggest that the fabricated sensor is highly sensitive to the change in the photocurrent with the number of each cell, the linear regression of the three cell types is as high as 99%. By measuring the slope of the photocurrent, we can identify the type of cells and the number of cells.

Experimental and theoretical study of hole scattering in RF sputtered p-type Cu2O thin films

One of the key materials of interest for p-type oxide semiconductor thin film electronics is cuprous oxide (Cu2O), due to its relatively high hole mobility. In this work, we use experiments, analytical models, and density functional theory calculations to study the scattering mechanisms that determine Hall mobility in two Cu2O samples. First, we examine a polycrystalline Cu2O thin film deposited by RF magnetron sputtering, and second, a single-crystalline Cu2O bulk substrate. Temperature-dependent Hall measurements indicate that neutral impurity and grain boundary scattering are dominant for the polycrystalline Cu2O thin film, while phonon scattering is dominant for single-crystalline Cu2O. Our first-principles calculations show that the room-temperature intrinsic hole mobility of Cu2O is 106 cm2 V−1 s−1, indicating the great promise of the material for p-type electronic devices. This intrinsic mobility is limited by phonon scattering, with the most dominant scattering modes having phonon energies of 88.4 and 17.1 meV. These results indicate that the key pathways to increase the hole mobility in Cu2O thin films are by reducing the impurity concentration and by increasing grain size. Our work thus sets the stage for the future development of high performance Cu2O-based p-type thin film transistors.

Study on photocatalytic properties of Cu2O/TiO2 heterojunction composite films

Cu2O/TiO2 semiconductor heterostructure photocatalytic composite thin films were prepared by the sol-gel method and magnetron sputtering technology. Uniform and transparent TiO2 thin films were prepared by sol dipping and pulling with butyl titanate as the raw material. P-type Cu2O thin films were reactive sputtered on the surface of TiO2 thin films with metal Cu as target source. The catalysts were characterized by SEM, XRD and UV-Vis. The photocatalytic activity of heterojunction composite films under simulated sunlight was investigated by dye degradation experiments, and its mechanism is discussed. The results show that the heterojunction film formed by the composite of TiO2 and Cu2O has good photocatalytic activity under simulated sunlight. The heterojunction composite expands the light response range and light response intensity of the catalyst and improves the quantum efficiency. It is a kind of photocatalytic composite film that makes full use of solar energy.

Tunable optical and electrical properties of p-type Cu2O thin films

The presented study stresses that the deposition temperature is an important parameter to determine the quality and properties of deposited Cu2O thin films on copper (Cu) and fluorine-doped tin oxide (FTO) substrates. The optical and electrical properties of chemical bath deposited (CBD) cuprous oxide (Cu2O) thin films with a variety of deposition temperatures (50, 60, 70, and 80 °C) have been extensively investigated. The X-ray diffraction studies reveal the cubic polycrystalline structure of deposited thin films. The scanning electron microscopy (SEM) exhibits a homogeneous thin film constituting Cu2O crystals for 60 °C. Optical studies show the least energy bandgap of 1.90 eV at the optimized deposition temperature. The Cu deposited Cu2O thin film possesses very little resistivity and higher charge carrier concentration mainly due to the contribution from the conducting Cu substrate. The Cu2O films exhibit p-type conductivity in addition to comparable Hall mobility and improved charge carrier concentration by two orders of magnitude in the case of FTO substrate (~ 1017 cm−3). The I–V characteristics of fabricated Schottky junction with the prepared optimized thin film is presented. This study establishes 60 °C as the optimum temperature for Cu2O thin film deposition on different substrates.

Fabrication and characterization of ZnO/Cu2O heterostructures for solar cells applications

Abstract Zinc oxide and cuprous oxide thin films are environmentally friendly and low-cost semiconductors and have various optoelectronic applications. The overall cost of the heterostructures they form can also be reduced via economic fabrication methods. ZnO and Cu2O thin films can be deposit under normal laboratory conditions via spin coating and electrodeposition methods. However, the main concerns of the low-cost methods are the growth of pure Cu2O and efficient interface between the films. On the other hand, it is still worth exploiting the low-cost spin coating and electrodeposition methods due to their efficient thin film growth potential. In this study, the one-step spin coating method was employed to prepare ZnO thin films. The electrodeposition of Cu2O thin film was achieved via developed a simple two electrodes cell. The structural, morphological, optical, and electrical measurements show that p-type Cu2O thin films were successfully deposited with our system. Although the open circuit voltage of the prepared heterojunction solar cell devices is quite low, the methods here we apply and the conditions have the potential to fabricate a solar cell. Open circuit voltage and thus efficiency will increase by improving interfaces with chemical methods and more effective annealing.

Pulsed laser deposition of single phase n- and p-type Cu2O thin films with low resistivity

Low resistivity (ρ ~ 3–24 mΩ·cm) with tunable n- and p-type single phase Cu2O thin films have been grown by pulsed laser deposition at 25–200 °C by varying the background oxygen partial pressure (O2pp). Capacitance data obtained by electrochemical impedance spectroscopy was used to determine the conductivity (n- or p-type), carrier density, and flat band potentials for samples grown on indium tin oxide (ITO) at 25 °C. The Hall mobility (μH) of the n- and p-type Cu2O was estimated to be ~0.85 cm2/V.s and ~ 4.78 cm2/V.s respectively for samples grown on quartz substrate at 25 °C. An elevated substrate temperature ~ 200 °C with O2pp = 2–3 mTorr yielded p-type Cu2O films with six orders of magnitude higher resistivities in the range, ρ ~ 9–49 kΩ.cm and mobilities in the range, μH ~ 13.5–22.2 cm2/V.s. UV–Vis-NIR diffuse reflectance spectroscopy showed optical bandgaps of Cu2O films in the range of 1.76 to 2.15 eV depending on O2pp. Thin films grown at oxygen rich conditions O2pp ≥ 7 mTorr yielded mixed phase copper oxide irrespective of the substrate temperatures and upon air annealing at 550 °C for 1 h completely converted to CuO phase with n-type semiconducting properties (ρ ~ 12 Ω.cm, μH ~ 1.50 cm2/V.s). The as-grown p- and n-type Cu2O showed rectification and a photovoltaic response in solid junctions with n-ZnO and p-Si electrodes respectively. Our findings may create new opportunities for devising Cu2O based junctions requiring low process temperatures.

Novel Boron-Doped p-Type Cu2O Thin Films as a Hole-Selective Contact in c-Si Solar Cells.

p-type Cu2O thin films doped with trivalent cation boron are demonstrated for the first time as an efficient hole-selective layer for c-Si heterojunction solar cells. Cu2O and Cu2O:B films were deposited by rf magnetron sputtering, and the optical and electrical properties of the doped and undoped films were investigated. Boron doping enhanced the carrier concentration and the electrical conductivity of the Cu2O film. The band alignment of the Cu2O:B/Si heterojunction was investigated using XPS and UPS measurements. The Cu2O:B/Si interface has a valance band offset of 0.08 eV, which facilitates hole transport, and a conduction band offset of 1.35 eV, which blocks the electrons. A thin SiOx tunnel oxide interlayer was also explored as the passivation layer. The initial trials of incorporating this Cu2O:B layer as a hole transporting layer in a single heterojunction solar cell with the structure, ITO/Cu2O:B/n-Si/Ag, and a cell area of 1 cm2 yielded an open-circuit voltage of 370 mV, a short-circuit current density of 36.5 mA/cm2, and an efficiency of 5.4%. This p-type material could find potential applications in various optoelectronic applications like organic solar cells, TFTs, and LEDs.

Highly photocatalytic p-type Cu2O thin films fabricated on a quartz glass substrate at 180°C in air, by spraying aqueous precursor solutions involving Cu(II) complexes

ABSTRACT The p-type Cu2O thin films on a quartz glass substrate were facilely fabricated at 180°C in air by spraying aqueous precursor solutions. The spray solutions were prepared in a diluted ammonia solution by dissolving Cu(II) formate and ammonium formate whose molar ratios to Cu(II) ion were 0, 2, 6 and 14. In the cases of the molar ratios at 6 and 14, the Cu2O thin films of 140 and 350 nm thickness respectively indicated a highly photocatalytic activity under visible-light irradiation of 0.45 mW cm–2, and the pseudo-first-order rate constants of 0.056 and 0.087 min–1 were respectively obtained by tracing the discoloration of a methyl orange solution. The O-defect site was found in the Raman spectra of these photocatalytic thin films whose adhesion strength onto the quartz substrate were larger than 5.6 N. The morphology, chemical component, and optical and electrical properties were also examined in detail.

Nitrogen-Doped Cu2O Thin Films for Photovoltaic Applications

Cuprous oxide (Cu2O) is a p-type semiconductor with high optical absorption and a direct bandgap of about 2.1 eV, making it an attractive material for photovoltaic applications. For a high-performance photovoltaic device, the formation of low-resistivity contacts on Cu2O thin films is a prerequisite, which can be achieved by, for instance, nitrogen doping of Cu2O in order to increase the carrier concentration. In this work, nitrogen-doped p-type Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. By adding N2 gas during the deposition process, a nitrogen concentration of up to 2.3 × 1021 atoms/cm3 in the Cu2O thin films was achieved, as determined from secondary ion mass spectroscopy measurements. The effect of nitrogen doping on the structural, optical, and electrical properties of the Cu2O thin films was investigated. X-ray diffraction measurements suggest a preservation of the Cu2O phase for the nitrogen doped thin films, whereas spectrophotometric measurements show that the optical properties were not significantly altered by incorporation of nitrogen into the Cu2O matrix. A significant conductivity enhancement was achieved for the nitrogen-doped Cu2O thin films, based on Hall effect measurements, i.e., the hole concentration was increased from 4 × 1015 to 3 × 1019 cm−3 and the resistivity was reduced from 190 to 1.9 Ω⋅cm by adding nitrogen to the Cu2O thin films.

Synthesis and photocatalytic properties of flexible Cu2O thin film

ABSTRACTIn this study, Cu2O thin film covering on a carbon network (CNW) was designed as composite structure with novel flexible characteristics. P-type Cu2O thin film with dominated (111) orientation was successfully deposited on the surface of the CNW via an electrochemical method. The CNW/Cu2O composite exhibits interesting tensile property and high photodegradation efficiency for methyl orange (MO) solution. Its recyclability is highly attractive in potential application in solving azo dye pollution problem.

Electrodeposited p-type Cu2O thin films at high pH for all-oxide solar cells with improved performance

We report the electrodeposition of cuprous oxide (Cu2O) films from cupric sulfate-lactate electrolytes at high pH 13.5 and their performance in all-oxide fluorine-doped tin oxide/Cu2O/aluminium-doped zinc oxide solar cells. The deposit grains are found to grow with rather randomly distributed <111> and <100> crystal orientations and have a poorly-definded morphology with evidence of chemical dissolution that takes place during the deposition process. Significant improvements in the solar cell performance with high power conversion efficiencies of up to 1.55% is achieved, which is much better that those (<0.2%) of solar cells with Cu2O layer electrodeposited at lower pH. The performance enhancement is primarily attributed to the improved electron transport in the Cu2O thin film due to partial merging of grains.

Fabrication of a p-type Cu2O thin-film via UV-irradiation of a patternable molecular-precursor film containing Cu(II) complexes

A patterned p-type Cu2O thin-film was fabricated using 4-mW cm−2 ultraviolet (UV) irradiation onto a preheated precursor-film formed on a Na-free glass by spin-coating a solution containing Cu(II) complexes of propylamine and ethylenediamine, and post-annealing. After a small Na-free glass plate was placed on the spin-coated and preheated precursor-film to provide a UV-shielded area, the film was UV-irradiated for 6 h at room temperature. X-ray diffraction measurement indicated that the UV-irradiation converted the Cu(II) complexes to crystallized Cu2O. The patterned film obtained by removal of the UV-shielded portion with immersion into water was then post-annealed at 400 °C for 3 min in an Ar-gas flow. The Hall effect measurement of the resultant film of a 90 nm thickness showed that the electrical resistivity, carrier concentration, and hole mobility were 1.4(2) × 102 Ω cm, 8(3) × 1016 cm−3, and 0.9(3) cm2 V−1 s−1, respectively.

Metal Oxide Thin-Film Heterojunctions for Photovoltaic Applications.

Silicon-based tandem solar cells incorporating low-cost, abundant, and non-toxic metal oxide materials can increase the conversion efficiency of silicon solar cells beyond their conventional limitations with obvious economic and environmental benefits. In this work, the electrical characteristics of a metal oxide thin-film heterojunction solar cell based on a cuprous oxide (Cu2O) absorber layer were investigated. Highly Al-doped n-type ZnO (AZO) and undoped p-type Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. The electrical and optical properties of these thin films were determined from Hall effect measurements and spectroscopic ellipsometry. After annealing the Cu2O film at 900 °C, the majority carrier (hole) mobility and the resistivity were measured at 50 cm2/V·s and 200 Ω·cm, respectively. Numerical modeling was carried out to investigate the effect of band alignment and interface defects on the electrical characteristics of the AZO/Cu2O heterojunction. The analysis suggests that the incorporation of a buffer layer can enhance the performance of the heterojunction solar cell as a result of reduced conduction band offset.

Electroless Deposition of p-type Cuprous Oxide Thin Film for Solar Application

Solar cells hold a promising prospect in the foreseeable future. Presently cuprous oxides (Cu2O), due to their excellent photovoltaic properties, are being considered as p-type semiconductor materials for solar cell. This work aims at electroless deposition of p-type Cu2O thin film on copper substrate and studying its various properties through characterizations. A bath containing varying amounts of CuCl2.2H20, CoCl2.6H20, NaH2PO2.6H20 and KNaTar.4H2O (Potassium sodium tartrate tetrahydrate) was used for the process. NaOH pellets were used in order to get the desired pH level ranging from 11 to 14. The bath temperature was varied between 30°C to 70°C. The deposited films were characterized by Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS), X-ray diffractometer (XRD) and UV spectroscopy. It was observed that thin films were deposited at different conditions and uniform deposition of Cu2O thin film was visible at pH 14. The coating thickness was found to be in the range of 0.48 to 4.6 μm. The bandgap for the deposited Cu2O was found to be in the range of 1.3-1.4 eV. Some variation in results at different pH were observed and the reasons were identified.

Photoelectrochemical Properties of a Cu2O Film/ZnO Nanorods Oxide p-n Heterojunction Photoelectrode for Solar-Driven Water Splitting

We report on the fabrication and photoelectrochemical(PEC) properties of a Cu2O thin film/ZnO nanorod array oxide p-n heterojunction structure with ZnO nanorods embedded in Cu2O thin film as an efficient photoelectrode for solardriven water splitting. A vertically oriented n-type ZnO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type Cu2O thin film was directly electrodeposited onto the vertically oriented ZnO nanorods array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were characterized using X-ray diffraction and scanning electron microscopy as well as Raman scattering. The PEC properties of the fabricated Cu2O/ZnO p-n heterojunction photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/ZnO photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., 0.77 mA/cm2 at 0.5 V vs Hg/HgCl2 in a 1 mM Na2SO4 electrolyte, revealing an effective operation of the oxide heterostructure. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs Hg/HgCl2, which made the device self-powered. The observed PEC performance was attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential, including the light absorption and separation processes of photoinduced charge carriers.

Heteroepitaxial growth of Cu2O films on Nb-SrTiO3 substrates and their photovoltaic properties

In this paper, p-type Cu2O thin films have been epitaxially grown on n-type semiconducting (001) oriented Nb-SrTiO3 (NSTO) substrates with different Nb doping concentration by pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy reveal a cube-on-cube epitaxial relationship between Cu2O and NSTO. It is found that the deposition temperature, the thickness of Cu2O films and the Nb doping concentration of NSTO substrates have critical impact on the photovoltaic (PV) properties of the Cu2O/NSTO heterojunction devices. A maximum PV performance is observed in ITO/Cu2O/NSTO device when the deposition temperature, film thickness and Nb doping concentration of NSTO are 550°C, 76nm, and 0.7wt% NSTO, respectively. The optimized PV output corresponds to the open circuit voltage, short-circuit current density, fill factor and photovoltaic conversion efficiency about 0.45V, 1.1mA/cm2, 46% and 0.23%，respectively. This work offers an insight into the strategy for developing and designing novel optoelectronics of NSTO-based oxide heterostructures.

Cyclic Voltammetry Measurement for Cu2O Based Homostructure Thin Film

This experiment is about fabrication of homojunction Copper Oxide (Cu2O) thin film by using electrodeposition method. The p-n homojunction Cu2O was successfully prepared by consecutively depositing p-type Cu2O layer on n-type Cu2O layer by using copper acetate based solution through potentiostatic electrodeposition. At first, the n-type Cu2O was fabricated at pH 6.2 and 6.5 with fixed potential of -0.125V vs Ag/AgCl and time deposition at 30 minutes. Cyclic voltammetry (CV) measurement was carried out on this sample to determine the ideal potential range for fabrication of p-type Cu2O on n-type Cu2O/FTO substrate. From the result, deposition potential of -0.35V and -0.4V vs Ag/AgCl were appropriated for p-type Cu2O thin film fabrication. These potential values were variable with the selected pH values of 12.0 and 12.5 to fabricate the p-type Cu2O thin film. The other parameters such as deposition time fixed at 2 hours bath temperature was set up at 60°C. It was found that the optimum potential deposition was -0.4V vs Ag/AgCl and pH value appropriate for homostructure Cu2O thin film was pH 12.5. Morphological, structural, optical and conductivity characterization of p-n homojunction Cu2O thin film was characterized using Field Emission Scanning Electron Microscopy, X-Ray Diffractometer, Ultraviolet-Visible Spectroscopy and Photoelectrochemical (PEC) cells, respectively.

Analysis of the Conduction Mechanism and Copper Vacancy Density in p-type Cu2O Thin Films

A quantitative and analytical investigation on the conduction mechanism in p-type cuprous oxide (Cu2O) thin films is performed based on analysis of the relative dominance of trap-limited and grain-boundary-limited conduction. It is found that carrier transport in as-deposited Cu2O is governed by grain-boundary-limited conduction (GLC), while after high-temperature annealing, GLC becomes insignificant and trap-limited conduction (TLC) dominates. This suggests that the very low Hall mobility of as-deposited Cu2O is due to significant GLC, and the Hall mobility enhancement by high-temperature annealing is determined by TLC. Evaluation of the grain size and the energy barrier height at the grain boundary shows an increase in the grain size and a considerable decrease in the energy barrier height after high-temperature annealing, which is considered to be the cause of the significant reduction in the GLC effect. Additionally, the density of copper vacancies was extracted; this quantitatively shows that an increase in annealing temperature leads to a reduction in copper vacancies.