CuI Films Research Articles

Study of temperature-dependent copper iodide thin film by thermal evaporation system

The development of heterostructure devices has gained significant attention towards scientific communities in the present time. This article reports on the effective use of the horizontal thermal evaporation (TE) method to successfully fabricate copper iodide (CuI) films on silicon (Si) substrates. By using the TE technique, CuI-based heterojunctions have been fabricated in this research . CuI exhibits semiconductor qualities of the p-type, making it a promising option for optoelectronic devices in the future. The temperature was varied from room temperature (RT) to 230 °C to synthesise the CuI/Si heterojunction. The structural, morphological, optical, and electrical analyses have been carried out with various substrate temperatures. The x-ray diffraction (XRD) data shows that the CuI films have demonstrated a polycrystalline character and have lattice parameters of 6.03 Å. The Raman spectroscopy study shows the microstructural analysis of CuI films. The field emission scanning electron microscopy (FESEM) study reveals the variation of grain size and shape with synthesis temperature. The atomic force microscope (AFM) was used to estimate the surface roughness. The CuI films were found to be p-type by the Hall effect measurement. The sample synthesised at 130 °C shows the highest mobility of 83.12 cm2 V−1 s−1 with a carrier concentration of 1019 cm−3. The UV-visible (UV–vis) spectroscopy measurements show good absorption of UV light by the CuI thin films. The CuI/Si heterojunctions are rectifying, as demonstrated by the I-V measurements, and those respond well to UV light irradiation.

Enhanced Performance of P-Channel CuIBr Thin-Film Transistor by ITO Surface Charge-Transfer Doping.

The process development and optimization of p-type semiconductors and p-channel thin-film transistors (TFTs) are essential for the development of high-performance circuits. In this study, the Br-doped CuI (CuIBr) TFTs are proposed by the solution process to control copper vacancy generation and suppress excess holes formation in p-type CuI films and improve current modulation capabilities for CuI TFTs. The CuIBr films exhibit a uniform surface morphology and good crystalline quality. The on/off current (ION/IOFF) ratio of CuIBr TFTs increased from 103 to 106 with an increase in the Br doping ratio from 0 to 15%. Furthermore, the performance and operational stability of CuIBr TFTs are significantly enhanced by indium tin oxide (ITO) surface charge-transfer doping. The results obtained from the first-principles calculations well explain the electron-doping effect of ITO overlayer in CuIBr TFT. Eventually, the CuIBr TFT with 15% Br content exhibits a high ION/IOFF ratio of 3 × 106 and a high hole field-effect mobility (μFE) of 7.0 cm2 V-1 s-1. The band-like charge transport in CuIBr TFT is confirmed by the temperature-dependent measurement. This study paves the way for the realization of transparent complementary circuits and wearable electronics.

Defect and dopant complex mediated high power factor in transparent selenium-doped copper iodide thin films

Copper iodide (CuI) is a promising p-type transparent thermoelectric material for near-room temperature energy harvesting. We report a high-power factor for selenium (Se)-doped CuI films. Ion beam-sputtered CuI films were doped using 30 keV 80Se+ implantation with Se concentration varying between 0.50% and 6.50%. Hall effect measurements showed a ∼34% increase in electrical conductivity (σ ≈ 36.1 Ω−1cm−1) due to a ∼54% increase in carrier density (pH ≈ 5.4 × 1019 cm−3) in the p-type γ-CuI film implanted with 5.0 × 1014 Se.cm−2. A high Seebeck coefficient, α ≈ 388.9 μVK−1−1, and moderate electrical conductivity, σ ≈ 29.1 Ω−1cm−1, yield a nearly 85% increase in the power factor, α2σ ≈ 439.7 μWm−1K−2, for a 1.0 × 1015 Se.cm−2 implanted film compared to the unimplanted film (α2σ ≈ 236.4 μWm−1K−2). Monte Carlo simulation and ab initio density functional theory calculations revealed that the increased displacement per atom values and the {SeI−VCu} defect complex-induced shallow acceptor could be attributed to the observed increase in hole density. Our results highlight that native defects and defect complexes are beneficial for enhancing the power factor in transparent CuI for thermoelectric applications.

A new strategy for fabricating low haze p-type CuI film

As an intrinsic p-type transparent conductor with a wide band gap of 3.1 eV, γ-CuI full of potential has gradually attracted the attention of researchers. However, γ-CuI films deposited by various techniques generally exhibit high haze with a frosted glass-like appearance, which significantly affects the device performance. Herein, a new strategy is proposed in which true p-type CuI thin films with low haze have been successfully synthesised at room temperature. The specular transmittance of the CuI film over 85% in the visible region (400–800 nm) can be achieved. The haze of the as-prepared γ-CuI films can be as low as 0.7%. Meanwhile, the as-prepared CuI film has an FOM as high as 230 MΩ−1. This ideal stable p-type optoelectronic performance was significant among various typical p-type transparent conductive films.

Surface-enhanced p-type transparent conducting CuI−Ga2O3 films with high hole transport performance and stability

CuI is a wide bandgap p-type transparent conductor with promising optoelectronic properties. However, conventional CuI films prepared through the iodination of Cu films exhibit rough surface, poor stability and excessively high hole concentration, hindering its application. Herein, we introduce CuI−Ga2O3 composite films as a substitution to overcome the shortcomings of pure CuI. During the iodination process, Ga2O3 hindered the mobility of CuI grain boundaries, resulting in small grain size and low surface roughness. After the charge re-equilibrium and low-energy carrier filtering at the interface between Ga2O3 and CuI, the hole concentration in the films decreased by an order of magnitude. Due to the interface effect of Ga2O3 at the grain boundaries of CuI, the hole mobility increased by 5 times, and the conductivity improved by 53%. The ultra-wide band gap of Ga2O3 enhanced the transmittance of CuI films in short wavelength region. Ga2O3 served to passivate the grain boundaries of CuI, preventing the oxidation of CuI and the loss of iodine, consequently improving the stability of the films. This work will deepen the understanding of the failure and hole transport mechanisms of CuI films.

Copper-Enriched Nanostructured Conductive Thermoelectric Copper(I) Iodide Films Obtained by Chemical Solution Deposition on Flexible Substrates

The objects of our research are flexible thin-film thermoelectric materials with nanostructured CuI layers 0.5–1.0 μm thick, fabricated by the chemical solution method Successive Ionic Layer Adsorption and Reaction (SILAR) on flexible polyethylene terephthalate and polyimide substrates. These cubic γ-CuI films differ from films obtained by other chemical solution methods, such as spin-coating, sputtering, and inject printing, in their low resistivity due to acceptor impurities of sulfur and oxygen introduced into CuI from aqueous precursor solutions during SILAR deposition. Energy barriers at the boundaries of 18–22 nm CuI nanograins and a large number of charge carriers inside the nanograins determine the transport properties in the temperature interval 295–340 K characterized by transitions from semiconductor to metallic behavior with increasing temperature, which are typical of nanostructured degenerate semiconductors. Due to the resistivity of about 0.8 mΩ· m at 310 K and the Seebeck coefficient 101 μV/K, the thermoelectric power factor of the CuI film 1.0 μm thick on the polyimide substrate is 12.3 μW/(m · K2), which corresponds to modern thin-film p-type thermoelectric materials. It confirms the suitability of CuI films obtained by the SILAR method for the fabrication of promising inexpensive non-toxic flexible thermoelectric materials.

Tunable photoresponse properties of CuI/Si self-powered photodetectors through Zn doping engineering

Zn doping engineering was achieved in copper iodide (CuI) films for CuI/Si heterojunction ultraviolet (UV) photodetectors (PDs) by employing a facile solution approach. The morphology, grain sizes and optical properties of CuI films with various Zn2+ doping concentrations are systematically investigated. Our results indicate that an appropriate Zn doping concentration can significantly improve the quality of CuI thin films, leading to an improved photodetection performance, while an excessive amount of Zn dopant can cause poor interface and quality of CuI films. The optimized Zn-doped CuI/Si UV PD exhibited remarkable photodetection performance with a high responsivity of 0.561 A/W at 0 V bias, surpassing all reported CuI-based photodetectors.

Fabrication of transparent p-CuI/n-ZnO heterojunction with excellent ideality factor

Copper iodide (CuI) is an intrinsically transparent p-type semiconductor with a wide band gap of about 3.1 eV. In this work, Cu3N films were prepared as precursors through high-power impulse magnetron sputtering and then were solid-phase iodinated at room temperature for the preparation of transparent CuI films. Subsequently, transparent p-CuI/n-ZnO heterojunctions were fabricated wherein ZnO layers were deposited by radio frequency magnetron sputtering. After the properties are optimized by annealing, the heterojunctions exhibit significant rectification characteristics. The influence of annealing temperature on the electrical properties of the heterojunctions have been investigated. The optimal ideality factor of about 1.22 can be obtained with a rectification ratio of 1.05 × 105 after the heterojunctions annealing at 100 °C. This value is superior to most of the results reported in the literature. Meanwhile, the light-to-dark current ratio and the transmittance in the visible region of the heterojunction have also been studied. The light-to-dark current ratio is significant at 6.42 × 106. The average transmittance of the heterojunctions is 72.7%. These findings demonstrate the potential applications of CuI for optoelectronic devices and the promising prospects of p-CuI/n-ZnO heterojunction-based photodetectors and other optoelectronic devices.

The impact of thickness-related grain boundary migration on hole concentration and mobility of p-type transparent conducting CuI films.

CuI films present promising optoelectronic properties for transparent conductors. However, the high hole concentration in CuI films hinders the controllable modulation of hole mobility, limiting their application in low-dimensional thin-film transistors. In this study, CuI films were prepared through a Cu film iodination method at room temperature, and a systematic investigation was conducted on the modulation of hole concentration and mobility with varying film thickness. The films exhibited a zinc blende structure (γ-phase) with increasing grain size as the thickness increased. The transmittance and optical bandgap of the films decreased with increasing thickness. The correlation of vacancy concentration with changing film thickness was analyzed through photoluminescence spectroscopy, revealing the influence of grain boundary migration on vacancy formation. The reduction in film thickness diminishes the migration of CuI grain boundaries, consequently reducing the probability of Cu vacancy and I vacancy formation, resulting in diminished hole concentration and enhanced hole mobility and film conductivity. The film with a thickness of 20 nm demonstrated optimal performance, with a transmittance of 90%, hole concentration of 4.09 × 1017 cm-3, hole mobility of 506.50 cm2 V-1 s-1, and conductivity of 33.19 S cm-1. This work deepens the understanding of hole transport such as hole concentration and mobility modulation in CuI films, highlighting the importance of controlling grain boundary migration during the film growth process.

A black electrochromic device based on a CuI film for energy-efficient applications

An electrochromic device based on a CuI film has been designed and fabricated, which increases the content of Cu ions in the device. The device shows excellent bistability and optical modulation ability after parameter optimization.

Solution-processed copper(i) iodide via co-doping for enhanced hole selective contacts in p-type crystalline silicon solar cells

We have demonstrated that solution-processed CuI films via Al3+ and I2 co-doping act as effective full-area hole-selective contact layers, generating a remarkable power conversion efficiency of 18.28% for Al3+–I2:CuI/p-Si heterojunction solar cells.

Highly efficient tandem organic light-emitting diodes using p-type metal halide copper iodide (CuI)

Efficient charge generation is essential for tandem organic light-emitting diode (OLED) devices. In this study, we introduce a p-type copper iodide (CuI) layer within the charge generation layer (CGL) that exhibits high charge generation efficiency in tandem OLED devices. Briefly, CuI is deposited as a thin layer via thermal evaporation technique. X-ray diffraction (XRD) analysis reveals the formation of γ-CuI, and the ultraviolet-visible (UV-Vis) spectral analysis demonstrates outstanding optical transparency (∼95%) of the deposited CuI films in the visible range. The current-voltage (I-V) and capacitance-voltage (C-V) analyses show that the p-type CuI layer is a vital and excellent charge generator and enhances the current density significantly. The tandem OLED device fabricated using Bphen:Liq/CuI/HAT-CN as the CGL results in a substantial 1.9-fold increase in current efficiency compared to the single-unit OLED device, approaching the theoretical two-fold increase. These findings highlight the potential of CuI as a promising p-type material for CGL design in tandem OLED devices.

Dependence of Microstructure of Thermally Evaporated CuI Films on the Flow Rate of Argon Gas

Dependence of Microstructure of Thermally Evaporated CuI Films on the Flow Rate of Argon Gas

Low-Voltage Solution-Processed Zinc-Doped CuI Thin Film Transistors with NOR Logic and Artificial Synaptic Function.

Low-voltage Zn-doped CuI thin film transistors (TFTs) gated by chitosan dielectric were fabricated at a low temperature. The Zn-doped CuI TFT exhibited a more superior on/off current ratio than CuI TFT due to the substitution or supplementation of copper vacancies by Zn ions. The Zn-doped CuI films were characterized by scanning electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. The Zn-doped CuI TFTs exhibited an on/off current ratio of 1.58 × 104, a subthreshold swing of 70 mV/decade, and a field effect mobility of 0.40 cm2V-1s-1, demonstrating good operational stability. Due to the electric-double-layer (EDL) effect and high specific capacitance (17.3 μF/cm2) of chitosan gate dielectric, Zn-doped CuI TFT operates at a voltage below -2 V. The threshold voltage is -0.2 V. In particular, we have prepared Zn-doped CuI TFTs with two in-plane gates and NOR logic operation is implemented on such TFTs. In addition, using the ion relaxation effect and EDL effect of chitosan film, a simple pain neuron simulation is realized on such a p-type TFTs for the first time through the bottom gate to regulate the carrier transport of the channel. This p-type device has promising applications in low-cost electronic devices, complementary electronic circuit, and biosensors.

Effect of grain boundary scattering on carrier mobility and thermoelectric properties of tellurium incorporated copper iodide thin films

Copper iodide (CuI) is a promising p-type transparent semiconductor with many potential applications in range of fields such as transistors, optoelectronics, solar cells, thermal sensors, and energy harvesting. We report compositional, structural, optical, electrical, and thermoelectric properties of optically transparent tellurium (Te) incorporated CuI films, (CuI)1-xTex where x=0–0.09, prepared by ion beam sputtering. The films are composed of γ-CuI with the presence of elemental tellurium clusters in films prepared with high Te concentration sputtering targets. The carrier mobility decreased from 6.9 ± 0.9 cm2V-1s-1 to 0.7 ± 0.1 cm2V-1s-1, and the electrical conductivity from 84.22 ± 8.45 Scm-1 to 3.97 ± 0.40 Scm-1 for the CuI and (CuI)0.91Te0.09 films, respectively, attributed to a transition from polar optical phonon to grain boundary scattering. The change in the mobility-limiting scattering mechanism decreased the power factor from 454 ± 57 μWm-1K-2 for the CuI film to 34 ± 4 μWm-1K-2 for the (CuI)0.91Te0.09 film. Our study shows that modulating the scattering mechanism in transparent thermoelectric materials is a powerful method to tune their thermoelectric properties.

Isolate Utilization of Plasmonic Hot Holes in Optoelectronic Enhancement for Copper Iodide (CuI): A Cross‐Investigation by Confocal Kelvin Probe Force Microscopy

AbstractNonradiative decays of surface plasmon (SP) can generate photocarriers in femtosecond, and it therefore has been attracting widespread research attention in ultrafast optoelectronics. Taking advantage of the probe technique, Kelvin probe force microscopy (KPFM) can characterize the spatial distribution of hot carriers in nanoscale and thereby provide necessary analysis for device investigation and engineering. In this work, the behavior of plasmonic hot holes is demonstrated for Ag nanoparticles (NPs) based on the fabrication of CuI hole transport layers. The morphological, optical, and electronic properties of Ag NPs and CuI films are systematically investigated. With the confocal lasers of over‐ and sub‐bandgap wavelength, reversed evolution trends of surface potentials are observed by KPFM, indicating the effective injection of hot holes into CuI valence band (VB). Cross‐verification is also performed based on the fabrication of metal–semiconductor–metal (MSM) photodetectors, and the photoelectrical tests highly dovetail with the surface potential evolution. This research provides an important reference for the plasmonic photoelectronics in both device design and research methods.

Self-Powered UV Photodetectors Based on Heterojunctions Composed of ZnO Nanorods Coated with Thin Films of ZnS and CuI

A simple, inexpensive solution process is used to deposit γ-CuI thin films, and many aspects of the films, such as morphology, crystalline phase, and its optical and electrical properties on annealing are studied. All of the grown films exhibited p-type conductivity and an average transmittance of 70 to 80% in the visible region. The film annealed at 200 °C is observed to be relatively smooth with root-mean-square roughness of 13.25 nm. CuI films annealed at 200 °C displayed a hole mobility of 0.53 cm2/Vs and a hole concentration of 8.36 × 1018 cm–3. Additionally, the potential of γ-CuI as a p-type material for photodetection is explored by fabricating transparent hybrid ultraviolet (UV) photodetectors based on p-CuI/n-ZnO nanorods and p-CuI/n-ZnS/ZnO nanostructures. The high-resolution transmission electron microscopy (HRTEM) image showed that the ZnO nanorods grew as a single crystal along the [001] direction and smaller CuI attached on their surface. A simple sulfurization procedure has created a poly-nanocrystalline ZnS shell layer over the ZnO nanorods. Crucial photodetector parameters such as responsivity, external quantum efficiency, and detectivity are analyzed with different illumination intensities and incident wavelengths. Under self-powered conditions, upon illumination with 372 nm and intensity of 0.25 mW/cm2, the p-CuI/n-ZnO nanorod showed significant responsivity of 25.11 mA/W and detectivity of 4.59 × 1013 Jones. Insertion of the ZnS layer between the ZnO and CuI has enhanced these parameters to 43.85 mA/W and 3.84 × 1014 Jones, respectively. This research underlines the potential of p-type CuI as a transparent, high-performance optoelectronic material.

High-performance p-channel CuIBr thin-film transistor synthesized from solution in the atmosphere

The p-type transparent semiconductor CuI has a high potential to be used in thin film transistors (TFTs) due to high hole mobility and solution processability. However, the lower copper vacancy formation energy and the subsequent high hole concentration in CuI lead to a low on/off current ratio (ION/IOFF) for CuI TFT devices. The density functional theory results suggest that the copper vacancy formation energy increases with the CuBr content in the Br-doped CuI film, resulting in lower hole concentration. Alloying CuI with CuBr is proposed to reduce the hole concentration in the CuIBr alloy. The CuIBr TFTs with Br content ranging from 0% to 10% were fabricated using the solution method. It is found that the hole mobility decreases from 8 to 1 cm2 V−1 s−1, while the ION/IOFF ratio increases from 102 to 104 with the increasing Br content. The CuIBr TFT with 7.5% Br content exhibits a high hole mobility larger than 5 cm2 V−1 s−1 and high ION/IOFF ratio of 104, which paves the way for inorganic-based CMOS circuits on flexible and transparent substrates.

Epitaxial Electrodeposition of Ordered Inorganic Materials.

ConspectusThe quality of technological materials generally improves as the crystallographic order is increased. This is particularly true in semiconductor materials, as evidenced by the huge impact that bulk single crystals of silicon have had on electronics. Another approach to producing highly ordered materials is the epitaxial growth of crystals on a single-crystal surface that determines their orientation. Epitaxy can be used to produce films and nanostructures of materials with a level of perfection that approaches that of single crystals. It may be used to produce materials that cannot be grown as large single crystals due to either economic or technical constraints. Epitaxial growth is typically limited to ultrahigh vacuum (UHV) techniques such as molecular beam epitaxy and other vapor deposition methods. In this Account, we will discuss the use of electrodeposition to produce epitaxial films of inorganic materials in aqueous solution under ambient conditions. In addition to lower capital costs than UHV deposition, electrodeposition offers additional levels of control due to solution additives that may adsorb on the surface, solution pH, and, especially, the applied overpotential. We show, for instance, that chiral morphologies of the achiral materials CuO and calcite can be produced by electrodepositing the materials in the presence of chiral agents such as tartaric acid.Inorganic compound materials are electrodeposited by an electrochemical-chemical mechanism in which solution precursors are electrochemically oxidized or reduced in the presence of molecules or ions that react with the redox product to form an insoluble species that deposits on the electrode surface. We present examples of reaction schemes for the electrodeposition of transparent hole conductors such as CuI and CuSCN, the magnetic material Fe3O4, oxygen evolution catalysts such as Co(OH)2, CoOOH, and Co3O4, and the n-type semiconducting oxide ZnO. These materials can all be electrodeposited as epitaxial films or nanostructures onto single-crystal surfaces. Examples of epitaxial growth are given for the growth of films of CuI(111) on Si(111) and nanowires of CuSCN(001) on Au(111). Both are large mismatch systems, and the epitaxy is explained by invoking coincidence site lattices in which x unit meshes of the film overlap with y unit meshes of the substrate.We also discuss the epitaxial lift-off of single-crystal-like foils of metals such as Au(111) and Cu(100) that can be used as flexible substrates for the epitaxial growth of semiconductors. The metals are grown on a Si wafer with a sacrificial SiOx interlayer that can be removed by chemical etching. The goal is to move beyond the planar structure of conventional Si-based chips to produce flexible electronic devices such as wearable solar cells, sensors, and flexible displays. A scheme is shown for the epitaxial lift-off of wafer-scale foils of the transparent hole conductor CuSCN.Finally, we offer some perspectives on possible future work in this area. One question we have not answered in our previous work is whether these epitaxial films and nanostructures can be grown with the level of perfection that is achieved in UHV. Another area that is ripe for exploration is the epitaxial electrodeposition of metal-organic framework materials from solution precursors.

Process ambient effects on defect state generation in CuI films: Toward multimodal sensor application via patternable CuI arrays

With the advent of CuI as one of promising metal halides, great attention is recently paid to optoelectronic applications. However, CuI formation and its defect states are rarely investigated according to atmospheric conditions exposed to Cu films before iodization. Here, CuI films, prepared for the respective atmospheric conditions (or glove box), are systematically studied via various peak analyses, elucidating that the absorbed oxygen and moisture on Cu film before iodization significantly affect the chemical composition ratio (I/Cu) as 1.06 ± 0.01 (or 0.73 ± 0.05) in the glove box (or atmospheric) ambient. Furthermore, the decrease of electrical conductivity and its improved photodetection properties (PDPs) for CuI devices are consistently demonstrated with the rise of holding time in atmospheric conditions, which is ascribed to the increased iodine vacancy (VI) in CuI film. Furthermore, for process durability, various solvents and their exposure effects on electro/optical properties, including chemical composition, are investigated for 7 × 7 CuI arrays, denoting that short-term exposure is compatible within 20 %. For the practical validation, multimodal sensors based on flexible CuI thermistors with the average of B and TCR (%) as (3846 ± 427) K and -(4.32 ± 0.47) % and array-based CuI photodetectors are successfully demonstrated, illustrating of the utility of these findings for the envisioned, flexible optoelectronics.