CuBr Films Research Articles

A self-powered p-CuBr/n-Si heterojunction photodetector based on vacuum thermally evaporated high-quality CuBr films

Violet heterojunction photodetectors based on p-CuBr/n-Si are prepared by the vacuum thermal evaporation technique. The photodetectors have a sensitive violet response with self-powered characteristics and excellent imaging capability.

Epitaxial Electrodeposition of Wide Bandgap Cuprous Bromide on Silver via a Silver Bromide Buffer Layer

Cuprous halides are an important class of wide bandgap p-type semiconductors used in opto-electronics. Cuprous bromide (CuBr) shows potential for short-wavelength devices due to a large exciton binding energy (108 meV) and near-ultraviolet bandgap (3.1 eV). However, the growth of high-quality epitaxial CuBr films by electrodeposition has remained a challenge. Here, we introduce a low-cost electrochemical procedure for producing epitaxial CuBr(111) on a Ag(111) substrate by a [111]-oriented silver bromide (AgBr) buffer layer. The AgBr buffer layer forms during the electrodeposition of the CuBr. The mismatch between CuBr(111) and AgBr(111) is −1.3%. A plausible mechanism for nucleation and growth of the epitaxial CuBr is proposed. X-ray techniques including high resolution X-ray diffraction and X-ray pole figures are used to determine the epitaxial relationship. CuBr(100) is also produced on a Ag(100) surface by a AgBr(100) buffer layer that is rotated in-plane 45° relative to the Ag(100) surface. This in-plane rotation reduces the lattice mismatch from +39.5% for an unrotated film to −1.4% for a 45° rotated film.

Chemical Vapor Deposition of Wide-Bandgap p-Type Semiconductor Cuprous Iodide for Optoelectronic Device Applications

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired.With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5].The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6].Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV.[1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020).[2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017).[3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019).[4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997).[5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020).[6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018).[7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017).[8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).

Facile and rapid fabrication of porous CuBr films by solution oxidation and their application for the exclusive detection of NH3 at room temperature

A porous CuBr film with exclusive NH3 sensing properties is prepared via a simple solution process, which offers the best opportunity for realizing low-cost, wearable devices for indoor air quality monitoring.

Porous and Nanostructured CuBr Networks for Selective Ammonia Sensing at Room-Temperature

Introduction Ammonia (NH3), a major industrial commodity (142 Mt in 2017 [1]), is toxic as well as a tracer for food spoilage detection and important breath marker for impaired kidney function [2]. As a result, there is a strong interest in selective sensors that detect NH3 concentrations over a large range: from 250 to 2900 ppb in mouth-exhaled breath down to few ppb in indoor air at high relative humidity. Also, it occurs usually in gas mixtures containing a myriad of compounds requiring also high NH3 selectivity. Most promising as a solid-state and low-cost sensor material is CuBr featuring high selectivity and sensitivity to low NH3 concentrations (e.g. 20 ppb [3]) even at room temperature. However, current fabrication methods usually result in micro-sized CuBr particles [3] and rather dense film morphologies [4] that could impede efficient NH3 diffusion in the film and interaction with the CuBr surface. Here, we introduce a novel fabrication route yielding highly porous and nanostructured CuBr films for improved NH3 sensitivity and fast response dynamics at room temperature [5]. Methods Porous and nanostructured CuBr films are obtained by a flame-aerosol based method on interdigitated electrodes. Their sensing performance was evaluated at room temperature in gas mixtures prepared with high-resolution mass flow controllers, as described in detail elsewhere [6]. In brief, analyte gases (i.e. NH3, isoprene, ethanol, methane, acetone, hydrogen, acetic acid, methanol, formaldehyde and CO) were supplied from calibrated cylinders (10 or 50 ppm in synthetic air, PanGas) and dosed to dry synthetic air (Pangas 5.0, CnHm and NOx ≤ 100 ppb) with calibrated mass flow controllers. Humidity was added by bubbling dry synthetic air through distilled water and admixing it to the analyte flow. All transfer lines were made of inert Teflon to minimized analyte gas adsorption and heated to 55 °C to avoid water condensation. The sensor film resistance was continuously monitored with a multimeter (Keithley, Integra Series 2700, USA). Results and Conclusions The porous CuBr films were tested for sensing of 5 - 5000 ppb NH3 at 90% RH (Figure 1a). When exposed to 5000 ppb of NH3, the resistance rapidly increases from 47 kΩ to 13 MΩ corresponding to a response (S) of 276. When exposed to NH3, the Cu+ as charge carriers are immobilized by forming that results in the observed resistance increase. Remarkably, this interaction is rapid and reversible even at room temperature, as indicated by the full recovery of the initial resistance baseline (dashed line, Figure 1a) and in line with literature [3]. Most impressively, NH3 concentrations down to 5 ppb (see also inset of Figure 1a for higher magnification) are detected and can be distinguished clearly from 10 and 20 ppb. The signal-to-noise-ratio (SNR, > 70) is remarkable and should enable the detection of even lower concentrations with an extrapolated lower limit of detection (LOD) of 210 parts-per-trillion (ppt) considering a typical SNR of 3. This is superior to state-of-the-art room temperature NH3 sensors: For instance, polyaniline sensors detect 40 ppb NH3 at ≥ 90% RH [7], but these are usually for single-use only as they recover too slowly.The porous CuBr sensor was tested with isoprene, ethanol, methane, acetone, hydrogen, acetic acid, methanol, formaldehyde and carbon monoxide (CO), all at a concentration of 1 ppm and 90% RH (Figure 1b). Most remarkably, the sensor responds strongest to NH3 with selectivity > 30 with CO being the highest one (> 290). This is similar to thermally deposited CuBr films with a CeO2 overlayer [3] for some of these analytes. Other NH3 sensors feature lower selectivities to these analytes. In fact, polymer-based PEDOT:PSS nanowires [8] are quite sensitive to ethanol (NH3 selectivity ~15 vs. CuBr ~40).In conclusion, such nanostructured and porous CuBr films are quite attractive for wearable breath analyzers [9] and detectors for distributed air and food quality monitoring networks with stringent power requirements.

Porous and Nanostructured CuBr Networks for Selective Ammonia Sensing at Room-Temperature

Introduction Ammonia (NH3), a major industrial commodity (142 Mt in 2017 [1]), is toxic as well as a tracer for food spoilage detection and important breath marker for impaired kidney function [2]. As a result, there is a strong interest in selective sensors that detect NH3 concentrations over a large range: from 250 to 2900 ppb in mouth-exhaled breath down to few ppb in indoor air at high relative humidity. Also, it occurs usually in gas mixtures containing a myriad of compounds requiring also high NH3 selectivity. Most promising as a solid-state and low-cost sensor material is CuBr featuring high selectivity and sensitivity to low NH3 concentrations (e.g. 20 ppb [3]) even at room temperature. However, current fabrication methods usually result in micro-sized CuBr particles [3] and rather dense film morphologies [4] that could impede efficient NH3 diffusion in the film and interaction with the CuBr surface. Here, we introduce a novel fabrication route yielding highly porous and nanostructured CuBr films for improved NH3 sensitivity and fast response dynamics at room temperature. Methods Porous and nanostructured CuBr films are obtained by a flame-aerosol based method on interdigitated electrodes. Their sensing performance was evaluated at room temperature in gas mixtures prepared with high-resolution mass flow controllers, as described in detail elsewhere [5]. In brief, analyte gases (i.e. NH3, isoprene, ethanol, methane, acetone, hydrogen, acetic acid, methanol, formaldehyde and CO) were supplied from calibrated cylinders (10 or 50 ppm in synthetic air, PanGas) and dosed to dry synthetic air (Pangas 5.0, CnHm and NOx ≤ 100 ppb) with calibrated mass flow controllers. Humidity was added by bubbling dry synthetic air through distilled water and admixing it to the analyte flow. All transfer lines were made of inert Teflon to minimized analyte gas adsorption and heated to 55 °C to avoid water condensation. The sensor film resistance was continuously monitored with a multimeter (Keithley, Integra Series 2700, USA). Results and Conclusions The porous CuBr films were tested for sensing of 5 - 5000 ppb NH3 at 90% RH (Figure 1a). When exposed to 5000 ppb of NH3, the resistance rapidly increases from 47 kΩ to 13 MΩ corresponding to a response (S) of 276. When exposed to NH3, the Cu+ as charge carriers are immobilized by forming that results in the observed resistance increase. Remarkably, this interaction is rapid and reversible even at room temperature, as indicated by the full recovery of the initial resistance baseline (dashed line, Figure 1a) and in line with literature [3]. Most impressively, NH3 concentrations down to 5 ppb (see also inset of Figure 1a for higher magnification) are detected and can be distinguished clearly from 10 and 20 ppb. The signal-to-noise-ratio (SNR, > 70) is remarkable and should enable the detection of even lower concentrations with an extrapolated lower limit of detection (LOD) of 210 parts-per-trillion (ppt) considering a typical SNR of 3. This is superior to state-of-the-art room temperature NH3 sensors: For instance, polyaniline sensors detect 40 ppb NH3 at ≥ 90% RH [6], but these are usually for single-use only as they recover too slowly.The porous CuBr sensor was tested with isoprene, ethanol, methane, acetone, hydrogen, acetic acid, methanol, formaldehyde and carbon monoxide (CO), all at a concentration of 1 ppm and 90% RH (Figure 1b). Most remarkably, the sensor responds strongest to NH3 with selectivity > 30 with CO being the highest one (> 290). This is similar to thermally deposited CuBr films with a CeO2 overlayer [3] for some of these analytes. Other NH3 sensors feature lower selectivities to these analytes. In fact, polymer-based PEDOT:PSS nanowires [7] are quite sensitive to ethanol (NH3 selectivity ~15 vs. CuBr ~40).In conclusion, such nanostructured and porous CuBr films are quite attractive for wearable breath analyzers [8] and detectors for distributed air and food quality monitoring networks with stringent power requirements.

Rapid and Selective NH3 Sensing by Porous CuBr.

Fast and selective detection of NH3 at parts‐per‐billion (ppb) concentrations with inexpensive and low‐power sensors represents a long‐standing challenge. Here, a room temperature, solid‐state sensor is presented consisting of nanostructured porous (78%) CuBr films. These are prepared by flame‐aerosol deposition of CuO onto sensor substrates followed by dry reduction and bromination. Each step is monitored in situ through the film resistance affording excellent process control. Such porous CuBr films feature an order of magnitude higher NH3 sensitivity and five times faster response times than conventional denser CuBr films. That way, rapid (within 2.2 min) sensing of even the lowest (e.g., 5 ppb) NH3 concentrations at 90% relative humidity is attained with outstanding selectivity (30–260) over typical confounders including ethanol, acetone, H2, CH4, isoprene, acetic acid, formaldehyde, methanol, and CO, superior to state‐of‐the‐art sensors. This sensor is ideal for hand‐held and battery‐driven devices or integration into wearable electronics as it does not require heating. From a broader perspective, the process opens exciting new avenues to also explore other bromides and classes of semiconductors (e.g., sulfides, nitrides, carbides) currently not accessible by flame‐aerosol technology.

Highly enhanced UV responsive conductivity and blue emission in transparent CuBr films: implication for emitter and dosimeter applications

UV-responsive giant and persistent enhancements in the room temperature electrical conductivity and blue emission in CuBr films in ambient air.

Influence of Oxygen Plasma on the Growth, Structure, Morphology, and Electro-Optical Properties of p-Type Transparent Conducting CuBr Thin Films

p-type transparent conducting CuBr thin films were grown by thermal evaporation of CuBr followed by oxygen plasma treatment. Efficient incorporation of oxygen into the CuBr films was revealed, and the influence of plasma exposure on the electrical, structural, optical, and electronic properties of CuBr films was investigated. X-ray diffraction (XRD) analysis indicated the Zincblende structure of the oxygen plasma treated CuBr (OCB) films with the formation of nanocrystalline grains preferentially oriented along the (111) direction. p-type conducting OCB films show >85% average transmittance along with hole concentration, conductivity and Hall mobility values of ∼1019 cm–3, ∼1.5 S cm–1 and ∼0.45 cm2 V–1 s–1, respectively. The X-ray photoelectron spectra of the OCB films demonstrated that the plasma exposure resulted in a significant increase in the O 1s signal at the surface of OCB films. On the basis of the experimental results from the Hall measurements and X-ray photoemission, a possible explanation comprising the formation of a surface CuO layer is also proposed to elucidate the increase in the p-type conductivity of the OCB films. Strong room temperature emission of OCB films at around 416 nm was also observed, the intensity of which decreased with the increase of oxygen plasma exposure time. The results present oxygen plasma exposure as a simple and promising technique for the production of CuBr-based p-type materials for future transparent electronics.

Deposition of earth-abundant p-type CuBr films with high hole conductivity and realization of p-CuBr/n-Si heterojunction solar cell

We present details of the deposition of transparent and earth-abundant p-type CuBr films with high hole conductivity and the fabrication and characterization of a prototype solar cell based on p-CuBr/n-Si heterojunctions. p-type CuBr films with typical resistivities and hole concentrations of 7×10−1Ωcm and 7.5×1019cm−3, respectively, are deposited by thermal evaporation followed by oxygen plasma treatment. The transparent p-type films show strong room temperature photoluminescence at ~2.97eV. The current voltage (I–V) characteristics of the heterojunctions show good diode behaviour. Power conversion efficiency of ~2% was achieved for the heterojunction device without any optimization of the cell structure under AM 1.5 illumination condition with a short circuit current (Jsc) and open circuit voltage (Voc) of 13.2mA/cm2 and 0.44V, respectively.

ChemInform Abstract: Dramatic Improvement of Excitonic Photoluminescence in Metal Halide Films

AbstractReview: 105 refs.

Inherent excitonic luminescence in metal halide promising for potential applications in light-emitting devices

So far, excitonic luminescence in metal halide (MH) has extensively been studied by many workers, with the interest not only in physics of excitons but also in its possible application in optoelectronics. In the actual MHs, however, excitonic luminescence is so weak that it is beyond the scope of applications. Here we report the rediscovery that inherent excitonic luminescence in MH is dominated by a dramatically high light-emitting mechanism. This is demonstrated using improved films of MH yielded by two simple, independent methods, both applicable to several MHs. For example, improved CsPbCl3 and CuBr films exhibit more than 103–104 times stronger excitonic luminescence than conventional films. Inherent excitonic luminescence in MH is promising for applications in exciton-based light-emitting devices, particularly in shorter-wavelength devices than the traditional, nonexcitonic ones because it is MH and only MH that includes many compounds with large band gap and large exciton binding energies.

Unusual Modification of CuCl or CuBr Films by He Plasma Exposure Resulting in Nanowire Formation

In this paper, we present a method for growing copper-based nanowires. The method is based on the unusual modification of a halogenated copper surface by exposure to a helium plasma. The nanowires have diameters ranging between 50 and 150 nm and lengths up to 50 microm. They are polycrystalline, and large parts of the wires have a pronounced core-shell structure with a dense shell and less material inside. The wires are grown in a plasma environment at room temperature, and large amounts can be grown in a matter of minutes. The critical process parameters for the growth process are the gas flow and pressure settings, and the impact thereof will be discussed in detail. In order to gain insight in a possible growth mechanism, our observations are compared with literature on the growth of silver whiskers from halogenated silver crystallites. Finally, photoluminescence spectra of the wires are discussed in view of the analytical data about the stoichiometry and structure of the nanowires.

Excellent CuBr films exhibiting times higher room-temperature free-exciton PL efficiency than conventional CuBr films

High-quality CuBr films are fabricated by film-substrate chemical reaction of CuCl on KBr. The films exhibit more than ∼104 times higher free-exciton photoluminescence (PL) efficiency at room temperature than conventional CuBr films. The room-temperature PL efficiency exceeds that of conventional CuCl films by a factor of ∼103 and even the cryogenic-temperature free-exciton PL efficiency of the same films by a factor of ∼102, despite the general recognition that the free-exciton PL efficiency of CuBr is much weaker than that of CuCl. The extreme PL efficiency of the CuBr is concluded to be mediated by the high-quality KBr− crystal surroundings, into which and out of which Cu+ and K+ ions migrate, respectively, during the film-substrate chemical reaction, thus generating high-quality CuBr crystallites in the surroundings.

CuBr films on KBr exhibiting 102 or 103 times higher efficiency of free-exciton luminescence than those on usual substrates such as Al2O3

CuBr films grown on KBr crystals show 102 or 103 times higher efficiency of free-exciton photoluminescence (PL) than those grown on conventional substrates such as Al2O3 or silica glass. The efficiency exceeds even that of CuCl films by a factor of several tens, despite the general recognition that the free-exciton PL from CuBr is much weaker than that from CuCl. The present result encourages the authors to challenge to rethink the exciton PL in CuBr as well as in CuCl, because the compounds are the model materials for basic and application studies of linear/nonlinear exciton-related PL properties of solids.

Extremely-high-intensity photoluminescence from CuBr films fabricated by film–substrate chemical reaction of CuCl films on KBr-crystal substrate

High quality CuBr film is fabricated by film–substrate chemical reaction of CuCl on KBr, where CuCl is vacuum-deposited film of the order of ∼ 100 nm thickness and KBr is fleshly-cleaved single crystal. The resulting CuBr films show ∼ 10 3 times higher efficiency of free-exciton photoluminescence (PL) than conventional CuBr films. The efficiency exceeds that of conventional CuCl films even by a factor of ∼ 10 2, despite the general recognition that the free-exciton PL from CuBr is much weaker than that from CuCl. The present result encourages us to challenge to rethink the exciton PL in CuBr as well as in CuCl, because the compounds are the model materials for basic and application studies of linear/nonlinear exciton-related PL properties of solids.

Application of CuBr Ion Conductor Thin-Films for Ammonia Gas Detection

ABSTRACTCuBr films are used to design an ammonia gas microsensor operating at ambient temperature, with high sensitivity and much improved selectivity in comparison with usual conductometric microsensors. The specific detection mechanism relies on adsorption of ammonia molecules and interactions with mobile Cu+ ions in the ionic conductor film. The CuBr films can be prepared by r.f. sputtering, but more simply and cost efficiently by chemical reaction of copper metal with bromine ions. Photolithographic techniques are applied to miniaturize the sensor.

Impedance analysis of CuBr films for ammonia gas detection

CuBr films prepared by magnetron sputtering can be used to design a selective and sensitive ammonia microsensor, operating at ambient temperature. Impedance spectra of the films under different gas atmospheres can be fitted by a simple equivalent circuit. The roughness of the electrode/solid electrolyte interface leads to a distribution of the electrode resistance and capacitance values. The evolution of the bulk resistance of CuBr can be attributed to sorption of ammonia molecules, which is also investigated by Fourier-transform infrared (FTIR) spectroscopy.

Morphology, Electrical Conductivity, and Reactivity of Mixed Conductor CuBr Films: Development of a New Ammonia Gas Detector

The microstructure, electrical properties, aging, and electrolytic decomposition of sputtered CuBr films are described and discussed with respect to the defect chemistry of this mixed Cu+ ion−elect...

Electrical properties and sensor characteristics for NH 3 gas of sputtered CuBr films

We show that sputtered CuBr films can be used to detect the presence of NH 3 gas. The increase of electrical resistance is very fast with a time constant of only a few seconds. The possible sensor mechanisms are discussed. Cross effects for various gases are investigated; only H 2S degrades irreversibly the film. Ageing experiments show a t 1/2 dependence of the film resistance.